Green River College: BIOL 100 Unit 3 Notes Latest Updated,100% CORRECT

Green River College: BIOL 100 Unit 3 Notes Latest Updated Chapter 6: Energy for life Learning Objectives: 1. Identify the cellular structure where photosynthesis occurs and describe its function. 2. State the overall chemical equation for photosynthesis. 3. Recognize what is meant by the terms reduction and oxidation. 4. Describe the function of photosynthetic pigments. 5. Explain the flow of electrons in the light reactions. 6. Explain how ATP and NADPH are generated in the light reactions of photosynthesis. 7. Summarize the three stages of the Calvin cycle and describe the major event that occurs during each stage. 8. Describe how ATP and NADPH are utilized in the reduction of CO2. 9. Summarize how the output of the Calvin cycle is used to make other carbohydrates. 10. Define C4 photosynthesis and explain why some plants must use this type of photosynthesis. 11. Describe both the advantages and the disadvantages of C4 photosynthesis over C3 photosynthesis. 12. Compare and contrast the leaf structure of a C3 plant with that of a C4 plant. 13. Explain CAM photosynthesis and describe the conditions under which plants can use it. Producers convert Solar Energy to Chemical Energy Photosynthesis: • Transforms solar energy into chemical energy(carbohydrates) • Producers—feed themselves and most of the consumers (most other living organisms on Earth) • Most food chains lead back to plants • Producers are also called autotrophs - organisms that capture energy and make organic molecules from inorganic nutrients Examples of photosynthetic organisms: Plant Anatomy Epidermis: protective outer layers Stomata: pores in the epidermis Leaf vein: brings water from roots Mesophyll Cells: photosynthetic cells with chloroplasts Chloroplasts - where photosynthesis happens! • Green portions carry on photosynthesis. • Carbon dioxide enters leaves through small openings - stomata • O2 diffuses out • Roots absorb water, then water enters the leaf through leaf veins • CO2 and H2O diffuse into mesophyll cells and then into chloroplasts Chloroplasts – organelles that carry out photosynthesis • Have a double membrane that surrounds the stroma –fluid • Chloroplasts have their own DNA and ribosomes Chloroplasts are packed with thylakoids (pancake-shaped structures) that have chlorophyll molecules in their membranes • Stacks of thylakoids are called grana • Chlorophyll is a pigment that absorbs solar energy Pigments are organic compounds that give plant and animal tissues color • Pigments absorb solar energy • Different pigments absorb and reflect different wavelengths of light • Solar energy can be described in terms of its wavelength and energy content. • Vision and photosynthesis are adapted to use the most prevalent wavelengths (visible light) • Shorter wavelengths contain more energy. • Longer wavelengths contain less energy The color we see is the light that is reflected The pigments found in photosynthesizing cells are primarily chlorophylls and carotenoids Chlorophyll: • absorbs violet, blue, and red wavelengths • reflects green wavelengths, so the leaves appear green Carotenoids (assessory pigments): • absorb violet, blue, green and red wavelengths • reflect yellow and orange wavelengths, so the leaves appear yellow or orange. Leaf colors • Warm weather (summer); more daylight hours • more chlorophyll is produced • Leaf absorbs all colors of light but green **Chlorophylls cover up other pigments that are there **We see the green reflected light • Cool weather (fall); fewer daylight hours • less chlorophyll is produced. • Leaf absorbs all colors but yellow to orange. • When chlorophylls are no longer produced we see the other pigments. **We see the yellow and orange reflected light In the process of photosynthesis, carbon dioxide and water in the presence of sunlight are converted into glucose and oxygen Write down the equation for photosynthesis: H2O +CO2 →(CH2O) + O2 Equation for Photosynthesis involves: • Reduction reaction – CO2 gains hydrogen atoms • Oxidation reaction – H2O loses hydrogen atoms The equation for photosynthesis tell us what the reactants and products are, but a lot goes on in between The word photosynthesis suggests a process that requires 2 sets of reactions o Photo – means light – reaction captures solar energy – Light Reactions o synthesis – to make – reactions that produce carbohydrate –Calvin Cycle reactions Photosynthesis • light reactions o Location? ▪ thylakoid o Reactants? ▪ Light energy H2O+CO2, o Products? ▪ NADPH and ATP • Calvin Cycle reactions o Location? ▪ Stroma o Reactants? ▪ CO2, NADPH and ATP o Products? o ADP +p, NADP Light Dependent Reactions occur in the chlorophyll pigments in the thylakoid membrane of chloroplasts. The Light Reactions involve the Harvesting of Energy Light reactions use 2 photosystems and the electron transport chain (ETC) Photosystem II • Absorbs light (solar energy) • Energizes electrons (e-). • Splits water into H+, e- and oxygen Electron transport chain (ETC) • Series of carriers pass high energy electrons along the chain from one carrier to the next • A proton pump moves H+ across the thylakoid membrane using energy from the e- o Creates a hydrogen ion gradient o Energy from this gradient is used to make ATP Photosystem I • Absorbs sunlight (solar energy) which energizes electrons • Electrons fuel the synthesis of NADPH • An e- and a H+ are added to NADP+ to become NADPH Follow the flow of energy by following the electrons Light Reaction Steps Occur in the thylakoid membrane 1. Solar energy (sunlight) is absorbed by the pigment (chlorophyll) in photosystem II • results in high energy electrons that move into the electron transport chain (ETC) • The e- in the pigments are replaced when water is split (e- are taken from the hydrogen) Equation for the splitting of water: H2O → 2 H+ + ½ O2 + e- 2. Electrons are passed through ETC, using their energy to pum H+ into the thylakoid lumen • This creates a H+ gradient • The H+ build up and move down its concentration gradient by flowing through the ATP synthase complex to generate ATP • Each time water is split (to provide e- for PSII), 2 H+ remain in the thylakoid space (lumen) • As e- move from carrier to carrier down the chain, the e- give up energy • This energy is used to pump more H+ into the thylakoid space • This leads to a concentration gradient where there are more H+ in the thylakoid space than in the stroma. • The H+ gradient contains a large amount of potential energy • The H+ flow down their gradient (from high concentration to low concentration), through the ATP synthase complex which uses that energy to produce ATP. 3. Solar energy (sunlight) is absorbed by the pigments in photosystem I • results in high energy electrons