Cell Signalling Pathways

Question 1

Cell signalling definition

Answer 1

Process by which a cell responds to substances outside the cell through signalling molecules found on the surface and inside the cell

Question 2

Why is cell signalling important

Answer 2

For cell growth, secretion, motility and metabolism

Question 3

Process of cell signalling

Answer 3

Ligand binds to its receptors
Alters the shape or activity of the receptor triggering a change inside the cell
Relayed through a chain of chemical messengers

Question 4

Forms of signalling

Answer 4

Paracrine
Autocrine
Endocrine
Signalling through cell-cell contact

Question 5

Paracrine signalling

Answer 5

Cells close together communicate through release of chemical messengers
E.g synaptic signalling

Question 6

Autocrine signalling

Answer 6

Cell signals to itself releasing a ligand that binds to receptors on its own surface

Question 7

Endocrine signalling

Answer 7

Signals produced by specialised cells and released into bloodstream which carries them to target cells in distant parts of the body
Endocrine glands release hormones

Question 8

Signalling through cell cell contact

Answer 8

Water filled channels allow small signalling molecules called intracellular mediators to diffuse between the two cells

Two cells may bind to one another because they carry complementary proteins on their surfaces
Proteins bind to one another causing a change in the shape of the protein transmitting a signal

Question 9

Hormone

Answer 9

Secreted by endocrine glands
Carried in the blood to target tissues

Question 10

neurotransmitters

Answer 10

secreted by neurones to conduct nerve impulses across a synapse

Question 11

local chemical mediators

Answer 11

produced by specialised or non specialised cells and affect other cells in the local environment

Question 12

Receptors

Answer 12

region of tissue or molecule in a cell membrane which responds specifically to a particular neurotransmitter, hormone, antigen or other substance
specific to an extracellular messenger

Question 13

formation of the ligand receptor complex

Answer 13

non covalent bonds
binding is irreversible

Question 14

4 receptor superfamilies

Answer 14

ligand gated ion channels (ionotropic receptors)
G protein coupled receptors
Kinase linked receptors
nuclear receptors (intracellular)

Question 15

ligand gated ion channels

Answer 15

fast synaptic transmission
post synaptic membrane
neurotransmitter
binding of a ligand causes a conformational change in shape of the protein

Question 16

dna binding receptors/ nuclear receptors

Answer 16

intracellular
ligand receptor complex binds to dna and stimulates transcription of specific target genes, mRNA is produced then translated by ribosomes and this causes an increase in concentration of protein encoded for by the gene transcribed

Question 17

mechanism of action of steroid hormones

Answer 17

carried in the blood bound to plasma proteins
binds with high affinity to steroid hormone binding domain of intracellular receptor protein that is specific
steroid hormone receptor complex migrates to the nucleus and binds to specific sites on DNA
these sites are palindromic - ‘Hormone response elements’
allows formation of stable complex of proteins including coactivators
increased production of mRNA results in increased translation into protein

Question 18

tyrosine kinase receptors

Answer 18

very large N terminal extracellular ligand binding domain - when hormone or growth factor binds to this is causes a conformational change that activates the tyrosine kinase
the C terminal intracellular domain has a protein kinase active site that can phosphorylate the amino acid tyrosine
binds to protein substrate to be phosphorylated and the ATP

Question 19

g protein couple receptors

Answer 19

binding of a ligand causes a conformational change and activates a G protein

Question 20

interaction of the b adrenergic receptor with g protein

Answer 20

in resting state, g protein is bound to a subunit
when a ligand binds, it causes a conformational change that exposes a g protein binding site
a subunit binds and GDP dissociates so that GTP can bind- a subunit is now active
activates adenylate cyclase, increases cAMP
binds to cAMP dependent protein kinase (PKA), conformational change
releases active subunits

Question 21

second messengers

Answer 21

binds to intracellular proteins and changes their biological activity
phosphorylate
sometimes there is a cascade of protein kinases
alter the activity of a target regulatory enzyme or protein
physiological response

Question 22

advantage of cascades

Answer 22

amplification of the response
activates many molecules
diversity of response

Question 23

t lymphocytes

Answer 23

white blood cells that mediate cellular immune response

Question 24

b lymphocytes

Answer 24

produce antibodies

Question 25

structure of an antibody

Answer 25

4 polypeptides- 2 heavy chains and 2 light chains variable chain constant region

Question 26

hypermutation

Answer 26

foreign antigen binds to antibody receptor with complementary shape b cell activated to divide and high rate of gene mutation these mutations alter the shape of the variable region

Question 27

epitope

Answer 27

part of the antigen that is recognised by antibodies