Basic structures of carbohydrates and carbohydrate metabolism

What are the four major classes of organic compounds in cells?

Carbohydrates, lipids, proteins, nucleic acids

How are carbohydrates classified?

Monosaccharides, disaccharides, oligosaccharides, polysaccharides

What are monosaccharides classified by?

Number of carbons and location of carbonyl group

What is an aldose sugar example?

Glucose

What is a ketose sugar example?

Fructose

What are the two stereoisomers of sugars?

D and L sugars

What forms can monosaccharides exist in?

Linear and ring forms

What are phosphorylated sugars?

Sugars with phosphate groups attached

What bond joins two monosaccharides in disaccharides?

Glycosidic bond

What is sucrose composed of?

Glucose + fructose

What is lactose composed of?

Glucose + galactose

What is maltose composed of?

Glucose + glucose

How many monosaccharides do oligosaccharides contain?

Less than 20

How many monosaccharides do polysaccharides contain?

More than 20 to thousands

What are the two components of starch?

Amylose and amylopectin

What percentage of starch is amylose?

15–20%

What percentage of starch is amylopectin?

80–85%

What is the structure of amylose?

Unbranched, linear, helical

What is the structure of amylopectin?

Highly branched

What linkage is found in amylose?

α1,4 glycosidic linkage

What linkages are found in amylopectin?

α1,4 glycosidic linkage and branch α1,6 glycosidic linkage

What is the storage form of carbohydrate in animals?

Glycogen

What is glycogen composed of?

Large, branched polysaccharide of glucose

What are the functions of carbohydrates?

Fuel source, conversion to other molecules, structural component, storage component

Where does glycolysis occur?

Cytosol of all cells

Does glycolysis require oxygen?

No, occurs with or without oxygen

How many reactions are in glycolysis?

Ten

What is substrate‑level phosphorylation?

Direct ATP synthesis from a substrate reaction

What is the net yield of glycolysis?

2 pyruvate, 2 NADH, 2 ATP per glucose

What vitamin is required for NAD+ synthesis?

Niacin (Vitamin B3)

What is the role of NAD+?

Electron acceptor and oxidizing agent

What is the clinical consequence of pyruvate kinase deficiency?

Hemolytic anaemia due to ATP shortage in RBCs

How does arsenic poisoning affect glycolysis?

Arsenate replaces phosphate, bypasses ATP generation, glycolysis continues without ATP

What is the aerobic fate of pyruvate?

Oxidized to acetyl‑CoA by pyruvate dehydrogenase

What are the products of aerobic pyruvate oxidation?

Acetyl‑CoA, CO₂, NADH

What coenzyme is required for pyruvate dehydrogenase?

Coenzyme A (derived from vitamin B)

What is the anaerobic fate of pyruvate?

Converted to lactate by lactate dehydrogenase

What is regenerated in anaerobic glycolysis?

NAD+

What is the Cori cycle?

Cycling of lactate between muscle and liver

What happens to lactate in muscle?

Transported to liver

What happens to lactate in liver?

Converted to glucose by gluconeogenesis

What happens to glucose after Cori cycle?

Re‑enters blood and used by muscle

Where does the Krebs cycle occur?

Mitochondrial matrix

What is the main function of the Krebs cycle?

Oxidation of acetyl‑CoA to produce ATP, NADH, FADH₂

What combines with acetyl‑CoA to start the cycle?

Oxaloacetate

What are the products per acetyl‑CoA in TCA cycle?

3 NADH, 1 FADH₂, 1 ATP, 2 CO₂

What is the reduced form of FAD?

FADH₂

What is gluconeogenesis?

Synthesis of glucose from non‑carbohydrate compounds

What are substrates for gluconeogenesis?

Lactate, glycerol, amino acids

Where does gluconeogenesis occur?

Liver and kidney

Does gluconeogenesis occur in muscle?

No

Where in the cell does gluconeogenesis occur?

Cytosol and mitochondria

How does gluconeogenesis relate to glycolysis?

Mostly reversal of glycolysis, differs at 3 steps

What is glycogenesis?

Synthesis of glycogen

What is glycogenolysis?

Breakdown of glycogen

Where does glycogen metabolism occur?

Liver and muscle cytosol

What is the role of liver glycogen?

Maintain blood glucose

What is the role of muscle glycogen?

Provide glucose‑6‑phosphate for muscle energy

Why can muscle glycogen not release free glucose?

Muscle lacks glucose‑6‑phosphatase

What enzyme converts glucose to glucose‑6‑phosphate?

Hexokinase or glucokinase

What enzyme converts glucose‑6‑phosphate to glucose‑1‑phosphate?

Phosphoglucomutase

What is glucose‑1‑phosphate converted to?

UDP‑glucose

What enzyme adds UDP‑glucose to glycogen?

Glycogen synthase

What enzyme creates branches in glycogen?

Branching enzyme

What enzyme breaks glycogen to glucose‑1‑phosphate?

Glycogen phosphorylase

What enzyme removes branches in glycogen?

Debranching enzyme

What enzyme converts glucose‑1‑phosphate to glucose‑6‑phosphate?

Phosphoglucomutase

What enzyme converts glucose‑6‑phosphate to glucose in liver?

Glucose‑6‑phosphatase

Where does the pentose phosphate pathway occur?

Cytosol

What are the main functions of PPP?

Produce NADPH and ribose‑5‑phosphate

What is NADPH used for?

Fatty acid and cholesterol synthesis

What is ribose‑5‑phosphate used for?

Nucleotide and nucleic acid synthesis

Does PPP produce ATP?

No, oxidation of glucose but not for energy

Which cells rely only on glycolysis for energy?

Erythrocytes

What does the Cori cycle transfer from muscle to liver?

Lactate

Which compound is not converted to glucose in liver?

Cholesterol