that get passed to an NADP+ molecule • NADP+ is the final electron acceptor • A H+ (and an e-) gets added to become NADPH Equation: NADP+ + H+ + e- → NADPH ***ATP and NADPH made in the light reactions power the Calvin cycle reactions*** The Calvin Cycle Reactions — Making Sugars The Calvin cycle is a series of enzyme driven reactions in which energy rich • ATP and NADPH generated by light reactions help convert CO2 into sugars • Occurs in stroma of chloroplasts • End product is G3P which is used to produce glucose C6H12O6 • Involves 3 steps: 1. Carbon dioxide fixation 2. Carbon dioxide reduction 3. Regeneration of first substrate, RuBP 1. Carbon fixation – CO2 from the atmosphere is fixed (attached) to RuBP (ribulose 1,5- bisphosphate) • Uses and enzyme called rubisco which is the most abundant enzyme on the planet • Results in a 6 carbon molecule that quickly splits into two 3-carbon molecules • Process of taking a carbon from an inorganic compound (CO2) and putting it into an organic compound (carbohydrate) Equation: CO2 + RuBP→ 2 3PG (3-phospoglycerate 2. Carbon reduction – electrons from NADPH are added in a series of reactions to form G3P • CO2 is reduced in the process • Requires NADPH and some ATP Equation: P ---3PG + ATP + NADPH →P ---G3P + ADP + P + NADP+ It takes 3 turns of the Calvin Cycle to allow one G3P molecule to exit for making glucose 3. Regeneration of RuBP – 5 molecules G3P and ATP are used to re-form 3 molecules of RuBP which are need to begin the next cycle of reactions Equation: P ●●● G3p P ●●● ATP P●●●●●P G3p ATP → RuBP P ●●● + ATP P●●●●●P + P G3p RuBP P ●●● P●●●●●P P G3p RuBP P ●●● G3p Summary: • 3 turns of the cycle makes 6 G3P molecules • One G3P leaves the cycle to make carbohydrates • Five G3P are used to make 3 molecules of RuBP (are recycled). Reality – these complex reactions need to happen 2 times to make 1 glucose ***It takes 2 G3P molecules to make glucose From a G3P molecule, plants and algae can make all the molecules they need • Amino acids to make proteins • Fatty acids and glycerol to make lipids • Glucose and sucrose to make carbohydrates o Cellulose o Starch. Fate of G3P • When N2 is added, they can form amino acids • Can be used to form fatty acid and glycerol • Olive oil, corn oil, etc. • Forms glucose for energy needs • Forms sucrose for transport through plant • Forms starch for storage • Forms cellulose for cell walls There are several different types of Photosynthesis Plants are physically adapted to the light and rainfall conditions of their environment. There are 3 basic types: • C3 • C4 • CAM Each form has advantages and disadvantages C3 photosynthesis • Occur in plants where light and rainfall are moderate • Called C3 plants • A 3-carbon compound formed after CO2 fixation • Examples of C3 plants: • Wheat • Rice • Potatoes • Grass • Most trees • Wild flowers Carbon dioxide (CO2) fixation and the Calvin cycle occur in the mesophyll cells in C3 plants. • The advantage of the C3 pathway is that it doesn't need to convert CO2 into an acid • The disadvantage is that C3 plants cannot survive in hot temperatures, because it loses too much water. C4 photosynthesis • C4 plants have evolved an extra step to their photosynthesis process that makes them more efficient during the heat of summer: o A 4-carbon compound is formed in the mesophyll cell before CO2 fixation. • Occurs in plants grown where the weather is hot with limited rainfall, so preventing water loss is critical • Plants close their stomata to limit water loss(advantage) • This limits CO2 intake and allows O2 buildup(disadvantage) • Examples of C4 plants o Corn o sugarcane o Weeds o Some grasses CO2 fixation occurs in mesophyll cells, while the Calvin Cycle occurs in the bundle sheath cells in C4 plants. CAM (Crassulacean-acid metabolism) Occurs in plants grown in warm, arid environments • Includes most succulent plants in a desert environment • CAM plants open stomata during the night when it is cooler • A C3 molecules fixes CO2 to form a C4 molecule • During the day, keep stomata closed to avoid water loss • Releases stored CO2 that then enter the Calvin cycle • Examples of CAM plants: • orchids • cacti • aloe CO2 fixation occurs at night and a C4 molecule releases CO2 to the Calvin cycle during the day Advantage of CAM photosynthesis is to prevent water loss Disadvantage of CAM photosynthesis is that less G3P is produced Chapter 7: Energy for Cells Learning Objectives 1. Define cellular respiration. 2. Describe the overall reaction for glucose breakdown. 3. Identify the four phases of cellular respiration and identify the location of each within the cell. 4. Explain the role of glycolysis in a cell. 5. Distinguish between the energy-investment and energy-harvesting steps of glycolysis. 6. Summarize how the metabolic pathway of glycolysis partially breaks down glucose. 7. Explain why fermentation pathways are beneficial when oxygen is not available. 8. Give examples of products made by fermenting yeast and bacteria. 9. Identify the role of the preparatory reaction and the citric acid cycle in the breakdown of glucose. 10. Detail how the electron transport chain produces most of the ATP during cellular respiration. 11. Identify the inputs and outputs of each pathway of aerobic cellular respiration. 12. Explain the role of oxygen in cellular respiration. 13. Calculate the amount of ATP produced by each glucose molecule entering cellular respiration. 14. Recognize how alternate metabolic pathways allow proteins and fats to be used for ATP production. All living things require energy Organisms use energy for: • Growth • Reproduction • Defense • To manufacture the many chemical compounds that make up living cells Law of Thermodynamics • Energy cannot be created or destroyed but can be changed from one form to another Cells cannot create energy from nothing, so they must take energy from one form and convert it into another form • involves the transfer of electrons Living organisms need to obtain energy in the form of electrons from food • Requires the e- to be attached to molecules in order to move them in and out of the cell • Cells use and store energy by transferring electrons via chemical reactions – metabolism. Metabolic activity requires energy • Cells need energy carriers to deliver usable energy “on-demand” • Every living cell uses ATP to carry energy from one location to another • ATP also provides the energy for most enzymatic reactions o If the cell runs out of ATP, it will die ATP molecules are produced during Cellular Respiration • Requires oxygen and glucose, produces carbon dioxide and water • Reason you breathe • • ATP generated during cellular respiration is the fuel for metabolic and enzymatic reactions. ATP functions to transfer energy from one location to another Cells continuously