Cell Signalling

Question 1

What are examples of Endocrine Communication?

Answer 1

( Hormone travels within blood to act on distant target cell )

Insulin produced in pancreas acting on liver, muscle, adipose tissue

Adrenaline produced in Adrenal glands acting on trachea

Question 2

What are examples of Paracrine Communication?

Answer 2

( Hormone acts on an adjacent cell )

Nitric oxide produced by endothelial cells in blood vessels

Osteoclast activating factors produced by adjacent osteoblasts

Question 3

How does Insulin have both endocrine and paracrine effects?

Answer 3

Endocrine : Effects on liver

Paracrine : Secreted from beta cells and inhibits release of glucagon from adjacent alpha cells

Question 4

What is an example of signalling between proteins attached to membranes?

Answer 4

Blood borne viruses are detected by antigens on APCs

They then digest pathogen to express a MHC with class II molecules on surface

T lymphocytes engage through their own TCR interaction

Question 5

What detects HIV GP120 glycoproteins?

Answer 5

CD4 receptors on T lymphocytes ( Membrane attached protein signalling )

Question 6

What is Autocrine signalling? What are some examples of it?

Answer 6

Signalling molecule acts on the same cell.

Acetylcholine on presynaptic M2- muscaranic receptors

Activated T cell releases IL-2 and expresses an IL-2 receptor

Question 7

During Neurotransmission, when is cell signalling used?

Answer 7

Propagration of action potential by depolarisation and repolarisation

NT released from vesicles

Activation of post synaptic receptors

Question 8

How do Ionotropic receptors work?

Answer 8

Ligand binds to receptor protein

Channel protein changes shape = pore

Ions move along gradient

Question 9

What is the structure of a G-coupled receptor?

Answer 9

The channel protein crosses cell membrane 7 times

Linked to intracellular G protein complex :
alpha subunit ( are separated into 3 categories )
beta-gamma subunit
GDP molecule

Question 10

How do Enzyme linked receptors work?

Answer 10

Ligand binding causes receptors to cluster

Clustering activates enzyme activity within cytoplasmic domain

Enzymes phosphorylate receptor

This causes signalling proteins to bind to cytoplasmic domain

Signalling recruits further signalling

Question 11

What are Intracellular receptors?

Answer 11

A membrane permeable ligand binds to receptors inside cells

Question 12

What type of receptor does the ligand ACh use?

Answer 12

Ionotropic receptor

Nicotinic Acetylcholine
In skeletal muscles
Causes muscle contraction

Question 13

What receptors are used for
GABA
Glutamate
5-HT

Answer 13

( Ionotropic )
GABA(A) - inhibition of neuronal activity
NMDA - synaptic plasticity and memory formation
5-HT(3) - anxiety, emesis

Question 14

Which three categories are G-alpha subunits separated in and what are their roles?

Answer 14

G-alpha q/11 - ( 2nd messenger) Activates PLC ( effect 1) PIP(2) hydrolysed into IP(3) and DAG ( effect 2 ) Ip(3) promoted Ca2+ release from intracellular stores . DAG activates non-selective ion channels

G-alpha s - ( 2nd messenger ) Activates AC ( effect 1 ) Converts ATP to cAMP ( effect 2 ) Activates PKA

G-alpha 1/o - ( 2nd messenger ) Inhibits AC ( effect 1 ) Reduces cAMP formation ( effect 2 ) inhibits PKA

Question 15

How are 7-TM receptor and heterotrimeric G-protein made active?

Answer 15

They are inactive

Ligand binding changes shape of receptor

Unassociated G-protein binds to receptor

Bound GDP molecule phosphorylated to GTP

G protein dissociated into an alpha and beta-gamma subunit

The subunits bind to their target proteins

Question 16

How are the 7-TM receptor and heterotrimeric G-protein made inactive?

Answer 16

GTPase in cell acts on alpha subunit which desphorylates the GTP into GDP

beta-gamma subunit also leaves target protein and both join to make the inactive G protein

• If 7-TM receptor is active because ligand remains bound, further heterotrimeric G proteins can be activated

Question 17

What do G-alpha and G-beta-gamma subunits act as?

Answer 17

Secondary Messengers

Question 18

Give Examples of G protein-coupled receptors with their respective ligands and physiological effects? (4)

Answer 18

Angiotensin II –> AT-1 receptor. G-alpha q subunit :
Vasoconstriction, increased blood pressure

Acetylcholine –> M3 muscarinic receptor. G-alpha q subunit : Bronchoconstriction, decreased air flow

NE/ Ad –> Beta1 adrenergic receptor. G-alpha s subunit :
Increased heart rate, increased force on contraction

Dopamine –> D1 receptor. G-alpha s subunit :
Increased neuronal growth

Question 19

Which Enzyme linked receptors do:

Insulin
ANP/BNP
TGF beta

Bind to?

Answer 19

Insulin CD220 receptor. Enzyme : Tyrosine kinase

NPR1 receptor. Enzyme : GC ( vasodilation, reduces bp )

TGF beta R1. Enzyme : Ser/Thr Kinase ( apoptosis )

Question 20

What do Steroid Hormones target?

Answer 20

They are hydrophobic so go directly to intracellular receptors.

Mostly transcription factors

Question 21

What are Type I intracellular receptors?

Answer 21

In cytosol

Receptors are bound to chaperone molecules

When hormone binds the chaperone molecule dissociates

The hormone-receptor complex joins another hormone-receptor complex to form a homodimer

Homodimer goes to nucleus to bind to DNA ( acts as transcription factor )

Question 22

What are Type II intracellular receptors?

Answer 22

In nucleus ( often already bound to DNA )

Hormone ligand binding leads to directly transcriptional regulation as Hormone-complex is activated straight away

Question 23

How does the hormone Cortisol cause stress, immunosuppression and gluconeogenesis?

Answer 23

Binds to GC-R in cytosol. ( Type I intracellular receptor )

Regulates transcription

Question 24

How does Estradiol result in female sexual development?

Answer 24

Binds to Cytosolic ER-alpha receptor. ( Type I intracellular receptor )

Regulates transcription

Question 25

How does Thyroxine cause increased metabolism and greater physical development?

Answer 25

Binds to nuclear TR-alpha receptor. ( Type II intracellular receptor )

Regulates transcription

Question 26

Which condition is due to a disorder of membrane-attached proteins

Answer 26

lupus
multiple sclerosis
Myasthenia gravis
rhuematoid arthiritis ?

(which one?)

Question 27

Which receptor class: ErbB receptor

Answer 27

Enzyme linked ( I think )