Cell Biology Exam 3: Chapter 10: Aerobic Cellular Respiration

What is chemotrophic energy metabolism?

The process by which organisms obtain energy from chemical compounds by breaking down/oxidizing chemical substances to release energy. Chemotrophs use this energy is later used to make ATP (the main energy-carrying molecule in cells).

What is aerobic respiration?

A specific type of energy-producing process that uses Oxygen.

During aerobic respiration, cells break down fuel molecules (commonly glucose and other organic fuels) in order to use Oxygen as the final electron acceptor in the electron transport chain. It releases energy that the cell captures in ATP.

What are the 2 main types of chemotrophs based on the chemicals they use for energy, and list who falls under each type?

1. Chemoorganotrophs: Obtain energy from organic compounds, such as glucose. Humans, animals, fungi, and many bacteria belong to this group.

2. Chemolithotrophs: Obtain energy by oxidizing inorganic substances, such as ammonia, hydrogen sulfide, iron, or hydrogen. Certain bacteria and archaea do this.

True or False: Chemotrophs may use oxygen, but they can also obtain energy through processes that do not require oxygen.

Explain your reasoning.

True

Reasoning: The statement is true because chemotrophs get their energy from chemical substances, not necessarily from oxygen. They use both aerobic and anaerobic respiration to obtain energy.

Aerobic Respiration occurs in….

Aerobic respiration occurs in humans, animals, plants, fungi, and many microorganisms.

Anaerobic respiration occurs in…

Anaerobic respiration occurs in cells or organisms that obtain energy without using oxygen, such as:

1. Certain bacteria and archaea that live in environments without oxygen.

2. Some microorganisms living in soil, mud, and deep-water environments.

During aerobic respiration:

1. _________ supplies the chemical energy.

2. __________ acts as the final electron acceptor.

3. ___________ and ___________ are produced.

4. _________ stores usable energy for cellular activities.

In this process:

• Glucose supplies the chemical energy.

• Oxygen acts as the final electron acceptor.

• Carbon dioxide and water are produced.

• ATP stores usable energy for cellular activities.

Aerobic respiration produces _______ ATP yield per glucose, while ATP production during chemotrophic energy metabolism ________________.

Aerobic respiration yields a HIGH ATP yield per glucose, whereas ATP production during chemotrophic energy metabolism varies by metabolic pathway!

How does aerobic vs. anaerobic respiration differ?

Aerobic and anaerobic respiration differ mainly in whether oxygen is used to release energy from food and how much energy is produced.

Aerobic vs. Anaerobic Respiration Chart:

1. Which requires Oxygen?

2. Compare how much energy is produced.

3. Compare glucose breakdown.

4. What are the products?

5. Give an example of each type of respiration.

Aerobic vs. Anaerobic Respiration

Feature	Aerobic respiration	Anaerobic respiration
Oxygen	Requires oxygen	Does not require oxygen
Energy produced	Usually more ATP	Often less ATP
Glucose breakdown	Usually completely broken down	Depends on the process; may be incomplete
Products	Carbon dioxide and water	Vary; may include lactic acid, ethanol, or other products
Example	Humans running while breathing normally	Certain bacteria living without oxygen

True or False: Both aerobic and anaerobic respiration are categorized as chemotrophic energy metabolism processes?

Explain your reasoning.

True!

Reasoning: they both obtain energy through chemical reactions.

__________ respiration: Uses oxygen to help release energy from chemical substances such as glucose.

Aerobic respiration

___________ respiration: Uses a substance other than oxygen as the final electron acceptor to release energy from chemical substances.

Anaerobic respiration

1. Define cellular respiration.

2. What are the 2 types of cellular respiration?

1. Cellular respiration is the process by which cells break down molecules like glucose (sugar) to release energy and store it in a usable form called ATP (adenosine triphosphate).

2. Two main types of cellular respiration

2A). Aerobic respiration: Requires oxygen and usually produces much more ATP.

