C2.1 Chemical signalling

Question 1

C2.1.1—Receptors as proteins with binding sites for specific signalling chemicals

Answer 1

Students should use the term “ligand” for the signalling chemical.

Question 2

C.2.1.2—Cell signalling by bacteria in quorum sensing

Answer 2

Include the example of bioluminescence in the marine bacterium Vibrio fischeri.

Question 3

C2.1.3—Hormones, neurotransmitters, cytokines and calcium ions as examples of functional categories of
signalling chemicals in animals

Answer 3

Students should appreciate the differences between these categories.

Question 4

C2.1.4—Chemical diversity of hormones and neurotransmitters

Answer 4

Consider reasons for a wide range of chemical substances being used as signalling chemicals. Include
amines, proteins and steroids as chemical groups of hormones. A range of substances can serve as
neurotransmitters including amino acids, peptides, amines and nitrous oxide.

Question 5

C2.1.5—Localized and distant effects of signalling molecules

Answer 5

Contrasts can be drawn between hormones transported by the blood system and neurotransmitters that
diffuse across a synaptic gap.

Question 6

C2.1.6—Differences between transmembrane receptors in a plasma membrane and intracellular receptors
in the cytoplasm or nucleus

Answer 6

Include distribution of hydrophilic or hydrophobic amino acids in the receptor and whether the signalling
chemical penetrates the cell or remains outside.

Question 7

C2.1.7—Initiation of signal transduction pathways by receptors

Answer 7

Students should understand that the binding of a signalling chemical to a receptor sets off a sequence of
responses within the cell.

Question 8

C2.1.8—Transmembrane receptors for neurotransmitters and changes to membrane potential

Answer 8

Use the acetylcholine receptor as an example. Binding to a receptor causes the opening of an ion channel
in the receptor that allows positively charged ions to diffuse into the cell. This changes the voltage across
the plasma membrane, which may cause other changes.

Question 9

C2.1.9—Transmembrane receptors that activate G proteins

Answer 9

Students should understand how G protein-coupled receptors convey a signal into cells. They should
appreciate that there are many such receptors in humans.

Question 10

C2.1.10—Mechanism of action of epinephrine (adrenaline) receptors

Answer 10

Include the roles of a G protein and cyclic AMP (cAMP) as the second messenger.

Question 11

C2.1.11—Transmembrane receptors with tyrosine kinase activity

Answer 11

Use the protein hormone insulin as an example. Limit this to binding of insulin to a receptor in the plasma
membrane, causing phosphorylation of tyrosine inside a cell. This leads to a sequence of reactions ending
with movement of vesicles containing glucose transporters to the plasma membrane.

Question 12

C2.1.12—Intracellular receptors that affect gene expression

Answer 12

Use the steroid hormones oestradiol, progesterone and testosterone as examples. Students should
understand that the signalling chemical binds to a site on a receptor, activating it. The activated receptor
binds to specific DNA sequences to promote gene transcription.

Question 13

C2.1.13—Effects of the hormones oestradiol and progesterone on target cells

Answer 13

For oestradiol, limit to cells in the hypothalamus that secrete gonadotropin-releasing hormone. For
progesterone, limit to cells in the endometrium.

Question 14

C2.1.14—Regulation of cell signalling pathways by positive and negative feedback

Answer 14

Limit to an understanding of the difference between these two forms of regulation and a brief outline of
one example of each.