Biology 224- Chapter 7- Cellular Respiration

What was added to Carbon Dioxide to produce Carbohydrates during Photosynthesis (Calvin-Benson)?

Energy (ATP) and
       Electrons (NADPH)

What is the goal of cellular respiration?

Turning energy into ATP

What is the overall reaction of aerobic respiration?

Glucose + 6O2 → 6CO2   + 6H2O (breakdown of glucose = catabolic)

What is the free energy of aerobic respiration? Is it Endergonic or Exergonic?

-686 kcal/mole, Exergonic

What is the first step I’m the breakdown of glucose for energy?

Glycolysis, which occurs in the cytoplasm

What happens In glycolysis?

Glucose is split into two molecules of pyruvate

What is the second step of glycolysis?

Pyruvate is transported from the cytoplasm into the matrix of the mitochondria

What happens after pyruvate is transported?

It is converted to Acetyl-CoA

What does the Krebs Cycle do to Acetyl CoA?

CO2 and electrons (NADH and FADH2)

What is the last step in glycolysis?

The energy in the electrons of NADH and FADH2 is converted to the energy of ATP by Electron Transport (oxidative phosphorylation)

Where does glycolysis occur in the cell?

In the cytoplasm (cytosol). All enzymes involved in glycolysis are located in the cytoplasm.

What happens during the energy-requiring (endergonic) phase of glycolysis?

2 ATP are invested to convert glucose into fructose-1,6-bisphosphate, which is then split into two 3-carbon molecules.

What happens during the energy-releasing (exergonic) phase of glycolysis?

Two G3P molecules are converted into two pyruvate molecules, producing 4 ATP and 2 NADH.

How are energy and electrons extracted from G3P during glycolysis?

G3P is oxidized, producing NADH, and dephosphorylated, producing ATP.

What occurs when a high-energy phosphate groups are transferred directly from a substrate (like PEP) to ADP to make ATP, without chemiosmosis, hydrogen ion pumping, or ATP synthase?

Substrate-level phosphorylation

What are the end products of glycolysis?

2 pyruvate, 4 ATP (2 invested), 2 NADH

What is the rate-limiting enzyme that controls the speed of glycolysis?

phosphofructokinase

How does ATP inhibit phosphofructokinase?

ATP acts as a noncompetitive inhibitor, slowing glycolysis when enough ATP is available.

Why does ATP inhibit phosphofructokinase?

To prevent the cell from making more ATP than it needs.

When is ATP produced during glycolysis?

During the second half, when phosphate groups are transferred to ADP.

What happens to pyruvate during aerobic respiration?

When oxygen is available and the Krebs cycle can operate, pyruvate is completely oxidized to carbon dioxide and water.

What happens to pyruvate during anaerobic pathways?

When oxygen or the Krebs cycle is unavailable, pyruvate is reduced by NADH and converted into a waste product.

What is an example of an anaerobic pathway?

Fermentation

What happens during pyruvate oxidation?

Pyruvate is converted into acetyl-CoA by the pyruvate dehydrogenase complex.

How many reactions are involved in pyruvate oxidation?

Three reactions

What happens during decarboxylation of pyruvate?

CO₂ is removed from pyruvate.

What happens when pyruvate is oxidized?

Electrons are transferred to NAD⁺, forming NADH.

How is acetyl-CoA formed?

The remaining 2-carbon compound (acetate) attaches to CoA, forming acetyl-CoA.

What do the 8 enzymes of the citric acid (Krebs) cycle do?

Convert acetyl-CoA into CO₂ and NADH.

Where do the Krebs cycle enzymes occur?

In the mitochondrial matrix.

What happens during decarboxylation in steps 3 and 4 of the Krebs cycle?

2 CO₂ are removed per acetyl-CoA.

What happens to citrate in decarboxylation?

Citrate is decarboxylated twice, from a 6-carbon molecule to a 5-carbon molecule.

What do steps 3, 4, and 8 do in the Krebs cycle?

Transfer electrons to NAD⁺.

What does step 6 do in the Krebs cycle?

Transfers electrons to FAD.

What happens during substrate-level phosphorylation in step 5 of the Krebs cycle?

Energy from converting Succinyl-CoA to Succinate adds a phosphate to ADP, forming ATP.

How many NADH are produced per glucose during glycolysis?

2 NADH.

How many NADH are produced per glucose during pyruvate oxidation?

2 NADH.

How many NADH and FADH₂ are produced per glucose during the Krebs cycle?

6 NADH and 2 FADH₂.

What is the rate-limiting enzyme of the Krebs cycle in humans and mammals?

Isocitrate dehydrogenase.

How do NADH and ATP regulate the Krebs cycle?

They act as noncompetitive inhibitors, slowing the cycle through feedback inhibition.

Where are cytochromes located in the cell?

In the inner mitochondrial membrane.

What do cytochromes form in the inner mitochondrial membrane?

Respiratory enzyme complexes (the electron transport chain).

Where does NADH pass its electrons in step 1 of electron transport?

 To NADH dehydrogenase.

What happens to H⁺ when NADH passes electrons into the respiratory chain?

H⁺ is released.

Why is NAD⁺ regenerated during electron transport?

So it can be reused in earlier stages of cellular respiration.

What does NADH dehydrogenase do?

Passes electrons to ubiquinone (Coenzyme Q) and pumps H⁺ into the intermembrane space.

How does ubiquinone receive electrons from FADH₂?

Through succinate reductase.

Does ubiquinone accept protons (H⁺)?

