Energy storage Flashcards
what are the main forms of energy storage
glycogen and fat
where is glycogen stored
- muscle
- liver
how is glycogen stored in the liver
granules
how much glycogen does the liver contain
100g
how much glycogen do muscles contain
300g
what is the difference in glycogen in liver and muscle
- in liver glycogen mobilised to buffer plasma glucose levels so transported to blood
- in muscle glycogen only used for muscle
what is advantage of storing glycogen as granules
minimal osmotic effect
describe the structure of glycogen
- polymer of glucose residues
- starts from dimer glycogenin
-residues linked by a-1,4 glycosidic bonds and branch points from a-1,6 glycosidic bonds
how often is a branch formed on glycogen
every 8-10 residues
what is glycogenesis
glycogen synthesis
what is the first step and enzyme of glycogenesis
glucose+ATP –> glucose-6-phosphate +ADP
enzyme: hexokinase/ glucokinase in liver
what is the second step and enzyme of glycogenesis
glucose-6-phosphate –> glucose-1-phosphate
enzyme: phosphoglucomutase
what is the third step and enzyme of glycogenesis
G1P +UTP +H2O– > UDP-glucose + Pi
enzyme: G1P uridlyltransferase
what is the final step in glycogenesis and what enzymes are required
glycogen (n residues) + UDP- glucose –> glycogen (n+1 residues) + UDP
- enzymes:
-1-4: glycogen synthase
-1-6: branching enzyme
what is glycogenolysis
glycogen degradation
what is the first step and enzymes in glycogenolysis
glycogen (n residues ) + Pi –> G1P + glycogen (n-1)
enzymes:
1-4: glycogen phosphorylase
1-6: de-branching enzyme
what is the second step and enzyme of glycogenolysis
G1P –> G6P
enzyme:
phosphoglucomutase
why is glycogenolysis not a reversal of glycogenesis
uses diff enzymes
what is the fate of G6P from glycogenolysis
- liver to turned to glucose by enzyme glucose-6-phosphotase transported to blood
- muscle G6P used for glycolysis
why can glycogen in muscle not be used to buffer blood plasma glucose but liver glycogen can
muscle lacks enzyme glucose-6-phosphotase so cannot convert G6P to glucose so cannot cross mem
- in liver G6P converted to glucose by glucose-6-phosphotase and glucose uses GLUT to transport to blood
what the rate limiting enzyme in glycogenesis
glycogen synthase
what is the rate limiting enzyme in glucogenolysis
glycogen phosphorylase
how does glucagaon and adrenaline affect glycogen synthase activity
decreases activity
how does glucagaon and adrenaline affect glycogen phosphorylase activity
increases
how does insulin affect glycogen synthase activity
increases
how does insulin affect glycogen phosporylase activity
decreases
give two examples of glycogen storage diseases
von Gierke’s disease (glucose-6-phosphotase deficiency)
McArdle disease (muscle glycogen phosphorylase deficiency)
what is gluconeogenesis
production of new glucose
when does gluconeogenesis occur
after 8 hours of fasting
liver glycogen stores start to deplete
where does gluconeogenesis occur
liver
to some extent the kidney medulla
what are the three precursors for gluconeogenesis
- lactate (Cori cycle)
- glycerol
- amino acids
why can acetyl CoA not be used for gluconeogenesis
pyruvate dehydrogenase reaction is irreversible so cannot be converted to pyruvate
what does the enzyme PEPCK do
converts oxaloacetate to phospholpyruvate
what are glucogenic amino acids converted to for gluconeogenesis
pyruvate or oxaloacetate
what is lactate converted to for gluconeogenesis
pyruvate
what is glycerol converted to for gluconeogenesis
dihydroxyacetone to fructose 1,6- bisphosphate
what are the three enzymes in gluconeogenesis
- PEPCK
- fructose-1,6-bisphosphoatase
- glucose-6-phosphatase
what are the two regulation enzymes in gluconeogenesis
- PEPCK
- fructose-1,6-bisphophatase
what is the effect of glucagon and cortisol on PEPCK and F16P activity
increases
what is the effect of insulin on PEPCK and F16P activity
decreases
what is an adipocyte
large lipid droplet mainly containing TAG and cholesterol ester
what adaptation of adipocyte allows it to hold alot of fats
can expand as more fat added
how many times can adipocytes increase in size before a new cell is made
4
where does lipogenesis occur
liver
what is lipogenesis
lipid synthesis
why are triacylglycerols a good storage molecule
- anhydrous
- energy content per gram twice that or carbs or proteins
what is the first step of lipogenesis
- citrate from TCA cycle leaves mitochondria as ACoA cannot be transported out mito (oxaloacetate +acetyl CoA) cleaved back into OAA and ACoA
what is the second step of lipogenesis for acetyl CoA
- acetyl CoA converted to Malonyl CoA by enzyme : acetyl CoA carboxylase using ATP
what is the second step of lipogenesis for oxaloacetate
converted to malate which is then converted to pyruvate by malic enzyme
what happens to malonyl CoA in lipogenesis
goes to fatty acid synthase complex with NADPH from PPP and formation of pyruvate from malate which makes the fatty acids which combines with glycerol-3-p to make TAG which are then pacakged to go elsewhere
why is acetyl CoA converted to malonyl CoA
want to add 2C and but we loose one from CO2 so as malonyl is 3 C adds 2C after loss of CO2
what is the regulatory enzyme in lipogenesis
acetyl-CoA carboxylase
what is the effect. of insulin and citrate on acetyl CoA carboxylase activity
increases
what is the effect. of glucagon/ adrenaline/ AMP on acetyl CoA carboxylase activity
decreases
what is lipolysis
fat mobilisation
what enzyme is involved in lipolysis
hormone sensitive lipase
what does hormone sensitive lipase do
converts TAG stored in adipose tissue to glycerol and FA in blood
how does glucagon affect hormone sensitive lipase
activates
how does insulin affect hormone sensitive lipase
inhibits
what type of energy storage differs between a health weight and overweight
TAGs
what is the normal plasma glucose level
5mmol/L
what is hypoglycaemia
low plasma glucose levels
