Signal Transduction

Question 1

What are the molecular mechanisms of signal transduction?

Answer 1

Specificity, Amplification, Cooperativity, Desensitization, Adaptation, Intergration

Question 2

How is specificity achieved?

Answer 2

Precise molecular complimentarity between signal molecule and receptor.

Question 3

How is amplification achieved?

Answer 3

Through enzyme cascade - one signal molecule affects a number of molecules that increases every step of the cascade

Question 4

How is desensitization/adaptation achieved?

Answer 4

Receptor activation results in negative feedback that shuts off the receptor

Question 5

What is integration of multiple signals?

Answer 5

When multiple signals come to the cell, the actual signal depends on the integrated input from both signals

Question 6

What is a gated ion channel?

Answer 6

Channels that open and close as a response to a change in membrane potential or binding of a ligand.

Question 7

What is a receptor enzyme?

Answer 7

A receptor that is activated by an extracellular ligand, and will catalyze the production of a second messenger?

Question 8

What is G-Protein Coupled Receptors?

Answer 8

Receptor proteins that through G-proteins activate enzymes that in turn will generate second messengers

Question 9

What is nuclear receptors?

Answer 9

They are in the nucleus and not the membrane; when bound by ligand they will alter the rate at which genes are transcribed and translated

Question 10

Explain how the influx and efflux of ions affect how the AP travel through the axon

Answer 10

A ligand gated ion channel opens to let Na+ or Ca2+ in the cell, which will depolarize the membrane. When the membrane get depolarized, local voltage gated Na+ channels opens and further depolarize the membrane. This causes voltage gated K+ channels to open and K+ will flow out, which will repolarize the membrane. At the end, voltage gated Ca2+ channels open and the rise of [Ca2+] will trigger the release of things through exocytosis

Question 11

What is the gene regulation of gene expression by insulin pathway?

Answer 11

Insulin binds to insulin receptor. Insulin receptor phosphorylates IRS-1. IRS-1 binds to Grb2. Sos binds to IRS-1/Grb2 complex and then to Ras. GTP binds to Ras, activating it. Activated Ras binds to Raf-1. Raf-1 phosphorylates MEK, which phosphorylated ERK, that moves into the nucleus and phosphorylates Elk1 which joins SRF, which induces transcription and translation.

Question 12

Describe the cascade triggered by epinephrine

Answer 12

Epinephrine binds to a GPCR, which activated the G-protein. Then, the G-protein activated adenylyl cyclase which converts ATP to cAMP. cAMP binds to PKA and activates it. The active subunits of PKA phosphorylates phosphorylase b kinase which in turn phosphorylates glycogen phosphorylase b, turning it into glycogen phosphorylase a (the active form)

Question 13

Which are the eicosanoid hormones?

Answer 13

Prostaglandins, thromboxanes and leukotrines

Question 14

How and when are eicosanoid hormones produced?

Answer 14

When needed, and are derivated from fatty acids

Question 15

How in insulin synthesized?

Answer 15

First as a single chain precursor (preproinsulin) with a signal sequence that makes it possible to transport it into a vesicle. Then, the signal sequence is cleaved off and disulfide bonds are formed, and the proinsulin is stored in granules. When they are to be released, proteases cleave the chains to form mature insulin.

Question 16

What are the effects of insulin?

Answer 16

Insulin signals that the blood glucose is higher than necessary. This will result in higher glucose uptake, higher glygogen synthesis and glycolysis. Higher fatty acid synthesis in liver. Lower glygogen breakdown.

Question 17

What are the effects of glucagon?

Answer 17

Signal that the blood glucose is too low. Higher glucogen breakdown and gluconeogenesis in liver, lower glygogen synthesis and glycolysis in liver.

Question 18

What are the effects of epinephrine?

Answer 18

Epinephrine is to prepare the body for activity. Higher glycogen breakdown, lower glycogen synthesis. Higher gluconeogenesis in liver and glycolysis in muscles.

Question 19

How is insulin secreted?

Answer 19

ATP gated K+ channels close in response to higher levels of ATP in beta cells. The following depolarization of the membrane opening voltage gated Ca2+ channels, and the influx of Ca2+ triggers release of insulin granules by exocytosis

Question 20

Which important enzymes does insulin effect and how?

Answer 20

Hexokinase (increased expression), glycogen phosphorylase (activating phosphorylase a phosphatase? PP1), PFK-2 and PFK-1, PDH complex

Question 21

Which important enzymes does glucagon effect and how?

Answer 21

Lower PFK-1 activity by lowering concentration of fructose 2,6-biphosphate (by higher FBPase-2), lower pyruvate kinase by phosphorylation, higher activity of glycogen phosphorylase by phosphorylation of phosphorylase b kinase

Question 22

Which important enzymes does epinephrine effect and how?

Answer 22

glycogen phosphorylase, PFK-1 and -2 (differently in muscle and liver cells)

Question 23

What type of process is triggered in the insulin receptor upon binding of insulin and how is the signal transferred into the recieving cell?

Answer 23

Autophosphorylation which causes an enzyme cascade

Question 24

What are some similiarities between insulin release and the release of neurotransmitters at the synaps of a nerve cell?

Answer 24

Both are dependent on voltage gated Ca2+ channels. Exocytosis are triggered by higher Ca2+ levels

Question 25

The actions of epinephrine and glucagon are similar, but also distinct. Mention at least one difference in their respective effects on energy metabolism.

Answer 25

Epinephrine trigger glycolysis in muscle cells.