Metabolism and Sugars

4/2/03

Carbohydrate and sugar structure

Carbohydrates or saccharides are essential components of living organisms.

(C•H2O)n Where n=3 or greater.

A single saccharide is called a monosaccharide.

Oligosaccharide is a few linked monosaccharides and are at time associated with proteins (glycoproteins) or lipids (glycolipids)

Polysaccharides consist of many monosaccharides i.e. cellulose or glycogen

Monosaccharides (D-aldoses)

The Fischer convention, the basis for the D- configuration in sugars comes from D-glyceraldhyde’s configuration around its asymmetric carbon.

CHO

OHH

HHO

OHH

OHH

CH2OH

CHO

OHH

HHO

OHH

HHO

CH2OH

D-glucose L-glucose

1

2

3

4

5

6

1

2

3

4

5

6

Epimers differ in configuration around one carbon atom i.e. D-glucose and D-mannose but D-glactose and D-glucose are not epimers because they very around two carbon atoms. There are 2n-2 stereoisomers

Carbohydrates are classified as to the nature of the carbonyl group : ketone = ketose aldehyde = aldose

Triose

Tetrose

Pentose

Hexose

2(n-3) stereoisomers of ketoses

Monosaccharides can form ring structures

O O

PyranFuran

Glycosidic binds are between two sugars

They can either be in the or configuration and can be linked through the 1-2, 1-4 or 1-6 linkage

Sugar Polymers The Polysacchrides

• Energy Storage– Starch -amylose and amypectin

• Structural– Cellulose and Chitin

• Glycosaminoglycans

• Proteoglycans

-amylose

Cellulose (polyglucose)

Glycosaminoglycans & Proteoglycans

Bacteria Cell Walls

Peptidoglycan

Metabolism

Metabolism is the overall process through which living systems acquire and utilize free

energy to carry out their functions

The coupling of exergonic reactions of nutrient breakdown to the endergonic processes is

required to maintain the living state

How do living things acquire the energy needed for these functions?

Phototrophs- acquire free energy from sunlight

Chemotrophs - oxidize organic compounds to make

ATPATP is the energy carrier for most

biological reactions

A road map of metabolic pathways.

Metabolic pathways

A series of consecutive biochemical reactions catalyzed by enzymes that produce a specific end product.

Catabolism- the breakdown of food stuffs to simple organic chemicals.

Anabolism- the synthesis of biomolecules from simple organic chemicals.

The breakdown of foods converge to a few simple compounds.

Very Few metabolites are used to synthesize a large variety of biomolecules

•Acetyl-Coenzyme A (acetyl-CoA)

•Pyruvate

•Citrate acid cycle intermediates

Three main pathways for energy production

•Glycolysis

•Citric acid cycle

•Oxidative-Phosphorylation

Certain pathways are involved in both breakdown and buildup of molecules these pathways are called amphibolic. The citric acid cycle is an example of this.

Metabolic pathways are irreversible

They have large negative free energy changes to prevent them running at equilibrium.

If two pathways are interconvertible (from 1 to 2 or 2 to 1), the two pathways must be different!

1

A2

XY

Independent routes means independent control of rates.

The need to control the amounts of either 1 or 2 independent of each other.