Hormones Structure and Function

Question 1

Most hormones are lipid soluble. True or false?

Answer 1

• Most water soluble (i.e adrenaline) and don’t cross the cell membrane
• Some hormones i.e. testosterone are lipid soluble therefore can cross the cell membrane

Question 2

What are Hormones?

Answer 2

• Hormones are chemical messenger (signalling) molecules that circulate in the blood . Released from secreting cell.
• Act on target cells (cell that responds to hormone)

Question 3

What are the three type of responses that hormones can generate?

Answer 3

• Support endocrine responses – generally delivered when the target cell is some distance away from the secretary cell
• Support paracrine responses – where the target cell is closer to the secretary cell, in some cases right next to (e.g. islets of Langerhans and pancreas)
• Support autocrine responses – where a hormone is released from a secretary cell which loops back and has an effect on itself e.g. beta cells in negative feedback loop

Question 4

Describe the structure of hormones

Answer 4

• Small Chemicals / modified amino acids: e.g. amines such as dopamine, adrenaline
• Peptides are generally in the range 3 to 20 amino acids (aa) e.g. endorphin. Anything more than 20, becomes small protein.

Anything larger e.g. growth hormones are considered large proteins

Question 5

Why is a knowledge of which hormones are peptides & proteins is important because:

Answer 5

Because molecules with similar shapes and structures bind to similar receptors and can cause side effects or cross reactivity.

Question 6

What are the anti diuretic hormone and oxytocin produced by?

Answer 6

The posterior pituitary.

Question 7

Difference between oxytocin and ADH?

Answer 7

The amino acid sequence differs at only two positions (Arg & Phe) (changes charge). Completely alters 3d structure.

Question 8

What cross reactions can occur due to the similarity of oxytocin and ADH?

Answer 8

• oxytocin has a slight anti-diuretic function (due to similar shape)
• High levels of ADH can cause uterine contractions

Question 9

What is growth hormone?

Answer 9

• Somatotropin or somatropin; not somatostatin!
• Stimulates growth, cell division & regeneration. It is a mitogen (stimulates mitosis) specific only to certain kinds of cells.

Question 10

Where is insulin produced?

Answer 10

• Insulin produced by the pancreas
• Hetero-dimer
• Produced by islets of langerhans in beta cells

Question 11

What is the structure of insulin?

Answer 11

• Insulin (monomer) protein consists of two polypeptide chains linked by disulphide bonds which forms a very specific 3D structure so it can lock on to its cognate receptor. Insulin can also form dimers and crystalline structures where you have high concentrations of insulin via zinc.

Question 12

Why can’t the oral route be used to administer insulin and what are the options?

Answer 12

Because proteins get digested

Options include:

(1) Injection intravenous or subcutaneous
(2) Aerosols for inhalation
(3) Depot formulations, modified release systems (e.g. microspheres) etc. used for delivery of growth hormone

Question 13

Structure of lipid derived steroid hormones?

Answer 13

• All have the same basic C17, 4 ring structure

e. g. progesterone C21, cortisol C21, testosterone C19, oestradiol C18