Chapter 12: The Cell Cycle (Mitosis) Questions and Answers Graded A+

Chapter 12: The Cell Cycle (Mitosis) Questions and Answers Graded A+ What are the three key roles of cell division? State each role and give an example Reproduction: an amoeba single celled eukaryote divides into two cells. Growth+Development: fertilized egg divides into two cells, beginning embryo formation. Tissue Renewal: dividing bone marrow will give rise to new blood cells What is meant by the cell cycle? the life of a cell from the time it's first formed from a dividing parent cell until its own division into two cells What is a Genome? the cell's entire collection of DNA eukaryotic genome (+human genome) many DNA molecules (human cell = 2m DNA) prokaryotic genome: a single long DNA molecule how many chromosomes are in a human somatic cell? 46 How many single-strand chromosomes are in a cell after S phase 92 chromatid: half of duplicated chromosome, genetically identical what is mitosis/ cytokinesis? division of the nucleus/ of the cytoplasm What occurs in meiosis & how is the chromosome # of daughter cells different? variation of cell division which yields nonidentical haploid daughter cells for cell division. Daughter cells have half the amount of chromosomes of the parent cell, but a mixture of traits from both parents. What are the components of the mitotic spindle and what is the source of these components? consists of microtubule fibers and associated proteins. source: the microtubules of the cytoskeleton partially disassemble. How does the mitotic spindle form & break apart? spindles from centrosomes elongate by polymerization: incorporating subunits of the protein tubulin & depolymerize by losing them What is another name for the centrosome? microtubule organizing center does the centrosome function just in mitosis? no in interphase too Are the pair of centrioles at the center of the centrosome important for cell division No plants don't have them, they aren't needed & no one knows why they're there What is the aster array of spindle fibers around the centrioles Describe what happens to the centrosome from interphase to prometaphase centrosome replicates to form 2 centrosomes that stay together near nucleus. Then during prophase & prometaphase they move apart as spindle microtubules grow out of them. Finally at the end of prometaphase, centrosomes are at opposite ends of the cell and short asters are extended from each. List the 4 things that occur during G2 of interphase -A nuclea envelope bound the nucleus. -the nucleus contains one or more nucleoli. -two centrosomes have formed by replication. -chromsomes, duplicated during S phase, can't be seen individually because they haven't yet condensed. List the 5 things that occur during Prophase -chromatin fibers become tightly coiled, condensing into discrete chromosomes. -nucleoli disappear. -each duplicated chromosome appears as two identical sister chromatids joined together at centromeres and all along their arms by cohesins. -the mitotic spindle begins to form. -centrosomes move away from each other, propelled by the lengthening microtubules between them. List the 5 things that occur during Prometaphase -nuclear envelope fragments so microtubules extending from each centrosome can now invade the nuclear area. -chromosomes have become even more condensed. -each of the two chromatids of each chromosome now has a kinetochore, a specialized protein structure located at the centromere -some of the microtubules attach to the kinetochores, becoming kinetochore microtubules and jerk the chromosomes back and forth. -nonkinetochore microtubules interact with those from the opposite pole of the spindle List the 3 things that occur during metaphase the centrosomes are at opposite poles of the cell. -chromosomes' centromeres line up on the metaphase plate, imaginary plane between both poles. -both kinetochores of all chromosomes have to be connected to kinetochore microtubules. If this doesn't happen, Anaphase can't begin. What is the longest phase of mitosis metaphase (20 minutes in humans) What is the shortest stage of mitosis Anaphase, a few minutes in humans 4 steps of anaphase -cohesin proteins are cleaved, and the two sister chromatids part suddenly. -the two liberated daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten. -cell elongates as nonkinetochore microtubules lengthen -At the end of anaphase, the two ends ot the cell have equivalent and complete collections of chromosomes. 