Aerobic Respiration: TCA Cycle Overview

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Questions and Answers

What are the overall products of a single TCA cycle?

2 NADH, 1 FADH2, 2 CO2, 1 ATP

3 NADH, 2 FADH2, 2 CO2, 1 ATP

3 NADH, 1 FADH2, 2 CO2, 1 GTP (correct)

2 NADH, 1 FADH2, 1 CO2, 1 GTP

Which coenzyme is produced from Vitamin B3 and plays a significant role in the TCA cycle?

Coenzyme A

NAD+ (correct)

GTP

FAD

What molecule can transfer a phosphate group to ADP to generate ATP during the TCA cycle?

FADH2

Acetyl-CoA

GTP (correct)

NADH

Which reaction in the TCA cycle is directly associated with citrate formation?

Acetyl-CoA condensation with oxaloacetate Signup and view all the answers

Which of the following inhibitors affects pyruvate dehydrogenase activity?

Acetyl-CoA Signup and view all the answers

Which intermediates of glycolysis and TCA pathways can be used to form glutamate?

a-ketoglutarate Signup and view all the answers

What is the energy yield from one NADH molecule when oxidized?

2.5 ATP Signup and view all the answers

How many irreversibly regulated reactions are present in the TCA cycle?

3 Signup and view all the answers

What is the primary function of anaplerotic reactions in metabolism?

Regenerate intermediates of glycolysis and the TCA cycle. Signup and view all the answers

Which complex of the electron transport chain is responsible for transferring electrons to oxygen?

Complex IV Signup and view all the answers

How many hydrogen ions (H+) are pumped by Complexes I and III in the electron transport chain?

4 H+ each Signup and view all the answers

Which shuttle mechanism is best described by the oxidation of cytoplasmic NADH to regenerate NAD+ while producing FADH2 in the mitochondrial matrix?

Glycerol-3-phosphate shuttle Signup and view all the answers

What roles do NADH and FADH2 play in oxidative phosphorylation?

They act as electron carriers donating electrons to the complexes. Signup and view all the answers

What mechanism controls the frequency of glucose uptake in cells?

Activity of GLUT transporters Signup and view all the answers

Which enzyme is primarily responsible for regulating the glycolytic pathway and can be activated by AMP?

Phosphofructokinase Signup and view all the answers

Which of the following substances can inhibit Complex I of the electron transport chain?

Rotenone Signup and view all the answers

What role does ATP synthase play in oxidative phosphorylation?

Facilitates the conversion of ADP and Pi to ATP. Signup and view all the answers

In which tissue is the inner mitochondrial membrane particularly permeable to H+ ions, leading to thermogenesis?

Brown adipose tissue Signup and view all the answers

Which condition is associated with impaired glucose metabolism due to a vitamin deficiency?

Beriberi Signup and view all the answers

Which of the following correctly describes substrate-level phosphorylation?

It provides ATP by adding a phosphate group to ADP directly. Signup and view all the answers

What is a consequence of a defect in the mitochondria related to energy production?

Impaired ATP production. Signup and view all the answers

How does insulin affect glucose transporters (GLUT) in the plasma membrane?

Regulates their frequency and activity. Signup and view all the answers

Study Notes

Aerobic Respiration (Continued)

TCA Cycle (Step 3)
- Occurs in mitochondrial matrix
- Key intermediate reactions summarized as "Our City Is Kept Safe and Sound From Malice"
- Breaks down carbohydrates, proteins, and lipids
- Acetyl-CoA combines with oxaloacetate to form citrate
- Citrate is oxidized, releasing 2 CO2 molecules and reducing NAD+ and FAD
- Oxaloacetate is reformed, with lost carbons originating from oxaloacetate
- Products of one cycle: 3 NADH, 1 FADH2, 2 CO2, 1 GTP
- GTP yields 1 ATP
- Significantly more ATP (15) than glycolysis (2)
NAD+ and FAD
- NAD+ (derived from Vitamin B3) is a coenzyme. NADH oxidation yields 2.5 ATP
- FAD is a prosthetic group bound to succinate dehydrogenase. FADH2 oxidation yields 1.5 ATP
TCA Cycle Regulation
- 3 irreversible reactions (1, 3, 4) are rate-limiting
- These reactions are inhibited by ATP, NADH, and acetyl-CoA
- Specific enzymes (e.g., pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase) are inhibited by these metabolites
Other Metabolic Pathways
- TCA cycle intermediates are used in other pathways
- α-ketoglutarate forms glutamate and other amino acids
- Oxaloacetate forms aspartate, amino acids, and pyrimidines
- Acetyl-CoA forms glycolipids and glycoproteins
- Pyruvate forms amino acids like serine
- Anaplerotic reactions regenerate TCA cycle intermediates
Oxidative Phosphorylation (Step 4)
- Oxidizes NADH and FADH2 to generate ATP
- Involves 5 membrane protein complexes (I, II, III, IV, ATP synthase) in inner mitochondrial membrane
- NADH donates electrons/protons to complex I
- FADH2 donates electrons to complex II
- Coenzyme Q transfers electrons from complexes I and II to III
- Cytochrome c transfers electrons to complex IV
- Complex IV transfers electrons to O2 (terminal electron acceptor), forming H2O
- Energy release pumps H+ into intermembrane space
- Complexes I and III pump 4 H+ each, IV pumps 2 H+
- H+ gradient drives ATP synthesis by ATP synthase
- Inhibitors of electron transport chain include rotenone (I), antimycin C (III), CO/cyanide (IV), and oligomycin (V)
Participation of Cytosolic NADH
- Two shuttle mechanisms allow cytosolic NADH to participate in oxidative phosphorylation
- Glycerol-3-phosphate shuttle: regenerates FADH2
- Malate-aspartate shuttle: regenerates NADH in matrix
Uncoupled Transport
- Brown adipose tissue's inner mitochondrial membrane is permeable to H+
- H+ diffuse back into matrix, releasing energy as heat (thermogenesis)
Substrate-Level Phosphorylation
- ATP synthesis directly coupled to a reaction, not electron transport
- e.g., phosphocreatine in muscle cells, GTP
Control of Metabolism
- Controlled at multiple points, including glucose uptake, enzyme activity/deactivation, etc.
- Key enzymes are regulated by substrate availability, product inhibition, and allosteric regulation.
- Primary control is often level of ATP; levels of intermediates influence local rates.
Organs and Metabolic Profiles
- Brain (uses 60% body glucose at rest), muscle (uses fatty acids at rest, glycogen under high demand), kidney (uses 10% body glucose), liver (major conversion site, including Cori cycle).
Diseases Associated with Defects in Metabolism
- Mitochondrial defects, Beriberi (vitamin B1 deficiency), mercury/arsenic poisoning, diabetes, Von Gierke's disease, McArdle's disease, Tauri disease, cancer (the Warburg effect).

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Description

Explore the key aspects of the TCA cycle, including its location, main reactions, and the role of coenzymes like NAD+ and FAD. Understand how the cycle contributes to ATP production and its regulation through various enzymes. This quiz delves into the biochemical processes crucial for cellular respiration.