biochemistry chapter 10: aerobic respiration

What type of bond does Acetyl-CoA contain?

High-energy thioester bond that drives reactions during hydrolysis.

How is Acetyl-CoA formed from pyruvate?

Via the pyruvate dehydrogenase complex, a five-enzyme complex in the mitochondrial matrix.

What does pyruvate dehydrogenase (PDH) do to pyruvate?

Oxidizes it to create CO₂ and requires thiamine pyrophosphate (TPP) and Mg²+.

What role does dihydrolipoyl transacetylase play?

Oxidizes the two-carbon molecule and transfers the acetyl group to CoA, forming Acetyl-CoA.

How does dihydrolipoyl dehydrogenase function?

Uses FAD to reoxidize lipoic acid, producing FADH₂.

What happens to FADH₂ after it's formed?

Transfers electrons to NAD+, forming NADH that enters the electron transport chain.

How does pyruvate dehydrogenase kinase regulate PDH?

Phosphorylates PDH when ATP or acetyl-CoA levels are high, turning it off.

What is the role of pyruvate dehydrogenase phosphatase?

Dephosphorylates PDH when ADP levels are high, turning it on.

What sources can lead to the formation of Acetyl-CoA?

From fatty acids, ketogenic amino acids, ketone bodies, and alcohol.

How do fatty acids enter the mitochondria?

They couple with CoA in the cytosol to form fatty acyl-CoA and pass into the intermembrane space.

What happens to the acyl group during fatty acid metabolism?

Transfers to carnitine to form acyl-carnitine, which crosses the inner membrane.

How is fatty acyl-CoA re-formed in the mitochondria?

The acyl group is transferred to mitochondrial CoA, reforming fatty acyl-CoA.

What process occurs after fatty acyl-CoA is formed?

Beta-oxidation occurs to form Acetyl-CoA.

What overall concept is covered in the document?

The metabolic pathways involving Acetyl-CoA and energy production in carbohydrate metabolism.

What is the main function of Acetyl-CoA?

To serve as a substrate for the citric acid cycle and various biosynthetic processes.

Where does the pyruvate dehydrogenase complex occur?

In the mitochondrial matrix.

What vitamins are required by Pyruvate dehydrogenase?

Thiamine (B₁) and magnesium (Mg²+).

What is produced alongside Acetyl-CoA during pyruvate oxidation?

CO₂ is released.

What factors activate Pyruvate dehydrogenase?

Low ATP and high ADP levels activate it by dephosphorylation.

What happens during the electron transport chain?

NADH and FADH₂ donate electrons, powering ATP synthesis via oxidative phosphorylation.

Which essential cofactor is used in the formation of Acetyl-CoA?

Coenzyme A (CoA) is essential for its formation.

What does the presence of acetyl-CoA indicate?

It reflects abundant energy sources available for cellular respiration.

Where does the citric acid cycle take place?

In the mitochondrial matrix.

What is the main purpose of the citric acid cycle?

To oxidize carbons to CO₂ and produce NADH, FADH₂, and GTP.

What does citrate synthase do?

Couples acetyl-CoA to oxaloacetate to form citrate.

By which mechanism is citrate synthase regulated?

Negative feedback by ATP, NADH, succinyl-CoA, and citrate.

What does aconitase do in the cycle?

Isomerizes citrate to isocitrate.

What is produced by isocitrate dehydrogenase?

a-ketoglutarate, CO₂, and NADH.

What characterizes the activity of isocitrate dehydrogenase?

It is the rate-limiting step, regulated by ATP and NADH.

What does the a-ketoglutarate dehydrogenase complex produce?

Succinyl-CoA, CO₂, and NADH.

How is the a-ketoglutarate dehydrogenase complex regulated?

Inhibited by ATP, NADH; activated by ADP and Ca²+.

What does succinyl-CoA synthetase produce?

Succinate and GTP from succinyl-CoA.

What does succinate dehydrogenase do?

Oxidizes succinate to fumarate, producing FADH₂.

What is the role of fumarase?

Hydrolyzes fumarate to form malate.

What does malate dehydrogenase do?

Oxidizes malate to oxaloacetate, producing NADH.

Where does the electron transport chain occur?

On the inner mitochondrial membrane.

What is the role of NADH in the ETC?

Donates electrons to the chain.

What is produced as electrons pass through the electron transport chain?

Reduction potentials increase, and Oxygen receives the electrons.

What does Complex I of the ETC do?

Transfers electrons from NADH to CoQ, translocating 4 protons.

What does Complex II of the ETC do?

Transfers electrons from succinate to CoQ, no proton pumping occurs.

What is the end product of the citric acid cycle?

Oxaloacetate is regenerated.

How is Acetyl-CoA involved in energy production?

It enters the citric acid cycle to generate electron carriers.

Which high-energy carriers are produced by the citric acid cycle?

NADH, FADH₂, and GTP.

What is the main energy yield of NADH and FADH₂?

NADH yields about 3 ATP; FADH₂ yields about 2 ATP.

What is the relevance of proton translocation in the ETC?

It creates a proton gradient for ATP synthesis.

Summarize the electron transport chain mechanism.

Electrons flow and reduce O₂ while protons are pumped to form ATP.

What is the function of the malate-aspartate shuttle?

Transfers electrons across the mitochondrial membrane.

Describe the process of ATP production in cellular respiration.

ATP is synthesized via substrate-level phosphorylation in the citric acid cycle and oxidative phosphorylation in the ETC.

What does Complex III in the electron transport chain use to transfer electrons?

An iron-sulfur cluster to transfer electrons from CoQH₂ to heme, forming cytochrome c.

How many protons are translocated by Complex III?

Four protons.

What does Complex IV do?

Transfers electrons from cytochrome c to oxygen, forming water.

What ions does Complex IV use in its reaction?

Cytochromes and Cu²+.

What shuttle mechanism is used in the transfer of electrons in the mitochondrial matrix?

The glycerol 3-phosphate shuttle and the malate-aspartate shuttle.

What occurs in the glycerol 3-phosphate shuttle?

Electrons are transferred from NADH to dihydroxyacetone phosphate (DHAP).

What does the malate-aspartate shuttle do?

Transfers electrons from NADH to oxaloacetate, forming malate.

What is the proton-motive force?

The electrochemical gradient generated by the electron transport chain.

Where is the concentration of protons higher in the mitochondria?

In the intermembrane space compared to the matrix.

What enzyme generates ATP from ADP?

ATP synthase.

What portion of ATP synthase acts as an ion channel?

The Fo portion.

What does the F₁ portion of ATP synthase do?

Uses energy from the proton gradient to phosphorylate ADP into ATP.

How many NADH and ATP are produced during glycolysis?

2 NADH and 2 ATP.

What is the NADH yield from pyruvate dehydrogenase?

1 NADH per molecule of pyruvate.

How many NADH are generated by the citric acid cycle per glucose?

6 NADH.

What is the total ATP yield from 10 NADH?

25 ATP.

How much ATP does each FADH₂ yield?

1.5 ATP.

What is the commonly accepted range for total ATP yield per glucose?

30-32 ATP per glucose.

Where is oxidative phosphorylation located?

In the inner mitochondrial membrane.