Lecture 7- Cell Communication 1

Question 1

What are the 5 types of cell communication?

Answer 1

• Contact dependent (e.g. gap junctions)
• Paracrine
• Autocrine
• Synaptic
• Endocrine

Question 2

Paracrine, autocrine and endocrine cell communication all involve hormones so how do they differ?

Answer 2

• Paracrine= a signaling cell releasing a hormone that acts only in the local area. It will have an effect on cells close by that exhibit the appropriate receptors
• Autocrine= the cell that is secreting the hormone has the appropriate receptor to receive the hormone. The hormone therefore is serving the function of feeding back on itself modulating secretion
• Endocrine= the cell secrets the hormone into the blood stream where it can travel to distance cells/ organs. These cells still must have the appropriate receptor for the hormone to have an effect.

Question 3

What are the four possible ‘outcomes’ for a hormone that has been secreted into the blood?

Answer 3

• The bulk ends up excreted in the urine/ feces
• Some inactivated by metabolism
• Some go directly to the target cells and bind to compatible receptor (produce cellular response)
• Some travel in precursor form until they are activated by metabolism, this activated version of the hormone can then travel to the target cells and bind to receptors like in 3.

Question 4

Increasing the rate of hormone secretion results in…

Answer 4

An increased chance that the hormone will reach the appropriate cells with compatible receptors (increases the chance that they will actually have an effect)

Question 5

What is synergy?

Answer 5

The idea that the maximum combined response (releasing two hormones together) is greater than the addition of maximum individual responses.

i.e. the sum is better than its parts

Question 6

What determines the sensitivity of a target cell to a hormone?

Answer 6

The number of receptors (specific) expressed

Question 7

What is upregulation?

Answer 7

(synthesis > degradation) this increases the number of receptors
expressed to increase the sensitivity of the target cell

Question 8

What is down-regulation?

Answer 8

(synthesis < degradation)

This decreases the number of receptors expressed to decrease the sensitivity of the target cell

Question 9

Receptor upregulation makes a target cell more sensitive to a hormone
BECAUSE receptor upregulation makes more of the hormone receptors
available for hormone binding.
Answer:-
A. if both statements are true, and the second causes the first.
B. if both statements are true but the second does not cause the first.
C. if the first statement is true and the second is false.
D. if the first statement is false and the second is true.
E. if both statements are false.

Answer 9

A. both are true, the second causes the first

Question 10

What are the 3 broad classifications of hormones?

Answer 10

Peptides – from three amino acids to large proteins
Amines – derivatives of tyrosine (amino acid)
Steroids – synthesized from cholesterol

Question 11

What are all sex steroid hormones synthesized from?

Answer 11

Cholesterol

Question 12

Why don’t steroids need a receptor on the surface of target cells?

Answer 12

They are lipid phillic/ hydro phobic.
This means they simply pass through membranes and act on intracellular receptors. These could either be in the cytoplasm or in the nucleus (effect transcription/ the formation of proteins)

Question 13

What do steroids need when they are outside cells?

Answer 13

Carrier proteins as the ECF is watery and the are hydrophobic. These carrier proteins drop the steroids to the target cells surface where they simply diffuse across the membrane without the need of a receptor.

Question 14

How are amines generated?

Answer 14

Start with tyrosine.
The enzyme tyrosine hydroxylase converts tyrosine into the precursor L-Dopa
From this precursor we form all Catecholamines

Question 15

Give three examples of Catecholamines and describe what happens to them once they are formed?

Answer 15

• Dopamine, Norepinephrine, Epinephrine
• These are packaged into vesicles (are not lipid soluble like steroids therefore won’t just slip through the membrane of these)
• Will require a receptor at the target cell’s surface

Question 16

What are the four steps for peptide formation and secretion?

Answer 16

• Synthesis at the RER
• Packaging at the Golgi apparatus
• Storage in secretory vesicles
• Secretion by exocytosis (full fusion/ kiss and run)

Question 17

What type of hormone is also classed as an amine? What is special about these?

Answer 17

• Thyroid hormones

- They can freely pass through the cell membrane and so don’t require vesicles/ cell surface receptors

Question 18

What do metatropric receptors trigger?

Answer 18

Secondary messenger cascade, this effects a wide variety of proteins in the cells and thus showing how the activation of a small number of receptors can have a big effect on the target cell

Question 19

What happens if a receptor responds to a signaling molecule by producing cAMP?

Answer 19

This produces protein kinases which go onto to phosphorylate lots of other molecules showing how the activation of a small number of receptors can have a huge effect on the target cell.

Question 20

How do secondary messenger cascades work in transcription activation?

Answer 20

• A messenger activates a metabotropic receptor
• This has the effect of activating proteins that work as transcription factors
• This has an effect in the nucleus of producing intermediate early genes
• mRNA then synthesizes other transcription factors and these work on other cell specific genes
• After this mRNA then produces proteins that mediate the response of the cell to the first messenger e.g. proliferation + differentiation

The important thing to take away from this is that the activation of a small number of receptors on the target cell can have a huge effect