Biochem Bain Lecture 2

What is the purpose and end-products of glycolysis?

Oxidize glucose to generate immediate ATP energy, reduced NADH, and metabolic intermediates

1 molecule of glucose→ net: 2 pyruvate, 2 ATP, 2 NADH, and 2H+, under anaerobic conditions→ pyruvate is reduced to lactate (in muscles) or ethanol + CO2 (yeast) to regenerate NAD+

How is hexokinase (Step 1) regulated in glycolysis?

Inhibited allosterically by its product, glucose 6-phosphate

How is phosphofructocommitment/ PFK-1 (step 3) regulated in glycolysis?

Primary rate-limiting enzyme, allosterically inhibited by high ATP and citrate, activated by AMP, ADP and fructose 2,6-bisphosphate

How is pyruvate kinase (step 10) regulated in glycolysis?

Inhibited by ATP, acetyl-CoA, alanine, and long-chain fatty acids; allosterically activated by fructose 1,6-bisphosphate

What is an isozyme?

Distinct molecular forms of an enzyme that catalyze the same biochemical reaction but exhibit different kinetic properties or regulatory controls

What is the importance of isozymes?

Enables tissue-specific metabolic adaptation. (ex: Hexokinase I in skeletal muscle has a lery low Km→ operating at max speed even during low blood glucose to ensure muscle energy supply, in contrast liver Hexokinase IV has high Km→ liver clear and store glucose only when blood concentration exceed normal levels

What is the clinical relevance of glycolysis in cancer detection? How do PET scans work?

Rapidly growing tumor cells→hypoxia→ increase glycolytic rate

PET scan application: inject radio labeled sugar → high-glucose malignant cells can be visualized using scan

What is the purpose and location of the citric acid cycle?

Complete aerobic oxidation of two-carbon acetyl units to CO2, capturing released electrons on high-energy carriers. Mitochondria matrix

What are the products of the citric acid cycle?

Each Acetyl-Coa→ 2CO2, 3NADH, 1FADH2, and 1 GTP

How is the CAC regulated?

Early at pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase. Inhibited by abundant every singals (ATP, NADH, Acetyl-CoA, Succinyl-CoA, citrate); activated by low energy indicators (ADP, AMP, NAD+) and Ca2+ ions

Why is the CAC so complex?

Serves dual functions; oxidizing acetyl fuels (catabolism) while also supplying intermediate precursors for the anabolism of AA, purines, pyrimidines, heme, glucose, and lipids

What are anaplerotic reactions?

Enzymes “filling-up” reactions that replenish CAC intermediates that have been drawn off for biosynthetic pathways (pyruvate carboxylase which converts HCO3- and ATP into oxaloacetate

What and where is Oxidative phosphorylation?

Convert the electron energy stored in NADH and FADH2 into a proton gradient across the inner membrane to synthesize ATP. Inner mitochondrial matrix

What does complex 1 do in oxidative phos.?

1 (NADH Dehydrogenase): accepts electrons from NADH and pumps 4H+ into the intermembrane space

What does complex 2 do in oxi. phos?

2 (Succinate Dehydrogenase): transfers electrons from succinate/FADH2 into the electron chain without proton pumping

What does complex 3 and ubiquinone do in oxi. phos.?

Complex 3: Pumps 4 H+ across the membrane

Ubiquinone: Mobile lipid-soluble electron shuttle transferring electrons from Complexes 1 and 2 → 3

What does cytochrome c and Complex 4 do in oxi. phos?

C: soluble intermembrane protein shuttle delivering electrons from complex 3 to 4

Complex 4: passes electrons to the terminal acceptor (O2) to form H2O, pumping 2H+ per electron pair

What is the mechanism of coupling for the electron transport chain?

Electron transport pumps protons out of the matrix into the intermembrane space, creating a transmembrane proton gradient, the return flow of H+ back into the matrix through the F0 proton pore of ATP synthase powers rotational catalysis within the F1 catalytic domain, driving ATP synthesis from ADP+P

How does cyanide inhibit ATP production?

Binds to Fe3+ in complex 4, arresting electron flow, stopping the proton gradient, and halting ATP production