KA 4

Question 1

Coordination Multicellular organisms signal between cells using?

Answer 1

Extracellular signalling molecules

Question 2

What are examples of extracellular signalling molecules?

Answer 2

Steroid hormones, peptide hormones, and neurotransmitters

Question 3

Receptor molecules of target cells are?

Answer 3

Proteins with a binding site for a specific signal molecule

Question 4

Binding changes what of the receptor? What does this do within the cell?

Answer 4

Conformation of the receptor, which initiates a response within the cell

Question 5

Different cell types produce specific signals that can only be detected and responded to by cells with?

Answer 5

The specific receptor

Question 6

Signalling molecules may have?

Answer 6

Different effects on different target cell types due to differences in the intracellular signalling molecules and pathways that are involved.

Question 7

In a multicellular organism, different cell types may show a…

Answer 7

Tissue-specific response to the same signal

Question 8

Hydrophobic signalling molecules can diffuse? And bind to?

Answer 8

Directly through the phospholipid bilayers of membranes, and so bind to intracellular receptors

Question 9

The receptors for hydrophobic signalling molecules are?

Answer 9

Transcription factors

Question 10

Transcription factors are?

Answer 10

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

Question 11

The steroid hormones oestrogen and testosterone are examples of?

Answer 11

Hydrophobic signalling molecules

Question 12

Steroid hormones bind to? In?

Answer 12

Specific receptors in the cytosol or the nucleus

Question 13

The hormone-receptor complex moves to… Where it binds…

Answer 13

The nucleus where it binds to specific sites on DNA and affects gene expression

Question 14

The hormone-receptor complex binds to? Called… Binding here influences?

Answer 14

Specific DNA sequences called hormone response elements (HREs).
Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes

Question 15

Hydrophilic signalling molecules bind to… What don’t they enter?

Answer 15

Transmembrane receptors and do not enter the cytosol

Question 16

Peptide hormones and neurotransmitters are examples of?

Answer 16

Hydrophilic extracellular signalling molecules.

Question 17

Transmembrane receptors change? When? What happens to the signal and signal molecule?

Answer 17

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 18

Transmembrane receptors act as? What does this alter?

Answer 18

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

Question 19

Transduced hydrophilic signals often involve?

Answer 19

G-proteins or cascades of phosphorylation by kinase enzymes

Question 20

G-proteins relay signals from?

Answer 20

Activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.

Question 21

Phosphorylation cascades allow?

Answer 21

More than one intracellular signalling pathway to be activated

Question 22

Phosphorylation cascades involve?

Answer 22

A series of events with one kinase activating the next in the sequence and so on.

Question 23

Phosphorylation cascades can result in?

Answer 23

The phosphorylation of many proteins as a result of the original signalling event.

Question 24

Binding of the peptide hormone insulin to its receptor results in?

Answer 24

An intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells

Question 25

Binding of insulin to its receptor causes?

Answer 25

A conformational change that triggers phosphorylation of the receptor.

Question 26

After binding insulin to the receptor what starts?

Answer 26

A phosphorylation cascade inside the cell, which eventually leads to GLUT4-containing vesicles being transported to the cell membrane.

Question 27

Diabetes mellitus can be caused by?

Answer 27

Failure to produce insulin (type 1) or loss of receptor function (type 2)

Question 28

Type 2 is generally associated with?

Answer 28

Obesity

Question 29

Exercise also triggers recruitment of GLUT4, so can improve?

Answer 29

Uptake of glucose to fat and muscle cells in subjects with type 2

Question 30

Resting membrane potential is a?

Answer 30

State where there is no net flow of ions across the membrane

Question 31

The transmission of a nerve impulse requires?

Answer 31

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

Question 32

An action potential is?

Answer 32

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

Question 33

Neurotransmitters initiate a response by?

Answer 33

Binding to their receptors at a synapse

Question 34

Neurotransmitter receptors are?

Answer 34

Ligand-gated ion channels.

Question 35

Depolarisation of the plasma membrane as a result of? What then results?

Answer 35

The entry of positive ions triggers the opening of voltage-gated sodium channels, and further depolarisation occurs

Question 36

Depolarisation is?

Answer 36

A change in the membrane potential to a less negative value inside.

Question 37

Inactivation of the sodium channels and the opening of potassium channels restores?

Answer 37

The resting membrane potential

Question 38

Binding of a neurotransmitter triggers?

Answer 38

The opening of ligand-gated ion channels at a synapse. Ion movement occurs and there is depolarisation of the plasma membrane. 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 39

What does binding of a neurotransmitter cause?

Answer 39

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

Question 40

Voltage-gated potassium channels… After binding of a neurotransmitter?

Answer 40

Open to allow potassium ions to move out of the cell to restore the resting membrane potential.

Question 41

Depolarisation of a patch of membrane causes?

Answer 41

Neighbouring regions of membrane to depolarise and go through the same cycle, as adjacent voltage-gated sodium channels are opened

Question 42

When the action potential reaches the end of the neuron it causes vesicles containing neurotransmitter to?

Answer 42

Fuse with the membrane — this releases neurotransmitter, which stimulates a response in a connecting cell

Question 43

Restoration of the resting membrane potential allows?

Answer 43

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 44

Ion concentration gradients are reestablished by the?

Answer 44

Sodium-potassium pump, which actively transports excess ions in and out of the cell

Question 45

Following repolarisation the sodium and potassium ion concentration gradients are?

Answer 45

Reduced

Question 46

The sodium-potassium pump restores the…

Answer 46

Sodium and potassium ions back to resting potential levels.

Question 47

The retina is the area within the eye that detects? What does it contain?

Answer 47

Light and contains two types of photoreceptor cells: rods and cones

Question 48

Rods function in?

Answer 48

Dim light but do not allow colour perception.

Question 49

Cones are responsible for?

Answer 49

Colour vision and only function in bright light.

Question 50

In animals the light-sensitive molecule retinal is combined with a? To form?

Answer 50

Membrane protein, opsin, to form the photoreceptors of the eye

Question 51

In rod cells the retinal-opsin complex is called?

Answer 51

Rhodopsin

Question 52

Retinal absorbs a?

Answer 52

Photon of light

Question 53

Rhodopsin changes conformation to?

Answer 53

Photoexcited rhodopsin

Question 54

A cascade of proteins amplifies the?

Answer 54

Signal

Question 55

Photoexcited rhodopsin activates a? What does this do?

Answer 55

Gprotein, called transducin, which activates the enzyme phosphodiesterase (PDE)

Question 56

A single photoexcited rhodopsin activates?

Answer 56

Hundreds of molecules of G-protein.

Question 57

Each activated G-protein activates one?

Answer 57

Molecule of PDE.

Question 58

PDE catalyses the hydrolysis of a molecule called?

Answer 58

Cyclic GMP (cGMP)

Question 59

Each active PDE molecule breaks down?

Answer 59

Thousands of cGMP molecules per second.

Question 60

The reduction in cGMP concentration as a result of its hydrolysis affects the? What does this result in?

Answer 60

Function of ion channels in the membrane of rod cells. 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 61

A very high degree of amplification results in?

Answer 61

Rod cells being able to respond to low intensities of light

Question 62

In cone cells, different forms of opsin combine with…

Answer 62

Retinal to give different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths: red, green, blue or UV 5