generate ATP from ADP and then use that energy to perform vital functions Cellular respiration begins in the cytoplasm but is completed in the Mitochondria Cellular respiration utilizes Oxidation Reduction reactions • involves the transfer of hydrogen ions (H+) • Involves the transfer of electrons (e-) Oxidation Reduction reactions involve the transfer of hydrogen ions (H+) Oxidation = removal of hydrogen atoms • Hydrogens are removed from glucose • Generates the waste product carbon dioxide Reduction = addition of hydrogen atoms • Oxygen accepts hydrogens • Become waste product water Oxidation Reduction reactions also involve the transfer of electrons (e-) • Glucose is oxidized (loses e-) • Oxygen is reduced (gains e-). The breakdown of glucose releases a lot of energy • The cell controls the reactions so the glucose molecules are broken down slowly • This allows the energy to be captured efficiently • This process is called glycolysis Breakdown of glucose involves four phases Phase 1: Glycolysis • takes place in the cytoplasm • Glucose (6 carbons) is broken down into two molecules of pyruvate (3 carbons) • Divided into 2 steps: • Energy-investment step • Energy-harvesting step Energy-investment step (takes energy to make energy) • 2 ATPs transfer phosphates to glucose • Causes glucose (6-carbons) to split into two G3Ps (3-carbons) • G3P = glyceraldehyde-3-phosphate Substrates (G3P) from the energy investment step are used for step 2, the energy harvesting steps H+ are removed from the G3Ps and added to NAD+: NAD+ + H+ = NADH X2 (start with 2 substrates) Ps are added to the G3Ps to make BPG P’s from the BPG’s are transferred to ADP to make 3PG and ATP ADP + P = ATP X2 Water is removed as a waste product P’s from the 3PG’s are transferred to ADP ADP + P = ATP X2 P’s to make the ATPs come from the intermediate substrates: BPG and 3PG A net of 2 ATPs is generated and 2 new substrates are formed - ATP Next step depends on oxygen availability • With oxygen, pyruvate enters the mitochondria • Aerobic respiration • Without oxygen, pyruvate undergoes reduction and cells use the fermentation pathway • Anaerobic respiration When oxygen is present, the cell enters the aerobic phase of cellular respiration • the next 3 phases take place inside the mitochondria • Preparatory reaction and the citric acid cycle take place in the matrix • The electron transport chain is located in the cristae Phase 2: Preparatory reaction • Occurs twice per glucose molecule • Pyruvate is oxidized (H is removed and added to NAD+), • NAD+ → NADH • CO2 is released • CoA is added to produce acetyl-CoA Phase 3: Citric Acid Cycle (aka TCA and Krebs cycles) • Takes place in the matrix of the mitochondria • Two cycles for each glucose molecule • Acetyl CoA transfers an acetyl group to a 4-carbon molecule to produce citric acid (6 carbons) • Acetyl group oxidized • Carbon dioxide is released • Both NAD+ and FAD accept H+ and electrons • NAD+ → NADH and FAD → FADH2 • Produces 2 ATPs Take home message: Acetyl CoA → NADH FADH2 2 ATP ATP, NADH and FADH2 are all energy carriers • Because of the phosphate bonds, ATP carries the most energy. Cellular respiration: • Glucose – G3P – pyruvate – acetyl CoA – citric acid – NADH and FADH2 • So far we have only made 4 ATPs • 2 from glycolysis • 2 from citric acid cycle • That brings us to phase 4 Phase 4: Electron Transport Chain • NADH and FADH2 (generated in the CAC) deliver their electrons to the carriers located in the cristae • Hydrogen atoms that are attached to NADH and FADH2 consist of e- and H+ • Carriers accept only e- • Series of carriers pass electrons from one carrier to another NADH and FADH2 deliver the high-energy electrons from the CAC to the carriers • Electrons get passed from one carrier to the next. • Energy from the e- is used to pump H+ into the intermembrane space • This creates a H+ gradient – many H+ in the intermembrane space, but few in the matrix **Final electron acceptor (also the final H+ acceptor) is oxygen—forms water The H+ gradient contains a large amount of potential energy (stored) energy • ATP synthase uses the energy as the H+ move down their concentration gradient into the matrix to make ATP The energy from the flow of H+ through the ATP synthase complex is used to make ATP from ADP + P ETC – the big picture: 10 NADH and 2 FADH2 →34 ATP (max) H20 Not all cells produce the max – there is a range of 36-38 total ATP Energy yield from glucose metabolism • Maximum of 38 ATP is made (in prokaryotes) • Eukaryotic cells make only 36 ATPs or less • 36–38 ATP about 40% of available energy in a glucose molecule • Rest is lost as heat Cellular respiration equation: C₆H₁₂O₆ + 6 O₂ + 36 ADP + 36 P --> 6 CO₂ + 6 H₂O + 36 ATP Without oxygen, a special set of reactions perpetuate glycolysis • Steps 2, 3 and 4 do not occur • Many bacteria live in oxygen-deficient swamps and deep layers of soil • Intense exercise exhausts the oxygen supply from our muscle cells • So organisms are able to extract energy via glycolysis alone • ATP is generated through the process of Fermentation • Fermentation — anaerobic breakdown of glucose • Cells can make ATP when O2 is in limited supply • Generates two ATPs per glucose Fermentation is essential in providing a rapid burst of ATP (like when a person sprints) • Can generate ATP when our muscles are working vigorously over a short period of time and the oxygen has been depleted, Fermentation in Animal cells • Pyruvate from glycolysis accepts 2 hydrogen atoms and is reduced to lactate (aka lactic acid) • It provides a brief burst of energy for muscle cells, but this leaves the body in an oxygen deficit • Recovery from oxygen deficit is complete when enough oxygen becomes available to completely break down glucose • Why we breathe heavily after exertions - to bring in the oxygen to pay back the oxygen deficit • Once oxygen becomes available, lactate is converted into pyruvate Bacteria use fermentation to produce • Lactate OR • Alcohol and carbon dioxide Yeast (a type of fungi) use fermentation to • extract energy from glucose • producing ethyl alcohol and CO2 • When making bread, CO2 make bread rise • Yeast ferments grapes to make wine • Yeast ferments wort to make beer • Product is ethyl alcohol In fermentation: Inputs: • glucose • 2 ATP • 4 ADP + 4 P Outputs: • 2 lactate OR • 2 alcohol and 2 CO2 • 4 ATP for a net of 2 ATP • Lactate formation from fermentation occurs in o animal cells o bacteria • Alcohol and CO2 formation from fermentation occur in o yeast o Bacteria Even though fermentation only produces 2 ATPs, it still provides quick energy for short- term activity Alternative metabolic pathways What about the proteins in the pepperoni? • The amino acids can enter the cellular respiration pathway at several points • Pyruvate • Acetyl-CoA • CAC • Depends on the length of the hydrocarbon chain • Only the hydrocarbons of the a.a. can be used to make ATP What about the fats in the pepperoni and cheese? • Glycerol enters the pathway at glycolysis • Fatty acids enter the pathway at acetyl CoA • Fatty acids have longer carbon chains—yields more ATP • ***fats generate more energy than glucose because they have more carbons Intermediate substrates can also be used to make other products • excess substrates from glycolysis can make glycerol • acetyl groups can make fatty acids • Extra carbs can be made into fat for storage Chapter 8: Cellular Reproduction Learning Objectives 1. Summarize the purpose of cellular reproduction. 