STUDY GUIDE EXAM 2: Biochemistry: Metabolism and ATP Generation

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Questions and Answers

Which of the following is a product of the Krebs cycle for each acetyl-CoA that enters?

2 ATP

2 NADH

2 CO2 (correct)

3 NADH (correct)

What is the primary location of ATP production in aerobic respiration?

Cytoplasm

Inner mitochondrial membrane (correct)

Plasma membrane

Krebs cycle

Which statement best describes glycolysis?

It requires oxygen to function.

It occurs in the mitochondria of all cells.

It is the only step in cellular respiration that produces ATP.

It breaks down glucose into pyruvate. (correct)

What is the final product of alcoholic fermentation?

Ethanol and CO2 Signup and view all the answers

During aerobic respiration, what role does oxygen play?

Acts as the final electron acceptor in the electron transport chain Signup and view all the answers

Which of the following correctly summarizes anaerobic respiration?

Does not require oxygen and can use sulfate or nitrate as acceptors Signup and view all the answers

What happens to pyruvate during the preparatory reaction before entering the Krebs cycle?

It is oxidized to acetyl-CoA and releases CO2. Signup and view all the answers

Which of the following pathways does NOT occur in anaerobic respiration?

Electron transport chain Signup and view all the answers

For each glucose molecule, how many ATP molecules are typically produced via aerobic respiration?

36-38 ATP Signup and view all the answers

Which enzyme synthesizes ATP using the proton gradient generated in the ETC?

ATP synthase Signup and view all the answers

What is the final electron acceptor used in aerobic respiration?

Oxygen Signup and view all the answers

Which process yields the highest amount of ATP per glucose molecule?

Aerobic respiration Signup and view all the answers

Where does anaerobic respiration primarily occur in prokaryotes?

Cytoplasm and plasma membrane Signup and view all the answers

What is an end product of fermentation?

Ethanol Signup and view all the answers

Which of the following processes does not require oxygen?

Glycolysis Signup and view all the answers

During which process is pyruvate converted to lactic acid or ethanol?

Fermentation Signup and view all the answers

What is the typical ATP yield for anaerobic respiration per glucose?

2 ATP Signup and view all the answers

Where does the Krebs cycle take place in eukaryotic cells?

Mitochondria Signup and view all the answers

Which of these is NOT a characteristic of fermentation?

Requires oxygen Signup and view all the answers

What distinguishes the final electron acceptors in anaerobic respiration compared to aerobic respiration?

Anaerobic uses organic molecules; aerobic uses oxygen Signup and view all the answers

What is the primary function of catabolic pathways?

To break down molecules and release energy Signup and view all the answers

Which of the following correctly describes an anabolic process?

Synthesizing proteins from amino acids Signup and view all the answers

What is produced during oxidative phosphorylation?

ATP Signup and view all the answers

How does ATP serve as an intermediary in metabolism?

By linking energy-releasing and energy-consuming processes Signup and view all the answers

Which of the following statements about metabolism is true?

Metabolism involves both catabolic and anabolic reactions Signup and view all the answers

What is the role of substrate-level phosphorylation?

To produce ATP using energy from enzyme-catalyzed reactions Signup and view all the answers

Why is glucose considered a crucial molecule for organisms?

It serves as a primary energy source Signup and view all the answers

Which of the following processes primarily occurs in mitochondria?

Oxidative phosphorylation Signup and view all the answers

What is the result of catabolic reactions?

Energy release and building blocks for anabolism Signup and view all the answers

Which energy transformation occurs during photophosphorylation?

Light energy is used to generate ATP Signup and view all the answers

Study Notes

Metabolism

Metabolism involves the breakdown and buildup of nutrients within a cell.
Catabolism breaks down complex molecules into simpler ones, releasing energy.
- Provides energy for ADP phosphorylation (ADP to ATP) and building blocks for anabolism.
- Exergonic reactions release energy.
Anabolism uses energy to build complex molecules from simpler ones.
- Endergonic reactions require energy.
- Essential for growth, repair, and maintenance of cellular structures.

ATP Generation

Substrate-level phosphorylation: An enzyme directly transfers a phosphate group from a substrate to ADP, forming ATP. Occurs in glycolysis and the Krebs cycle.
Oxidative phosphorylation: Energy from the electron transport chain (ETC) is used to generate ATP. Electrons are passed along a series of proteins, creating a flow of protons (H+) across a membrane. Occurs during cellular respiration in mitochondria (eukaryotes) or the plasma membrane (prokaryotes).
Photophosphorylation: Light energy is used to add a phosphate group to ADP, forming ATP. Creation of ATP via ETC and ATP synthase in chloroplasts (photosynthesis).

Metabolic Pathways

Metabolic pathways are series of enzymatically catalyzed reactions in a cell.
Catabolic pathways break down molecules to release energy.
Anabolic pathways build up molecules by using energy.
Metabolic pathways extract energy from nutrients or light and convert it into usable forms like ATP.
They produce building blocks for the cell, minimizing waste and conserving resources.

ATP as a Link Between Catabolism and Anabolism

ATP acts as an intermediary in cellular metabolism.
In catabolism, energy released from breaking down molecules is stored in ATP.
In anabolism, ATP provides the energy needed for the synthesis of complex molecules.

