1. 1!
Metabolism of Carbohydrates
The Energy Metabolism of Glucose
Entry of other Carbohydrates into
Glycolysis
Pyruvate Metabolism
Biosynthesis of Carbohydrates
Regulation of Carbohydrate Metabolism
2!
Metabolism of carbohydrates
3!
Carbohydrate metabolism
4!
Energy metabolism of glucose
Glycogen (animals)
Starch (plants)
Glucose Pyruvate Acetyl CoA
Lactate
Ethanol
Ribose-5-phosphate
+ NADPH + H+
Disaccharides
ATP +
NADH + H+
catabolism
anabolism
phosphogluconate
pathway
glycolysis
gluconeo-
genesis
aerobic
anaerobic,muscles
anaerobic,yeast
5!
Glycolysis
6!
First five reactions of glycolysis
glucose
glucose-6-P
fructose-6-P
fructose-1,6-bisP
glyceraldehyde-3-P dihydroxyacetone-P
ATP
ADP
ATP
ADP
6 carbon
stage
Requires
energy
3. 13!
Entry of other carbohydrates
into glycolysis
Galactose
Galactose-1-phosphate
UDP-galactose UDP-glucose
Glucose-1-phosphate
Glucose-6-phosphate
galactokinase
galactose-1-
phosphate uridyl
transferase
UDP-galactose
-4-epimerase
UDP-glucose
pyrophosphorylase
Phospho-
glucomutase
14!
Pyruvate metabolism
15!
Fermentation
16!
Lactate fermentation
17!
Alcohol fermentation
Used by anaerobic bacteria to obtain
additional energy from glucose.
18!
Biosynthesis of carbohydrates
4. 19!
Biosynthesis of carbohydrates
Skeletal muscles
Glycogen
glucose-6-P
exercise rest
glucose-6-P
pyruvate
lactate
Liver
Glycogen
glucose-6-P
glucose-6-P
pyruvate
lactate
glucose
Muscles lack enzyme needed to convert pyruvate to
glucose-6-P. Must be sent to liver.
Blood
20!
Gluconeogenesis
Oxaloacetate
Phosphoenolpyruvate
Pyruvate
Pyruvate Malate
Malate
Oxaloacetate
Lactate
Pyruvate
Pyruvate
Oxaloacetate
Phosphoenol
pyruvate
Stage I
mitochondria
21!
Gluconeogenesis
Glycogen
Glucose
UDP-glucose
+ UDP
H O
2
Pi
ATP
H O
2
Pi
Fructose-1,6-bisphosphate
Glyceraldehyde-3-phosphate
Phosphoenolpyruvate
3-Phosphoglycerate
2-Phosphoglycerate
Glucose-1-phosphate
Glucose-6-phosphate
Fructose-6-phosphate
ATP
Stage III
Stage II
22!
Gluconeogenesis
The process is sometimes called ‘reverse
glycolysis’ but that is a misnomer.
Only seven of the ten steps in glycolysis
are reversible. The three steps to be
bypassed are:
1. glucose + ATP glucose-6-phosphate + ADP
3. fructose-6-phosphate + ATP fructose-1,6
-bisphosphate + ADP
10. PEP + ADP pyruvate + ATP
23!
Gluconeogenesis
24!
Gluconeogenesis
6. 31!
Synthesis of glycogen
Glucose, activated and tagged by attachment
of UDP, is added to the nonreducing ends of
an existing glycogen.
Glycogen synthase catalyzes the formation
of a new ! (1 4) glycosidic linkage.
UDP-glucose + (glucose)n + H2O
(glucose)n+1 + UDP
32!
Synthesis of starch
Similar to glycogen formation except
glucose is activated by ADP, not UDP.
Starch synthase catalyzes the addition of
glucose to an existing starch molecule by
formation of ! (1 4) glycosidic linkage.
ADP-glucose + (glucose)n
(glucose)n+1 + ADP
33!
Synthesis of lactose
This disaccharide is actively synthesized in
the mammary glands of mammals.
It is produced by combining activated
galactose with glucose using lactose
synthase. A "(1 4) linkage results.
UDP-galactose + glucose
UDP + lactose
34!
Synthesis of sucrose
Sucrose is present in most fruits and
vegetables. It is produced by a two step
process.
UDP-glucose + fructose-6-phosphate
sucrose-6-phosphate + UDP sucrose + Pi
sucrose-6-
phosphate
synthase
phosphatase
H2O
35!
Synthesis of cellulose
Cellulose- major structural polysaccharide in
cell walls of plants and some bacteria.
It’s synthetic route is similar to starch except
a "(1 4) linkage is produced.
UDP-glucose or GDP-glucose + (glucose)n
UDP or GDP + (glucose)n+1
36!
Regulation of glycolysis