2. Understand the relationship of sister chromatids to chromosomes. 3. Explain the role of histones and the nucleosome in the compaction of the chromatin. 4. Summarize the activities that occur in the cell during interphase, mitosis, and cytokinesis. 5. Explain the significance of the S and G0 stages of the cell cycle. 6. Summarize the events in each phase of mitosis. 7. Compare cytokinesis in a plant cell and an animal cell. 8. Summarize the role of checkpoints in the cell cycle. 9. Explain how checkpoints are regulated by internal and external signals. 10. Describe the process of apoptosis. 11. Distinguish between proto-oncogenes and tumor suppressor genes in regard to cancer. 12. Explain the role of telomerase in stem cells and cancer cells. 13. Summarize how chromosomal rearrangements may cause some forms of cancer. 14. Identify the relationship between certain genes and cancer. Cellular Reproduction • Multicellular organisms begin life as a single cell. • Humans become trillions of cells because of cellular reproduction. • Cellular reproduction continues as we grow and to replace worn-out or damaged tissues. Cellular reproduction occurs when: 1. We grow - from a baby to an adult 2. Our tissues need repair 3. Single-celled organisms reproduce 4. A zygote develops into a multicellular organism) Cellular reproduction is necessary for asexual reproduction • Doesn’t require sperm or egg • New organisms are produced that are identical to the original (parent) • Undergo binary fission - split into two new individuals • Ex: amoebas and bacteria Cellular reproduction is necessary for zygotes to develop • Sexual reproduction requires sperm and an egg • Offspring are produced that are different from the parent • After fertilization, cell division occurs repeatedly to develop into a multicellular organism Cell Theory - All cells come from preexisting cells Cellular reproduction is necessary for the production of both new cells and new organisms 2 processes involved with cellular reproduction • Growth — cell duplicates its contents • including DNA and organelles • Cell division — contents of the parent cell divides into two daughter cells • DNA gets distributed from the original cell to the new cells The nucleus contains chromatin - a network of fibrils made of DNA and proteins Chromatin is periodically wound around a core of 8 protein molecules called histones • Nucleosome – complex of DNA wrapped around the histones In preparation for cell division, it is important that DNA is replicated and condensed • DNA replication is the copying of DNA • Full set of DNA is passed to each daughter cell ▪ DNA is then packaged into chromosomes • Thickened complex of DNA and proteins • Makes it easier to distribute the DNA to daughter cells (new cells) Histones are responsible for packaging the chromatin so that it fits in the nucleus. DNA replication forms sister chromatids joined at the centromere ▪ Each sister chromatid has identical DNA • Sister chromatids, when attached are one chromosome • When they split apart they are two separate but identical chromosomes The Cell Cycle is an orderly sequence of stages that takes place between the time a new cell has arisen to the point where it gives rise to two new daughter cells Consists of: • Interphase – the time when the cell performs its usual functions • Most of the cell cycle is spent in this phase • M (Mitotic) Stage – includes mitosis (nuclear division) • Cytokinesis (division of the cytoplasm). The amount of time a cell takes to complete the cell cycle varies widely depending on the type of cell • Embryonic cells – a few hours • Adult cells – about 24 hours The majority of the cell cycle is spent in interphase ▪ 3 stages • G1 • S (DNA synthesis) • G2 G1 — growth phase – occurs before DNA replication ▪ Cell doubles its organelles ▪ Accumulates materials for DNA synthesis ▪ Makes decision whether to divide or not ▪ If the cell doesn’t go on to divide, it enters G0 phase - cell division is stopped • Ex: nerve cells • Ex: cardiac cells • Ex: muscle cells If the cell decides to divide, it moves on to the next phase: S — synthesis phase DNA synthesis is required for DNA replication ▪ Need an extra copy for for the new cell ▪ Results in each chromosome being composed of two sister chromatids G2 — growth phase - stage following DNA synthesis ▪ Makes proteins needed for cell division ▪ Ex: protein found in microtubules – part of the cytoskeleton needed to move chromosomes (centrioles) Centrioles – short barrel shaped organelles composed of microtubules ▪ Located in the centrosome – a microtubule organizing center ▪ Essential for movement of the chromosomes during cell division ▪ Occur in pairs that lie at right angles ▪ Found in animal cells, but not in plant cells. Interphase Details - time between mitotic divisions (G1, S, and G2) • Cell contents duplicate (organelles double, cytoskeletal proteins are made) • DNA replicates • Centrosomes are visible – • Nuclear envelope is intact **The majority of the cell cycle is spent in interphase The first phase of the cell cycle – interphase • Growth (doubling of organelles), DNA replication, and growth (making of proteins) The next phase of the cell cycle – mitosis and cytokinesis • Mitosis and cytokinesis occur after interphase During the M (mitotic) phase - cell and DNA divide Cell division occurs in 2 steps: • Division of nucleus - mitosis ▪ Creates two identical daughter nuclei • Division of cytoplasm – cytokinesis Mitosis – process where a parent cell divides into 2 identical daughter cells ▪ Occurs in the somatic cells (non-sex cells) o All the cells of the body except the sperm and egg Daughter nuclei produced by mitosis are genetically identical to each other and to the parent nucleus ▪ Every animal has an even number of chromosomes—each parent contributes half of the chromosomes to the new individual. DNA needs to be copied before a cell can divide The nuclear contents (DNA) of the parent cell is duplicated and equally distributed to the daughter cells ▪ Each sister chromatid has the same genetic information ▪ Daughter chromosomes form when