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Question 1

Signalling in unicellular organisms

Answer 1

• Prokaryotes respond to changes in environment
• These changes are detected at the cell surface
• Information is relayed inside the cell
• Expression of genes enable the cell to cope with new environment

Question 2

Signalling in multicellular organisms

Answer 2

• Control of gene expression enables cells to carry out specialised functions
• Cooperation and coordination ensure correct function of whole organism and prevent uncontrolled proliferation
• Signalling can occur over a range of distances

Question 3

What are the four basic tissue types?

Answer 3

• Endothelial
• Connective
• Muscle* (skeletal, smooth and cardiac)
• Nervous*
• Electrically excitable

Question 4

Dictostelium aggregation

Answer 4

• An amoeba that is essentially a bag of nuclei
• Can exist as a single cellular or multicellular organism
• The multicellular form is generated when the cells are starved

Question 5

Cell-to-cell communication by extracellular signalling

Answer 5

• Synthesis of signalling molecule by signalling cell
• Release of signal by signalling cell
• Transport of signal to target cell
• Detection of signal by a specific receptor protein
• Change in cellular behaviour triggered by receptor-signal complex
• Removal of the signal to terminate cellular response

Question 6

Plasma membrane

Answer 6

• Defines the interface between the cell and the environment
• Huge distance for a signal to cross
• Hydrophobic signals are able to pass through without a carrier, but need carriers outside of the membrane

Question 7

Lipid rafts

Answer 7

• More solid lipid micro-environments on the cell surface containing proteins with specific post translational modifications
• These areas can favour specific protein interactions and activate signalling cascades

Question 8

Gap junctions

Answer 8

• Allow direct communication between adjacent cells
• Exist where plasma membranes are close together and connexion proteins form tubes; allows the passage of small molecules such as cAMP and Ca2+

Question 9

What is signal transduction in multicellular organisms?

Answer 9

The process by which extracellular signals bring about their characteristic effects inside the cells; information is converted from one form to another

Question 10

Intercellular

Answer 10

Between cells

Question 11

Intracellular

Answer 11

Within cells

Question 12

What are ligands (signals/first messengers)?

Answer 12

• Hormones, growth factors, neurotransmitters, etc.

- Bind/activate specific receptors, either within or on the surface of target cells

Question 13

What happens to the ligand after binding?

Answer 13

It is unchanged by the interaction, only the receptor protein is changed

Question 14

What do receptor proteins do?

Answer 14

Bind to and interact with physiologically active substances to relay signals across the membrane or into the nucleus

Question 15

What do receptor-ligand complexes regulate?

Answer 15

• Cellular metabolism
• Enzyme activity
• Nuclear activity leading to the transcription of specific genes
• Cell development/differentiation/division
• Changes in cytoskeleton

Question 16

What does generating an intracellular response usually involve?

Answer 16

The release of a second messenger within the target cell

Question 17

Endocrine signals

Answer 17

• Long-distance signals, e.g. hormones via blood, transpiration stream
• These signals are transported

Question 18

Paracrine signals

Answer 18

• Short-distance signals, e.g. growth factors, neurotransmitters
• These signals diffuse, and their concentration may generate different responses

Question 19

Autocrine signalling

Answer 19

Essentially a type of signalling where the signalling cell is also the target cell

Question 20

Signalling by plasma membrane-attached proteins

Answer 20

• This type of signalling occurs during development, and only affects adjacent cells which are very close by
• One cell has a particular molecule on its surface, and the other has a receptor for the molecule

Question 21

What does delta do?

Answer 21

Delta chooses particular cells to become neurones; it is perceived by adjacent cell receptors called notch, which when bound to delta, prevent other cells from producing delta and thus becoming neurones