Cell signalling

Question 1

what is signal transduction

Answer 1

a way in which cells gain information about the environment
the coversions of signals into cellular responces

Question 2

outline the process of signal transduction

Answer 2

1) a ligand binds to a specific binding pocket on the extracellular membrane of the receptor
2) binding causes a conformational of the receptor activating messengers
3) these messengers induce a specific cellular responce

Question 3

why is signal transduction relevant

Answer 3

1) mediates direct cell to cell communication
2) coordinates metabolic processes within cells, the growth and differenciatino of tissues and the synthesis of proteins
3) coordinates the aggregation of free living cells for sexual mating

Question 4

what causes receptor activation

Answer 4

1) binding of molecules
2) changes in conc of a metabolite
3) physical stimuli

Question 5

what are the different types of signalling

Answer 5

1) endocrine
2) paracrine
3) autocrine

Question 6

what is endocrine signalling

Answer 6

when signalling molecules are released by a cell and affect target cells distant from site of synthesis
e.g. hormones

Question 7

what is paracrine signalling

Answer 7

the signalling molecules released by a cell affect target cells only in close proximity
e.g. growth factors or conduction by a neurotransmitter from one nerve cell to the next

Question 8

what is autocrine signalling

Answer 8

when cells respond to substances that they themselves have released
e.g.
tumour cells produce growth factors which stimulate proliferation of themselves

Question 9

what is intracellular signal transduction

Answer 9

pathways inside the cell which transduce signals downstream from the cell surface activation

Question 10

outline the process of intracellular signal transduction

Answer 10

1) binding of ligands to cell surface receptors leads to a change in conc of low molecular weight intracellular signalling molecules (SECNDARY MESSENGERS)
2) the altered conc leads to activation of intracellular proteins within the signal transduction pathway

Question 11

give some examples of secondary messengers

Answer 11

1) cycloic nucleotides e.g. cAMP
2) lipid messengers e.g. DAG
3) ions such as CA2+

Question 12

outline the adenyl cyclase pathway

Answer 12

1) epinephrine binds to a G-coupled receptor
2) G protein activates adenyl cyclase
3) adenyl cyclase releases cAMP (secondary messenger)
4) cAMP activates kinase A protein which activates the enyme within the pathway
5) enzyme produces the desired product

Question 13

what proteins are used to help transduce signals downstream from activated cell surface

Answer 13

1) G-proteins
2) kinases
3)phosphatases

Question 14

what are G proteins

Answer 14

guanine nucleotide-binding proteins
- interact with other proteins to change and perpetuate the signal and is in a state of ‘on of off’

Question 15

what are protein kinases

Answer 15

enzymes which catalyse the addition of phosphates to a substarte protein

Question 16

what are phosphatases

Answer 16

enzymes which catalyse the removal of a phosphate from a substrate proteins

Question 17

when is a G protein considered on and off

Answer 17

on- GTP bound
off - GDP bound

Question 18

what happens when a G protein is on

Answer 18

1) two protein domains are bound to the terminal phosphate of GTP allowing the protein to bind and activate other signalling proteins

Question 19

what happens when a G protein is off

Answer 19

release of the phosphate by GTPase catalysed hydrolysis causes domain I and II to releax into GDP

Question 20

what are the two protein kinases found in animal cells

Answer 20

1) add phosphate group to the hydroxyl group tyrosine residues

2) add phosphate gro0up to the hydroxyl group of serine and threnonine residues

Question 21

outline the structure of G protein-coupled receptors

Answer 21

1) several membrane spanning regions
2) N-terminal segment o the exoplasmic face outside the cell
3) C-terminal segment on the cytosolic face inside the cell of the plasma membrane

Question 22

where can G protein coupled receptors be found

Answer 22

1) light activated receptors in the eye
2) odarant receptors in the mammalian nose
3) receptors for a number of hormones and neurotransmitters

Question 23

outline how G proteins are associated with ligand induced activation of effector proteins

Answer 23

1) trimeric G proteins are tethered to the membrane by covalent attached lipid molecules
2) ligand binds to the receptor
3) receptor binds to G protein causing a conformational change in the alpha subunit
4) GDP dissociates with GTP activates G protein causing another change
5) this activates alpha subunit and beta-gamma complex and alpha dissociates
6) now can regulate activity of target proteins relaying signal
7) alpha hydrolysis GTP to GDP which reforms inactive g protein with beta-gamma complex

Question 24

what is meant by ligand induced activation associated with G proteins

Answer 24

many G proteins coupled receptors have an extracellular ligand domain and when a protein ligand binds to this domain the receptor undergoes a conformational change which activates a trimeric GDP protein

Question 25

what is the structure of trimeric G protein

Answer 25

composed of three protein subunits called alpha beta and gamma
the alpha and beta have covalently attached lipid tails which anchor protein to membrane

Question 26

how can G proteins activate ion channels

Answer 26

binding of acetylcholine triggerd activation of G protein

the release of G-beta subunit binds to and opens associated effector, the K+ channel

Question 27

give an example of light activated G-coupled receptors

Answer 27

the human retina has two photoreceptors rods and cones

Question 28

what are the rods and cones of the eye involved in

Answer 28

cones = colour vision = G proteim coupled receptor is iodopsin

rods= stimulated by weak light GPTC= rhodospsin