1 - Intro to Hormone Signalling

Question 1

Stimuli triggers what?

Answer 1

Signal transduction

Question 2

What is signal transduction?

Answer 2

Signal transduction is a cascade of biochemical changes that occur inside the cell which mediates how a cell responds to a particular stimulus

Question 3

What does stimuli include in humans?

Answer 3

Hormones, neurotransmitters, and growth factors (but also light photons, odorants, and taste)

Question 4

What do growth factors refer to?

Answer 4

A particular type of hormone that controls cell growth and division and have an intimate role in cancer

Question 5

What do stimuli bind to?

Answer 5

Most stimuli bind to receptor proteins in the target cell causing responses, i.e., signal transduction and biochemical changes that control the activity of a cell

Question 6

Example of stimuli binding

Answer 6

Neurotransmitters allow nerve cells to communicate across synapses by interacting with post-synaptic receptors and opening ion channels (response). In this case, the stimuli of the neurotransmitters bind receptors and trigger responses, which is the opening of the ion channels, and the entry and exit of ions is the signal transduction which controls changes in cell behaviour

Question 7

Steps of hormone-initiated signal transduction

Answer 7

1. BIOSYNTHESIS of a hormone
2. STORAGE and SECRETION of the hormone
3. TRANSPORT of the hormone to target cell
4. RECOGNITION by the hormone receptor protein
5. RELAY and AMPLIFICATION of the signal that leads to defined biochemical sections within the target cell
6. REMOVAL of the hormone

Question 8

1. BIOSYNTHESIS of a hormone

Answer 8

Biosynthesis in the endocrine gland

Question 9

2. STORAGE and SECRETION of the hormone

Answer 9

• stored in the endocrine gland until they are required for secretion
• storage primes the system - don’t need to rely on de novo synthesis of new hormones
• often they are already stored and ready for action in their particular endocrine gland

Question 10

3. TRANSPORT of the hormone to target cell

Answer 10

The transport of hormones can involve a particular transport protein - which allows the hormone to mix with the bloodstream

Question 11

4. RECOGNITION by the hormone receptor protein

Answer 11

Causes a conformational change to take place

Question 12

5. RELAY and AMPLIFICATION of the signal that leads to defined biochemical reactions within target cell

Answer 12

Translated and amplified by biochemical changes or signal transduction inside the target cell which causes changes in cell activity

Question 13

6. REMOVAL of the hormone

Answer 13

• it is important to switch off the signal once a desired effect has been reached
• if we don’t then it can lead to serious disease states, so we often have what’s called “negative feedback” effects, whereby the production of hormone will then lead to changes resulting in the same production being switched off
• removal of the hormone from the system so it’s no longer able to interact with target receptors
• removal can involve degradation of the hormone by particular enzymes

Question 14

What are hormones?

Answer 14

Chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

Question 15

Where do hormones travel? (include example)

Answer 15

• hormones reach all parts of the body but only target cells have receptors for that hormone
• for example, insulin will be secreted from the pancreas - it will travel through the bloodstream but will only regulate cells that express insulin receptors on the cell surface

Question 16

What is the function of the endocrine system?

Answer 16

Chemical signalling by hormones is the function of the endocrine system

Question 17

What is the endocrine signalling system?

Answer 17

• a system of glands inside the body that produce and secrete hormones into the bloodstream
• “endo” because they secrete into the body

Question 18

Give four examples of how cells communicate

Answer 18

1. Direct
2. Synaptic
3. Paracrine
4. Endocrine

Question 19

What is direct communication? [include chemical messengers (1), mechanism of transmission (2), and examples(3)]

Answer 19

1. ions, small molecules
2. direct movement through gap junctions linking the cytoplasm of adjacent cells
3. ions flowing between cardio muscle cells

Question 20

What is synaptic communication? [include chemical messengers (1), mechanism of transmission (2), and examples(3)]

