Cellular Respiration and Energy Metabolism
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Questions and Answers

What is the primary source of energy for living cells?

  • Solar energy
  • Inorganic compounds
  • Mechanical energy from movement
  • Chemical energy in organic molecules (correct)

What process generates O2 and organic molecules in ecosystems?

  • Decomposition
  • Cellular respiration
  • Fermentation
  • Photosynthesis (correct)

Which type of respiration occurs without the presence of O2?

  • Anaerobic respiration
  • Both A and B (correct)
  • Aerobic respiration
  • Fermentation

What is the main product of aerobic respiration?

<p>ATP (C)</p> Signup and view all the answers

In what organelle does cellular respiration primarily occur?

<p>Mitochondria (B)</p> Signup and view all the answers

What type of respiration uses compounds other than O2?

<p>Anaerobic respiration (C)</p> Signup and view all the answers

How does energy flow through an ecosystem?

<p>It is lost as heat after each trophic level (D)</p> Signup and view all the answers

Which statement accurately describes fermentation?

<p>It is a partial degradation of sugars without O2. (A)</p> Signup and view all the answers

What is the main purpose of glycolysis?

<p>To convert glucose into pyruvate and harvest energy. (C)</p> Signup and view all the answers

How many NADH molecules are generated in glycolysis?

<p>2 NADH (A)</p> Signup and view all the answers

What occurs in the mitochondrion after pyruvate is oxidized?

<p>The citric acid cycle continues the oxidation of organic molecules. (D)</p> Signup and view all the answers

What is the total ATP yield from one glucose molecule at maximum, through cellular respiration?

<p>30 or 32 ATP (B)</p> Signup and view all the answers

Which metabolic pathway is described as the 'splitting of sugar'?

<p>Glycolysis (C)</p> Signup and view all the answers

What is produced during the energy investment phase of glycolysis?

<p>2 NADH and 2 ATP used (A)</p> Signup and view all the answers

What is the net gain of ATP from glycolysis per glucose molecule?

<p>2 ATP (D)</p> Signup and view all the answers

In terms of energy, what role do electron shuttles play in the mitochondrion?

<p>They carry electrons to the electron transport chain. (B)</p> Signup and view all the answers

Which of the following correctly describes glycolysis?

<p>It generates ATP without the need for oxygen. (D)</p> Signup and view all the answers

What role does NADH play during cellular respiration?

<p>It transports electrons to the electron transport chain. (B)</p> Signup and view all the answers

In which stage of cellular respiration is the majority of ATP produced?

<p>Oxidative phosphorylation (A)</p> Signup and view all the answers

What is the primary outcome of the citric acid cycle?

<p>Completion of glucose breakdown. (B)</p> Signup and view all the answers

Which process is characterized by an explosive release of energy?

<p>Uncontrolled reactions (B)</p> Signup and view all the answers

What represents the controlled release of energy in cellular respiration?

<p>Electron transport chain. (B)</p> Signup and view all the answers

Which reactant is necessary for the oxidative phosphorylation stage of cellular respiration?

<p>Oxygen (D)</p> Signup and view all the answers

What is formed as a direct result of the reaction involving $H_2$ and $1/2 O_2$?

<p>Water (C)</p> Signup and view all the answers

What is produced when pyruvate is converted to acetyl CoA?

<p>NADH + H+ (C), CO2 (D)</p> Signup and view all the answers

How many ATP molecules are produced per turn of the citric acid cycle?

<p>2 (C)</p> Signup and view all the answers

What role do NADH and FADH2 play in cellular respiration?

<p>They act as electron carriers. (C)</p> Signup and view all the answers

Which of the following describes the citric acid cycle?

<p>It completes the breakdown of pyruvate to CO2. (D)</p> Signup and view all the answers

How many NADH molecules are generated from two turns of the citric acid cycle?

<p>6 (B)</p> Signup and view all the answers

What is acetyl CoA's primary function in cellular respiration?

<p>To link glycolysis with the citric acid cycle. (D)</p> Signup and view all the answers

What key molecule is produced alongside each turn of the citric acid cycle?

<p>ATP (A)</p> Signup and view all the answers

Which enzyme complex is responsible for the conversion of pyruvate to acetyl CoA?

<p>Pyruvate dehydrogenase complex (D)</p> Signup and view all the answers

What is the primary final electron acceptor in fermentation?

<p>Pyruvate or acetaldehyde (A)</p> Signup and view all the answers

How much ATP is produced during fermentation per glucose molecule?

