Signal Transduction

Question 1

Steroid Receptor

Answer 1

general type of transducer

steroids bind to receptors in the cell (usually the nucleus)

Penetrate the cell membrane to gain access to their specific intracellular receptors with or without the aide of extracellular receptors.

Question 2

Gated Ion Channel

Answer 2

• Receptor linked to ligand or voltage-gated ion
channel

• Binding of neurotransmitter causes channel
to open

• Results in rush of ions through ion channel
altering membrane potential promoting or
inhibiting nerve impulse transmission

Question 3

Receptor enzyme (Catalytic receptor)

Answer 3

Transmembrane catalytic receptors that have
enzymatic activity as part of their structure

tyrosine-specific protein kinase phosphorylates tyrosine residues of intracellular target proteins

EX: Insulin binding to a tyrosine kinase receptor for increased glucose uptake in the cells by GLUT-4 translocation to the cell membrain

Question 4

G-Protein Coupled Receptors (GPCRs)

Answer 4

Alpha 1-andrenergic and beta andrenergic types

• Receptors indicate receipt of a signal through the
production a “second messenger” inside the cell

• Second messengers trigger a cascade of
intracellular events in response to the binding of a
hormone to its receptor

Question 5

Beta Andrenergic Receptor

Answer 5

Epinephrine or norepinephrine binds the receptor

G protein has its GDP replaced by a GTP which causes it to disassociate from the receptor and activates Adenylate cyclase forming the G-alpha subunit (a GTPase from G-alpha will eventally deactivate the G protein)

Adenylate cyclase catalyzes the formation of cAMP

cAMP activates Protein Kinase A which phosphorylates cellular proteins to cause a cellular response

(cAMP is degraded by phosphodiesterases)

Question 6

Glucagon Receptor

Answer 6

GPCR Receptor binds glucagon and conducts a response using Adenylate Cyclase, cAMP and PKA

Question 7

cAMP second Messenger

Answer 7

activated/formed by Adenylate cyclase

activates PKA and is degraded by cellular phosphdiesterases.

Caffiene and theophylline can inhibit phosphidiesterases resulting in increased cAMP signaling in the cell.

Question 8

CREB

Answer 8

cellular protein that when phosphorylated by PKA enters the nucleus and increases gene expression

Question 9

ADP-ribosylation

Answer 9

ADP-ribosylation of G-alpha results in the
inactivation of the GTP-ase activity.

Therefore Adenylate Cyclase is continuously forming cAMP

Question 10

Cholera / E. coli Toxins and GPCRs

Answer 10

ADP-ribosylates Gs resulting in continuous adenylate cyclase activity affecting the CFTR causing an increase efflux of Cl-

excess Cl- will pull Na+ and H2O out of the cell resulting in diarrhea

Question 11

Alpha 1 Andrenergic Receptor

Answer 11

Binds Epinephrine or norepinephrine

G protein binds to phospholipase C which cleaves IP2 in the plasma membrane to IP3 and diacylglycerol (DAG)

IP3 will bind to a Ca++ channel for an influx of Ca++

Ca++ and DAG together activate Protein Kinase C

Protein Kinase C then phosphorylates intercellular proteins for cellular response

Question 12

Gi vs. Gs vs. Gq

Answer 12

Gi is used in Alpha 2 andrenergic receptors (susceptible to Pertussis)

Gs is used in Beta andrenergic receptors (glucagon receptor) (susceptible to cholera and E.Coli)

Gq is used in Alpha 1 andrenergic receptors (DAG, IP3, Ca++)

Question 13

NO signaling in smooth muscle

Answer 13

NO activates cytocolic Guanylate cyclase that facilitates the rise of cGMP which activates PKG