Unit 1 - Communication and Signalling

Question 1

Give 3 examples of extracellular signalling molecules.

Answer 1

Steroid hormones, peptide hormones and neurotransmitters.

Question 2

What do multicellular organisms use to signal between cells?

Answer 2

Extracellular signalling molecules.

Question 3

Can hydrophobic signalling molecules diffuse through the phospholipid bilayers of proteins?

Answer 3

Yes - they then bind to intracellular receptors which are transcription factors.

Question 4

What are transcription factors?

Answer 4

Proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.

Question 5

Give two examples of hydrophobic signalling molecules.

Answer 5

The steroid hormones oestrogen and testosterone.

Question 6

Describe the process of a steroid hormone which results in a change in gene expression of many different genes.

Answer 6

Steroid hormones bind to specific receptors in the cytosol and form a hormone-receptor complex which moves to the nucleus where it binds to specific DNA sequences called hormone response elements. Binding at these sites influences rate of transcription and affects gene expression.

Question 7

Where do hydrophilic signalling molecules bind?

Answer 7

Hydrophilic signalling molecules bind to transmembrane receptors and do not enter the cytosol.

Question 8

Give two examples of hydrophilic extracellular signalling molecules.

Answer 8

Peptide hormones and neurotransmitters.

Question 9

What is signal transduction?

Answer 9

Transmembrane receptors convert the extracellular
ligand-binding event into intracellular signals,
which alters the behaviour of the cell.