2B). Anaerobic respiration: Does not require oxygen and uses a different method to obtain energy.

What is the equation for aerobic cellular respiration?

True or False: Without cellular respiration, cells would not be able to efficiently obtain the energy they need to function.

Explain your reasoning!

True!

Reasoning: Without cellular respiration, cells would lose a major way of producing ATP. Some cells can still make ATP through processes such as glycolysis, but they generally could not meet their energy needs as efficiently.

1. Define anaerobic fermentation.

2. Compare and contrast anaerobic fermentation with anaerobic respiration.

1. Anaerobic fermentation is a process cells use to release a small amount of energy from glucose without needing oxygen.

2. Fermentation: Gets energy through glycolysis and regenerates NAD⁺ so glycolysis can continue.

2. Anaerobic respiration: Uses an electron transport chain but substitutes another substance, such as nitrate or sulfate, for oxygen as the final electron acceptor.

Anaerobic Fermentation vs. Anaerobic Respiration:

1. Uses Oxygen?

2. Uses an electron transport chain?

3. Energy production?

4. Give an example of each one.

Here’s the key difference:

Feature	Fermentation	Anaerobic respiration
Uses oxygen?	No	No
Uses an electron transport chain?	No	Yes
Energy produced	Small amount (2 ATP per glucose)	Varies; often more than fermentation
Example	Yeast making alcohol	Bacteria using nitrate instead of oxygen

How much ATP per glucose does anaerobic fermentation produce?

Fermentation produces only 2 ATP per glucose through glycolysis.

2 ATP (poor quantity!)

What are the 3 general requirements for aerobic cellular respiration?

1. Uses an electron acceptor to oxidize substrates to CO₂. Explanation: Glucose is oxidized, releasing electrons and producing CO₂.

2. Needs a coenzyme.
   Explanation: Coenzymes such as NAD⁺ and FAD carry electrons.

3. Needs O₂ as the final electron acceptor.
   Explanation: Oxygen accepts electrons at the end of the electron transport chain.

In Eukaryotic cells, aerobic respiration occurs in the ________________.

Mitochondria!

What are coenzymes and why do they matter in cellular respiration?

Coenzymes are small, non-protein molecules that help enzymes carry out chemical reactions. In cellular respiration, they are especially important because they help transport electrons and energy from one reaction to another.

NAD⁺: Accepts electrons and hydrogen, becoming ________.

NADH

FAD: Accepts electrons and hydrogen, becoming __________.

FADH₂

________ and ___________ deliver high-energy electrons to the electron transport chain during aerobic respiration, helping the cell produce ATP.

NADH and FADH₂

Think of coenzymes as delivery trucks 🚚

Why are coenzymes necessary?

Enzymes speed up chemical reactions, but some reactions also need helper molecules. Coenzymes help enzymes transfer electrons or chemical groups so reactions can proceed.

What are the 2 electron-carrying coenzymes that are used in cellular respiration?

NAD⁺ and FAD = electron-carrying coenzymes used in cellular respiration.

Define glucose.

Glucose is a simple sugar that cells use as a major source of energy. Its chemical formula is C6H12O6.

During aerobic cellular respiration, cells use __________ and ________ to produce carbon dioxide, water, and usable energy in the form of ATP.

During aerobic cellular respiration, cells use glucose and oxygen to produce carbon dioxide, water, and usable energy in the form of ATP.

Define glycolysis.

Glycolysis is the first step of cellular respiration. It breaks down one glucose molecule into two smaller molecules called pyruvate, producing a small amount of energy in the form of ATP.

True or False: Glycolysis does not require oxygen!

True!

Reasoning: Oxygen is not needed.

The first stage of cellular respiration (glycolysis), occurs in the ___________ of the cell, and breaks down ___ ________ molecule into _________ ________ molecules.

Glycolysis is the first stage of cellular respiration. It occurs in the cytoplasm of the cell and breaks down one glucose molecule into two pyruvate molecules.

What are the products of glycolysis per glucose molecule?

