1.4 : communication and signalling

Question 1

how do multicellular organisms signal between molecules

Answer 1

through extracellular signalling molecules

Question 2

examples of signalling molecules

Answer 2

steroid hormones, peptide hormones, neurotransmitters

Question 3

what are receptor molecules

Answer 3

receptor molecules are proteins with a binding site for a specific molecule

Question 4

what does the binding of the receptor change

Answer 4

changes the conformation of the receptor which initiates a response in the cell

Question 5

signal specificity

Answer 5

different cell types produce different signals that can only be detected and responded by cells with the specific receptor

Question 6

why do signalling molecules have different effects on different cell types

Answer 6

will have different effects due to differences in intracellular signalling molecules and the pathways involved

Question 7

what will different cell types show in response to the same signal

Answer 7

a tissue specific response

Question 8

hydrophobic

Answer 8

molecules that are seemingly repelled by large masses of water. these molecules are also known as non-polar

Question 9

hydrophobic signalling molecules movement

Answer 9

diffuse directly through phospholipid bi layer of membrane and bind do intracellular receptors

Question 10

what are the receptors for hydrophobic molecules

Answer 10

transcription factors

Question 11

what are transcription factors

Answer 11

transcription factors proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.

Question 12

examples of hydrophobic signalling molecules

Answer 12

steroid hormones such as estrogen and testosterone

Question 13

where do steroid hormones bind

Answer 13

they bind to specific receptors in the cytosol or the nucleus

Question 14

what does the binding of steroid hormones form

Answer 14

hormone receptor complex

Question 15

how does the hormone receptor complex work

Answer 15

The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression .

The hormone-receptor complex binds to specific DNA sequences called hormone response elements (HRE’s)

Question 16

what does the binding of the complex to HRE’s influence

Answer 16

influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes .

Question 17

hydrophilic

Answer 17

A molecule that is attracted to water molecules and tends to be dissolved by water. Also known as polar molecules.

Question 18

hydrophilic signalling molecules movement

Answer 18

they do not enter the cytosol and instead bind to transmembrane receptors

Question 19

examples of hydrophilic extracellular signalling molecules

Answer 19

peptide hormones and neurotransmitters .

Question 20

transmembrane receptors

Answer 20

Transmembrane receptors change conformation when the ligand binds to the extracellular face. The signal molecule does not enter the cell, but the signal is transduced across the plasma membrane.

Question 21

transduction

Answer 21

Process by which a chemical or physical signal is transmitted through a cell by a series of molecular events resulting in a cellular response.

Question 22

how to transmembrane receptors act as signal transducers

Answer 22

by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.

Question 23

what do transduced hydrophilic signals involve

Answer 23

G-protiens, cascades of phosphorylation by kinase enzymes

Question 24

what do G-protiens do

Answer 24

relay signals from activated receptors to target proteins such as enzymes and ion channels .

Question 25

what are activated receptors

Answer 25

receptors that have bound a signalling molecule

Question 26

what do phosphorylation casacdes do

Answer 26

Phosphorylation cascades allow more than one intracellular signalling pathway to be activated. They involve a series of events with one kinase activating the next in the sequence and so on.

Question 27

what do phosphorylation casacdes result in

Answer 27

Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.

Question 28

what does the binding of insulin do

Answer 28

Binding of the peptide hormone insulin to its receptor results in an intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells.

Question 29

step 1 of insulin binding

Answer 29

Binding of insulin to its receptor causes a conformational change that triggers phosphorylation of the receptor.

Question 30

step 2 of insulin binding

Answer 30

This starts a phosphorylation cascade inside the cell

Question 31

step 3 of insulin binding

Answer 31

This phosphorylation eventually leads to GLUT4-containing vesicles being transported to the cell membrane.

Question 32

what is diabetes mellitus

Answer 32

caused by failure to produce insulin (type 1 ) or loss of receptor function (type 2 ). Type 2 is generally associated with obesity.

Question 33

what does exercise trigger

Answer 33

triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2 diabetes.

