Communcation And Signalling

Question 1

Coordination

Answer 1

Multicellular organisms signal between cells using extra cellular signalling molecules

Question 2

Examples of extra cellular signalling hormones

Answer 2

Steroid hormones, peptide hormones, and neurotransmitters

Question 3

What is a receptor ?

Answer 3

They are proteins with a binding site for a specific signal molecule

Question 4

What does binding do

Answer 4

It changes the confirmation of the receptor, which initiated a response in the cell

Question 5

What do different cell types do ?

Answer 5

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

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

Question 6

What do multicellular organisms , different cell types show

Answer 6

A tissue specific response to the same signal

Question 7

What are hydrophobic signals ?

Answer 7

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

They can do this the tails of phospholipids in the plasma membrane are also hydrophobic and allow the molecules to pass across

Question 8

What are the receptors of hydrophobic signalling

Answer 8

Transcription factors

They are proteins that when they bind to dna they inhibit initiation of transcription or stimulate it .

Question 9

Examples of hydrophobic signalling molecules

Answer 9

Testosterone and oestrogen

Question 10

What are steroid hormones and what do they do

Answer 10

They bind to specific receptors in the cytosol or the nucleus

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

Question 11

How do steroid hormones do this ?

Answer 11

The hormone-receptor complex binds to 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 12

What do hydrophilic and transduction hydrophilic signalling molecules bind to ?

Answer 12

The transmembrane receptor and do not enter the cytosol

Question 13

peptide hormone and neurotransmitters are examples of what ?

Answer 13

Hydrophilic extracellular signalling molecules

Question 14

What do transmembrane receptors do ?

Answer 14

They change the confirmation when the ligand binds to the extracurricular face, signal molecules do not enter the cell but it’s transducer across the plasma membrane

Question 15

What do transmembrane receptors act as ?

Answer 15

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

Question 16

What are transduced hydrophilic signals often involved with ?

Answer 16

G-proteins or cascades of phosphorylation by kinase enzymes

Question 17

What is the the function of G-proteins?

Answer 17

G-proteins relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels. Details of G- proteins subunits are not required.

Question 18

What is cascade phosphorylation ?

Answer 18

Phosphorylation cascades allow for more than one intracellular pathway to be activated

Question 19

Describe the process of cascades phosphorylation?

Answer 19

Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on. Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.

Question 20

What is the action of insulin and how does it go about ?

Answer 20

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 21

What does the binding of insulin to a receptor

Answer 21

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 22

What is type 1 diabetes?

Answer 22

Caused because of failure of production production of insulin

Question 23

What is type 2 diabetes?

Answer 23

Loss of receptor function, generally associated with obesity, Exercise also triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2

Question 24

Events of in cell signalling

Answer 24

1. Extra cellular signal molecules released from cell
2. Extracellular signal molecule travel to target cell
3. Signal molecule binds to the receptor
4. Binding causes a confirmational change
5. This allows a response from the cell

Question 25

What is membrane potential?

Answer 25

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

Question 26

What does a transmission of a nerve impulse require ?

Answer 26

Change is the membrane potential of the neurons plasma membrane

Question 27

What is an action potential ?

Answer 27

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

Question 28

How do neurotransmitters imitate a response

Answer 28

Binding to the synapses receptors

And neurotransmitters receptors are ligand gated channels

Question 29

What is depolarisation of the plasma membrane?

Answer 29

It results in the entry of positive ions which then triggers the opening of voltage gated sodium channels and further depolarisation occurs

Question 30

What is depolarisation?

Answer 30

It’s the change of membrane potential to the less negative value

Question 31

What happens when you inactivate the sodium channels and open the potassium channels ?

Answer 31

It restore the resting membrane potential

Question 32

How does this process happen ?

Answer 32

Binding of a neurotransmitter triggers 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. This leads to a rapid and large change in the membrane potential. A short time after opening, the sodium channels become inactivated. Voltage-gated potassium channels then open to allow potassium ions to move out of the cell to restore the resting membrane potential.

Question 33

What happens when you depolarise a patch of membrane ?

Answer 33

It causes neighbouring regions to depolarise and go through the same process of other voltage gated channels

Question 34

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

Answer 34

it causes vesicles containing neurotransmitter to fuse with the membrane — this releases neurotransmitter, which stimulates a response in a connecting cell

Question 35

Restoring the membrane potential, how is this done ?

Answer 35

When you restore the resting membrane potential allows the inactive voltage gated sodium channel to return to the conformation that allows them to open again in response to depolarisation of the membrane.

Question 36

What happens after repolarisation?

Answer 36

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

Question 37

Nerve impulses in the eyes

Answer 37

retina is the area within the eye that detects light and contains two types of photoreceptor cells: rods and cones

Question 38

What do the rods do ?

Answer 38

The is 125 million rods

Rods are sensitive to light intensity, Rods function in dim light but do not allow colour perception.

Nocturnal animals have a greater degree of rods

Question 39

What do cones do ?

Answer 39

The is 6 million cones

Not as sensitive to light as rods , they are sensitive to particular colours, Cones are responsible for colour vision and only function in bright light.

Question 40

What are photoreceptors and how are they made ?

Answer 40

They are mode from retinal and ops in to form photoreceptors

Question 41

What are rods cells in the retinal ops in complex called ?

Answer 41

Rhodopsin

Question 42

What do come cells do in the process ?

Answer 42

Different forms of ops in combine with retinal give different photoreceptor proteins in each with a max sensitivity to specific wavelengths

Question 43

What does a cascade of proteins do ?

Answer 43

Amplifies the signal

Question 44

Retinal response to light ?

Answer 44

1. Retinal absorbed light and rhodopsin changes confirmation to photoexcited rhodopsin
2. Photoexcited rhodopsin activates a G- protein, called transducin, which activates the enzyme phosphodiesterase (PDE)
   (A single photoexcited rhodopsin activates hundreds of molecules of G-protein.)(activated G-protein activates one molecule of PDE.)
3. PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP)

Question 45

Retinal response to light pt 2

Answer 45

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

5

Question 46

Random facts

Answer 46

A very high degree of amplification results in rod cells being able to respond to low intensities of light

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