Cell Communication (Part II)

Question 1

many intracellular signalling proteins behave like what?

Answer 1

molecular swtiches: on receipt of a signal they switch from an inactive to active state, until another proces switches them off

• signalling often occurs from phosphorylation

Question 2

what does kinases and phosphatase do?

Answer 2

kinases: ADD P

phosphatases: REMOVE p

Question 3

what are phosphorylation cascades?

Answer 3

• many of the signalling proteins controlled by phosphorylation are themselves protein kinases

*important to know that this

(A phosphorylation cascade is a sequence of signaling pathway events where one enzyme phosphorylates another, causing a chain reaction leading to the phosphorylation of thousands of proteins)

Question 4

what are the two different types of cell receptors?

Answer 4

1. cell surface receptors
2. intracellular receptors

Question 5

what are the different types of cell-surface receptors?

Answer 5

1. ion channel linked receptor

2. G-protein linked receptor

3. Enzyme linked receptor

Question 6

explain ion-channel linked receptors - neurotransmitters

structure?

mode of action/

Answer 6

• they are: homologous multi-pass transmembrane proteins
• structure: within the subunits that cross the membrane - there is an alpha helix. hydrophobic a.a. stick out of alpha helix and interact with hydrophobic lipid membrane. hydrophilic a.a. are tucked into the alpha helix
• neurotransmitting signalling often use these:
• neurotransmitters bind and transiently open / close the ion channel
• membrane then becomes permeable to ion. activates action potential

Question 7

explain ion-channel linked receptor: nicotinic actylcholine receptor

structure?

what bind to?

how work?

Answer 7

• five subunits across the membrane
• two binding sites for acetylcholine
• binding opens channel and allows sodium to enter cell ->skeletal muscle contraction

Question 8

which family of receptors are the largest family of cell surface receptors?

Answer 8

G-protein linked receptors

Question 9

how do G-protein linked receptors work? (basic)

Answer 9

• act indirectly to regulate the activity of a seperate plasma membrane-bound target
• enzyme or ion channel is effected as a result of G-protein linked receptor

Question 10

explain how g-protein linked receptor initites enzyme action

Answer 10

• signal molecule binds to extracellular side of receptor
• causes G protein to intracellular part of receptor
• G-protein activated
• subunit in G-protein activates enzyme
• Activated enzyme leads to biological response

Question 11

explain how g-protein linked receptor initites ion channel to open

Answer 11

• signal molecule binds to receptor
• binding and activation of g-protein

one of subunits of G proteins opens ion channel

Question 12

what type of protein receptor is acetylcholine receptor?

Answer 12

G-protein- linked receptor

Question 13

how does muscarininc acetylcholine receptor work?

Answer 13

• acteylcholine binds to acteylcholine receptor
• trimeric G-protein activated
• alpha subunit of trimeric G-protein binds to activated ion channel

-

Question 14

how do enzyme linked receptors work?

Answer 14

• have a catalyic domain within the receptor
• ligand bind site is outside of cell
• one alpha helix goes across membrane
• can be either:
• dimeric signalling molecule binding to receptor activates catylitc domain (which is intracellular)

OR

• siganlling molecule binding and this cause dimerezation of receptor, activates enzyme (intraellular)

Question 15

which cell-surface receptors are homologous in structure, which are heterogenous?

Answer 15

heterogenous: enyzme linked receptor

homologous: G-protein linked receptor, ion channel linked receptor

Question 16

tyorisine kinases (a receptor)

Answer 16

• each tyrosine on receptor acts a binding site for intracellular proteins. can all be phosphorylated when ligand binds to receptor
• in order to end the signalling protein tyrosine phosphatases remove the phosphates
• different tyrosine kinases recruit different signalling molecules
• there are several signalling molecules and pathways commonly activated by tyrosine kinsaseas

Question 17

how are intracellular receptor proteins activated?

Answer 17

• hydrophobic signal molecules diffuse directly across plasma membrane and bind to intracellular receptor proteins
• e.g signal molecules include: steroid hormones, thyroid hormones, retinoids
• then, intracellular receptors bind to specific DNA sequences adjacent to the genes the ligand regulates

inactive receptor

• each receptor will bind to short DNA-binding domain
• a receptor protein in its inactive state is bound to its inhibitory proteins

active receptor

• ligand binds to receptor and causes the (ligand-binding domain of the receptor to clamp shut around the ligand) inhibitory protein to dissociate
• receptor is active

Question 19

what is diabetes mellitus caused by?

Answer 19

type 1: not enough insulin signal. insulin receptor is a tyrosine kinase receptor

type 2: resistance to effects of insulin or a defect in insulin secretion

= high levels of glucose in blood

Question 20

what happens with cell signalling when have a stroke?

Answer 20

• dying cells release large amounts of neurotransmitter: glutamate

- glutamate is toxic at high concs

• excitoxicity -> glumatate spreads outside area of initial damage = braindamage