<p>2 ATP (D)</p> Signup and view all the answers

Which of the following describes obligate anaerobes?

<p>Organisms that cannot survive in the presence of oxygen (A)</p> Signup and view all the answers

What role does glycolysis play in both aerobic and anaerobic processes?

<p>It oxidizes glucose to produce ATP. (D)</p> Signup and view all the answers

Which of the following statements is true regarding the evolutionary significance of glycolysis?

<p>It was the first metabolic pathway used by ancient prokaryotes. (C)</p> Signup and view all the answers

What is the end product of lactic acid fermentation?

<p>Lactic acid (C)</p> Signup and view all the answers

Which organisms are considered facultative anaerobes?

<p>Organisms that can survive using fermentation or cellular respiration (A)</p> Signup and view all the answers

What is the main purpose of glycolysis in cellular metabolism?

<p>To oxidize glucose and generate ATP. (C)</p> Signup and view all the answers

What is the primary function of the electron transport chain in the mitochondrion?

<p>To transfer electrons and pump protons (C)</p> Signup and view all the answers

What is the final electron acceptor in the electron transport chain?

<p>O2 (D)</p> Signup and view all the answers

How does ATP synthase generate ATP during chemiosmosis?

<p>By converting ADP and inorganic phosphate using the proton gradient (D)</p> Signup and view all the answers

What is the main energy source for the ATP produced during cellular respiration?

<p>Glucose through NADH (D)</p> Signup and view all the answers

What role do protons (H+) play in the electron transport chain?

<p>They are pumped into the intermembrane space to create a gradient (D)</p> Signup and view all the answers

What percentage of energy from glucose is typically transferred to ATP during cellular respiration?

<p>34% (A)</p> Signup and view all the answers

What happens to oxygen at the end of the electron transport chain?

<p>It combines with protons and electrons to form water (B)</p> Signup and view all the answers

Which component of the inner mitochondrial membrane is primarily responsible for phosphorolating ADP into ATP?

<p>ATP synthase (C)</p> Signup and view all the answers

What process utilizes the proton gradient established by the electron transport chain?

<p>Chemiosmosis (B)</p> Signup and view all the answers

What are the multi-protein complexes within the electron transport chain primarily composed of?

<p>Proteins (C)</p> Signup and view all the answers

Flashcards

Aerobic Respiration

The process by which organisms obtain energy from organic molecules using oxygen. This process releases carbon dioxide, water, and ATP, the energy currency of cells.

Anaerobic Respiration

This is a type of cellular respiration that occurs without oxygen. It produces less ATP compared to aerobic respiration.

Fermentation

A process that breaks down sugars without using oxygen. It occurs in the absence of oxygen and produces a small amount of ATP.

Energy Flow

Energy enters the ecosystem as sunlight and is converted into chemical energy in organic molecules through photosynthesis.

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Photosynthesis

The process by which plants and some bacteria use sunlight to convert carbon dioxide and water into glucose and oxygen.

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ATP (Adenosine Triphosphate)

A high-energy molecule that serves as the primary energy currency for cells.

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Catabolic Pathways

The breakdown of organic molecules to release energy.

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Photosynthesis

A chemical process that transforms energy from sunlight into chemical energy stored in glucose. It occurs in chloroplasts of plant cells.

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Cellular Respiration

The process where cells break down glucose to generate energy in the form of ATP. It involves three main stages: glycolysis, the citric acid cycle, and oxidative phosphorylation.

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Glycolysis

The first stage of cellular respiration, where glucose is broken down into two pyruvate molecules. Occurs in the cytoplasm and yields a small amount of ATP.

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Citric Acid Cycle (Krebs Cycle)

The second stage of cellular respiration, where pyruvate is broken down further, generating electron carriers (NADH and FADH2) and some ATP. It occurs in the mitochondria and is a cyclical process.

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Oxidative Phosphorylation

The third and final stage of cellular respiration, where most ATP is produced. It involves the electron transport chain and chemiosmosis.

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Electron Transport Chain

A series of protein complexes embedded in the mitochondrial membrane that pass electrons from one to another, releasing energy along the way.

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Chemiosmosis

The process of using the proton gradient generated by the electron transport chain to drive ATP synthesis.

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Free Energy Change (ΔG)

The difference in free energy between reactants and products. It determines whether a reaction is exergonic (releases energy) or endergonic (requires energy) and whether it will occur spontaneously.

