Types of signalling and hormones (steroid vs peptide)
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Flip to reveal answersName the four modes of chemical signalling, by distance.
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Question
Name the four modes of chemical signalling, by distance.
Answer
**Endocrine** (hormone via blood, long range), **paracrine** (local/nearby cells), **autocrine** (a cell signals itself) and **neurotransmitter** (across a synapse).
Question
What is endocrine signalling?
Answer
A **hormone** is released into the **blood** and carried to **distant** target cells — the longest-range mode.
Question
Why does a peptide hormone bind a SURFACE receptor?
Answer
It is **hydrophilic (water-soluble)**, so it **cannot cross** the phospholipid membrane — its receptor must be on the cell surface, and the signal is then **transduced** inside.
Question
Why can a steroid hormone bind an INTRACELLULAR receptor?
Answer
It is **lipid-soluble**, so it **diffuses straight through** the membrane and binds a receptor **inside** the cell.
Question
How does a steroid hormone change the cell's behaviour?
Answer
The **hormone–receptor complex acts in the nucleus**, switching **genes on/off** so different proteins are made.
Question
Peptide vs steroid — which is faster and why?
Answer
**Peptide** is faster (seconds–minutes) because it activates existing machinery; **steroid** is slower (hours) because new proteins must be made — but it lasts longer.
Question
Is adrenaline a peptide or a steroid in how it acts?
Answer
It acts like a **peptide** — it is **hydrophilic**, so it binds a **surface receptor** and works by **signal transduction** (not via intracellular gene action).
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Chemical signalling
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