W1: Hormone-Receptor Interaction & Signalling Mechanisms

Question 1

intracellular vs intercellular signalling

Answer 1

com w/in a cell

com btwn diff cells (I.e. extracellular signalling)​ -
Endocrine, autocrine, paracrine, neuroendocrine, NT​

Question 2

ligand (key)

Answer 2

any molecule that binds to a specific site on a protein or other molecule e.g. hormone that binds to a receptor

Question 3

receptor (lock)

Answer 3

a molecule that recognises & binds to a ligand w/ high specificity

Question 4

affinity

Answer 4

Some hormones can bind to multiple diff receptors, but w/ diff affinities​

Some ligands don’t fit exactly into the receptor, but do work w/ a bit of adjustment

Question 5

what molecules can a ligand be?

Answer 5

protein, lipid or carbohydrate

Question 6

ligands - agonist vs antagonist

Answer 6

molecules that bind to a receptor & trigger a signalling pathway
molecules that bind to a receptor but do NOT trigger signalling (block the signal)

Question 7

ligands - precursor form

Answer 7

e.g pro-hormones

Question 8

ligands - binding partner

Answer 8

if ligand not soluble in blood, needs something to carry it around blood system

Question 9

characteristics of protein & peptide hormones

Answer 9

Small or large​

Often pro-hormone (prod as AA chain, then processed)​

Hydrophilic​

Soluble (free) in blood, so shorter half-life (bc don’t always need carrier protein, so get degraded faster)​

Degraded by proteolytic enzymes​

Extracellular receptor (bc ligand can’t easily cross cell mem)​

Stored & rapid release (bc can’t get out of cell easily, able to make it inside cell then store it)

Question 10

characteristics of steroid hormones

Answer 10

Small​

Hydrophobic​

Bound to plasma proteins, so longer half-life (protected from degradation)​

Intracellular receptor (bc ligand can cross mem)​

Synthesised on demand (bc tricky to store inside, as they’re able to cross plasma mem)​

Excreted (thru urinary system)

Question 11

characteristics of thyroxine

Answer 11

Small, potent​
Hydrophobic​
Bound to plasma proteins​
Intracellular receptor​
Stored in thyroid by binding partner (has BP inside cell, so able to build up amount before releasing)

Question 12

characteristics of epinephrine

Answer 12

Small, potent​
Hydrophilic ​
Soluble (free) in blood​
Degraded​
Extracellular receptor​
Stored in adrenal medulla

Question 13

receptors

Answer 13

Proteins​
Molecular switches​
Trigger cellular mechanism​
Extracellular or intracellular​
Specificity - accuracy​
Affinity - strength, higher affinity constant (Ka) = stronger​
Avidity = total strength (sometimes ligands bind at multiple places on receptor, so multiple interactions, so helpful to work out total strength)

Question 14

types of intracellular receptors

Answer 14

Some receptors are cytoplasmic (e.g. cortisol, oestradiol, testosterone, progesterone)​

Some are nuclear (e.g. thyroid hormones) (affect gene reg, so take longer to have an effect)

Question 15

how does extracellular signalling work?

Answer 15

Signalling cascades ‘amplify’ the original signal (i.e. highly sensitive to hormone - often potent) (can also include gene reg)​

Question 16

which hormones use extracellular receptors?

Answer 16

Cortisol, oestradiol, testosterone, progesterone, vit D​

Question 17

what are GPCRs?

Answer 17

G Protein Coupled Receptors​
7 transmembrane domains​
Once activated, trigger action inside cell

Question 18

examples of GPCRs

Answer 18

adrenaline receptor
glucagon receptor
oxytocin
PTH
somatostatin
thyrotropin
vasopressin
dopamine

Question 19

what are enzyme-coupled receptors?

Answer 19

Only 1 transmembrane domain​
Ligand binds to 2 receptors, bringing them closer together (dimerisation)​
Activates intrinsic enzyme activity

Question 20

examples of enzyme-coupled receptors

Answer 20

insulin receptor
GH receptor
platelet derived growth factor receptor
epidermal growth factor receptor

Question 21

what are phosphorylation cascades?

Answer 21

Commonly kinases (add phosphate group)​
Amplification​
High sensitivity (small input causes big output)​
Multiple possible outcomes
Reg of enzymes in signalling cascades commonly by phosphorylation (tyrosine, threonine & serine residues)
(But phosphorylation doesn’t always switch on!)

Question 22

kinases vs phosphatases

Answer 22

add phosphate

remove phosphate

Question 23

what are second messengers? what do they do?

Answer 23

Small intracellular signalling molecules​

Generated in large numbers in response to extracellular signal (amplification)​

Diffuse away from their source, broadcasting the signal throughout the cell​

Activate ‘downstream’ signalling molecules

Question 24

examples of second messengers

Answer 24

caMP
diacylglycerol (DAG)
IP3
Ca2+