sister chromatids separate Chromatid- sister chromatid- daughter chromosomes- Mitosis in animal cells ▪ Although mitosis is divided into phases, it is a continuous process ▪ DNA is replicated before mitosis begins ▪ Each chromosome consists of 2 sister chromatids attached at a centromere ▪ Mitosis is followed by cytokinesis • Division of the cytoplasm Mitosis is traditionally divided into 4 phases ▪ Prophase ▪ Metaphase ▪ Anaphase ▪ Telophase Prophase • chromosomes condense • sister chromatids are formed • nuclear membrane breaks down • spindle fibers attach to the chromosomes at the centromeres DNA condensation prevents tangling and DNA damage Prophase summary: • nuclear envelope breaks down • DNA condenses into chromosomes • Spindle fibers attach to the centromeres Spindle fibers are microtubules that contract, resulting in separation of the chromosomes Metaphase – Chromosomes line up at the equator Anaphase • Chromatids separate • each pole (end of the cell) receives a set of daughter chromosomes Telophase – nuclear membranes form around the daughter chromosomes • Forms 2 nuclei In Animal cells, Cytokinesis follows mitosis ▪ Cleavage furrow forms as anaphase ends ▪ Contractile ring forms, a band of actin filaments ▪ As the ring constricts, it gets smaller until it splits the cell in 2 ▪ Divides the cytoplasm In Plant cells, the rigid cell wall does not permit cytokinesis by furrowing, instead ▪ A cell plate forms which becomes a new plasma membrane ▪ New membrane releases molecules that form new plant cell walls • The cell plate forms midway between the 2 daughter nuclei The cell cycle must be controlled • Ensures that the stages occur in order and that the cycle continues only when the previous stage is successfully completed • Cell cycle requires the following checkpoints: • G1 checkpoint • G2 checkpoint • Mitotic stage checkpoint G1 checkpoint • DNA integrity checked • Proper growth signals must be present • Cell committed to divide after this point ▪ If the cell can’t pass the G1 checkpoint, it goes to G0 where it cannot divide G2 checkpoint • Verifies that DNA replicated • Allows time for minor DNA damage to be repaired **Mitosis will not occur until DNA has replicated. Mitotic stage checkpoint • Between metaphase and anaphase • All chromosomes must be attached to spindle fibers to pass • This makes sure the chromosomes get distributed accurately to the daughter cells ***Mitosis stops until chromosomes are properly aligned. Part of an organism’s natural growth and development also includes a process of self- destruction (cell death) - called apoptosis Ex: At the end of a cell’s lifespan, it undergoes cellular suicide Apoptosis is programmed cell death – series of events that destroy the cell ▪ Allows an organism to control its cell death ▪ Unleashed by internal or external signals ▪ Helps keep number of cells at appropriate level ▪ Prevents tumors from developing Apoptosis is a normal part of growth and development • An important aspect of embryological development • Ex: Tail of a tadpole undergoes apoptosis as it becomes a frog • Webbing between human fingers and toes of an embryo disappears Steps of Apoptosis • Cell rounds up, and nucleus collapses • Chromatin condenses, and DNA fragments • Plasma membrane blisters • Cell and DNA fragments • Cell fragments get taken up by white blood cells by phagocytosis Apoptosis is different from necrosis, which is unprogrammed cell death • Necrosis is the death of cells due to disease or injury • Ex: after a heart attack the cells of the heart are deprived on oxygen and nutrients, the cells die and cause inflammation, which can kill the surrounding cells • Apoptosis does not cause inflammation and doesn’t spread to surrounding cells. What controls the cell cycle? • Internal and external signals ▪ Signal —a molecule that stimulates or inhibits cellular functions ▪ Internal signals come from inside the cell: ▪ Kinases are enzymes that remove a phosphate from ATP and add it to other molecules • Remove the nuclear membrane • Cause the chromosomes to condense ▪ Cyclins are proteins that allow the cell to proceed through the phases (G1 to S, and G2 to M) External signals come from outside the cell • Epidermal growth factor (EGF) stimulates skin near an injury to finish cell cycle and repair injury • Estrogen a hormone that stimulates the cells lining the uterus to divide and prepare for egg implantation External signals are often hormones – they start a cascade of events that stimulate cell division Non-hormonal external signal: ▪ Contact inhibition — cells stop dividing when they touch • Prevents overgrowing • Cells “remember” how many times they have divided and stop when it reaches a certain number What happens when the body loses control over the cell cycle? • Cancer • Can result from imbalance of the pathways that regulate cell division • cellular reproduction occurs repeatedly Cancerous cells • resistant to hormones • grown on top of each other (no contact inhibition) • check points are broken • resistant to apoptosis They do not respond to the normal external and internal signals Development of cancer ▪ A mutated cell has the ability to start a tumor ▪ Tumors can release their own growth factors ▪ Tumors lack contact inhibition ▪ Both promote continuous cell division ▪ Cancer cells can travel to other parts of the body and start new tumors - metastasis What makes a cell do that? • Environmental insults can attack DNA and change its chemical structure • Mutations can arise from spontaneous errors during cell division for example and A may be switched to a T, C or a G • Sometimes mutations lead to variations and other times can lead to cancer. Mutant genes can also be inherited from parents • Cancer can course through families. When cancer develops, the cell cycle occurs repeatedly, largely due to a mutation in 2 types of genes: • Proto-oncogenes • Tumor suppressor genes A Proto-oncogene is a normal gene that codes for proteins that promote normal cell growth and division and inhibit apoptosis • They are like the gas pedal of a car because they accelerate the cell cycle • When proto-oncogenes mutate, they become cancer-causing genes called oncogenes Oncogenes stimulate an abnormal cell cycle • Cell division gets out of control • Puts the cell on the path to become a cancer cell. Tumor suppressor genes are normal genes that code for proteins that inhibit the cell cycle and promote apoptosis • When tumor suppressor genes mutate, they become abnormal genes • their products no longer inhibit the cell cycle nor promote apoptosis. Cell division gets out of control Other genetic changes that can result in cancer • Chromosomal rearrangements • a portion of a chromosome may break off and reattach to another chromosome -- called translocations. Mutation