Unit 1 : Cells and Proteins Key Area 4

Question 1

What are multicellular organisms made of?

Answer 1

Billions of cells that must communicate with each other.

Question 2

Why must multicellular organisms cells communicate with eachother?

Answer 2

ensure a co-ordinated response to stimuli

Question 3

what do extracellular signalling molecules do?

Answer 3

allows cells to communicate and these signals are often produced by either endocrine or nervous system.

Question 4

Name 3 examples of extracellular signalling molecules

Answer 4

Steroid hormones, peptide hormones and neurotransmitters.

Question 5

Target cells have ____________ receptors

Answer 5

Complementary

Question 6

What happens if a cell doesn’t have receptors for that specific signal molecule?

Answer 6

It will not bind and the cells will not respond

Question 7

These complementary receptors can be described as?

Answer 7

Specific to signalling molecules

Question 8

What causes the response by the cell?

Answer 8

the conformational change of the receptor

Question 9

Note steps involved in cell to cell communication

Answer 9

1. receptor molecules of target cells are proteins with a binding site for a specific signal molecule.
2. binding changes the conformation of the receptor.
3. initiates a response within the cell through the intracellular pathways

Question 10

Different tissues can react differently to what?

Answer 10

The same signalling molecules

Question 11

What’s this tissue-specific response caused by ?

Answer 11

Intracellular signalling molecules and pathways

Question 12

What’s an example of different tissues reacting differently to the same signalling molecules?

Answer 12

acetylcholine causes opposite effects in skeletal and heart muscle because these cell types produce different kinds f acetylcholine receptors that trigger different intracellular signalling pathways.

Question 13

How do hydrophobic signalling molecules travel through the phospholipid bilayer?

Answer 13

Diffuse through phospholipid bilayer and bind to receptors in the intracellular part of the cell.

Question 14

What is the name for the receptors for hydrophobic signalling molecules?

Answer 14

transcription factors

Question 15

name two hydrophobic signalling molecules include steroid hormones;

Answer 15

oestrogen and testosterone

Question 16

What does steroid hormones bind to?

Answer 16

Specific receptors in the cytosol or the nucleus

Question 17

What’s a transcription factor

Answer 17

Proteins which can affect gene expression by binding to DNA and stimulating/inhibiting transcription of genes

Question 18

Describe the stages of steroid hormones influencing transcription

Answer 18

1. hydrophobic signalling molecules can pass through the membrane directly.
2. hydrophobic signalling molecule binds to a receptor to create the hormone-receptor complex (HRC)
3. HRC moves to the nucleus where it binds to specific sections of DNA called hormone response elements (HRE’s)
4. HRC is a transcription factor + so it influences the transcription/expression lots of genes in the DNA - it can stimulate/ inhibit it.

Question 19

Hydrophilic signalling molecules _________ pass through the plasma membrane

Answer 19

cannot

Question 20

What do the hydrophilic signalling molecules bind to?

Answer 20

Transmembrane receptors on the extracellular surface of target cells

Question 21

examples of hydrophilic signalling molecules (3)

Answer 21

peptide hormones, insulin and neurotransmitters

Question 22

Does the signal enter the cell?

Answer 22

no - but the transmembrane proteins, to which it binds, changes conformation on binding and the signal is transduced (converted into intracellular signals)

Question 23

What do transduced hydrophilic signals often involve?

Answer 23

Cascades activated by G-proteins or phosphorylation by kinase enzymes

Question 24

What do G-proteins often do?

Answer 24

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

Question 25

What does phosphorylation cascades cause?

Answer 25

the phosphorylation of multiple proteins and allow more than one intracellular signalling pathway to be activated.

Question 26

Whats insulin?

Answer 26

A peptide hormone produced by the pancreas when blood glucose levels are high

Question 27

Whats the phosphorylation cascade started by?

Answer 27

the binding of the insulin to receptors causes the recruitment of GLUT4 glucose transporters into the plasma membrane of fat and muscle cells.

Question 28

Whats GLUT4?

Answer 28

a transporter protein - glucose moves by facilitated diffusion down it concentration gradient

Question 29

Describe steps involved in the recruitment of GLUT4 transporters?

Answer 29

1. insulin binds to etracellular receptor, causing conformational change + phosphorylation at the receptor.
2. triggers an intracellular signalling phosphorylation cascade.
3. vesicles move GLUT4 transporters to membrane
   (recruitment)
4. glucose moves into the cell through the GLUT4 transporters, down its concentration gradient. this is an example of facilitated diffusion.

Question 30

Cause and treatment of type 1 diabetes?

Answer 30

Failure to produce insulin, genetic - insulin injections

Question 31

Cause and treatment of type 2 diabetes?