5 steps of telophase -two daughter nuclei form in the cell -nuclear envelopes arise from the fragments of the parent cell's nuclear envelope and other portions of the endomembrane system -nucleoli reappear -chromosomes become less condensed -mitosis, division of nucleus into two genetically identical nuclei, is complete 2 steps of cytokinesis in animal cells -division of cytoplasm is usually well underway by late telophase, so the two daughter cells appear shortly after the end of mitosis. -cleavage furrow (contractile ring of actin + myosin proteins) pinches the cell in two. how is the cell plate formed in plant cells vesicles from golgi apparatus containing cellulose move along microtubules to the center of the cell, coalesce, and form a cell plate. New cell wall materials (cellulose) fuse with cell membrane & old cell wall, forming a separation between the two new daughter cells. what is the function of nonkinetochore microtubules also called polar microtubules, extend & verlap each other from poles. When is the mitotic spindle complete? when mictrotubules of the aster are in contact with plasma membrane, and all kinetochores are attached at which end do kinetochore mictrotubules shorten during anaphase & how does this happen they shorten at their kinetochore ends as de-polymerization of the microtubule occurs. motor proteins "walk" chromosome along microtubule, spitting out tubluin subunits as it goes ("pacman") Describe the 4 steps of binary fission and origin of replication. 1. origin of replication (area where the DNA mc is attached to plasma membrane) replicates, and chromosome replication begins. 2. origins move to opposite sides of the cell and replication continues 3. replication finishes, cell wall & plasma membrane grow inward 4. two daughter cells result between prokaryotic & eukaryotic cells: mode of reproduction, number of 1-strand chromosomes, shape of bacterial chromosome -binary fission/mitosis or meiosis -1 -> 2 -> 1 in prokaryotes. 46 1-strand (23 pairs) in somatic cell -> 92 -> 46. 23 1-strand in gametes -> 46 when fertilized. Shape= not condensed vs. condensed into individual chromosomes with certain genes What controls the cell cycle? checkpoints and specific signaling molecules present in cytoplasm encourage stage progression: cell cycling control system -> cyclically operating set of molecules in cell that both triggers & coordinates key events in cycle What is a cell cycle checkpoint? control point where cells receive stop or go ahead signals. At G1, G2, and M. signals transmitted by signal transduction pathways -> built in stop until overridden by go ahead signal G1 checkpoint if cell doesn't receive message to enter the S phase, it will enter the Go phase, not dividing and performing functions until death. Some cells like liver cells can be called back from Go phase to the cell cycle by external cues, like growth factors released during injury. checkpoint affected by cell size, growth factor, environment Mitosis does not occur in the abcense of this molecule: cdc2 kinase the 5 steps of the fluctuation of MPF activity & cyclin concentration during the cell cycle 1. synthesis of cyclin begins in late S phase & continues through G2. Because cyclin is protected from degradation during this stage, it accumulates. 2. Accumulated cyclin molecules combine with recycled cdk molecules, producing enough MPF molecules for the cell to pass the G2 checkpoint and initiate mitosis. 3. MPF promotes mitosis by phosphorylating various proteins, and MPF activity peaks during metaphase. 4. During Anaphase, cyclin component of MPF is degraded, terminating the M phase. The cell enters G1. 5. During G1, conditions in the cell favor degradation of cyclin and the cdk component of MPF is recycled. G2 Checkpoint stimulates beginning of mitosis after all mistakes in DNA replication have been repaired. Also, high concentrations of MPF in the cell encourage it to pass G2 & enter mitosis. checkpoint affected by DNA replication complete, DNA damage, cell size M checkpoint Anaphase won't begin until all the chromosomes are properly attached to the spindle at the metaphase plate and kinetochores are all attached. Then once regulatory protein is activated, it sets off the process of cleavage of cohesins. checkpoint affected by if spindle fibers are attached to kinetochores. What is a protein kinase? enzymes that activate or inactivate other proteins by phosphorylating them. Certain pk's give the go-ahead signals at the G1 & G2 checkpoints by attaching to cyclins and activating them. pk's are inactive in a growing cell. kinases drive the cell cycle, but they must be activated by attachment of a _____ phosphate the activity of cyclin-dependent kinases rises and falls. Why? kinases must be attached to cyclins to be