1. The cell produces a net gain of 2 ATP.

2. It produces 2 NADH, which carry high-energy electrons.

3. 2 pyruvate (3C) molecules from glucose (6C)

** All 3 are a result of ONE glucose molecule.

What is pyruvate and how is it generated?

Pyruvate is a small molecule produced when glucose is broken down during glycolysis. It is the next molecule the cell can use to continue obtaining energy.

Glucose → Glycolysis → Pyruvate → Further energy production

Define ATP.

ATP (adenosine TRIphosphate) is the main energy-carrying molecule that cells use to power their activities. Think of it as a rechargeable energy battery for your cells! 🔋

Define ADP.

ADP (adenosine DIphosphate) is a molecule that can be converted into ATP to store usable energy for cells.

1. How does ATP become ADP?

2. How many phosphate groups does each have?

1. When ATP’s terminal phosphate is removed, ATP becomes ADP and a phosphate is released.

2. The main difference is that ATP has 3 phosphate groups, while ADP has 2.

What is the difference between NADH and FADH₂?

NADH and FADH₂ are both coenzymes that carry high-energy electrons during cellular respiration. The main difference is that they enter the electron transport chain at different points, so NADH generally helps produce more ATP than FADH₂.

What is the electron transport chain entry of NADH and FADH₂?

NADH enters at Complex I

FADH₂ enters at Complex II

How much ATP does each coenzyme produce? Which produces more ATP?

a. NADH

b. FADH₂

a. NADH = ~2.5 ATP per molecule (produces more)

b. FADH₂ = ~1.5 ATP per molecule

What is GTP?

GTP = Guanosine TRIphosphate

• Stores transferable chemical energy.

• Can power cellular processes.

What is GDP?

GDP = Guanosine DIphosphate

• Has two phosphate groups.

• Can gain another phosphate to become GTP.

• Is produced when GTP loses a phosphate group.

How are GTP and GDP related?

GTP releases energy when it loses a phosphate group.

Energy can also be used to convert GDP back into GTP.

GTP is to ___, as GDP is to ________.

GTP is to ATP, as GDP is to ADP.

What is acetyl CoA?

Acetyl-CoA (acetyl coenzyme A) is a molecule that carries a small, 2-carbon group into the Krebs cycle so the cell can continue extracting energy from food.

(Think of it as a delivery vehicle that brings fuel into the next stage of cellular respiration. 🚚)

How does acetyl-CoA form?

After glycolysis, one glucose molecule has been split into two pyruvate molecules. When oxygen is available, each pyruvate is converted into acetyl-CoA.

__________ is the “main” product of glycolysis.

Pyruvate

What is PDH?

PDH stands for pyruvate dehydrogenase. It's an enzyme complex that helps convert pyruvate into acetyl-CoA, connecting glycolysis to the Krebs cycle during cellular respiration.

What happens during the PDH reaction? Draw out the overall reaction equation.

For each pyruvate molecule:

• One carbon is released as carbon dioxide (CO₂).

• NAD⁺ becomes NADH by accepting electrons.

• The remaining 2-carbon group attaches to coenzyme A, forming acetyl-CoA.

What is pyruvate oxidation?

Pyruvate oxidation is the step in cellular respiration that converts pyruvate into acetyl-CoA so it can enter the Krebs cycle.

How does pyruvate oxidation work?

The three main things that happen

1. CO₂ is released: Pyruvate loses one carbon atom.

2. NADH is produced: NAD⁺ accepts electrons and becomes NADH.

3. Acetyl-CoA is formed: The remaining two-carbon group attaches to coenzyme A.

In eukaryotic cells, such as human cells, pyruvate oxidation occurs in the ________________.

mitochondrial matrix!

Arrange the following stages into the correct order of aerobic cellular respiration:

Word Bank: Kreb’s Cycle, Glycolysis, Electron Transport Chain, Pyruvate Oxidation

Glycolysis → Pyruvate oxidation → Krebs cycle → Electron transport chain

1. What is CoA?

2. In terms of cellular respiration, how is CoA used?

1. CoA stands for coenzyme A. It’s a molecule that helps carry carbon-containing molecules from one reaction to another during cellular respiration.

