Unit 1 - Communication and Signalling

Question 1

How do multicellular organisms signal between cells?

Answer 1

using extracellular signalling molecules

Question 2

What are examples of extracellular signalling molecules?

Answer 2

Steroid hormones, peptide hormones, and
neurotransmitters are examples of
extracellular signalling molecules.

Question 3

What are receptor molecules of target cells?

Answer 3

Receptor molecules of target cells are
proteins with a binding site for a specific
signal molecule

Question 4

What does the binding of a signal molecule result in?

Answer 4

Binding changes the conformation of the
receptor, which initiates a response within the
cell

Question 5

Why do signalling molecules have different effects on different cell type?

Answer 5

due to differences in the intracellular signalling molecules and pathways that are involved

Question 6

How do different cell types attract to a specific receptor?

Answer 6

produce specific signals that can only be detected and responded to by cells with the specific receptor

Question 7

How do hydrophobic signalling molecules work?

Answer 7

Hydrophobic signalling molecules can diffuse
directly through the phospholipid bilayers of
membranes, and so bind to intracellular
receptors

Question 8

What are the receptors for hydrophobic signalling molecules?

Answer 8

The receptors for hydrophobic signalling
molecules are transcription factors

Question 9

What are transcription factors?

Answer 9

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

Question 10

Where do steroid hormones bind to?

Answer 10

Steroid hormones bind to specific receptors
in the cytosol or the nucleus

Question 11

What do hormone- receptor complex bind to?

Answer 11

Specific DNA sequenced called Hormone Response Elements (HREs)

Question 12

What does binding at HRE sites influence?

Answer 12

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

Question 13

What doe hydrophilic signalling molecules bind to?

Answer 13

bind to transmembrane receptors and do not enter the cytosol

Question 14

What are examples of extracellular signalling molecules?

Answer 14

Peptide hormones and neurotransmitters are
examples of hydrophilic extracellular
signalling molecules.

Question 15

What happens when an extracellular signalling molecule bind to the membrane?

Answer 15

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 16

What do transmembrane proteins act as in Hydrophilic signalling?

Answer 16

Transmembrane receptors act as signal
transducers by converting the extracellular
ligand-binding event into intracellular signals,
which alters the behaviour of the cell

Question 17

What does transduced hydrophilic signalling often involve?

Answer 17

Transduced hydrophilic signals often involve
G-proteins or cascades of phosphorylation by
kinase enzymes

Question 18

What do G-proteins do?

Answer 18

G-proteins relay signals from activated
receptors (receptors that have bound a
signalling molecule) to target proteins such
as enzymes and ion channels

Question 19

What do protein cascades allow?

Answer 19

allow more than one intracellular signalling pathway to be activated

Question 20

What do phosphorylation cascades involve?

Answer 20

Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on.

Question 21

What does the binding of peptide hormone insulin do to its receptor in intracellular signalling?

Answer 21

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 22

What happens to the receptor when insulin binds to it?

Answer 22

Binding of insulin to its receptor causes a
conformational change that triggers
phosphorylation of the receptor. This starts a
phosphorylation cascade inside the cell,
which eventually leads to GLUT4-containing
vesicles being transported to the cell
membrane.

Question 23

What is Type 1 diabetes caused by?

Answer 23

by failure to
produce insulin

Question 24

What is Type 2 diabetes caused by?

Answer 24

loss of receptor
function

Question 25

What is Type 2 diabetes associated with?

Answer 25

Obesity

Question 26

What does exercise do for diabetes?

Answer 26

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

Question 27

What is the resting membrane potential?

Answer 27

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

Question 28

What does the transmission of a nerve impulse require?

Answer 28

changes in the membrane potential of the neuron’s plasma membrane

Question 29

What is an action potential?

Answer 29

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

Question 30

What do neurotransmitters do?

Answer 30

Neurotransmitters initiate a response by
binding to their receptors at a synapse

Question 31

What are neurotransmitter receptors?

Answer 31

Neurotransmitter receptors are ligand-gated ion channels

Question 32

What is depolarisation?

Answer 32

Depolarisation is a change in the membrane
potential to a less negative value inside

Question 33

What causes depolarisation?

Answer 33

Depolarisation of the plasma membrane as a
result of the entry of positive ions triggers the
opening of voltage-gated sodium channels,
and further depolarisation occurs

Question 34

What restores the resting membrane potential?

Answer 34

The Inactivation of the sodium channels and the opening of potassium channels

Question 35

What does the binding of neurotransmitters trigger?

Answer 35

• the opening of ligand-gated ion channels at a synapse
• Ion movement occurs and there is
  depolarisation of the plasma membrane

Question 36

What happens if there is sufficient ion movement and the threshold is met?

Answer 36

If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of voltage-gated sodium channels is triggered and sodium ions enter the cell down their electrochemical gradient

Question 37

What does sodium ions entering the cell cause?

Answer 37

This leads to a rapid and large change in the
membrane potential. A short time after
opening, the sodium channels become
inactivated.

Question 38

What happens when the sodium channels are inactivate?

Answer 38

Voltage-gated potassium
channels then open to allow potassium ions
to move out of the cell to restore the resting
membrane potential

Question 39

What happens when the action potential reaches the end of the neuron?

Answer 39

When the action potential reaches the end of
the neuron it causes vesicles containing
neurotransmitter to fuse with the membrane
— this releases neurotransmitter, which
stimulates a response in a connecting cell

Question 40

What happens to the sodium channels during restoration of the resting membrane potential do?

Answer 40

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

Question 41

What does the sodium-potassium pump do?

Answer 41

The sodium-potassium pump restores the sodium and potassium ions back to resting potential levels.

Question 42

What cells of the eye detects light?

Answer 42

Two types of
photoreceptor cells: rods and cones

Question 43

What is the function of rods?

Answer 43

Rods function in dim light but do not allow
colour perception.

Question 44

What are cones responsible for?

Answer 44

Cones are responsible for colour vision and only function in bright light.

Question 45

What does retinal combine with to form?

Answer 45

retinal is combined with a membrane protein, opsin, to form the photoreceptors of the eye

Question 46

What is the retinal-opsin complex called?

Answer 46

Rhodopsin

Question 47

What happens when retinal absorbs a photon of light?

Answer 47

Retinal absorbs a photon of light and
rhodopsin changes conformation to
photoexcited rhodopsin

Question 48

What does photoexcited rhodopsin activate?

Answer 48

G-protein called transducin.

Question 49

What does transducin activate?

Answer 49

which activates the
enzyme phosphodiesterase (PDE)

Question 50

What does each G-protein molecule activate?

Answer 50

PDE

Question 51

What does PDE catalyse?

Answer 51

the hydrolysis of a molecule
called cyclic GMP (cGMP)

Question 52

What does cGMP cause?

Answer 52

This results in the closure of ion channels in
the membrane of the rod cells, which triggers
nerve impulses in neurons in the retina

Question 53

Why do rod cells respond to low intensities of light?

Answer 53

A very high degree of amplification

Question 54

What does opsin combine with retinal to form different form of?

Answer 54

Photoreceptor proteins with specific wavelengths, red, green, blue or UV

Question 55

What happens to the ion concentration gradients during the restoration of the resting membrane potential.

Answer 55

Ion concentration gradients are re-established by the sodium-potassium pump, which actively transports excess ions in and out of the cell

Question 56

what do phosphorylation cascades result in?

Answer 56

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