Answer 20

1. neurotransmitters
2. diffusion from a neutron across a narrow space (synaptic cleft) to a cell bearing the appropriate receptors
3. acetylcholine

Question 21

What is paracrine signalling? [include chemical messengers (1), mechanism of transmission (2), and examples(3)]

Answer 21

1. local hormones
2. diffusion through extracellular fluid to nearby cells bearing the appropriate receptors
3. prostaglandins

Question 22

What is endocrine signalling? [include chemical messengers (1), mechanism of transmission (2), and examples(3)]

Answer 22

1. hormones
2. carried in the bloodstream to near or distant cells bearing the appropriate receptors
3. insulin

Question 23

What are the 3 major classes of hormones?

Answer 23

polypeptides, steroids, amines

Question 24

What are polypeptide hormones?

Answer 24

• made up of strings of amino acids, and can range from about 10 amino acids up to hundred of amino acids
• insulin is included in this polypeptide hormone class

Question 25

What are steroid hormones?

Answer 25

- derived from the chemical cholesterol - these are a particular class of hormones which are largely non-polar

Question 26

What are amine hormones?

Answer 26

- derived from animo acids - generally water soluble like polypeptide hormones - travel through bloodstream

Question 27

What is the signalling pathway of water soluble hormones?

Answer 27

- water soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors - receptors need to be at the cell surface because they hormones can't pass through the cell membrane

Question 28

Give 2 examples of water soluble hormones

Answer 28

1. insulin belongs to the polypeptide class of large water soluble proteins 2. epinephrine (amine class) - derived from a single amino acid tyrosine

Question 29

Give 2 examples of lipid soluble hormones

Answer 29

1. thyroxine (thyroid hormone produced by the thyroid gland) - an amino acid hormone 2. cortisol

Question 30

What is thyroxine?

Answer 30

- thyroid hormone produced by the thyroid gland - 2 separate tyrosine molecules that have been decorated with iodine (unusual- thyroid hormones are the only ones in the body with iodine attached to them) - largely hydrophobic because of the two aromatic rings with iodines - tends to mix with the cell membrane and require transport proteins to allow it to travel through the bloodstream

Question 31

Features of steroid hormones

Answer 31

- steroid hormones are classic examples of the lipid soluble hydrophobic hormones - derived from the structure of cholesterol which gives the four ring structure - planar, very hydrophobic and that lends the hydrophobic properties to the molecules - aliphatic in nature - are able to pass through the cell membrane and interact with intracellular receptors

Question 32

Give an example of a steroid hormone

Answer 32

- cortisol is a long term stress hormone nd is produced by the adrenal glands, but the steroid hormones also tend to have some charged residues attached, e.g., hydroxyls, which makes them behave a little bit like fats

Question 33

What is the lipid soluble (steroid) hormone pathway?

Answer 33

1. steroid hormones enter through the cell membrane 2. secreted into the bloodstream 3. travel through the bloodstream, bound to transport proteins 4. recognise target cell by the intracellular receptor 5. dissociate from the transport protein when they sense the receptor 6. pass through the cell membrane of target cells and interact with the receptor inside the cell

Question 34

What is the lipid soluble (steroid) hormone pathway?

Answer 34

1. steroid hormones enter through the cell membrane 2. secreted into the bloodstream 3. travel through the bloodstream, bound to transport proteins 4. recognise target cell by the intracellular receptor 5. dissociate from the transport protein when they sense the receptor 6. pass through the cell membrane of target cells and interact with the receptor inside the cell

Question 35

How can steroid hormones directly stimulate transcription?

Answer 35

- directly stimulate transcription of genes to make certain protein - the receptors become activated and interact directly with target genes and change gene expression - this causes responses in the cytoplasm, leading to long term changes

Question 36

Are steroid hormones or peptide hormones faster?

Answer 36

- because steroids work by triggering gene activity, the response is slower than peptide hormones