Biochemistry Flashcards
Within the pancreatic islets, which cells are in the majority?
Beta cells
What do beta cells produce?
insulin
What are the other cells present within the pancreatic islets?
alpha
gamma
PP
What do PP cells secrete?
pancreatic polypeptide
What do gamma cells secrete?
somatostatin
Where exactly in beta cells is insulin produced?
In the ribosomes of the RER
What does the RER actually synthesise before it forms into insulin?
Preproinsulin- a type of preprohormone
What molecular chains does insulin contain?
2 polypeptide chains, joined by a disulphide bond
Cows and pigs were used for insulin in the past, why are they not used now?
Sometimes induce antibodies against the insulin, over a prolonged period of time.
Which glucose transporter is on the cell membrane of beta cells ?
GLUT2
What does glucosekinase do?
Converts glucose to glucose-6-phosphate where it can be used in metabolism
In what process is the most ATP formed?
Oxidative phosphorylation during glucose metabolism
What effect does ATP have on the K+ channel?
It inhibits K+ channel, which leads to depolarisation of cell membrane
What mineral change does cell membrane depolarisation have?
Influx of Ca++
How is insulin released within the cell?
Ca++ binds with secretory vesicles and releases insulin
True or False.
Insulin release is triphasic.
False.
It is biphasic.
What is the first phase of insulin release?
Release of readily releasable pool (RRP) of insulin granules
What is the second phase of insulin release?
Granules which undergo preparatory reactions are released.
Which class of drugs mechanism of action inhibits K+ channels?
Sulphonylureas
What 2 proteins make up K+ channel?
Kir6.1
SUR1
What does the drug diazoxide do?
Inhibits insulin secretion so good for hypoglycaemia
What does MODY stand for?
Maturity-onset diabetes of the young.
What is the pathogenesis of MODY?
Monogenic diabetes with genetic defect in B cell function.
What is the relevance of HNF transcription factors?
A genetic abnormality in HNF causes MODY
What is the pathology of type 1 diabetes?
Loss of beta cells so no insulin secretion.
What is the pathology of type 2 diabetes?
Reduced insulin sensitivity or defect in the insulin composition
What is insulin’s receptor?
Tyrosine kinase receptor
What does phosphorylation require?
ATP –> ADP + Pi
What is the insulin receptor made up of?
2 extracellular alpha subunits which bind insulin
2 transmembrane beta subunits.
Bound by a disulfide bond
What happens when the alpha subunits of the insulin receptor are activated?
The beta subunits undergo self phosphorylation and therefore the insulin receptor substrates (IRS) are phosphorylated
What do IRS activate?
PI3K and then PKB..
What role does PKB play in glycogen synthesis?
PKB causes translocation of GLUT4 to cell membrane so glucose can enter the cell.
Where do ketone bodies come from?
Acetyl-CoA from beta oxidation.
Formed in liver mitochondria.
What are ketones used for?
Energy metabolism for heart and renal cortex.
How are ketones used for energy metabolism?
ketones are converted back to acetyl-CoA which enters TCA cycle.
What are examples of ketones?
Acetone
Acetoacetic acid
beta-hydroxybutate
What is consumed in gluconeogenesis?
Oxaloacetate
What happens when ketone bodies accumulate in the blood?
Acidosis occurs.
DKA is classic in DM1 or DM2?
DM1
Which three amino acids can be phosphorylated?
Serine
Threonine
Tyrosine
Which enzyme converts glucose to sorbitol?
Aldose reductase
How does sorbitol cause diabetic complications?
causes osmotic damage e.g.gathering in the lens
True or False
Inhaled steroids can cause osteoporosis
False
Only oral
True or False
A direct effect of steroids is an increase in calcium absorption
False.
Decreases Ca absorption
True or False
An indirect effect of steroids is inhibition of gonadal steroid production
True.
Also adrenal
