Lecture 19a
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Transcript of Lecture 19a
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.