Lecture 33 Flashcards
What is the fuel mobilisation process for carbohydrates?
Glycogenolysis to obtain glucose for glycolysis
What is the fuel mobilisation process for fats?
Lipolysis to obtain FAs for beta-oxidation
What is the fuel mobilisation process for proteins?
Proteolysis to obtain amino acids for energy
What are fuel mobilisation processes controlled by?
Hormones; glucagon and adrenaline
What is glucagon?
A peptide hormone secreted by pancreatic alpha-cells
What is proglucagon?
A polypeptide precursor that gives rise to glucagon in pancreatic alpha cells and GLP-1 in L-cell and brain
(E.g. of different processing pathways in different cells)
What is glucagon secretion stimulated by?
Fasting and starvation, low blood glucose, amino acids, exercise and stress (via adrenaline)
What does glucagon do?
Activates processes that increase blood glucose
What is adrenaline?
A hormone and neurotransmitter synthesised from tyrosine in the adrenal gland
When is adrenaline released?
During physical or psychological stress perceived by the hypothalamus which signals to the adrenal gland
How does the hypothalamus signal to the adrenal gland?
Via the sympathetic nervous system
What does adrenaline do?
Stimulates liver and muscle to activate processes that increase blood glucose and primes the body for a ‘fight or flight’ response (e.g. increased heart rate, bronchodilation, redirection of blood flow and increased blood sugar)
What do adrenaline and glucagon bind to?
G-protein coupled receptors that cause a conformation change, activating the G-protein
What do the activated G-proteins do?
Activate adenylyl cyclase enzyme
What does adenylyl cyclase do?
Increase cAMP levels which activates protein kinase A (PKA) via allosteric activation
What does PKA do?
The activity of PKA can activate (catabolic processes) or inhibit downstream (anabolic processes) enzymes
What happens to signalling pathways once they are stimulated?
They are reset to respond to future signals
Where do ligands diffuse during GPCR signalling down regulation?
Away from the receptor
When are g-proteins active?
When there is a GTP bound
When are g-proteins inactive?
When there is a GDP bound
What are the two mechanisms that can lead to g-protein downregulation?
Intrinsic GTPase and PDE
How does intrinsic GRPase work?
Intrinsic GTPase activity in the ativated Gs subunit of the g-protein converts it back to the inactive state
How does PDE work?
Phosphodiester enzyme (PDE) metabolises cAMP to prevent PKA activation
What inhibits PDE?
Caffeine
