Explain why the effects of adrenaline on target cells are short-lived compared with the effects of steroid hormones.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Adrenaline is a hormone released from the adrenal medulla in response to stress. Steroid hormones, such as cortisol, are released from the adrenal cortex and also help the body respond to stress, but over a longer timescale.
Model answer (4 marks)
Adrenaline is not lipid‑soluble and therefore cannot cross the cell membrane; it binds to a membrane‑bound receptor and activates a second‑messenger system. The second messenger, cAMP, is rapidly hydrolysed by phosphodiesterase, so the intracellular signal is quickly terminated, giving a short‑lived effect.
In contrast, steroid hormones are lipid‑soluble and can diffuse through the cell membrane. They bind to intracellular receptors in the cytoplasm or nucleus and act as transcription factors, directly altering gene expression. This leads to new protein synthesis and a prolonged effect.
In contrast, steroid hormones are lipid‑soluble and can diffuse through the cell membrane. They bind to intracellular receptors in the cytoplasm or nucleus and act as transcription factors, directly altering gene expression. This leads to new protein synthesis and a prolonged effect.
Examiner tips
- Mention the lack of lipid solubility for adrenaline and the rapid cAMP breakdown; contrast with steroid hormone diffusion and gene‑expression action. Keep the explanation concise and use the exact terminology.
Common mistakes
- Forgetting that adrenaline signals via a second messenger; confusing the site of steroid hormone action; not recognising the rapid degradation of cAMP by phosphodiesterase.
Mark scheme (4 marks)
- Adrenaline cannot enter the cell / is not lipid-soluble, so acts via a membrane-bound receptor and a second messenger system
- The second messenger (cAMP) is rapidly broken down by phosphodiesterase, so the intracellular signal is quickly terminated
- Steroid hormones are lipid-soluble so they cross the cell surface membrane and bind to receptors in the cytoplasm or nucleus
- Steroid hormones directly alter gene expression / act as transcription factors, leading to sustained protein synthesis, prolonging the effect
Key terms in this question
Related
- All OCR A-Level Biology A (H420) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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