2a Energy storage (glycogen & fat) Flashcards
(49 cards)
Energy storage 70kg male (TAGs)
15 kg
Energy storage 70kg male (glyocgen)
0.4 kg
Energy storage 70kg male (muscle protein)
6 kg
How long before glycogen stores depleted and gluconeogenesis occurs?
8-12 hours
Two types of glycosidic bonds in glycogen
a1-4 and a1-6 (branch points)
Where is glycogen stored?
As granules in liver (100g) and skeletal muscle (300g)
has no specialised storage tissue
Properties of glycogen
Highly branched, large (minimal osmotic effect), polar
Glycogenesis steps
- glucose + ATP > glucose-6-P + ADP (hexokinase, glucokinase in liver)
- glucose-6-P <> glucose-1-P (phosphoglucomutase)
- glucose-1-P + UTP + H2O > UDP-glucose + 2Pi
- glycogen (n) + UDP-glucose > glycogen (n+1) + UDP (glycogen synthase for a1-4, branching enzyme for a1-6)
Use of UDP-glucose
Highly activated form of glucose, intermediate for synthesis of sugar containing molecules and interconversion of glucose and galactose
When is glycogen degraded?
When fasting in liver, stress response
Equation of glycogenolysis
glycogen (n) + nPi > 0.9n G-6-P + 0.1n glucose
Glycogenolysis steps
- glycogen (n) + Pi > G-1-P + glycogen (n-1) (glycogen phosphorylase on a1-4 bonds, phosphorolysis)
- G-1-P <> G-6-P (phosphoglucomutase, in muscle G-6-P enters glycolysis so only for muscle cells)
ONLY IN LIVER: 3. G-6-P + H2O > glucose + Pi (glucose-6-phosphatase, glucose released to bloodstream so for all tissues)
Which enzymes are controlled to regulate glycogen metabolism?
Glycogen synthase, glycogen phosphorylase
How are glycogen metabolism enzymes controlled?
Allosteric control (AMP activates muscle phosphorylase only), covalent modification in response to hormones
Effect of glucagon and adrenaline on glycogen synthase
Phosphorylates and decreases activity (glucagon no effect on muscles)
Effect of glucagon and adrenaline on glycogen phosphorylase
Phosphorylates and increases activity (glucagon no effect on muscles)
Effect of insulin on glycogen synthase
De-phopshorylates and increases activity
Effect of insulin on glycogen phosphorylase
De-phopshorylates and decreases activity
What results in glycogen storage diseases?
Abnormality in one or other enzymes of glycogen metabolism
Major features of glycogen storage diseases
Tissue damage (excess storage), fasting hypoglycaemia (low blood glucose), poor exercise tolerance, abnormal glycogen structure, affected muscles and/or liver
What is the major site of gluconeogenesis?
Liver (kidney cortex also does it during starvation)
What are possible substrates of gluconeogenesis?
Pyruvate, lactate, glycerol, essential + non-essential AAs (not Acetyl-CoA as reaction catalysed by PDH irreversible)
Equation of gluconeogenesis
2 pyruvate + 4 ATP + 2 GTP + 2 NADH > glucose + 2NAD+ + 4ADP + 2GDP + 6Pi + 2H+
What are the key control enzymes of gluconeogenesis?
Fructose 1,6-bisphosphatase, PEPCK