2. In particular, CoA carries a 2-carbon acetyl group to form acetyl-CoA, which enters the Krebs cycle.

   
   

** Easy way to remember: CoA is like a carrier that transports the acetyl group to the Krebs cycle. CoA itself isn't the acetyl group; it carries it.

Illustrate how CoA functions in the Krebs cycle.

1. Glycolysis breaks glucose into pyruvate.

2. During pyruvate oxidation, pyruvate loses a carbon as CO₂.

3. CoA attaches to the remaining 2-carbon acetyl group, forming acetyl-CoA.

4. Acetyl-CoA carries that group into the Krebs cycle.

What is the Electron Transport Chain (ETC)?

** It is also referred to as the Electron Transport System (ETS)

It is the fourth stage of aerobic cellular respiration.

Its main job is to use electrons from NADH and FADH₂ to help produce ATP (energy) which occurs in Stage 5 of aerobic respiration.

Where does ETS/ETC occur in:

1. Eukaryotic cells =

2. Prokaryotic cells =

1. In eukaryotic cells: Inner mitochondrial membrane

2. In prokaryotic cells: Cell membrane

_______ and ______ carry high-energy electrons from earlier stages of cellular respiration. They ________ these electrons to the ETS.

NADH and FADH₂ carry high-energy electrons from earlier stages of cellular respiration. They donate these electrons to the ETS.

Some textbooks combine ETS and ATP synthesis into one stage called oxidative phosphorylation.

Illustrate all of these steps and write out the equation

🔬 How does the ETS work?

Step 1: NADH and FADH₂ deliver electrons

• NADH and FADH₂ carry high-energy electrons from earlier stages of cellular respiration.

• They donate these electrons to the ETS.

Step 2: Electrons move through proteins

• Electrons pass through a series of proteins embedded in the membrane.

• The energy released is used to pump hydrogen ions (H⁺) across the membrane.

Step 3: Hydrogen ions build up

• H⁺ ions accumulate on one side of the membrane.

• This creates a concentration gradient, like water building up behind a dam.

Step 4: ATP is produced

• H⁺ ions flow back through an enzyme called ATP synthase.

• ATP synthase uses this energy to convert ADP + phosphate into ATP.

Step 5: Oxygen accepts electrons

• Oxygen (O₂) is the final electron acceptor in aerobic respiration.

• Oxygen combines with electrons and H⁺ to form water (H₂O).

⚡ How much ATP does it produce?

Equation:

NADH/FADH₂ → ETS → H⁺ gradient → ATP synthase → ATP

The ETS and ATP synthase together produce approximately _____________________________ per glucose molecule.

26–28 ATP per glucose molecule.

At the end of aerobic cellular respiration, ______ accepts the electrons and helps form __________.

Oxygen accepts the electrons at the end and helps form water.

The Electron Transport System (ETS) is located in the _________ of the mitochondria.

cristae (the folds of the inner mitochondrial membrane)

_______ are the folds of the inner mitochondrial membrane.

Cristae

What is the difference between substrates and enzymes in the Kreb’s Cycle?

The main difference is:

• Substrates: Molecules that enzymes act on during a chemical reaction. These are the molecules that get changed or converted during the Kreb’s Cycle.

• Enzymes: Proteins that speed up chemical reactions without being used up.

__________ are molecules that get changed or converted during the Kreb’s cycle, while ________ help convert one substrate into another.

Substrates are molecules that get changed or converted during the Kreb’s cycle, while enzymes help convert one substrate into another.

Between the substrate and the enzyme, which one gets changed and which one causes the change?

Substrate = what gets changed.

Enzyme = what causes the change.

Citrate → Aconitase → Isocitrate

In the (correct) equation above, identify the substrate, the enzyme, and the product.

