Extracellular Signalling

Question 1

What are the two principle forms of communication in multicellular organisms?

Answer 1

Nervous and Hormonal

Question 2

What is the function of an extra cellular signalling molecule?

Answer 2

Cell releases the molecule that another cell detects and responds to.

Question 3

Why is the communication between cells important?

Answer 3

To make possible the integration and coordination of cellular activities

Question 4

What are extracellular signalling molecules?

Answer 4

Signals which originate from outside the target cell

Question 5

How can a target cell respond to many different instructions?

Answer 5

Signal molecules can stimulate different target cells in different ways, and the target cell may have many receptors, each specific to a different signalling molecule.

Question 6

What are hormones?

Answer 6

Extra cellular signalling molecules that are secreted by one tissue into the blood.

Question 7

When does the hormone leave the blood stream?

Answer 7

When the hormone reaches the target receptor or is broken down

Question 8

Give examples of hydrophobic and hydrophilic hormones.

Answer 8

Hydrophilic: Peptide hormones such as Insulin, ADH, and HGH
Hydrophobic: Steroid hormones such as testosterone.

Question 9

What are neurotransmitters?

Answer 9

The signalling molecules released during nervous communication.

Question 10

What type of molecule are neurotransmitters?

Answer 10

Hydrophilic

Question 11

Where are neurotransmitters released?

Answer 11

Into the synaptic gape between a nerve cell and its neighbour

Question 12

Why is nervous communication considered very specific in comparison to hormonal communication?

Answer 12

Due to the intimate association between the signalling cell and the target cell.

Question 13

When does an extra cellular signalling molecule cause an effect?

Answer 13

When it binds to its specific target receptor molecule

Question 14

Where do you find the receptor molecules for hydrophilic and hydrophobic signalling molecules?

Answer 14

Hydrophobic signal molecules : Within the nucleus or cytoplasm
Hydrophilic: They are integral proteins as they cannot pass through the plasma membrane

Question 15

Why can hydrophobic molecules pass through the plasma membrane?

Answer 15

They are lipid soluble and so are able to move across the hydrophobic part of the membrane by diffusion.

Question 16

What is the receptor for a steroid hormone?

Answer 16

A gene-regulatory protein

Question 17

What happens when the steroid binds to the gene-regulatory protein?

Answer 17

It causes a conformational change to the protein, activating it and allowing it to bind directly to the DNA and regulate the transcription of specific genes.

Question 18

What happens when a hydrophilic signal molecule binds to the integral protein?

Answer 18

The conformation of the transmebrane protein alters in some way. Resulting in signal transduction into the cell and a change in the behaviour of the cell.

Question 19

What may be the result of cell transduction into the cell?

Answer 19

An ion channel at the cell surface may open or a secondary messenger within the cell cytosol may be released.

Question 20

How can secondary messengers alter cell behaviour?

Answer 20

By activation of proteins by kinase enzymes and phosphorylation.
Through pathways involving involving calcium ion release from the endoplasmic reticulum.

Question 21

What does each peptide hormone require?

Answer 21

A specific receptor protein at its target cells surface.

Question 22

Why can the action of peptide hormones be highly specific?

Answer 22

Since only the target cells have the appropriate receptors at their surface.

Question 23

Give examples of neurotransmitters

Answer 23

Acetylcholine + noradrenaline (hydrophilic peptides)

Question 24

What is acetylcholine?

Answer 24

The transmitter at the neuromuscular junction connecting motor nerves to muscles

Question 25

Give information about noradrenaline

Answer 25

HAs a role in the central nervous system and the sympathetic nervous system. Usually noradrenaline can also act as a stress hormone if released into the blood.