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Pyruvate Oxidation

The process of converting pyruvate into acetyl-CoA, releasing carbon dioxide and generating NADH. This occurs in the mitochondria of eukaryotic cells.

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Citric Acid Cycle

A series of reactions that further oxidizes acetyl-CoA, generating ATP, NADH, and FADH2. This occurs in the mitochondrial matrix.

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ATP

A high-energy molecule that is the primary energy currency of cells. It is used to power cellular processes.

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Passive Transport

The movement of molecules across a membrane from a region of high concentration to a region of low concentration, requiring no energy.

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Pyruvate to Acetyl-CoA Conversion

The process of converting pyruvate into acetyl-CoA, which serves as a link between glycolysis and the citric acid cycle. This occurs within the mitochondria with the aid of a multienzyme complex.

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Pyruvate dehydrogenase complex

A multienzyme complex that catalyzes the conversion of pyruvate to acetyl-CoA in three sequential steps. This complex is essential for the transition between glycolysis and the citric acid cycle.

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Citric acid cycle energy yield

Each turn of the citric acid cycle generates 2 ATP, 6 NADH, and 2 FADH2, representing the energy yield of the cycle. These energy carriers are then used in the electron transport chain to produce additional ATP.

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Citric acid cycle steps

The citric acid cycle involves eight distinct steps, each catalyzed by a specific enzyme. These enzymes control the rate and direction of the cycle.

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Electron transport chain role

NADH and FADH2, produced by the citric acid cycle, carry high-energy electrons to the electron transport chain, where they are used to generate a proton gradient that powers ATP synthesis.

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What is the location of the electron transport chain?

The inner membrane of mitochondria, folded into cristae, houses the electron transport chain.

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What is the Electron Transport Chain?

A series of protein complexes embedded in the inner mitochondrial membrane that transfer electrons from one to another, releasing energy along the way.

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How are protons (H+) moved across the mitochondrial membrane?

Protons (H+) are pumped from the mitochondrial matrix to the intermembrane space by the proteins of the electron transport chain.

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What is the final electron acceptor in the electron transport chain?

Oxygen is the final electron acceptor in the electron transport chain, combining with electrons and protons to form water.

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What is chemiosmosis?

The process by which the energy stored in the proton gradient across the mitochondrial membrane is used to drive ATP synthesis.

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What is ATP synthase?

An enzyme embedded in the inner mitochondrial membrane that uses the flow of protons to drive the phosphorylation of ADP to ATP.

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How does the electron transport chain create a proton gradient?

The energy released during electron transport drives the pumping of protons across the mitochondrial membrane, creating a gradient.

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How much ATP is produced from a glucose molecule during cellular respiration?

Cellular respiration, including the electron transport chain, captures about 34% of the energy in glucose, producing roughly 32 ATP molecules.

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Describe the energy flow in cellular respiration.

The energy flow in cellular respiration follows this pathway: glucose -> NADH -> electron transport chain -> chemiosmosis -> ATP.

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Why is the exact number of ATP produced in cellular respiration uncertain?

The number of ATP produced during cellular respiration is not precise due to factors like the efficiency of the process and the use of some energy for proton pumping.

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Obligate Anaerobes

These organisms only survive on fermentation or anaerobic respiration. They cannot thrive in the presence of oxygen.

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Facultative Anaerobes

These organisms can survive using either fermentation or cellular respiration. They can switch between using oxygen and not using oxygen.

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Lactic Acid Fermentation

This refers to the process where pyruvate is converted to lactic acid. It is a key process in producing yogurt and cheese.

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Alcoholic Fermentation

This refers to the process where pyruvate is converted to ethanol and carbon dioxide. It is critical in making alcoholic beverages.

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Study Notes

Cellular Respiration and Fermentation

  • Living cells require energy from outside sources
  • Some animals eat plants, others eat organisms that eat plants
  • Energy flows into an ecosystem as sunlight and leaves as heat
  • Photosynthesis generates oxygen and organic molecules which are used in cellular respiration
  • Cells use chemical energy stored in organic molecules to regenerate ATP which powers work
  • Aerobic respiration consumes organic molecules and O2 and yields ATP
  • Anaerobic respiration is similar to aerobic respiration but uses compounds other than O2 for consumption
  • Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration
  • Glucose is the common fuel trace in cellular respiration (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat))

The Principle of Redox

  • Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions or redox reactions
  • In oxidation, a substance loses electrons, or is oxidized
  • In reduction, a substance gains electrons, or is reduced
  • OIL RIG = Oxidation Is Loss, Reduction Is Gain