in other genes: • BRCA1 and BRCA2 – breast cancer • RB gene – eye tumors • RET gene – thyroid cancer Absence of telomere shortening • The telomere is like a protective cap at the end of the DNA • Telomeres regulate cell division • Every time a cell divides, the telomere gets a bit shorter • When the telomeres don’t shorten, the cells continue to divide – results in uncontrolled cell division – cancer Environmental factors can damage DNA that can lead to cancer (the National Cancer Institute lists at least 26 known substances from the environment that are known to cause cancer) • Ex: Tobacco smoke • Has 60 cancer-causing agents • Many are also mutagens – promotes mutations in DNA, including proto- oncogenes and tumor suppressor genes • Ex: UV radiation from the sun • Can lead to skin cancer • Asbestos Both Asbestos & Radon Can lead to lung cancer • Radon. Whether cancer is induced from the environment, spontaneous mutations or inheritance from ancestors, the result is the same: • Inappropriate activation or inactivation of genetic pathways that control growth • Causes dys-regulated cellular division • Cancer cells arise via mutation, survival, natural selection and growth. Carcinogenesis—development of cancer ▪ Results when control of the cell cycle is lost and the cells divide uncontrollably ▪ Cells become immortal—divide repeatedly Characteristics of cancer cells ▪ Cancer cells lack differentiation — they lose their specialization and do not contribute to body function ▪ Have abnormal nuclei with abnormal number of chromosomes ▪ Do not undergo apoptosis ▪ Do not exhibit contact inhibition ▪ Form tumors —do not respond to inhibitory signals ▪ Undergo metastasis (cells travel to start new tumors) ▪ Can undergo angiogenesis- form new blood vessels to nourish themselves Tumors are abnormal growths in the body • Benign —contained within a capsule • Are not cancer • Grow in one place • Malignant —invasive and may spread • Are cancer • Can start tumors in other parts of the body (metastasis) Cancer treatment ▪ Either remove tumor or interfere with the ability of cancer cells to reproduce ▪ As rapidly dividing cells, they are susceptible to radiation therapy and chemotherapy ▪ Treatment: • Damages DNA or some aspect of mitosis • Leads to side effects ▪ Hormone therapy designed to prevent cells from receiving signals for continued growth and division Prevention of cancer ▪ Protective behaviors • Avoid smoking—accounts for about 30% of all cancer deaths • Avoid sun exposure major factor in development of most dangerous type of skin cancer, melanomas • Avoid heavy drinking- prone to particular cancers ▪ Protective diet • Weight loss can reduce cancer risk • Increase consumption of foods rich in vitamins A and C • Include cabbage family members in the diet A healthy diet helps prevent cancer because it contains • antioxidants – protect against DNA Damage . Chapter 9: Meiosis and the Genetic Basis of Sexual Reproduction ! Learning Objectives 1. Explain the purpose of meiosis. 2. Describe the human life cycle. 3. Define the terms diploid, haploid, sister chromatid, and homologous chromosomes. 4. Describe the processes of synapsis and crossing-over, and explain why these processes occur during meiosis. 5. List the phases of meiosis and briefly explain what events occur during each phase. 6. Contrast the alignment of chromosomes during metaphase I and metaphase II of meiosis. 7. Contrast the events of meiosis I and meiosis II with the events of mitosis. 8. Contrast the events of meiosis I with the events of meiosis II. 9. Define nondisjunction and briefly explain how nondisjunction may bring about an abnormal chromosome number. 10. List the causes and symptoms of Down syndrome. 11. List the syndromes that may result from an abnormal sex chromosome number and briefly explain the cause of each. . Chapter 29: Reproduction 1. Distinguish between asexual and sexual reproduction in animals. 2. List the steps of spermatogenesis 3. List the steps of oogenesis Animals usually reproduce sexually but some can reproduce asexually (1 parent) Types of asexual reproduction: • Binary fission o Primary reproductive method for prokaryotes o Ex: Archaea and bacteria o Some eukaryotes • Fragmentation • Budding • Some organisms can use more than one form o Ex: sea anemones can undergo binary fission and fragmentation. Fission – organism constricts into two halves and each half can regenerate into new individuals • Occurs in amoebas, paramecium, euglena, flatworms Fragmentation- The breaking of the parent body into several pieces that regenerate into new individuals • Occurs in sponges, corals, and echinoderms Budding - New individual (bud) is outgrowth of parent ▪ Occurs in hydras, sponges, tunicates What are the advantages of asexual reproduction? 1. It’s fast – some bacteria can divide every 20 minutes 2. It is simple - it requires less energy compared with sexual reproduction 3. Better chance of survival for the species - With a large number of organisms, species would still survive even when conditions change and the number of predators increases 4. Can out-compete – large number of colonies vie with other organisms for nutrients and water 5. Finding a mate is easy 6. It does not need mobility. What are the disadvantages of asexual reproduction? 1. No genetic diversity - the offspring are identical to the parent 2. There is less variation - they will become less adapted to certain environmental changes, unfavorable conditions such as extreme temperatures can wipe out entire colonies 3. It makes adaption more difficult - the entire colony would be susceptible to diseases and predators 4. Competition for food and space - offspring are close together. Modification of sexual reproduction • Parthenogenesis - Development of an egg cell into a whole organism without fertilization ▪ In honeybees, the queen can fertilize eggs that become females (workers) OR ▪ She doesn’t fertilize them and they become males (drones) Sexual reproduction- ▪ Each parent produces gametes in gonads • Testes produce sperm (males) • Ovaries produce eggs (females) ▪ Zygote formed by the union of egg and sperm Many aquatic animals practice external fertilization • Egg and sperm unite outside the parent’s body • External fertilization usually requires a medium such as water o The females lay eggs in the water and the male squirts the sperm in the same area ▪ Ex: fish and amphibians (such as frogs) Land animals typically undergo internal fertilization • Occurs by copulation - Sperm unites with egg inside female body Advantages: 1. Embryo is protected from predators 2. Offspring are more likely to survive Disadvantages: 1. Energy is required to find a mate 2. Fewer offspring are produced 3. More energy is required to raise and care for the offspring. Egg laying