Integration of Metabolism 1 Flashcards
What do changes in the circulating hormones allow the body to do? 2 things
- store metabolic fuel
- metabolise this fuel when it is in starvation
What are changes in metabolic pattern achieved by and examples?
- Variation in the amount of substrate e.g. FA used in starvation
- Allosteric effects on enzymes e.g. AMP and PFK in muscle
- Covalent modification of enzymes e.g. phosphorylation of glycogen phosphorylase and synthetase
- Changes in enzyme synthesis e.g. Glucokinase and dietary CHO
What does AMP presence suggest? What occurs?
Energy is low and this activates PFK and this increases glycolysis rate.
Glucagon activates —– to increase blood glucose levels.
Km of glucokinase is —– than hexokinase which means that glucose will only be taken up by the liver to turn to glycogen if blood glucose levels are ——
Glycogen phosphorylase
Lower
High
What does the enzyme HMG CoA reductase regulate?
Cholesterol production
What type of hormone is insulin?
How about glycogen?
Hypoglycaemic
Hyperglycaemic
Other than insulin and glucagon, what other hormones regulate blood glucose levels and where do they come from?
Adrenaline (adrenal medulla) - reduces insulin production so blood glucose levels increase
Cortisol (adrenal cortex)
Growth hormone (anterior pituitary)
What does the FED state mean and what occurs?
Do liver transporters have a high or low affinity to glucose?
The increase in blood glucose after eating.
In a beta cell, glucose is metabolised and then insulin in released.
Low
What organ secretes insulin and glucagon?
Pancreas
Give some details on the islets of Langerhans
- endocrine part of the pancreas
- 2% of the total pancreatic mass
- adult pancreas contains 1 million islets
- beta cells (60-70%) secrete insulin
- alpha cells (30-40%) secrete glucagon
- deta cells secrete somatostanin (growth hormone that regulates the endocrine system, affecting neurotransmission and cell proliferation)
What is insulin secretion stimulated by? (long)
What inhibits it?
- a rise in blood glucose
- a rise in amino acid
concentration in blood - gut hormones (secretions and other GI hormones release after food intake before blood glucose is elevated
- glucagon to provide the fine tuning of blood glucose homeostasis
Inhibited by adrenaline
What is the process which leads to insulin secretion?
- Glucose comes in and is metabolised
- This closes potassium channels so the cell depolarises (K+ cannot leave)
- Calcium channels open to cause more depolarisation
- This causes secretion of insulin from vesicles in the beta cell
What happens to the insulin once it leaves the beta cell?
Insulin comes out the vesicles and comes in contact with the protease enzyme. This creates 2 chains (one alpha and one beta). C-peptide comes off of this (clinical use to tell if someone is producing insulin)
What is the secretion of glucagon stimulated by?
- low blood glucose
- high concentration of amino acids in blood (prevents hypoglycaemia)
- adrenaline (glucagon secreted stimulated in periods of stress regardless of blood glucose)
- can be stimulated by insulin production to stop a sudden fall in blood glucose
What are the metabolic effects of insulin? (5 things)
- Promotes fuel storage after a meal
- Promotes growth
- Stimulates glycogen synthesis and storage
- Stimulates fatty acid synthesis (once enough glycogen in liver) and storage from CHO when the intake exceeds glycogen storing capacity
- Stimulates amino acid uptake and protein synthesis
What type of receptor is the insulin receptor?
Tyrosine Kinase receptor
Explain the activation of Akt protein kinase when insulin binds
Insulin binds to the receptor (catalytic receptor). This receptor is a tyrosine kinase (involved in growth). This causes the receptor to phosphorylate itself.
The activated receptor is called P13. This leads to a cascade of phophorylysing all these enzymes which gives us a active protein kinase B
What is the effect of insulin on glucose transport?
More glucose is taken up into the cell and converted to glycogen by activating glycogen synthase (dephosphorylating it) to cause glucagon production.
Explain what GLUT 4 is and what it does
It is a transporter on a membrane.
When glucose levels are low, GLUT 4 is inside the cell and it is taken to the cell surface when insulin is present. It works to get more glucose into the cell.
How is fat breakdown stopped?
Inhibition by insulin through activation of Akt/PKB, and inhibition of hormone sensitive lipase.
This is processed by cAMP. Protein kinase A activates hormone sensitive lipase to breakdown triglycerides into glycerol and fatty acids.
Remove cAMP to stop the breakdown of the fatty acids due to no activation of protein kinase A
Explain how insulin links to RAS and MAPK
This is how insulin affects gene expression.
RAS binds to GDP which causes a phosphorylating cascade producing MAPK.
This forms transcription factors which can then affect protein transcription and translation.