1.4 communication and signalling

Question 1

receptor molecules

Answer 1

proteins with a binding site of a specific signalling molecule
binding causes a conformational change, initiating a response

Question 2

hydrophobic signalling molecules

Answer 2

diffuse through the bilayer
bind to intracellular receptors

Question 3

examples of hydrophobic signalling molecules

Answer 3

steroid hormones:
oestrogen and testosterone

Question 4

transcription factors

Answer 4

receptors for hydrophobic signalling molecules
when bound to DNA, can initiate/prevent transcription

Question 5

hydrophobic signalling molecules pathway

Answer 5

steroid hormones bind to specific receptors in the cytosol/nucleus
hormone-receptor complex moves to the nucleus and binds to hormone response elements (specific DNA sequences)
the rate of transcription and gene expression is altered

Question 6

hydrophilic signalling molecules

Answer 6

bind to transmembrane receptors
don’t enter the cytosol

Question 7

examples of hydrophilic signalling molecules

Answer 7

peptide hormones (insulin)
neurotransmitters

Question 8

transmembrane receptors

Answer 8

act as signal transducers across the plasma membrane
convert extracellular ligand-binding to intracellular signals

Question 9

G-proteins

Answer 9

relay signals from activated receptors to target proteins

Question 10

phosphorylation cascades

Answer 10

a series of events with one kinase activating the next in the sequence etc.
results in the phosphorylation of many proteins
activates multiple intracellular signalling pathways

Question 11

insulin binding pathway

Answer 11

insulin binds to its receptor
receptor changes conformation
receptor undergoes phosphorylation
phosphorylation cascade is triggered in the cell
vesicles containing GLUT4 are transported to the cell membrane

Question 12

type 1 diabetes

Answer 12

caused by the failure to produce insulin

Question 13

type 2 diabetes

Answer 13

caused by the loss of receptor function
exercise triggers recruitment of GLUT4, so can improve glucose uptake in fat and muscle cells

Question 14

resting membrane potential

Answer 14

a state where there is no net flow of ions across the membrane

Question 15

action potential

Answer 15

a wave of electrical excitation along a neuron’s plasma membrane

Question 16

nerve impulse transmissions

Answer 16

requires a change in membrane potential
when action potential reaches the end of a neuron, vesicles containing neurotransmitters fuse with the membrane
neurotransmitters are released and stimulate a response in a connecting cell

Question 17

neurotransmitter receptors

Answer 17

ligand-gated ion channels at a synapse

Question 18

define depolarisation

Answer 18

change in membrane potential to a less negative value inside the cell

Question 19

effects of depolarisation of plasma membrane

Answer 19

(due to entry of positive ions) opens voltage-gated sodium channels
neighbouring regions of membrane are also depolarised

Question 20

depolarisation cycle

Answer 20

neurotransmitter binding opens ligand-gated ion channels at synapse
ion movement and depolarisation
depolarisation beyond a certain threshold opens voltage-gated sodium channels
sodium enters down electrochemical gradient
change in membrane potential inactivates sodium channels
voltage-gated potassium channels open
potassium enters, restoring resting membrane potential

Question 21

define retina

Answer 21

area within the eye that detects light

Question 22

function of rods

Answer 22

function in dim light
don’t allow colour perception

Question 23

function of cones

Answer 23

function in bright light
allow colour colour perception

Question 24

formation of photoreceptors

Answer 24

retinal (light-sensitive molecule) combined with opsin (membrane protein)

Question 25

define rhodopsin

Answer 25

retinal-opsin complex in rod cells

Question 26

nerve impulse in retina pathway

Answer 26

retinal absorbs a photon of light
rhodopsin changes conformation to form photoexcited rhodopsin
activates transducin (G-protein)
activates phosphodiesterase (PDE)
catalyses hydrolysis of cyclin GMP (cGMP)
ion channels in rod cell membrane close
nerve impulse in retina neurons

Question 27

why rod cells function in dim light

Answer 27

protein cascade amplifies the signal

Question 28

why cone cells detect colour

Answer 28

different forms of opsin combine with retinal producing different photoreceptor proteins
each have maximal sensitivity to specific wavelengths