15) Unit 1 - Hydrophilic Signalling

Question 1

What do hydrophilic signals require to pass across the cell membrane and why

Answer 1

They require receptors to be on the surface of the cell as they cannot readily pass across the membrane.

Therefore signal molecule does not enter the cell but the signal is TRANSDUCED across the membrane

Question 2

examples of hydrophilic signals?

Answer 2

• Peptide hormones e.g. insulin, ADH

* Neurotransmitters

Question 3

List the Process of hydrophilic signal that is transduced across the membrane

Answer 3

1) Reception
2) Transduction
3) Response

Question 4

1) reception:

Describe the process when the ligand (signalling molecule) binds to its receptor outside the cell

Answer 4

• Transmembrane protein changes its conformation when the ligand binds to it outside the cell
• The signal molecule does not enter the cell but the signal is transduced across the cell

Question 5

What can transduced hydrophilic signals result in?

Answer 5

Cascade of G protein or Phosphorylation by kinase enzymes

Question 6

Describe the process of transduction by a cascade of G proteins

Answer 6

1) G-protein coupled receptors are linked to a G-protein.
2) When a hydrophilic signal molecule binds to the GPCR a cascade of events is initiated
3) Initially the G-protein is inactive as it is bound to GDP
4) Once the signal molecule is bound to the receptor, GTP replaces GDP and the G-protein becomes activated
5) The G-protein can stimulate enzymes or open channels which lead to a response in the cell

Question 7

Describe the process of transduction by Phosphorylation

Answer 7

1) Receptor Tyrosine Kinase (RTK) is a transmembrane receptor for hydrophilic signals
2) On stimulus of appropriate ligand, RTKs phosphorylate themselves
3) This causes there kinase domain to become activated and this allows RTK to activate enzymes by phosphorylating them if they come into close contact.
4) Activated enzymes will create an intracellular response.

Question 8

Name a type of RTK

Answer 8

JAK-STAT

Question 9

What is insulin’s role in the body

Answer 9

Insulin regulates glucose concentration in the blood by allowing fat and muscle cells to absorb glucose from the blood stream

Question 10

Describe the cascade of events that happen when insulin binds to its receptor on the surface of fat and muscle cells

Answer 10

• Binding of insulin to its receptor triggers the recruitment of GLUT 4 (glucose transporter) to the cell membrane of fat and muscle cells
• GLUT 4 transporter allows glucose to pass across the cell membrane and enter the cell.
• This lowers the blood glucose levels.

Question 11

What cause diabetes

Answer 11

failure in the insulin signalling pathway

Question 12

what causes type 1 and type 2 diabetes

Answer 12

type 1: failure to produce insulin in the pancreas

type 2:loss of insulin receptor function, associated with obesity

Question 13

What also triggers the recruitment of GLUT 4 to the surface of fat and muscle cells other than insulin?

What importance does this have medically?

Answer 13

Exercise.

Help subjects with type 2.

Question 14

What are the functional units of the kidney called

Answer 14

nephrons

Question 15

What produces ADH and where is it strored

Answer 15

ADH is produced by the hypothalamus and stored in the pituitary gland.

Question 16

what is the function of ADH

Answer 16

ADH lets the kidneys know how much water they need to keep in, or get out the body (affects the rate of water reabsorption in the nephrons)

Question 17

describe the events that occur when there is an decrease in water concentration in the blood.

+ when there is an increase of water concentration in the blood

Answer 17

• If there is a decrease in blood water concentration, more ADH is released by the pituitary gland, and they bind to their receptors on the collecting ducts of kidneys.
• Signal transduction occurs resulting in the recruitment of AQP2 channels in the membrane of the collecting ducts
• This increases the rate of water reabsorption and a small volume of concentrated urine is produced
• If there is an increase, less ADH is released by P gland.
• Less AQP2 channels are recruited so less water is reabsorbed, resulting in dilute urine.

Question 18

What do AQP2 channels allows?

Answer 18

Allow efficient transmembrane movement of water. This negative feedback effect allows the control of water balance, in terrestrial vertebrates.

Question 19

what is diabetes insipidus

Answer 19

disease where water conservation mechanism of the kidney fails

Question 20

Name and describe the two types of diabetes insipidus

Answer 20

Central Diabetes Insipidus:
•failure to produce ADH

Nephrogenic Diabetes Insipidus:
•The receptor for ADH becoming de-sensitised

Question 21

List 2 symptoms of diabetes insipidus

Answer 21

• excessive thirst - blood water concentration is always low

* production of large quantities of dilute urine