Summary

This document provides a summary of various metabolic processes, including the Citric Acid Cycle, Glycogenesis, Glycogenolysis, and Gluconeogenesis. It details the steps, enzymes, locations, and regulation of each process. The information is suitable for undergraduate-level biology or biochemistry students.

Full Transcript

1. Citric Acid Cycle (Krebs Cycle): a) Location and Function: - Occurs in the mitochondrial matrix - Central hub for carbohydrate, fat, and protein metabolism - Main purpose: oxidize acetyl groups from acetyl-CoA to CO2, generating reducing equivalents (NADH and FADH2) b) Steps of the cycle:...

1. Citric Acid Cycle (Krebs Cycle): a) Location and Function: - Occurs in the mitochondrial matrix - Central hub for carbohydrate, fat, and protein metabolism - Main purpose: oxidize acetyl groups from acetyl-CoA to CO2, generating reducing equivalents (NADH and FADH2) b) Steps of the cycle: 1. Acetyl-CoA (2C) + Oxaloacetate (4C) → Citrate (6C) 2. Citrate → Isocitrate (both 6C) 3. Isocitrate → α-Ketoglutarate (5C) + CO2 4. α-Ketoglutarate → Succinyl-CoA (4C) + CO2 5. Succinyl-CoA → Succinate (4C) 6. Succinate → Fumarate (4C) 7. Fumarate → Malate (4C) 8. Malate → Oxaloacetate (4C) c) Key enzymes and their cofactors: - Citrate synthase - Aconitase (requires Fe2+) - Isocitrate dehydrogenase (requires NAD+) - α-Ketoglutarate dehydrogenase complex (requires NAD+) - Succinyl-CoA synthetase (produces GTP) - Succinate dehydrogenase (uses FAD) - Fumarase - Malate dehydrogenase (requires NAD+) d) Energy yield: - Per acetyl-CoA: 3 NADH, 1 FADH2, 1 GTP - NADH → 2.5 ATP in respiratory chain - FADH2 → 1.5 ATP in respiratory chain - GTP → 1 ATP - Total: 10 ATP per acetyl-CoA e) Regulation: - Allosteric inhibition by ATP and NADH - Activation by ADP and NAD+ 2. Glycogenesis: a) Definition: The process of glycogen synthesis from glucose b) Location: Primarily in liver and skeletal muscle c) Steps: 1. Glucose → Glucose-6-phosphate (by hexokinase/glucokinase) 2. Glucose-6-phosphate → Glucose-1-phosphate (by phosphoglucomutase) 3. Glucose-1-phosphate + UTP → UDP-glucose (by UDP-glucose pyrophosphorylase) 4. UDP-glucose + glycogen(n) → glycogen(n+1) + UDP (by glycogen synthase) d) Branching: - α-1,6 glycosidic bonds created by branching enzyme - Transfers a segment of 6-7 glucose residues from a chain of at least 11 residues to a nearby chain e) Primer requirement: - Glycogenin protein acts as the initial primer for glycogen synthesis 3. Glycogenolysis: a) Definition: The breakdown of glycogen to glucose-1-phosphate b) Location: Liver (for blood glucose regulation) and muscle (for local energy needs) c) Key enzymes: - Glycogen phosphorylase: Cleaves α-1,4 glycosidic bonds - Debranching enzyme: Handles α-1,6 branch points d) Steps: 1. Glycogen(n) + Pi → Glucose-1-phosphate + Glycogen(n-1) 2. Glucose-1-phosphate → Glucose-6-phosphate (by phosphoglucomutase) 3. In liver: Glucose-6-phosphate → Glucose (by glucose-6-phosphatase) e) Regulation: - Activated by glucagon and epinephrine (via cAMP) - Inhibited by insulin 4. Glycogen Storage Diseases: a) Von Gierke's disease (Type I): - Deficiency in glucose-6-phosphatase - Accumulation of glycogen in liver and kidney b) Pompe's disease (Type II): - Deficiency in lysosomal α-1,4-glucosidase - Glycogen accumulation in lysosomes c) Cori's disease (Type III): - Deficiency in debranching enzyme - Accumulation of limit dextrin d) Andersen's disease (Type IV): - Deficiency in branching enzyme - Accumulation of abnormal glycogen with few branches e) McArdle's syndrome (Type V): - Deficiency in muscle phosphorylase - Reduced exercise tolerance 5. Hexose Monophosphate Shunt (Pentose Phosphate Pathway): a) Function: Generates NADPH and ribose-5-phosphate b) Location: Cytosol of liver, adipose tissue, adrenal cortex, red blood cells c) Key steps: 1. Glucose-6-phosphate → 6-Phosphogluconolactone (generates NADPH) 2. 6-Phosphogluconate → Ribulose-5-phosphate (generates NADPH and CO2) 3. Non-oxidative interconversions of 3, 4, 5, 6, and 7 carbon sugars 6. Gluconeogenesis: a) Definition: Synthesis of glucose from non-carbohydrate precursors b) Location: Liver and kidney c) Key substrates: Lactate, amino acids, glycerol d) Important enzymes: - Pyruvate carboxylase - Phosphoenolpyruvate carboxykinase - Fructose-1,6-bisphosphatase - Glucose-6-phosphatase e) Regulation: - Stimulated by glucagon and cortisol - Inhibited by insulin

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