Communication and Signalling

Question 1

How do multicellular organisms signal between cells?

Answer 1

They signal between cells using extracellular signalling molecules

Question 2

Examples of extracellular signalling molecules

Answer 2

Steroid hormones, peptide hormones and neurotransmitters

Question 3

what are receptor molecules

Answer 3

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

Question 4

What does binding do to a receptor and response

Answer 4

Binding changes the 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 the specific receptor.

Answer 5

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

Question 6

Why are molecules specific to receptors

Answer 6

different cell types may show a tissue-specific response to the same signal

Question 7

What can hydrophobic signals do?

Answer 7

They can diffuse directly through the phospholipid bilayers of membranes, and so bind to intacellular receptors.

Question 8

What are the receptors called for hydrophobic signalling

Answer 8

Transcription factors

Question 9

What are transcription factors?

Answer 9

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

Question 10

What do steroid hormones bind to and where

Answer 10

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

Question 11

What are examples of hydrophobic signalling molecules

Answer 11

Steroid hormones, testosterone and oestrogen.

Question 12

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

Answer 12

The hormone receptor complex binds to specific DNA sequences called Hormone response elements ( HRE’s ). Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.

Question 13

What can hydrophilic signals do?

Answer 13

They can bind to transmembrane receptors and do not enter the cytosol

Question 14

What are the types of hydrophilic signals

Answer 14

Peptide hormones

Neurotransmitters

Question 15

What happens to transmembrane proteins when a ligand binds?

Answer 15

They change conformation when a ligand binds

Question 16

As hydrophilic signals do not enter the cytosol how does the signal get through?

Answer 16

The signal molecule does not enter the cell but it is transduced across the membrane.

Question 17

How do transmembrane receptors act as signal transducers?

Answer 17

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

Question 18

What do transduced hydrophilic signals involve?

Answer 18

G-proteins or cascades of phosphorylation by kinase enzymes.

Question 19

What are G-proteins and their function?

Answer 19

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

Question 20

What do phosphorylation cascades allow?

Answer 20

They allow more than one intracellular signalling pathway to be activated.

Question 21

What brings about a phosphorylation cascade?

Answer 21

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

Question 22

What is a result of phosphorylation cascades?

Answer 22

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

Question 23

What is the result of the peptide hormone insulin to its receptors?

Answer 23

It results in an intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells.

Question 24

What does the binding of insulin do to the receptor?

Answer 24

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 25

What are the features of type 1 diabetes?

Answer 25

Failure to produce insulin

Question 26

What are the features of type 2 diabetes?

Answer 26

Loss of receptor function and is generally associated with obesity

Question 27

How can exercise improve type 2 diabetes?

Answer 27

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