WEEK 4 cellular respiration
Learning Objectives Breakdown:
1. Describe the stages of aerobic respiration: Aerobic respiration is the process by which cells generate energy (in the
form of ATP) using oxygen. It occurs in three main stages:
a. Glycolysis:
○ Location: Cytoplasm.
○ Process: Glucose (a 6-carbon molecule) is broken down into two molecules of pyruvate (a 3-carbon molecule).
This process produces a small amount of energy in the form of 2 ATP molecules and 2 NADH molecules.
○ Oxygen requirement: None. Glycolysis is anaerobic (does not require oxygen).
2. b. Citric Acid Cycle (Krebs Cycle):
○ Location: Mitochondria (in eukaryotes).
○ Process: Each pyruvate is further broken down into carbon dioxide and high-energy electron carriers (NADH
and FADH2). The cycle produces 2 ATP molecules per glucose molecule.
○ Oxygen requirement: Oxygen is needed to oxidize NADH and FADH2 later in the process.
3. c. Electron Transport Chain (ETC):
○ Location: Inner mitochondrial membrane.
○ Process: NADH and FADH2 donate electrons to the chain, which are passed through protein complexes. As
electrons move through the chain, protons (H+) are pumped into the intermembrane space, creating an
electrochemical gradient. Oxygen acts as the final electron acceptor, forming water. This flow of electrons
powers the ATP synthase to produce about 34 ATP molecules through oxidative phosphorylation.
○ Oxygen requirement: Oxygen is essential as the final electron acceptor in the ETC.
4. Total ATP produced in aerobic respiration: Approximately 38 ATP molecules per glucose molecule.
5. Describe anaerobic respiration vs. fermentation:
Anaerobic Respiration:
○ Process: Similar to aerobic respiration, but occurs in the absence of oxygen. Instead of using oxygen as the
final electron acceptor, anaerobic respiration uses alternative molecules (e.g., sulfate, nitrate).
○ ATP Yield: Anaerobic respiration generally produces less ATP than aerobic respiration. The electron transport
chain operates without oxygen, resulting in an incomplete electron flow.
○ Example: Certain bacteria and archaea use sulfate or nitrate as electron acceptors in environments lacking
oxygen.
6. Fermentation:
○ Process: A type of anaerobic respiration that only involves glycolysis. Since there is no oxygen available, the
pyruvate produced in glycolysis is converted into other molecules (e.g., lactic acid in animals or ethanol and
CO2 in yeast) to regenerate NAD+ so that glycolysis can continue and produce ATP.
○ ATP Yield: Fermentation produces only 2 ATP molecules per glucose molecule, much less efficient than aerobic
respiration.
○ Types of fermentation:
■ Lactic Acid Fermentation: Occurs in animal cells (e.g., muscles) when oxygen is scarce, resulting in
the production of lactic acid.
■ Alcoholic Fermentation: Occurs in yeast and some bacteria, resulting in ethanol and carbon dioxide
as byproducts.
7. Key Differences:
○ Anaerobic respiration uses the electron transport chain and generates more ATP than fermentation, which only
uses glycolysis.
○ Fermentation occurs in the absence of oxygen but does not rely on an alternative electron transport chain.
8. Understand the purpose of respiration for sustaining life:
Purpose of Respiration:
○ Energy Production: Respiration is crucial for life because it produces ATP, the energy currency of the cell. ATP
is needed for virtually all cellular activities, including muscle contraction, protein synthesis, and active transport
of molecules.
○ Metabolic Pathways: Cellular respiration is part of a larger network of metabolic pathways that integrate the
breakdown of nutrients (carbohydrates, fats, and proteins) into energy. The conversion of food molecules into
usable energy is essential for growth, repair, and reproduction in organisms.
○ Oxygen and Carbon Dioxide Balance: Aerobic respiration involves the consumption of oxygen and the
production of carbon dioxide, a gas that must be expelled to maintain homeostasis. This balance is essential for
, maintaining optimal conditions in the body and the environment (e.g., in humans, to maintain blood pH and
oxygen levels).