Answer 31

loss of receptor function, lifestyle choices (ie. obesity) - lifestyle changes (healthier diet and more exersize) - triggers recruitment of GLUT4

Question 32

Whats the membrane potential of a cell?

Answer 32

is the difference in electrical charge across the membrane and is also known as the electrical potential difference or voltage.

Question 33

How is the membrane potential of a cell maintained?

Answer 33

by the sodium-potassium pump which also contributes to the electrochemical gradient

Question 34

describe the meaning of the term ‘resting membrane potential’?

Answer 34

Where there is no net flow of ions across the membrane and so the membrane potential is called the resting membrane potential. This is usually around -70mv (the cell is more -ve inside than outisde)

Question 35

What does the transmission of a nerve impulse require?

Answer 35

changes in the membrane potential of the neurons plasma membrane

Question 36

Neurotrasmitters cross the synaptic cleft and bind to what?

Answer 36

Specific receptors on the post-synaptic neuron - these receptors are ligand-gated sodium ion channels

Question 37

what happens when the neurotransmitter binds?

Answer 37

it changes the conformation of the ion channel and allows sodium ions to move into the cell. if there is enough in movement an action potential is generated.

Question 38

what is an action potential?

Answer 38

a wave of electrical excitation along a neurons plasma membrane

Question 39

What’s depolarisation?

Answer 39

when the cell becomes more positive due to the influx of sodium ions as a result of neurotransmitter binding at the synapse.

Question 40

What Neurotransmitters are involved in depolarisation? what do they do?

Answer 40

Ligand-gated sodium ion channels - open to allow the sodium ions to diffuse into the cell down their electrochemical gradient. This causes the initial depolarisation of the neuron plasma membrane.

Question 41

What happens once a threshold depolarisation is reached?

Answer 41

voltage gated sodium channels open causing rapid further depolarisation as more sodium ions enter the cell.
The triggering of one voltage gated sodium channel depolarises the membrane, so triggering the adjacent voltage-gated sodium channel and so on. this passes the signal along the neuron, depolarising the next section of the membrane.

Question 42

what is repolarisation?

Answer 42

after the wave of depolarisation passes along the neuron, there has to be a process to re-establish the resting potential, ready for the next impulse.

Question 43

what happens when the volatge reaches a critically high level?

Answer 43

the Na+ channels close again and the volatge gained K+ channels open.

Question 44

What does the positive potassium ions do during repolarisation?

Answer 44

They diffuse out the neuron cell down their electrochemical gradient - making the inside more negative. This can go too far and the cell can become more negative than the resting membrane potential - hyperpolarisation.

Question 45

what happens following repolarisation?

Answer 45

The Na+ and K+ ion concentration gradients are reduced. The sodium-potassium pump restores the Na+ and K+ ions back to resting potential levels.

Question 46

What happens to K+ channels once resting potential is reached?

Answer 46

They close

Question 47

What does restoration of the resting membrane potential allow?

Answer 47

Allows the inactive voltage-gated Sodium channels to open again in response to depolarisation of the membrane.

Question 48

When light enter the eye, what part of the eye does it hit?

Answer 48

The retina

Question 49

What is the retina made up of?

Answer 49

Two photoreceptor cells - called rods and cones.

Question 50

What is the function of rods?

Answer 50

Function in dim light but don’t allow colour perception.

Question 51

What is the function of cones?

Answer 51

Responsible for colour vision but only function in bright light.

Question 52

What are rod cells particularly sensitive to?

Answer 52

Light intensity - nocturnal animals have a greater proportion of rod cells = better night vision.

Question 53

What are cone cells particularly sensitive to?

Answer 53

specific colours (wavelengths) of light : green, red, blue and (in some animals) UV. - cone cells allow animals to have colour vision.

Question 54

How does light lead to vision in rod cells?

Answer 54

Light sensitive molecules called retinal combine with a protein in the membrane of rod cells called opsin. This forms the molecule rhodopsin which can absorb photons of light, causing a conformational change in the protein to become photoexcited rhodopsin.

Question 55

How do cone cells see colour?

Answer 55

Different forms of opsin combine with retinal to give different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths: green, red, blue or UV

Question 56

Note the steps involved in the generation of a nerve impulse within the retina?

Answer 56

1. a photon is absorbed by retinal molecule.
2. photoexcited rhodopsin activates 100s of g-proteins called transducin.
3. each transducin activates one molecule of the enzyme phosphdiesterase (PDE)
4. each PDE catalyses the hydrolysis of 100s of cGMP into GMP per second.
5. the reduced concentration of cGMP causes the Na+ ion channel to close.
6. the lack of postive Na+ ions hyperpolarises the cell and triggers the nerve impulse in the rod cell.