Biochem Lecture

Lecture 7

Glycolysis, The Citric Acid Cycle, and Catabolism

Metabolism: Common themes

Sections:

14.2 - 14.3, 15.1

- 15.2, 15.4 15.6, 16.1-16.2

17.3 - 17.4

Glycolysis: Pathway

Sections:

13.1 - 13.4,

14.1 - 14.2, 14.5,

16.1 - 16.2

Overall energy production

Glycolysis: Enzyme mechanisms

The Citric Acid Cycle: Enzyme mechanisms

Other pathways: Glycogen storage, gluconeogenesis, the

pentose phosphate pathway

1

Glucose – Cellular Energy Source

Natural sugars are D -stereoisomers

Glucose can be part of more complex

structures

Disaccharides (two sugars): Sucrose

Polysaccharides (multiple sugars):

starches, cellulose

Sugars are linked by ether bonds

Either α or β glycosidic linkage (depends

on orientation of anomeric C-O to ring)

2

Generating Energy in Cells

Glucose is the major source of metabolic energy

Full oxidation oxidation of glucose: 2,840 kJ/mol

Glucose + 6 O2

6 CO2 + 6 H2O

+ ATP

Cellular cycle produces net 32 ATP: 1440 kJ/mol

Direct oxidation does not occur spontaneously, occurs in

a series of enzyme catalyzed steps to generate high

energy intermediates and electron carriers for energy

generation in respiration

The first phase prepares glucose for further breakdown

upon entry into the citric acid cycle (TCA)

3

Energy from Molecules

NADH, etc

During glycolysis, substrates are activated to form unstable compounds which can

donate a phosphate group to ADP to form ATP.

Electron carriers like NADH drive protons across the membrane, which is used to

generate ATP via F1-ATP synthase (active transport run backward).

4

Common Enzymatic Mechanisms

Proximity: bringing partners together in correct orientation

Protection of reactive intermediates

Transition state stabilization

Direct functional group catalysis: Acid/base, etc.

Covalent enzyme intermediates: Like Ser protease

Assistance from cofactors and metals

A variety of enzymatic mechanisms are observed in the reactions of...