Topic 5: Energy Transfers: Glycolysis

Aerobic respiration

Glycolysis → link reaction → Krebs cycle → electron transport chain

Glycolysis: Cytoplasm: breakdown of glucose into pyruvate molecules

Main products: per glucose molecule; 2 ATP, 2 reduced NAD, 2 pyruvate

Link reaction: Mitochondrial matrix: conversion of pyruvate into acetyl coenzyme A

Main products: per pyruvate molecule: 1 acetyl coenzyme A, 1 reduced NAD,1 carbon dioxide

Krebs cycle: Mitochondrial matrix: series of reactions starting with acetyl coenzyme A

Main products: per acetal coenzyme A molecule: 1 ATP, 3 reduced NAD,1 reduced FAD, 2 carbon dioxide molecules

Oxidative phosphorylation (electron transport chain): inner mitochondrial membrane: transfer of electrons through proteins, creating a proton gradient that allows the synthesis of ATP

Main products: approximately 30 ATP, water

While glucose is the primary fuel, other respiratory substances such as fatty acids and amino acids can also be used in respiration

Oxygen is essential for aerobic respiration. This is why breathing is vital, as it supplies oxygen for ATP synthesis

Glycolysis

• The first stage of aerobic respiration

• Occurs in the cytoplasm of cells

• Breaks glucose (six carbon molecule) into two three carbon pyruvate molecules

• This happens through a series of reactions involving specific enzymes

• Does not require oxygen (anaerobic process)

• Produces small amounts of ATP and an electron carrier called reduced NAD (NADH)

Process of glycolysis

1. Phosphorylation

2. Lysis

3. Dehydrogenation

4. Production of ATP

Phosphorylation

Two ATP molecules donate phosphate groups to glucose

Lysis

The phosphorylated glucose molecule is split into two molecules of triose phosphate

Dehydrogenation

A hydrogen is removed from each triose phosphate molecule (they are oxidised) and used to form two molecules of reduced NAD

Production of ATP

The triose phosphate molecules are converted into two pyruvate molecules, also producing four ATP molecules through substrate - linked phosphorylation

After glycolysis, if oxygen is available,

Pyruvate moves through mitochondrial membranes by active transport

Reactants: one glucose molecule and two ATP molecules

Products: four ATP molecules, two reduced NAD molecules, two pyruvate molecules

Net energy gain from glycolysis is two ATP molecules and two reduced NAD molecules per glucose molecule processed

Products (pyruvate and reduced NAD) have roles in following stages of cellular respiration that generate a larger yield of energy