Cell communication

Question 1

What is the name for chemical transmission between cells

Answer 1

Cell - cell (synapse)​

Cell - several cells (paracrine)​

Many cells - many cells (endocrine)​

Question 2

Chemical synapse properties

Answer 2

Cell - cell using chemical transmitter​

Effect depends on transmitter and the receptor it acts on​

One way transmission​

Common in nervous system​

Question 3

Sequence of a synapse

Answer 3

Impulse arrives at terminal of presynaptic cell​

Transmitter released from storage vesicles​

Transmitter diffuses in synaptic cleft​

Transmitter binds to receptor on postsynaptic cell​

Alters postsynaptic cell:​

‘excitatory’ e.g. impulse generated; muscle contracts; gland secretes​

‘inhibitory’: cell is switched off​

Question 4

What is paracrine

Answer 4

-One cell communicates with several cells locally​
-Often used by defence cells (inflammation)​
-Can be part of a ‘cascade’ of reactions​

Question 5

What is autocrine communications

Answer 5

Where chemical acts on cell releasing it (feedback)​

Question 6

Describe endocrine transmission

Answer 6

Chemical sent to all parts of the body via the blood stream​

Hormone acts only on cells with the correct membrane receptor protein (target cells)​

Question 7

Similarities of nerves and hormones

Answer 7

both are used for communication in organisms

Question 8

Communication by nerves advantages

Answer 8

-Actions are very specific or localised
-Quick impulse transmission
-Suitable for rapid and specific response

Question 9

Examples of nervous communication

Answer 9

-control of voluntary muscle contractions​
-sensory systems​
-salivary gland responses​
-control of blood pressure

Question 10

Properties of hormonal communication

Answer 10

-Can affect many cells in different parts of body​
-Coordinated, body-wide actions​
-Slow to act, but effect persists

Question 11

Examples of hormonal commmunications

Answer 11

-gastro-intestinal gland responses​
-control of metabolism and growth​
-regulation of menstrual cycle​

Question 12

What are steroids

Answer 12

Lipids that can pass through the outer cell membrane

Question 13

Function of steroids

Answer 13

They act on receptors inside the target cell (step 3)​

The steroid-receptor complex acts on the DNA in the nucleus to initiate protein synthesis (steps 4, 5, 6)​

The protein then alters cell function (step 7)​

Question 14

First messenger

Answer 14

the chemical transmitter which acts on a receptor protein​
Some first messengers can pass through the target cell membrane and act on receptors inside the target cell while some cannot enter the cell.

Question 15

Whycant Peptide transmitters pass through the cell membrane

Answer 15

Peptide and other transmitters cannot pass through the cell membrane because they bind to plasma membrane receptors and set up a series of reactions controlled by ’G-proteins’​

These in turn activate 2nd messenger systems such as:​

Cyclic AMP (cAMP)​

Calcium ions (Ca++)​

Question 16

Why is there a delayed reaction with steroid transmitters

Answer 16

As the protein needs to be produced, takes time

Question 17

Second messengers:
G-protein and Cyclic AMP - 1

Answer 17

The transmitter binds to a membrane receptor

G-protein is activated by GTP (guanosine triphosphate

ATP (in cytosol) is converted to cyclic AMP by the enzyme adenyl cyclase

Note: Adenyl cyclase is also called adenylate cyclase​cAMP activates an enzyme, called protein kinase,

This, in turn activates a specific enzyme which catalyses a chemical reaction

Resulting in formation of molecule, e.g. protein​

Question 18

calcium as a secondary messenger

Answer 18

Transmitter binds to a membrane receptor (step 1)​

This activates a G-protein, which activates an enzyme: phospholipase C

This in turn causes opening of Ca2+ channels; Ca2+ enters by diffusion

Ca2+ binds to a protein in the cytosol; here, it is calmodulin
(There are other Ca-binding proteins, such as Troponin, which is involved in muscle contractions​)

Ca2+-calmodulin complex acts as a 2nd messenger, ​
Then which regulates an enzyme which regulates a chemical reaction

….In some cells, the Ca 2+ is released from stores within the cell, but the basic principle is much the same.