Biochemistry final exam part 1: glucose and gluconeogenesis

Glucose Role: Energy Production

Glucose is broken down via glycolysis, TCA cycle, and oxidative phosphorylation to produce ATP

Glucose Role: Storage

Excess glucose is stored as glycogen in liver and muscle for later use

Glucose Role: Biosynthesis of Nucleotides

Glucose enters pentose phosphate pathway to produce ribose-5-phosphate and NADPH

Glucose Role: Structural Components

Glucose contributes to glycoproteins/glycolipids for membranes and signaling

Why gluconeogenesis ≠ reverse glycolysis

Key glycolysis steps (Hexokinase, PFK-1, Pyruvate Kinase) are irreversible

Energetic reason for gluconeogenesis being different

Reverse glycolysis has large positive ΔG values — must be bypassed using ATP/GTP

Regulation reason for separate pathways

Having distinct enzymes allows tight reciprocal control to prevent a futile cycle

Physiological need for gluconeogenesis

Liver & kidney use it during fasting to maintain blood glucose levels

Bypass of Pyruvate Kinase in gluconeogenesis

Pyruvate → OAA (via Pyruvate Carboxylase) → PEP (via PEPCK)

Bypass of PFK-1 in gluconeogenesis

F-1,6-bisP → F-6-P via Fructose-1,6-bisphosphatase (FBPase-1)

Bypass of Hexokinase in gluconeogenesis

G-6-P → Glucose via Glucose-6-phosphatase (in ER)