MEH Energy Storage - Glycogen and Fat Flashcards
Why can’t glucose get into the brain when it is below a certain level in plasma? How does the body prevent low blood glucose occurring during starvation?
Because when Glucose conc falls below the Km value of the brain transporter then flu cannot get into the brain –> coma
Store of glycogen
What is glycation of Hb and how can it be used clinically? Is it enzyme dependent?
Glucose attached to Hb - used as a clinical marker for diabetes - Hba1C
What is glycogen - what is it’s structure. How and where is glycogen stored?
As granules in the liver and muscle.
Polymer consisting of chains and branches of glucose residues linked with alpha 1,4 and 1,6 glycosidic bonds
What is glycogenin?
A protein that forms a dimer in the centre of a glycogen molecule
What main enzyme is responsible for glycogen synthesis vs glycogenolysis? Are they reverse reactions?
Glycogen synthase
Glycogen phosphorylase
Does synthesis of glycogen require energy?
Yes
What happens to glucose 6 phosphate once glycogen has broken down in muscle vs liver? Why is it different?
Muscle - straight to glycolysis
Liver - can form glucose release glucose into blood for use by other tissues
Muscle lacks G6P (Glucose 6 phosphatase) so cannot produce glucose - liver has it.
Which is the better buffer for blood glucose - liver or muscle and why?
Liver - as it has G6P so can convert glucose 6 P to glucose and release into blood
What is the effect of glucagon/adrenaline and insulin on glycogen synthase and phosphorylase? Is it the same for liver and muscle?
Glucagon/adrenaline - increases glycogen phosphorylase inhibits glycogen synthase
Insulin - decreases glycogen phosphorylase, increases glycogen synthase
Muscle is different as glucagon has no effect
Apart from being modulated by hormones, how else can glycogen synthesis/metabolism be modulated?
By AMP - allosteric modulator of muscle enzyme glycogen phosphorylase. Not of the liver form of the enzyme
After 8 hours starvation what occurs to get glucose in the body?
Gluconeogensis
What precursors for gluconeogensis are there?
Lactate Glycerol - released from adipose on breakdown of triglycerides Amino Acids Pyruvate G6P from glycogen breakdown in the liver
Where does lactate come from for gluconeogenesis (2)
Exercising muscle - anaerobic respiration
RBC - Cori Cycle
Which kind of amino acids can be precursors for gluconeogenesis? What are the other types of amino acids?
Glucogenic
Ketogenic
Which is the most common amino acid used in gluconeogenesis?
Alanine
Where does gluconeogenesis occur (2)?
Liver mainly
Also kidney cortex
Why are the 3 main enzymes for gluconeogenesis?
1) G6P
2) Fructose 1,6 bisphosphatase
3) PEPCK
Which of the enzymes for gluconeogensis bypasses the irreversible step of glycolysis?
PEPCK
Which two of the enzymes are hormonally regulated?
PEPCK
Fructose 1,6 bisphosphatase
What effect does Glucagon/Cortisol, and insulin have on PEPCK and F1,6BP?
Glucagon and cortisol - increase enzyme/activity
Insuline - inhibits enzyme/activity
What two functions do adipocytes have?
Store TAGs
Leptin - endocrine function
What are the main steps of lipogenesis? Say the main regulatory enzyme and what energy is used. Where are lipids made?
1) Glucose - major source of carbon skeleton
2) Glycolysis in cytosol —> pyruvate
3) Pyruvate enters mitochondria and forms acetyl co A and OAA (oxaloacetate)
4) AcoA and OAA form citrate in mitochondria
5) Citrate leaves mitochondria and is broken down into AcoA and OAA again
6) Acetyl co A –> malonyl co A (Acetyl co A carboxylase)
7) Malonyl co A enters the FA synthase complex - FA are build by adding 2C from malonyl co A
8) ATP and NADPH required (NADPH from pentose phosphate pathway or malate shuttle)
In the liver
How is lipogenesis regulated?
Acetyl co A carboxylase is regulated by:
Glucagon/adrenaline–> Inhibitory
Insulin/citrate (allosteric) –> Increase lipogenesis
How is fatty acid mobilisation regulated (lipolysis)
Hormone sensitive lipase
Glucagon and adrenaline –> increase activity of HSL
Insulin –> inhibition of HSL