animals are oviparous – produce eggs that hatch after they leave the body ▪ Ex: reptiles and birds ▪ Eggs have yolk that provides nutrients for the developing embryo Some animals are ovoviviparous - eggs are retained in body until they hatch - releases fully developed offspring ▪ Ex: sea horses, garter snakes Some mammals still lay eggs ▪ Ex: Duckbilled platypus and spiny anteater Most mammals are viviparous - Produce living young 2 types: 1. Marsupials - mammals that have offspring born in a very immature state and finish development in a pouch • Ex: Kangaroo 2. Placental mammals - Most mammals have a placenta that nourishes the embryo during its development ▪ Materials (nutrients and O2) are exchanged with the mother. Humans, like most other animals, practice sexual reproduction in which 2 parents pass chromosomes(DNA) to their offspring • The physical and genetic characteristics of siblings differ from each other and from their parents because of meiosis Meiosis is a type of nuclear division that is important in sexual reproduction • Because of meiosis, two individuals can create offspring genetically different from themselves • This makes each one of us unique and allows for genetic variation of the species Fun fact: there are more than 70 trillion different genetic combinations possible in the mating of two individuals **Meiosis serves 2 major functions** • Reduces the chromosome number • Shuffles the chromosomes to produce genetically different gametes (sperm and egg) In sexually reproducing organisms, the life cycle refers to all the reproductive events that occur from one generation to the next ▪ Involves both mitosis and meiosis ▪ Mitosis is involved in continued growth of a child and repair of tissues throughout life • As a result, somatic (body) cells are diploid ▪ A double set of genetic information ▪ 46 chromosomes in humans Meiosis is a process that reduces the chromosome number from diploid to haploid • Gametes (egg and sperm) are haploid – a single set of genetic information • Spermatogenesis produces sperm in the testes • Oogenesis produces eggs in the ovaries haploid: 1 set of unpaired chromosomes • represented by 1n • 23 in human gametes diploid: paired chromosomes • represented by • 46 in somatic cells Fertilization is the fusion of 2 gametes that results in a single cell called the zygote • Egg and sperm join together • 2 haploid cells join to make one diploid cell The zygote inherits a haploid set of chromosomes from each gamete, thus restoring a complete set of genetic information to the offspring. Life cycle of humans. Meiosis in Males The testes is the male gonad that produces sperm and sex hormones ▪ The testes is composed of lobules ▪ Each lobule contains 1–3 seminiferous tubules ▪ Cells in seminiferous tubules undergo spermatogenesis – the process of producing sperm by meiosis During spermatogenesis meiosis reduces the chromosome number from diploid (2n) to haploid (n) Meiosis in Females The ovary is the female gonad that produces an egg and sex hormones • Oogenesis – production of eggs by meiosis Fertilization 1. Sperm make its way through the follicle cells 2. Acrosomal enzymes digest the zona pellucida 3. Sperm fuses with the egg plasma membrane 4. Sperm nucleus enters the cytoplasm of the egg 5. Sperm and egg nuclei fuse to produce a zygote Sperm provide nuclear DNA to the zygote Eggs provide nuclear DNA and mitochondrial DNA • DNA in the nucleus come from the mother and father • Mitochondrial DNA only comes from the mother Review: Chromatid – one complete copy of a single chromosome DNA replication forms sister chromatids -Each sister chromatid has identical DNA Chromosomes occur in pairs called homologous chromosomes • A homologous chromosome pair consists of two copies – one maternal and one paternal – of the same type of chromosome • Have the same size and shape of chromatid, and same location of the centromere • Contain the same types of genes arranged in the same order for the same traits 1 homologous pair = 2 chromosomes with same gene locations side by side (after the chromosomes are replicated) • 1 chromosome is from the mother and 1 from the father • Both chromosomes have all the same genes at the same locations (colored strips) • But each chromosome has different versions of the gene (different shades) Sister chromatids are exact replicas, but homologous chromosomes are not • Various alleles are located at specific locations – gene locus • Duplicated chromosomes are sister chromatids that have identical alleles Both males and females have 23 pairs of chromosomes • Chromosomes are long filamentous structures that contain tens of thousands of genes linked together in chains • 22 pairs are autosomes – chromosomes that are not X or Y (same in males and females) • 1 pair are called the sex chromosomes - they contain the genes that determine gender o XX female or XY male. Karyotype – chromosomes are arranged in homologous pairs according to size, shape and appearance in metaphase • The banding pattern (colors) of the chromosome pairs are the same indicating the same genes A gene is a portion of a DNA strand within a chromosome that functions as a hereditary unit • They are found at particular locations on specific chromosomes • They code for a specific protein – leads to a specific trait. Homologous pairs may contain different versions of the same gene • Alternate forms of a specific gene are called alleles • One allele comes from the father and one comes from the mother • Ex: 2 versions of the allele: attached or free Meiosis creates 4 haploid daughter cells that give rise to the sperm and egg • Each chromosome has to be duplicated before meiosis can begin • The diploid parent cell goes through two cell divisions– Meiosis I and Meiosis II o Each involving a round of nuclear division followed by cytokinesis. Meiosis I Homologous chromosomes pair up and form a tetrad, a process called synapsis ▪ Each tetrad consists of two chromosomes, with each chromosome containing two identical chromatids, for a total of four chromatids Ex: both copies of the same chromosome match up (one maternal copy and one paternal copy). After the tetrads form, non-sister chromatids may exchange identical DNA segments in a process called crossing-over • The DNA that is “swapped” is for a specific gene o Ex: brown hair for blonde hair • Results in sister chromatids with a different mix of alleles • Creates variation in the chromosomes o Increases variability of the genes in the gametes and, therefore, the offspring Different than translocation which can promote cancer – DNA that is swapped contains different genes. synapsis nonsister chromatids crossing-over between nonsister chromatids after 4 different chromosomes ***Crossing over creates new combinations of alleles Gene from the