active, and only then can they drive the cell cycle. Highest activity at chekcpoints, cdk concentration rises & falls with cyclin concentration. what does MPF trigger? Maturation-Promoting Factor phosphorylates proteins that initiate mitosis. Also activates other kinases. Causes fragmentation of nuclear envelope during prometaphase, and contributes to chromosomes condensing & spindle forming. What constitutes the cell's genome? all the DNA in a cell what are chromosomes packaged DNA + proteins containing many genes 1 DNA molecule = _________ chromosome 1 single-strand chromosome what is chromatin complex of DNA & protein that is loose for cell replication & condenses into chromosomes in eukaryotic cell division what kind of cell does mitosis occur in? only in eukaryotic cells G1 phase simplified cell grows & DNA prepare to replicate simplify S phase DNA replicates simplify G2 phase check/ repair of DNA what phase of interphase does the cell grow in? all 3 phases What is a telomere? cap on end of chromosomes to protect them, gets shorter every division. Eventually can't divide any more in normal cells, but HeLa cells keep dividing What are the 4 steps of prokaryotic cell division? growth + ORI replication -> ORI on both sides of cell, cell growth -> DNA replicates -> cell divides (size signals) -> genetically identical daughter cells what activated molecule has a part in the G1 phase? cyclin D activates to form cdk4 complex, phosphorlyates enzymes for G1 activity, breaks down at the end of G1 metastasis: cancer cells traveling throughout the body what external factors can affect cell division (3) temp, sunlight, moisture levels how do platelets help heal wound indirectly? clot wound & release growth factor to stimulate nearby cells to divide, replacing ruined cells 4 factors that control entry into Mitosis: 1. mass factor (crowding) 2. growth rate factor 3. time (different events are synchronized) 4. replication factor- checks for typos/ deletions. Malignant tumors ignore all what is the goal of meiosis I to reduce chromosome # : 46 pairs -> 23 pairs 3 sources of genetic variation toward the end of mitosis: 1. crossing over 2. mostly maternal/paternal could go left or right 3. random assortment of sperm & egg what are growth factors? how does PDGF stimulate fibroblast division & what is it? proteins released by other cells that stimulate cells to divide. PDGF (platelet derived growth factor) is an example of essential nutrient in ECM that cells need to divide. PDGF stimulates fibroblasts to replicate by binding to receptors and stimulating signal transduction pathway that allows cells to pass G1 + divide. What is density-dependent inhibition? when croded cells stop dividing (after vacancy is filled). Binding of cell-surface proteins to each other on adjoining cells sends growth inhibiting signal to both cells, so they can't advance even if growth factor is present. what is anchorage dependence? to divide, cells must be attached to something- ECM or culture jar. Anchorage signals involve plasma membrane proteins what is transformation? process that converts normal cell to cancer cell. These are normally caught by the immune system, but otherwise it replicates & forms tumor. Benign tumor if abnormal cells remain at original site, can be removed by surgery. 4 things a malignant tumor could do/ could have -impair the functions of one or more organs -unusual #s of chromosomes -could disable metabolism of organism -abnormal changes on cell surface allow them to detach from ECM & spread to nearby tissue (ignoring anchorage dependence) -could secrete signals that cause blood vessels to grow toward them, then spread through blood vessels & lymph vessels. how can cancer cells keep dividing? 4 possibilities: -may not need growth factor -may make a required growth factor for themselves -may have a signaling pathway that conveys growth factor signal even in absence -abnormal cell cycle control system The decline of MPF activity at the end of mitosis is due to: a. the destruction of the protein kinase cdk b. decreased synthesis of cyclin. c. the degradation of cyclin c: the degradation of cyclin cdk and cyclin together form MPF, but which one degrades & forms again, and which one gets recycled? cdk gets recycled and cyclin gets degraded/reformed Which of these phases encompasses all of the stages of mitosis? cytokinesis mitosis the mitotic phase mitosis: The M phase includes cytokinesis, which is not a part of mitosis. Centromeres divide and sister chromosomes become full-fledged chromosomes during _____. anaphase Spindle fibers attach to kinetochores during _____. prometaphase