Question 34

what is a nerve impulse

Answer 34

a signal transmitted along a nerve fibre

Question 35

what is the resting membrane

Answer 35

state where there is no net flow of ions across the membranes

Question 36

what does the transmission of a nerve impulse require

Answer 36

requires change in the membrane potential of the neurons plasma membrane

Question 37

what is the action potential

Answer 37

wave of electrical excitation along a neurons plasma membrane

Question 38

what are neurotransmitters

Answer 38

chemicals that transmit a signal across a synapse

Question 39

what do neurotransmitters do

Answer 39

initiate a response by binding to their receptors at the synapse

Question 40

what type of receptors are neurotransmitter receptors

Answer 40

ligand gated ion channels

Question 41

what is depolarisation

Answer 41

a sudden change in membrane potential, usually from a relatively negative to positive internal charge

Question 42

what is depolarisation the result of

Answer 42

the entry of positive ions which triggers the opening of voltage gated sodium channels and causes further depolarisation

Question 43

how does the restoration of the membrane potential occur

Answer 43

the inactivation of the sodium channels and the opening of potassium channels

Question 44

what does the binding of a neurotransmitter do

Answer 44

triggers the opening of ligand-gated ion channels at the synapse

Question 45

how do sodium ions enter the cell

Answer 45

down a concentration gradient

Question 46

what do sodium ions lead to

Answer 46

rapid and large change in membrane potential

Question 47

action potential graph step 1

Answer 47

an external stimulus starts a rapid change in the voltage or action potential, this must reach above the threshold to start depolarisation

Question 48

action potential graph step 2

Answer 48

depolarisation is caused by a rapid rise in membrane potential by opening sodium channels in the membrane resulting in a large influx of sodium ions

Question 49

action potential graph step 3

Answer 49

repolarisation results from rapid sodium channel inactivation leading to a large influx of potassium ions from activated protien channels

Question 50

action potential graph step 4

Answer 50

hyperpolarisation is a lowered membrane potential caused by the effect of the loss of pottasium ions and the closing of pottasium channels

Question 51

action potential graph step 5

Answer 51

resting state is when membrane potential returns to resting voltage that it was before stimulus occurred

Question 52

what does depolarisation of a patch of membranes do

Answer 52

causes neighbouring regions of membranes to depolarise and go through same cycle as adjacent voltage gated sodium channels are opened

Question 53

what happens when action potential reaches the end of the neuron

Answer 53

causes vesicles containing neurotransmitters to fuse with membrane which releases neurotransmitters to stimulate a response to a connecting cell

Question 54

what does restoration of the resting membrane potential allow

Answer 54

inactive voltage gated sodium channels to return to original conformation that allows them to open again in response to depolarisation of the membrane

Question 55

what is reestablished by the sodium pottasium pump

Answer 55

ion concentration gradient

Question 56

how is ion concentration gradient re-established

Answer 56

by the sodium pottasium pump which actively transports excess ions in and out of the cell

Question 57

what follows repolarisation

Answer 57

the sodium and pottasium ion concentration gradients are reduced. the sodium pottasium pump restores the sodium and pottasium ions back to resting potential levels

Question 58

what is the retina

Answer 58

the area in the eye that detects light and contains 2 photoreceptor cells

Question 59

what are the two photoreceptors cells in the retina

Answer 59

rods and cones

Question 60

what are rods

Answer 60

function in dim light but do not allow colour perception

Question 61

what are cones

Answer 61

responsible for colour vision, need bright light to function

Question 62

what is combined to make the photoreceptors of the eye

Answer 62

retinal and opsin

Question 63

what is the retinal-opsin complex called

Answer 63

rhodopsin

Question 64

initiation of a nerve impulse in response to a stimulus (1)

Answer 64

rhodopsin absorbs a photon of light and changes conformation and becomes photoexcited rhodopsin

Question 65

what amplifies the signal from photoexcited rhodopsin (2)

Answer 65

a cascade of protiens

Question 66

initiation of a nerve impulse in response to a stimulus (3)

Answer 66

the photoexcited rhosopin activates G-protiens called transducin which activates enzyme PDE. a single photoexcited molecule activates hundreds of transducin, each molecule then activates 1 PDE. PDE then catalyses the hydrolysis of cyclic GMP

Question 67

initiation of a nerve impulse in response to stimulus (4)

Answer 67

each PDE molecule breaks down thousands of cGMP per second. this affects the function of ion channels in membrane of rod cells results in the closure of ion channels which trigger nerve umpulses across the retina

Question 68

what allows opsin to function at low lights

Answer 68

a higher amplification allows opsin to function at lower light intensities

Question 69

what do different forms of opsin do in cone cells

Answer 69

give different photoreceptor protiens, each with maximal sensitivy to different wavelegnths of light such as red, blue , green and UV