Cell Signalling

Question 1

why do cells need to communicate?

Answer 1

1) processing information (e.g. visual processing)
2) self-preservation (innate reflex response to move away from danger - e.g. spinal reflex arc)
3) voluntary movement
4) homeostasis

Question 2

what are the different modes of intercellular signalling?

Answer 2

1) Nerve fibres of the central and peripheral nervous system

2) The blood vessels of the cardiovascular system

Question 3

what happens when a person is hypoglycaemic?

Answer 3

1) glucagon recreated by alpha cells in the islet of langehans
2) glucagon travels in blood vessels to liver
3) glycogenolysis + gluconeogeneisis are stimulated = incr. blood glucose levels

Question 4

define “endocrine signalling”

Answer 4

a hormone travelling within blood vessels to act on a distant target cell
e.g. adrenaline - adrenal gland → trachea

Question 5

what happens when a person is hyperglycaemic?

Answer 5

1) insulin recreated by beta cells in the islet of langehans
2) has a PARACRINE effect: inhibits glucagon secretion by targeting cells adjacent to it (beta cells)
3) also has a ENDOCRINE effect as it travels to the liver and causes uptake of glucose as glycogen

Question 6

define “paracrine signalling”

Answer 6

hormone acts on adjacent cell

e.g. insulin produced by beta-cells acting on alpha-cells to prevent the release of glucagon

Question 7

define the type of signalling between “membrane-attached proteins”

Answer 7

plasma membrane proteins on adjacent cells interacting

e. g. APC macrophages interacting with T lymphocytes through a T-cell receptor interaction
e. g. CD4 receptor on T lymphocytes and HIV when HIV infects

Question 8

define “autocrine signalling”

Answer 8

signalling molecule acting on the same cell

e.g. growth factors from tumour cells, acetylcholine, interleukin-2 on t-lymphocytes

Question 9

what are the four types of intercellular signalling?

Answer 9

1) endocrine
2) paracrine
3) autocrine
3) signalling between membrane attached proteins

Question 10

what type of signalling is neurotransmission?

Answer 10

paracrine signalling

Question 11

what are the steps of neurotransmission?

Answer 11

1) propagation of an action potential
2) neurotransmitter released from vesicles
3) activation of postsynaptic receptors

Question 12

what type of signalling is involved with post-synaptic receptors?

Answer 12

intracellular signalling pathways

Question 13

what does the ionotropic receptor do?

Answer 13

1) ligand binds
2) conformational change in the channel protein which it opens ion permeable pore
3) allows movement of ions through this channel according to conc gradients

e.g. ACh neuromuscular junction
GABA receptor in brain which inhibits neuronal activity

Question 14

what does a G-protein coupled receptor do?

Answer 14

1) heterotrimetric g-protein (G-alpha, G-beta-gamma, GDP molecule) is inactive and close to a receptor
2) ligand binding to nearby receptor = conformational change in the receptor
3) causes it to associate with the G-protein complex = active=ates it and:

• GDP molecule being phosphorylated to a GTP molecule or GDP is exchanged to GDP
• G-alpha dissociates from G-beta-gamma and they can both act as secondary messengers involved in a protein cascade

4) when the ligand dissociates internal GTPase on the Gα subunit hydrolyses GTP to GDP+ Gα and Gβγ subunits re-associate and are once again

Question 15

what does an enzyme linked receptor do?

Answer 15

-require clustering of more than one receptor protein to activate the intracellular enzyme

Question 16

define the term heterotrimeric protein?

Answer 16

made up of three main components

Question 17

mechanism of an enzyme linked receptor?

Answer 17

1) ligand binding → receptor clustering
2) this then activates enzyme activity within the cytoplasm
3) receptor phosphorylated by the enzymes
4) signalling proteins bind to the cytoplasmic domain after they are phosphorylated
5) signal generated as more signalling proteins are recruited
6) signal is terminated when a phosphatase dephosphorylates the receptor

e.g. insulin receptor

Question 18

tyrosine kinase receptors

Answer 18

enzyme-linked receptors involved in the insulin mechanism so glucose uptake and lipid metabolism

Question 19

why does the homones need to be lipophilic in intracellular receptors?

Answer 19

as it targets intracellular receptors to get through the membrane

Question 20

type I cytoplasmic intracellular receptor

Answer 20

-located within the cytoplasm

1) when hormone binds = chaperone protein dissociates
2) homodimer formed between two hormone receptor complexes
3) homodimer translocates to the nucleus → binds to DNA → acts as a transcription factor

-end point is almost always changes to dna (protein translation) = slower process

Question 21

nuclear intracellular receptor

Answer 21

-located within nucleus

1) often already bound to the nucleus
2) direct transcriptional regulation by the activated hormone-receptor complex

e. g. cortisol - glucocorticoid receptor
(stress) , thyroxine - thyroid receptor (metabolism)