Why study metabolism?

• “You are a generous and warm character, and you are determined to become a famous doctor and save many, many lives every day, without asking anything in compensation but the admiring gazes of the populace. Metabolism is an ever so tiny, yet regrettably indispensable part of the tremendous knowledge you have to master in order to fulfill your destiny” Dr. Palmer ’04

• Short answer – “You want to pass this class.”

What is cellular respiration?

• Chemical process used by our cells to harness the energy from glucose

Glucose + O2 CO2 + H2O + ATP

• 4 stages: – glycolysis - Krebs cycle– pyruvate oxidation - ETC (electron

transport chain and chemiosmosis)

Overall Goals of Cellular Respiration

1. To break the bonds in glucose to produce six CO2 molecules

2. To move the hydrogen atoms from glucose to oxygen to produce six water molecules

3. To keep as much of the free energy from the reactions to store as ATP

Combustion of Glucose

Glyco = sugarLysis = splitting

Glycolysis

• Occurs in cytoplasm when glucose a hexose (6C) sugar is broken down into two molecules of pyruvate (3C)

• Glycolysis involves ten individual steps, each catalysed by an enzyme.

• Think of glycolysis in two phases:– Energy investment phase (glucose BPG)– Energy payoff phase (BPG pyruvate)

• Energy is released and there is a net production of 2 ATP molecules.

• Reduced NAD is formed, which has the potential to produce more ATP.

Overview of Glycolysis

1. Phosphorylation of glucose • Glucose is first

phosphorylated (by kinase enzymes), i.e. two phosphate groups are added, in two steps. Two molecules of ATP are required for this process.

• Phosphorylation activates glucose and makes it more reactive.

• Phosphorylated glucose cannot leave the cell by being transported across the membrane.

Glucose

2 ATP

2 ADP

Hexose disphosphate

2. Splitting of hexose bisphosphate

• The hexose bisphosphate is split into two molecules of phosphorylated triose (3C) sugar.

Hexose disphosphate

Triose phosphate

Triose phosphate

3. Oxidation of triose phosphate

• The two triose phosphate molecules are oxidised by dehydrogenase enzymes.

• The H atoms are transferred to NAD, forming NADH/H+.

• Two molecules of ATP are formed from each triose diphosphate converted to pyruvate. (Total 4 ATP)

Triose phosphate

Pyruvate

2 NAD

2 NADH/H+

2 ADP + Pi

2 ATP

Summary

• Overall yield for one molecule of glucose undergoing glycolysis:2 molecules of ATP (4 generated, but 2 used in initial phosphorylation of glucose).

2 molecules of NADH/H+2 molecules of pyruvate

Summary animation

This extension work – be sure that you understand the basics before you look at this animation!

Summary of energy transfers

D

D