○ Energy Efficiency: Aerobic respiration is more efficient than anaerobic processes (like fermentation) because it
produces significantly more ATP per molecule of glucose. This high ATP yield is crucial for sustaining the
energy needs of large, complex organisms like humans and other animals.
9. In summary, respiration is vital for producing the energy necessary to carry out the biological processes that sustain life.
Whether through aerobic respiration (in the presence of oxygen) or anaerobic processes (in the absence of oxygen),
respiration ensures that cells have the energy they need to function, grow, and maintain homeostasis.
Pathways: Catabolic vs Anabolic
1. Catabolic Pathways:
○ Function: Break down large molecules into smaller ones, releasing energy (e.g., glycolysis, cellular respiration).
○ Energy: Releases energy used to produce ATP.
○ Example: Breakdown of glucose into pyruvate.
2. Anabolic Pathways:
○ Function: Build larger molecules from smaller ones, requiring energy input (e.g., protein synthesis, DNA
replication).
○ Energy: Consumes energy (usually ATP or GTP).
○ Example: Formation of proteins from amino acids.
Key Differences:
● Catabolic: Breaks down molecules, releases energy.
● Anabolic: Builds molecules, consumes energy.
These pathways balance energy release and storage, supporting cellular functions like growth and energy production.
,Types of Reactions: Redox Reactions
1. Oxidation:
○ Definition: The process where a substance loses electrons.
○ Effect: The substance becomes more positively charged as it loses electrons.
○ Example: In the reaction of hydrogen with oxygen to form water, hydrogen is oxidized (loses electrons).
2. Reduction:
○ Definition: The process where a substance gains electrons.
○ Effect: The substance becomes more negatively charged or less positively charged.
○ Example: In the same reaction, oxygen is reduced (gains electrons) to form water.
Key Concept:
● Redox Reactions: Always occur together. If one substance is oxidized (loses electrons), another is reduced (gains
electrons).
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Learning Objectives Breakdown:
1. Describe the stages of aerobic respiration: Aerobic respiration is the process by which cells generate energy (in the
form of ATP) using oxygen. It occurs in three main stages:
a. Glycolysis:
○ Location: Cytoplasm.
○ Process: Glucose (a 6-carbon molecule) is broken down into two molecules of pyruvate (a 3-carbon molecule).
This process produces a small amount of energy in the form of 2 ATP molecules and 2 NADH molecules.
○ Oxygen requirement: None. Glycolysis is anaerobic (does not require oxygen).
2. b. Citric Acid Cycle (Krebs Cycle):
○ Location: Mitochondria (in eukaryotes).
○ Process: Each pyruvate is further broken down into carbon dioxide and high-energy electron carriers (NADH
and FADH2). The cycle produces 2 ATP molecules per glucose molecule.
○ Oxygen requirement: Oxygen is needed to oxidize NADH and FADH2 later in the process.
3. c. Electron Transport Chain (ETC):
○ Location: Inner mitochondrial membrane.
○ Process: NADH and FADH2 donate electrons to the chain, which are passed through protein complexes. As
electrons move through the chain, protons (H+) are pumped into the intermembrane space, creating an
electrochemical gradient. Oxygen acts as the final electron acceptor, forming water. This flow of electrons
powers the ATP synthase to produce about 34 ATP molecules through oxidative phosphorylation.
○ Oxygen requirement: Oxygen is essential as the final electron acceptor in the ETC.
4. Total ATP produced in aerobic respiration: Approximately 38 ATP molecules per glucose molecule.
5. Describe anaerobic respiration vs. fermentation:
Anaerobic Respiration:
○ Process: Similar to aerobic respiration, but occurs in the absence of oxygen. Instead of using oxygen as the
final electron acceptor, anaerobic respiration uses alternative molecules (e.g., sulfate, nitrate).
