Hormone and cell signalling

Question 1

What are the types of cell communication?

Answer 1

Autocrine - Affects cell producing them e.g., growth factors
Paracrine - Diffuse short distance to affect cells nearby e.g., neurotransmitters
Endocrine - Acts on target cells distance from site of synthesis - hormones

Question 2

What are the types of hormones?

Answer 2

lipid soluble
water soluble

Question 3

Describe the features of lipid soluble hormones

Answer 3

Transported in blood by carrier proteins
Diffuse through plasma membrane
Alters gene expression at level of nucleus
e.g. steroid hormones, thyroid hormones, retinoids, Vitamin D

Question 4

Describe the features of water soluble hormones

Answer 4

Travel easily in blood
Binds to receptors on cell surface (cannot cross plasma membrane because they are hydrophilic)
Results in series of intracellular events

Question 5

How do lipid soluble hormones affect the cell at the level of the nucleus?

Answer 5

hormone diffuses into cell across plasma membrane
binds to receptor
Complex diffuses into nucleus and alters DNA => protein synthesis => biological response

Question 6

How do nuclear receptors alter gene expression?

Answer 6

Inactive nuclear receptors are bound to inhibitory proteins
When hormones bind to nuclear receptors they recruit additional coactivator proteins and inhibitory proteins dissociate
Coactivator proteins bind to receptors on the transcription-activating domain => gene transcription

Question 7

What are the components of cell membrane receptor?

Answer 7

External domain (binds signal/hormone)
Transmembrane domain
Cytoplasmic/intracellular domain

Question 8

How do cell membrane receptors cause a signalling pathway in the cell?

Answer 8

Ligand binds to extracellular ligand-binding domain => conformational change in cytoplasmic domain => receptor phosphorylates intracellular proteins => signal transduction

Question 9

What are growth factors and cytokines?

Answer 9

Growth factors: polypeptides that promote cell growth &/or proliferation
Cytokines: general term for factors associated with blood cells i.e., derived from immunology

Question 10

What is the function of growth factors and cytokines?

Answer 10

Cell division/proliferation
Cell differentiation
Apoptosis

Question 11

How do growth factors cause a response?

Answer 11

Bind to receptors which have tyrosine kinase (enzyme) activity
Enzyme is activated => initates signal that is propagated through cell by phosphorylation
Activates transcription factors => production of growth response genes

Question 12

what is the half life a signalling molecule?

Answer 12

time taken for conc of molecule to half

Question 13

what are the main classes and functions of cell surface receptors?

Answer 13

Ion-channel-linked receptors - Rapid synaptic signalling
G-Protein linked receptor - Act indirectly to activate separate plasma membrane bound protein
Tyrosine kinase-linked receptor - Directly associated with enzyme they activate
Receptors with intrinsic enzymatic activity - Functions directly as enzyme

Question 14

How do ion channels work?

Answer 14

Signalling molecule (neurotransmitter) bind to receptor => opens or closes ion channel => movement of ions into cell by diffusion => excitability of post-synaptic cell altered

Question 15

Give examples of ion channels

Answer 15

post-synaptic membranes
Neuromuscular junction
Nicotinic acetylcholine receptor
GABA receptors

Question 16

How do G-protein linked receptors work?

Answer 16

Receptor-protein interaction mediated by G protein
e.g., muscarinic acetylcholine receptor

Question 17

Describe the interaction between G-protein and adenylate cyclase

Answer 17

Subunit of G-protein activates adenylate cyclase => ATP converted to cAMP => intracellular phosphorylations
e.g., epinephrine acting through adrenergic-B-receptor

Some G-proteins inhibit adenylate cyclase e.g., norepinephrine acting through a-2-receptor on pre-synaptic nerve

Question 18

What are the key processes involved in intracellular cell signalling?

Answer 18

Protein phosphorylation (enzyme = protein kinases
Reversal of protein phosphorylation (enzyme = phosphoprotein phosphatase)

Question 19

Describe the types of molecular switch

Answer 19

Phosphorylation activates protein, dephosphorylation inactivates protein
Signalling protein exchanges bound GDP (inactive) for GTP (active)