Oxidation of Organic Fuel Molecules during Cellular Respiration

  • During cellular respiration, the fuel (such as glucose) is oxidized, and O₂ is reduced
  • C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy

Stepwise Energy Harvest via NAD+ and the Electron Transport Chain

  • In cellular respiration, glucose and other organic molecules are broken down in a series of steps
  • Electrons from organic compounds are usually first transferred to NAD+, a coenzyme
  • As an oxidizing agent during cellular respiration, NAD+ accepts electrons
  • NADH (the reduced form of NAD+) represents stored energy tapped to synthesize ATP
  • NADH passes the electrons to the electron transport chain
  • Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction
  • O₂ pulls electrons down the chain in an energy-yielding tumble
  • The energy yielded is used to regenerate ATP

The Stages of Cellular Respiration: A Preview

  • Harvesting energy from glucose has three stages
  • Glycolysis: breaks down glucose into two molecules of pyruvate
  • The Citric Acid Cycle: completes the breakdown of glucose
  • Oxidative phosphorylation: accounts for most of the ATP synthesis

Glycolysis

  • Glycolysis ("splitting of sugar") breaks down glucose into two molecules of pyruvate
  • Glycolysis occurs whether or not O2 is present
  • Net products of glycolysis: 2 ATP, 2 NADH, 2 pyruvate, and 2H2O
  • Energy Investment Phase: uses 2 ATPs
  • Energy Payoff Phase: creates 4 ATPs, 2 NADH, net of 2 ATPs.

Oxidation of Pyruvate to Acetyl CoA

  • Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links glycolysis to the citric acid cycle
  • This step is carried out by a multienzyme complex that catalyzes three reactions
  • The products are CO2, NADH, and Acetyl CoA

The Citric Acid Cycle

  • The citric acid cycle, also called the Krebs cycle, completes the breakdown of pyruvate to CO2
  • The cycle oxidizes organic fuel derived from pyruvate, generating (per turn x2 = 2 turns) : 2 ATP, 6 NADH, and 2 FADH2
  • The citric acid cycle has eight steps, each catalyzed by a specific enzyme
  • The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain

Oxidative Phosphorylation

  • Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration
  • A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation
  • For each molecule of glucose degraded to CO₂ and water by respiration, the cell makes up to 32 molecules of ATP

Chemiosmosis

  • Chemiosmosis couples electron transport to ATP synthesis
  • NADH and FADH2 donate electrons to the electron transport chain, powering ATP synthesis via oxidative phosphorylation
  • The electron transport chain is in the inner membrane (cristae) of the mitochondrion
  • Most of the chain's components are proteins in multi-protein complexes
  • Protons (H+) are pumped from the matrix to the intermembrane space by the ETC proteins

Fermentation

  • Fermentation is a partial degradation of sugars that occurs without O₂
  • Most cellular respiration requires O₂ for ATP production
  • Without O2, the electron transport chain will stop
  • Glycolysis couples with fermentation or anaerobic respiration to produce ATP
  • Two common types of fermentation are lactic acid and alcohol fermentation

Lactic Acid Fermentation

  • In lactic acid fermentation, pyruvate is reduced to NADH, forming lactic acid as an end product, with no release of CO₂
  • Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt
  • Human muscle cells use lactic acid fermentation to generate ATP when O₂ is scarce

Alcoholic Fermentation

  • In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO₂
  • Alcohol fermentation by yeast is used in brewing, winemaking, and baking

Comparing Fermentation with Aerobic Respiration

  • All use glycolysis (net ATP = 2) to oxidize glucose and harvest chemical energy of food
  • In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis
  • The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O₂ in cellular respiration
  • Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

Other Metabolic Pathways involved in Glycolysis and the Citric Acid Cycle

  • Proteins, carbohydrates, and lipids are other metabolic pathways involved in glycolysis and the citric acid cycle
  • Amino acids contribute to glycolysis and the citric acid cycle via sugars

Regulation of Cellular Respiration through Feedback Mechanism

  • Cellular respiration regulation mechanisms include feedback through glycolysis and citric acid cycle
  • Enzymes involved in glycolysis and citric acid cycle can be regulated to maintain overall homeostasis

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Description

Test your knowledge on cellular respiration, energy flow in ecosystems, and the various metabolic pathways involved. This quiz covers topics such as glycolysis, fermentation, and ATP production. Perfect for students studying biology or related fields.

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