• Citrate = substrate

• Aconitase = enzyme

• Isocitrate = product

Define allosteric regulation.

Allosteric regulation is when a molecule binds to an enzyme at a site other than its active site, causing the enzyme to become more or less active.

The TCA cycle (also called the Krebs cycle or citric acid cycle) uses _____________ to control how quickly it runs based on the cell's energy needs.

allosteric regulation

What are the 2 types of allosteric regulation in the Krebs cycle?

Two Types of Allosteric Regulation

• Allosteric activation: A molecule binds to an enzyme and increases its activity.

• Allosteric inhibition: A molecule binds to an enzyme and decreases its activity.

What effects do the following molecules have on the Kreb’s Cycle?

1. ATP

2. ADP

3. NADH

4. Ca²⁺

Molecule	Effect on TCA Cycle	Meaning
ATP	Inhibits	Cell has plenty of energy
ADP	Activates	Cell needs more energy
NADH	Inhibits	Cell has plenty of high-energy electrons
Ca²⁺	Activates certain enzymes	Signals increased energy demand

What is the TCA cycle car analogy using ADP, ATP, and NADH?

Think of the TCA cycle like a car:

🟢 ADP = Gas pedal

• Low energy → Speed up the TCA cycle.

🔴 ATP = Brake pedal

• High energy → Slow down the TCA cycle.

🔴 NADH = Brake pedal

• Lots of electron carriers already filled → Slow down the cycle.

High ATP and NADH → TCA cycle _______ down.

High ADP and Ca²⁺ → TCA cycle __________ up.

High ATP and NADH → TCA cycle slows down.

High ADP and Ca²⁺ → TCA cycle speeds up.

Which enzymes in the Krebs cycle can be regulated to control how fast the cycle runs?

Dehydrogenases

All four NADH generated dehydrogenases are inhibited by ______ and their ________.

All four NADH generated dehydrogenases are inhibited by NADH and their products

List all 4 of the dehydrogenase enzymes.

1. Pyruvate Dehydrogenase

2. Isocitrate dehydrogenase

3. ⍺-Ketoglutarate dehydrogenase

4. Malate dehydrogenase

_____________ are enzymes that remove hydrogen and electrons from molecules during chemical reactions.

Dehydrogenases

Dehydrogenases transfer electrons to carriers such as:

• NAD⁺ → _________

• FAD → ___________

• NAD⁺ → NADH

• FAD → FADH₂

List the activators and inhibitors for:

1. Isocitrate dehydrogenase

2. α-Ketoglutarate dehydrogenase

Enzyme	Activators 🟢	Inhibitors 🔴
Isocitrate dehydrogenase	ADP, Ca²⁺	ATP, NADH
α-Ketoglutarate dehydrogenase	Ca²⁺	NADH, succinyl-CoA

Example: Isocitrate Dehydrogenase

What happens when ATP is LOW? What happens when ATP is HIGH?

When ATP is LOW:

1. ADP levels increase.

2. ADP binds to isocitrate dehydrogenase at a regulatory site.

3. The enzyme becomes more active.

4. The TCA cycle speeds up.

5. More NADH is produced to help generate ATP.

When ATP is HIGH:

1. ATP helps inhibit isocitrate dehydrogenase.

2. The enzyme becomes less active.

3. The TCA cycle slows down.

4. Less NADH is produced.

Dehydrogenases = enzymes that produce __________ and ___________.

Dehydrogenases = enzymes that produce NADH or FADH₂.

True or False: Allosteric regulation = molecules that turn enzyme activity up or down.

True!

Define proteolysis.

Proteolysis is the process of breaking down proteins into smaller peptides or amino acids.

What enzymes carry out proteolysis?

Proteases are the enzymes that carry out proteolysis.

Illustrate the process of proteolysis.

Protein → Smaller peptides → Amino acids

________ are enzymes that break _______ bonds in proteins.

Proteases are enzymes that break peptide bonds in proteins.

🧬How Does the Citric Acid Cycle Help Break Down Fats and Proteins?

