LIFE210 Unit 4: Cellular Metabolism

Metabolism

The series of chemical reactions in living things that convert food into energy and build cellular parts.

Gibbs Free Energy (ΔG)

Indicates whether a chemical reaction is thermodynamically spontaneous (-ΔG) or non-spontaneous (+ΔG).

Activation Energy

The free energy barrier required to overcome transition states in chemical reactions.

Enzymes

Proteins that catalyze reactions by reducing the magnitude of the activation energy barrier.

Metabolic Pathways

A series of chemical reactions, each catalyzed by a specific enzyme.

Catabolism

The process of breaking down and oxidizing molecules to produce energy and activated carriers.

Anabolism

The process of building cellular molecules using building blocks and energy from catabolism.

Amphibolic Metabolism

Pathways that consist of both catabolic and anabolic parts, such as the citric acid cycle.

Coupled Metabolic Reactions

Pairing thermodynamically unfavorable anabolic reactions with favorable ones like ATP hydrolysis.

Activated Energy Carriers

Molecules like ATP, NADH, NADPH, and Acetyl-CoA that store and transport useful cellular energy.

Steady State vs. Equilibrium

Steady state requires continual work to maintain constant levels; equilibrium is a dead state with no free energy.

Three Main Types of Metabolic Pathways

Catabolic (break down/oxidize), Anabolic (build macromolecules), and Amphibolic (do both).

Connection Between Metabolic Pathways

Catabolic processes generate ATP, which is then utilized by anabolic processes to drive synthesis.

ATP Structure & Energy Storage

Stores energy in phosphoanhydride bonds; hydrolysis releases negative charge repulsion, making it highly favorable.

NADPH and NADH Function

Energy carriers that donate high-energy electrons and a proton (hydride ion) to reduce substrates.

Acetyl-CoA Function

Carries energy via a high-energy bond to an acetyl group that can be transferred to a substrate.

ATP:ADP Steady State Significance

Maintaining a high ATP:ADP ratio far from equilibrium ensures sufficient energy to drive vital anabolic processes.

Stepwise Oxidation of Glucose

Breaking oxidation into enzyme-catalyzed steps allows energy to be captured in activated carriers rather than lost as heat.

Glycolysis Overview

Ten enzyme-catalyzed steps converting glucose to pyruvate without O2, yielding a net of 2 ATP and 2 NADH.

Three Stages of Glycolysis

1) Investment (uses ATP), 2) Cleavage (splits into 3-carbon sugars), 3) Energy harvest (produces ATP and NADH).

Citric Acid Cycle (CAC)

Harvests energy from food molecules (like pyruvate) primarily as NADH, releasing CO2 as waste.

Electron Transport Chain (ETC)

Inner mitochondrial membrane proteins that catalyze redox reactions to pump protons from the matrix.

Oxidative Phosphorylation

The process where the mitochondrial proton gradient powers ATP synthase to phosphorylate ADP into ATP.

Proton Gradient

A difference in H+ concentration across a membrane that stores potential energy to drive ATP synthesis.

Key Regulated Glycolytic Enzymes

Hexokinase (HK), phosphofructokinase (PFK), and pyruvate kinase (PK) catalyze irreversible steps with huge -ΔG.

Hexokinase (HK)

Catalyzes the first step of glycolysis by phosphorylating a six-carbon sugar.

Phosphofructokinase (PFK)

Catalyzes the rate-limiting step of glycolysis, converting fructose 6-phosphate into fructose 1,6-bisphosphate.

Pyruvate Kinase (PK)

Catalyzes the final step of glycolysis, transferring a phosphate to ADP to generate ATP.

Insulin's Transcriptional Role

Signals increased transcription of glycolytic enzymes like hexokinase to increase enzyme abundance.

Insulin's Role in Glucose Import

Signals glucose transporters to open, allowing the import of glucose into the cell.

Aerobic vs. Anaerobic

Aerobic environments contain molecular oxygen (O2), while anaerobic environments lack O2.

Lactic Acid Fermentation

Transfers a hydride ion from NADH to pyruvate to form lactate, regenerating NAD+ for glycolysis in low O2.

Warburg Effect (Aerobic Glycolysis)

Cancer cells rely heavily on glycolysis and produce lactate even with O2 present to supply building blocks for anabolism.

Fluoro-2-deoxyglucose (FDG)

A radioactive glucose analogue used in PET scans to detect regions of high glucose absorption like tumors.

Glycolysis Inhibition in Cancer Therapy

Targeting cancer glycolysis halts energy and anabolic precursors, but risks severe off-target effects in healthy tissues.