maternal chromosome is exchanged with the gene from the paternal chromosome, but the exchange of DNA is for the same trait (not a mutation – natural process) Meiosis I - One cell divides into 2 cells, each new cell will contain half of the tetrad – 1 tetrad = 2 homologous chromosomes = 4 chromatids 1 dyad = 1 chromosome = 2 chromatids Meiosis II is different • No duplication of chromosomes (no interphase) • Chromosomes start out as dyads—composed of two sister chromatids Meiosis II -Two cells divide into 4 cells, each cell will contain half of the dyad (1 sister chromatid) Chromosome number is reduced to half - haploid The importance of meiosis ▪ Produces haploid gametes so chromosome number stays constant in each new generation (zygote: 1n + 1n =2n) ▪ Generates genetic variations • Every possible combination of chromosomes can occur in daughter cell • Fertilization produces new combinations • 70,368,744,000,000 chromosomally different zygotes are possible, even assuming no crossing-over Meiosis produces gametes that are: • genetically different from each other • genetically different from the parent cell All possible combinations of chromosomes are possible because which chromosome moves to which cell is totally random • Essentially shuffles the chromosomes into new combinations. Meiosis involves two divisions: meiosis I and meiosis II meiosis I: Homologous chromosomes separate meiosis II: Sister chromatids separate ▪ Each division is broken down into four phases: • Prophase • Metaphase • Anaphase • Telophase ▪ Meiosis I and Meiosis II differ in the way the chromosomes line up during metaphase Meiosis I – The first division - Homologous chromosomes separate Prophase I • Tetrads form (synapsis) • Crossing-over occurs • Nuclear envelope fragments Metaphase I • Tetrads align at the equator • Either homologue can face either pole • Spindle fibers attach to the centromeres Anaphase I • Homologues separate • Dyads move to poles (pulled to opposite ends of the cell by the contraction of the spindle fibers) Telophase I • Spindle fibers disappear • New nuclear membranes surround the daughter nuclei • Daughter nuclei are haploid, having received one duplicated chromosome from each homologous pair • Cytokinesis creates 2 daughter cells. Meiosis II – the second cells division – sister chromatids separate The events of meiosis II are essentially the same as those for mitosis, except that the cells are haploid • During cytokinesis, the plasma membrane pinches off to form 2 complete cells • Each cell is haploid (n) • The gametes are genetically different because they contain different combinations of chromosomes. Meiosis I has generated 2 cells, so Meiosis II occurs in both of the cells Prophase II • Chromosomes condense • nuclear envelope fragments. Metaphase II • The dyads align at the spindle equator. Anaphase II • Sister chromatids separate and they become daughter chromosomes. **It is totally random as to which chromatid goes to which new cell **Allows the gametes to contain all possible combinations of chromosomes Telophase II • Four haploid daughter cells are formed that are different from each other and from the parent cell. Meiosis Compared with Mitosis • Meiosis - two consecutive nuclear divisions; mitosis - only one nuclear division • Meiosis produces four daughter cells; mitosis results in two daughter cells • Following meiosis, the four daughter cells are haploid (have half the chromosome number as the parent cell); following mitosis, the daughter cells have the same chromosome number as the parent cell. • Following meiosis, the daughter cells are genetically different to each other and to the parent cell; following mitosis, the daughter cells are genetically identical to each other and to the parent cell. Mitosis and Meiosis Occur at Different Times Meiosis occurs only at certain times of the life cycle of sexually reproducing organisms ▪ Occurs only in specialized tissues (testes and ovaries) ▪ Provides genetic variation ▪ Reduces the chromosome number Mitosis is much more common. ▪ Occurs in all tissues during embryonic growth ▪ Occurs during growth and repair ▪ It keeps the chromosome number constant ▪ Every cell has the same genetic material What is the benefit of sexual reproduction? Genetic variation Due to: • Alleles come from 2 parents • Crossing-over • Independent assortment of homologous chromosomes Changes in chromosome number can occur The normal number of chromosomes in human cells is 46, but sometimes chromosomes fail to separate correctly – nondisjunction ▪ Results in humans that are born with an abnormal number of chromosomes ▪ If nondisjunction occurs during meiosis I— both members of a homologous pair go into the same daughter cell Nondisjunction during meiosis I. Results in: 2 Gametes with one less chromosome 2 Gametes with one extra chromosome If nondisjunction occurs during meiosis II—sister chromatids fail to separate ▪ If an egg gets 24 chromosomes and is fertilized with a sperm, it gets 3 • copies of a chromosome - trisomy ▪ If an egg that has 22 instead of 23 chromosomes gets fertilized by a sperm, monosomy occurs (only has a single copy of the chromosome Nondisjunction during meiosis II. Results in: Gametes with either one less or one extra chromosome 2 Gametes with a normal number of chromosomes Down syndrome is also called Trisomy 21 ▪ A condition where the individual has 3 copies of chromosome 21 ▪ Recognizable characteristics • Short stature, eyelid fold, stubby fingers, mental disabilities The chance of a woman having a Down syndrome child increases rapidly with age, starting at about 40 • Below the age of 40, the frequency of having a Down syndrome child is 1 in 800, after age 40 it is 1 in 80. Why is the age of a female a factor in Down syndrome? the longer it takes between the start and end of meiosis, the greater the chance that nondisjunction will occur If nondisjunction occurs with the sex chromosomes (during oogenesis or spermatogenesis), it can result in gametes that have an abnormal number of sex chromosomes ▪ Too few or too many X or Y chromosomes ▪ Newborns with abnormal sex chromosome numbers are more likely to survive than those with abnormal autosome numbers ▪ Altered number of sex chromosomes usually means the individual will be sterile (cannot have children). Y chromosome determines maleness • SRY (sex-determining region Y) gene on chromosome ▪ So no matter how many X chromosomes a person has, if they have a Y chromosome, they will be male ▪ Turner syndrome (45, XO) ▪ Absence of second sex chromosome (indicated by the “O”) ▪ Are female ▪ Klinefelter syndrome (47, XXY) ▪ Have an extra X chromosome but it is inactivated ▪ Are male **If you turn in these notes completely filled out, you will earn 25 extra credit points** - email them to me by March 1st.