Glucose: a Key Molecule

Glucose is a primary source of energy.
Cellular respiration breaks down glucose to produce ATP.
Glucose is a universal fuel, utilized by most cells.
Serves as a starting point for various metabolic pathways, like glycolysis.

Aerobic Respiration

Breaks down glucose, lipids, or proteins to produce ATP, requiring oxygen.
Reaction equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP
In eukaryotic cells: Primarily occurs in the mitochondria.
In prokaryotic cells: Occurs in the cytoplasm (glycolysis and Krebs cycle) and across the plasma membrane (ETC).

Glycolysis

The first stage of cellular respiration.
Breaks down 6-carbon glucose (C6H12O6) into two 3-carbon pyruvate molecules (C3H6O3).
Does not require oxygen (anaerobic).
Produces a net gain of +2 ATP and +2 NADH molecules.
Occurs in the cytoplasm of both prokaryotes and eukaryotes.

Preparatory Reaction (Pyruvate Oxidation)

Occurs after glycolysis and before the Krebs cycle.
Converts each pyruvate molecule into acetyl-CoA.
Does not require oxygen.
Releases one carbon atom from pyruvate as CO2 (the first CO2 released in cellular respiration).
Produces +2 NADH "hydrogen transport" molecules.
The remaining 2-carbon molecules (acetate) bind to Coenzyme A to form acetyl-CoA, which enters the Krebs cycle.

Krebs Cycle

Turns twice per glucose molecule since glycolysis produces 2 pyruvate molecules.
Occurs in the mitochondrial matrix (eukaryotes) and the cytoplasm (prokaryotes).
Products per acetyl-CoA:
- 3 NADH (electron carrier)
- 1 FADH2 (electron carrier)
- 1 ATP
- 2 CO2 (released as a waste product)

Electron Transport Chain (ETC)

Located in the inner mitochondrial membrane (eukaryotes) and the plasma membrane (prokaryotes).
Final step in aerobic respiration.
Transport of hydrogen as NADH to ETC membrane system.
ATP production: Electrons from NADH and FADH2 are passed through protein complexes, creating a proton (H+) gradient across the membrane. This gradient drives ATP synthase, which synthesizes ATP from ADP and Pi.
Oxygen serves as the final electron acceptor, combining with protons and electrons to form water. Generates 32-34 ATP per glucose.

NAD+ in the ETC

NAD+ is reduced to NADH during glycolysis, the preparatory reaction, and the Krebs cycle.
NADH donates electrons to the first complex of the ETC.
As electrons are passed down the chain, protons (H+) are pumped across the membrane, contributing to the proton gradient that drives ATP synthesis.

Comparison of Aerobic and Anaerobic Respiration

Feature	Aerobic Respiration	Anaerobic Respiration
O2 requirement	Requires O2	Does not require O2
ATP yield per glucose	36-38 ATP	Less than 30 ATP
Final electron acceptor	Oxygen	Nitrate, sulfate, or other compounds
Location in eukaryotes	Mitochondria	Cytoplasm
Location in prokaryotes	Cytoplasm and plasma membrane	Cytoplasm and plasma membrane
End products	CO2, H2O	CO2, Nitrate, or Sulfide
Process involved	Glycolysis, Krebs cycle, ETC	Glycolysis, Krebs cycle, ETC

Fermentation

Anaerobic process occurring after glycolysis when oxygen is unavailable.
Regenerates NAD+ by transferring electrons from NADH to pyruvate or its derivatives.
Does not require oxygen.
Does not use the Krebs cycle or ETC.
Occurs in the cytoplasm.
Produces small amounts of ATP (2 ATP per glucose).
Types of fermentation:
- Lactic acid fermentation: Pyruvate is reduced to lactic acid. Occurs in muscle cells and some bacteria (yogurt production).
- Alcohol fermentation: Pyruvate is converted to ethanol and CO2. Occurs in yeast and some bacteria (brewing and baking).

Products of Fermentation

Lactic acid (cheese, yogurt)
Ethanol (beer, wine)
Acetone (pharmaceutical, industrial use)
Citric acid (flavoring)

Energy Yield Comparison

Aerobic respiration: 36-38 ATP per glucose
Anaerobic respiration: Less than 30 ATP per glucose
Fermentation: 2 ATP per glucose

Lipid and Protein Entry into Respiration

Lipids: Fats are broken down into glycerol and fatty acids. Glycerol enters glycolysis. Fatty acids are broken down into acetyl-CoA through beta-oxidation and enter the Krebs cycle.
Proteins: Broken down into amino acids. Amino acids have their nitrogen removed and are converted into molecules that can enter different stages of respiration (glycolysis, preparatory reaction, Krebs cycle).

Common Step in Respiration

The common step in aerobic, anaerobic, and fermentation is glycolysis.

Respiration Summary

Aerobic respiration: Glycolysis → Krebs cycle → ETC (using oxygen as the final electron acceptor)
Anaerobic respiration: Glycolysis → Krebs cycle → ETC (using a non-oxygen acceptor)
Fermentation: Glycolysis → fermentation (conversion of pyruvate to lactic acid, ethanol, etc.)

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Description

This quiz covers the fundamental concepts of metabolism, including catabolism and anabolism, as well as the mechanisms of ATP generation through substrate-level and oxidative phosphorylation. Test your understanding of how energy is transformed in biological systems and the roles of different processes in cellular function.