○ ATP Yield: Anaerobic respiration generally produces less ATP than aerobic respiration. The electron transport
chain operates without oxygen, resulting in an incomplete electron flow.
○ Example: Certain bacteria and archaea use sulfate or nitrate as electron acceptors in environments lacking
oxygen.
6. Fermentation:
○ Process: A type of anaerobic respiration that only involves glycolysis. Since there is no oxygen available, the
pyruvate produced in glycolysis is converted into other molecules (e.g., lactic acid in animals or ethanol and
CO2 in yeast) to regenerate NAD+ so that glycolysis can continue and produce ATP.
○ ATP Yield: Fermentation produces only 2 ATP molecules per glucose molecule, much less efficient than aerobic
respiration.
○ Types of fermentation:
■ Lactic Acid Fermentation: Occurs in animal cells (e.g., muscles) when oxygen is scarce, resulting in
the production of lactic acid.
■ Alcoholic Fermentation: Occurs in yeast and some bacteria, resulting in ethanol and carbon dioxide
as byproducts.
7. Key Differences:
○ Anaerobic respiration uses the electron transport chain and generates more ATP than fermentation, which only
uses glycolysis.
○ Fermentation occurs in the absence of oxygen but does not rely on an alternative electron transport chain.
8. Understand the purpose of respiration for sustaining life:
Purpose of Respiration:
○ Energy Production: Respiration is crucial for life because it produces ATP, the energy currency of the cell. ATP
is needed for virtually all cellular activities, including muscle contraction, protein synthesis, and active transport
of molecules.
○ Metabolic Pathways: Cellular respiration is part of a larger network of metabolic pathways that integrate the
breakdown of nutrients (carbohydrates, fats, and proteins) into energy. The conversion of food molecules into
usable energy is essential for growth, repair, and reproduction in organisms.
○ Oxygen and Carbon Dioxide Balance: Aerobic respiration involves the consumption of oxygen and the
production of carbon dioxide, a gas that must be expelled to maintain homeostasis. This balance is essential for
, maintaining optimal conditions in the body and the environment (e.g., in humans, to maintain blood pH and
oxygen levels).
○ Energy Efficiency: Aerobic respiration is more efficient than anaerobic processes (like fermentation) because it
produces significantly more ATP per molecule of glucose. This high ATP yield is crucial for sustaining the
energy needs of large, complex organisms like humans and other animals.
9. In summary, respiration is vital for producing the energy necessary to carry out the biological processes that sustain life.
Whether through aerobic respiration (in the presence of oxygen) or anaerobic processes (in the absence of oxygen),
respiration ensures that cells have the energy they need to function, grow, and maintain homeostasis.
Pathways: Catabolic vs Anabolic
1. Catabolic Pathways:
○ Function: Break down large molecules into smaller ones, releasing energy (e.g., glycolysis, cellular respiration).
○ Energy: Releases energy used to produce ATP.
○ Example: Breakdown of glucose into pyruvate.
2. Anabolic Pathways:
○ Function: Build larger molecules from smaller ones, requiring energy input (e.g., protein synthesis, DNA
replication).
○ Energy: Consumes energy (usually ATP or GTP).
○ Example: Formation of proteins from amino acids.
Key Differences:
● Catabolic: Breaks down molecules, releases energy.
● Anabolic: Builds molecules, consumes energy.
These pathways balance energy release and storage, supporting cellular functions like growth and energy production.
,Types of Reactions: Redox Reactions
1. Oxidation:
○ Definition: The process where a substance loses electrons.
○ Effect: The substance becomes more positively charged as it loses electrons.
○ Example: In the reaction of hydrogen with oxygen to form water, hydrogen is oxidized (loses electrons).
2. Reduction:
○ Definition: The process where a substance gains electrons.
○ Effect: The substance becomes more negatively charged or less positively charged.
○ Example: In the same reaction, oxygen is reduced (gains electrons) to form water.
Key Concept:
● Redox Reactions: Always occur together. If one substance is oxidized (loses electrons), another is reduced (gains
electrons).
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