Zeidi Insulin pathways and signaling Flashcards Preview

COM Anatomy, Biochemistry, OS > Zeidi Insulin pathways and signaling > Flashcards

Flashcards in Zeidi Insulin pathways and signaling Deck (16):

Insulin "big picture" stuff

glucose upregulates preproinsulin mRNA transcription. afterwards it is cleaved to preinsulin in the ER lumen and then cleaved to insulin in the Golgi

there are two pools: rapidly ready release pool (less than 5% of total insulin supply) which can be released at the get-go, but 95% requires time to transcribe

Glucose increases insulin stability


when are the 3 disulfide bonds added to insulin?

in the ER lumen


what glucose transporter is used in the liver?

how is it trapped in the cell?

GLUT2 and glucokinase phosphorylates it, trapping in hepatocyte


how does glucose "cause" the release of insulin?

glucose metabolism creates an unswing in the ATP/ADP ratio, which inactivates something called the Katp channel. this leads to activation of Ca channels, whose sudden upsurge intracellularly causes readily release pools to bind to the membrane and release insulin


Ras dependent PW "big picture"

leads to phosphorylation of GRB2 ---> RAS protein activation, followed by Ras-Map PW--->

ultimately, it leads to glucokinase transcription, which increases glucose trapping in the cell


Ras independent PW "big picture"

ultimates leads to GLUT4 (muscle and adipose tissue) and glycogen synthase synthesis, allowing glucose into the cell and converted into storage form


the Ras independent PW activates what protein?

PI3 and PKB


RTK: what sets the stage for the RAS and RAS-indepedent PWs?

RTK receives insulin message causing autophosphorylation

insulin receptor substrate 1 (IRS1) recognizes the P site and binds, causing RTK to phosphorylate IRS-1 on its own tyrosine: SH2 domain proteins GRB and PI3 bind to IRS1


Ras dependent details

GRB2 which activates RAS


Ras independent details

PI3 which produces two compounds "phosphatidyl-bisphosphate and phsophatidyl-trisphosphate (PIP3)"

these crecuit protein kinase B to the membrane (PKB)

PKB is also known as Akt, it helps phosphorylate proteins and induces GLUT4's insertion into the membrane of muscle and adipose tissue

promotes glycogen synthesis by inhibiting glycogen synthase kinase 3 (GSK-3)


insulin resistance

quantifiable parameter; measured as amount of glucose cleared from blood in response to a dose of insulin


possible causes of insulin resistance

failure of GLUT4 to insert in membrane of adipose and muscle cells

also, 75 different mutation in insulin receptor identified


biochemical cause of insulin resistance (2)

Ser/thr kinases phosphorylate serine residues instead of tyrosine in the IR region of the IRS: this inhibits activation and signaling

IRS1 effectively disabled


what activates Ser/Thr Kinases?

activated by cytokines, free fatty acids, DAG


under ged conditions, insulin

glycogen synthesis, stimulating glycolysis, and inhibiting the activity and synthesis of enzymes for gluconeogenesis


insulin resistance, glucagoon, epindephrine, and cortisol

in the absence of insulin signals, glucagon is produced

glucagon promotes glycogen catabolism to increase blood sugar levels, as well as inhibiting glycogen synthesis

epinephrine promotes glucagon synthesis and therefore glycogen breakdown

once glucagon is exhausted, cotisol (steroid based) stimulates gluconeogenesis by inducing enzymes involved in pathway