No, it only accepts electrons.

Where does ubiquinone pass electrons in step 3 of electron transport?

To cytochrome b-c₁.

What does cytochrome b-c₁ do in step 4 of electron transport?

Passes electrons to cytochrome c and pumps H⁺ into the intermembrane space.

Does cytochrome c accept protons (H⁺)?

No, it only accepts electrons.

Where does cytochrome c pass electrons in step 5 of electron transport?

To cytochrome oxidase.

What does cytochrome oxidase do in step 6 of electron transport?

Passes electrons to oxygen and pumps H⁺ into the intermembrane space.

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

Oxygen

What forms when oxygen combines with electrons and H⁺?

Water (H₂O).

Which three complexes pump H⁺ from the mitochondrial matrix into the intermembrane space?

NADH dehydrogenase, cytochrome b-c₁, and cytochrome oxidase.

What does H⁺ pumping establish across the inner mitochondrial membrane?

An electrochemical gradient.

How do H⁺ ions flow back into the mitochondrial matrix?

Through ATP synthase.

How does ATP synthase produce ATP?

By oxidative phosphorylation as H⁺ ions flow back into the matrix.

What type of protein is ATP synthase?

A multimeric protein.

What are the three main parts of ATP synthase?

A membrane-embedded base, a rotating shaft, and a stationary head.

What causes the ATP synthase shaft to rotate?

H⁺ ions passing between the a and c subunits in the base.

What does the 120° rotation cause?

Conformational changes in the head.

What happens in the first β-subunit conformation?

ADP and phosphate bind.

What happens in the second β-subunit conformation?

ADP and phosphate are joined to form ATP.

What happens in the third β-subunit conformation?

ATP is released.

How is H⁺ flow related to ATP synthesis?

H⁺ flow is coupled to ATP synthesis.

What substances combine to form metabolic water?

Oxygen, electrons originally from carbohydrates, and H⁺ ions.

What is metabolic water?

Water produced through cellular metabolism.

Why is cellular respiration called aerobic respiration?

Because it uses oxygen.

How many additional ATP are produced per glucose through oxidative phosphorylation?

A maximum of 30–34 additional ATP.

Why might aerobic respiration produce less ATP than the maximum?

NADH and FADH₂ may be used for other reactions.

Why might some energy-yielding intermediates not be used to produce ATP?

They may be used to produce other types of molecules.

What inhibits cytochrome oxidase in electron transport?

ATP acts as a noncompetitive inhibitor.

What happens when ATP levels are high?

ATP binds to cytochrome oxidase, inhibiting it.

How does ATP inhibition of cytochrome oxidase affect the cell?

It slows electron transport and reduces additional ATP production.

How are starch and glycogen used in cellular respiration?

They are digested into glucose subunits that enter glycolysis.

How does fructose enter glycolysis?

Fructose is converted to G3P, which then enters glycolysis.

How is lactose used in cellular respiration?

Lactose is broken down into glucose and galactose. Galactose is converted to glucose-1-phosphate, which enters glycolysis.

How are proteins used in cellular respiration?

Proteins are digested into amino acids, which undergo deamination (removal of amino groups) to form organic acids.

Where do the organic acids from protein breakdown enter cellular respiration?

They enter pyruvate oxidation or the Krebs cycle.

What happens to the organic acids formed by deamination of amino acids?

They are intermediates of pyruvate oxidation or the Krebs cycle, or are easily converted into them.

How are triglycerides broken down for cellular respiration?

They are digested into glycerol and fatty acids.

Where does glycerol enter cellular respiration?

Glycolysis

How are fatty acids used in cellular respiration?

They are split into acetyl groups, which enter the Krebs cycle.

How does the energy yield of proteins compare to carbohydrates?

They provide about equal energy per unit weight.

How does the energy yield of lipids compare to proteins and carbohydrates?

Lipids provide about 2× more energy per unit weight.

Why are fermentation and anaerobic pathways useful when oxygen or Krebs cycle enzymes are unavailable?

They allow glycolysis to continue producing a net 2 ATP per glucose by regenerating NAD⁺.

What happens to NADH when the electron transport chain is unavailable?

NADH cannot efficiently release its electrons through the electron transport chain, so it can build up and become harmful at high concentrations.

What is the purpose of fermentation?

To convert NADH back into NAD⁺ so glycolysis can continue.

What is the net energy yield of fermentation per glucose?

2 net ATP from glycolysis.

What happens during lactate fermentation?

Pyruvate is reduced by NADH to form lactate, and NADH is oxidized back to NAD⁺.

What is the main purpose of lactate fermentation?

To regenerate NAD⁺ so glycolysis can continue.

How is NADH converted back to NAD⁺ during aerobic respiration?

Through the electron transport chain during oxidative phosphorylation.

What happens during ethanol fermentation?

Pyruvate loses CO₂ to form acetaldehyde, which is reduced by NADH to form ethanol. NADH is oxidized back to NAD⁺.

What is the purpose of ethanol fermentation?

To regenerate NAD⁺ so glycolysis can continue producing ATP.

What is anaerobic respiration?

Respiration used by some organisms, such as bacteria, when oxygen is unavailable.

What enzyme can replace cytochrome oxidase during anaerobic respiration?

Nitrate reductase.

What does nitrate reductase do during anaerobic respiration?

It accepts electrons and reduces nitrate (NO₃⁻) to nitrite (NO₂⁻).

Where is nitrate reductase located in these bacteria?

In the cell membrane, where it functions in place of cytochrome oxidase.