C 2.1 chemical signaling

1. What is chemical signaling?

Cell communication using chemical signals (ligands) that bind specific receptors.

2. Why is ligand‑receptor binding specific?

Ligands only bind receptors with matching shape/chemistry.

3. Do ligands change after binding?

No — they remain unchanged and can activate multiple receptors.

4. What is quorum sensing?

Bacterial communication to detect population density.

5. Example organism?

Vibrio species.

6. What response does quorum sensing trigger?

Expression of luciferase → bioluminescence.

7. What are hormones?

Long‑distance signals via bloodstream; long‑lasting effects.

8. What are neurotransmitters?

Short‑distance signals across synapses; rapid, short‑lived.

9. What are cytokines?

Local signals; less specific; regulate immune responses.

10. What role do calcium ions play?

Signal muscle contraction and neurotransmitter release.

11. Hormone chemical types?

Steroids, amines, peptides. (e.g., testosterone, melatonin, insulin)

12. Neurotransmitter chemical types?

Amines, peptides, gases, esters. (e.g., dopamine, endorphins, NO, acetylcholine)

13. What ligands bind intracellular receptors?

Hydrophobic ligands that cross the membrane (e.g., steroids).

14. What ligands bind transmembrane receptors?

Hydrophilic ligands that cannot cross the membrane.

15. What determines receptor location?

Whether ligand can enter the cytoplasm.

16. What happens when a ligand binds a transmembrane receptor?

Conformational change → secondary messengers → cellular response.

17. What happens when a ligand binds an intracellular receptor?

Ligand‑receptor complex enters nucleus → regulates transcription.

18. What does estradiol regulate?

GnRH secretion in hypothalamus.

19. What does progesterone do?

Stimulates endometrial cell proliferation.

20. What does acetylcholine do?

Binds transmembrane receptors → opens ion channels → nerve impulse.

21. What percentage of drugs target GPCRs?

~70%.

22. What happens when a ligand binds a GPCR?

GDP → GTP on alpha subunit → alpha activates downstream effectors.

23. What does epinephrine activate?

A GPCR → adenyl cyclase → converts ATP → cAMP.

24. What does cAMP trigger?

Glycogen breakdown → glucose release (“fight or flight”).

Glycogen breakdown → glucose release (“fight or flight”).

Transfer phosphate from ATP to tyrosine residues.

26. What happens when insulin binds its receptor?

Receptor dimerizes → autophosphorylation → glucose transporters move to membrane.

27. Why must signaling be regulated?

Ligands remain unchanged → could activate receptors continuously.

28. What is positive feedback?

Amplifies signal (e.g., IP3 → Ca²⁺ release → more IP3 activation).

29. What is negative feedback?

Inhibits initial signal (e.g., testosterone inhibits GnRH).