The Citric Acid Cycle (TCA or Krebs cycle) plays a central role in the breakdown of carbohydrates, fats, and proteins because all three can be converted into molecules that enter the cycle.

🥑 How Fats Enter the Citric Acid Cycle?

Fats (triglycerides) are broken down into:

• Glycerol

• Fatty acids

These components follow different pathways.

Step 1: Glycerol can enter glycolysis after being converted into a glycolytic intermediate.

Step 2: Fatty acids undergo beta-oxidation, which breaks them into 2-carbon acetyl-CoA units.

Step 3: Acetyl-CoA enters the citric acid cycle.

Step 4: The cycle produces NADH and FADH₂, which deliver electrons to the ETS to help make ATP.

Fat → Fatty acids → Beta-oxidation → Acetyl-CoA → Krebs cycle → ATP production

🍗 How Proteins Enter the Citric Acid Cycle?

Proteins are broken down into amino acids through a process called proteolysis.

Step 1: Proteases break proteins into smaller peptides and amino acids.

Step 2: Amino acids undergo processes such as deamination or transamination, which remove or transfer their amino groups.

Step 3: The remaining carbon skeletons can be converted into:

• Pyruvate

• Acetyl-CoA

• α-Ketoglutarate

• Succinyl-CoA

• Fumarate

• Oxaloacetate

Step 4: These molecules enter the citric acid cycle directly or are converted into molecules that can enter it.

Remember:

Protein → Amino acids → Removal of amino group → Carbon skeleton → Krebs cycle

⚡ How Carbohydrates Enter the Citric Acid Cycle

Glucose → Glycolysis → Pyruvate → Acetyl-CoA → Krebs cycle

This is why the citric acid cycle is so important: it connects the breakdown of carbohydrates, fats, and proteins.

Draw the comparison table showing what carbohydrates, fats, and proteins are broken down into and how they enter the TCA cycle.

Nutrient	Broken Down Into	How It Enters the TCA Cycle
Carbohydrates 🍞	Glucose → Pyruvate	Acetyl-CoA
Fats 🥑	Glycerol + Fatty acids	Mainly acetyl-CoA
Proteins 🍗	Amino acids	Acetyl-CoA or TCA intermediates

Illustrate the path for

1. Fat catabolism

2. Protein catabolism

3. Carbohydrate catabolism

1. Fat catabolism: Fatty acids → Beta-oxidation → Acetyl-CoA

2. Protein catabolism: Proteolysis → Amino acids → Carbon skeletons

3. Carbohydrate catabolism: Glycolysis → Pyruvate → Acetyl-CoA

1gram fat = _____ kcal and 1 gram of carbohydrate or protein = _____ kcal

1 g fat = 9 kcal, 1 g of carbohydrate or protein = 4 kcal

Why is it called the TRIcarboxylic acid cycle (TCA)?

The Tricarboxylic Acid (TCA) Cycle gets its name because citrate (citric acid), the first molecule formed in the cycle, contains three carboxyl groups (-COOH).

Define the Krebs Cycle.

The Krebs cycle, also called the Citric Acid Cycle or TCA Cycle, is a series of chemical reactions that help cells produce energy (ATP) by breaking down acetyl-CoA.

List the products for ONE turn of the Krebs cycle (1 acetyl-CoA)

Product	Amount
NADH	3
FADH₂	1
ATP (or GTP)	1
CO₂	2

Since one glucose produces 2 acetyl-CoA, the Krebs cycle turns TWICE per glucose… how would this change the number of products produced?

Product	Amount
NADH	6
FADH₂	2
ATP (or GTP)	2
CO₂	4

Draw out the entire equation for ONLY the citric acid cycle.

Draw out the entire equation for aerobic cellular respiration (including glycolysis, pyruvate decarboxylation, and the citric acid cycle)

Define Beta-oxidation.

Beta-oxidation is the process of breaking down fatty acids into smaller 2-carbon units called acetyl-CoA.