Signaling Molecules & Receptors Overview

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These flashcards review key concepts about receptors, signaling molecules, GPCRs, ligand-gated ion channels, second messengers, receptor regulation, and clinical correlations such as diabetes.

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24 Terms

1
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What are the two main classes of signaling molecules discussed in the lecture?

Hormones and neurotransmitters.

2
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From which tissues are hormones and neurotransmitters released, respectively?

Hormones are released from endocrine (glandular epithelial) tissue, while neurotransmitters are released from neurons.

3
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Why do signaling molecules require receptors on target cells?

Without receptors to bind and initiate downstream responses, the molecules would have no functional effect.

4
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What is receptor specificity?

The property that only certain signaling molecules (sometimes just one) can bind to a given receptor.

5
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Which receptor type functions as both a receptor and an ion channel?

Ligand-gated ion channels.

6
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Describe the immediate cellular effect of a ligand-gated sodium channel opening.

Sodium influx depolarizes the cell.

7
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Give one classic example of a ligand-gated ion channel and its ligand.

Cholinergic nicotinic receptor with acetylcholine as its ligand.

8
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What primary structural components make up most receptors?

Proteins that span the plasma membrane.

9
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Why do polar (lipophobic) signaling molecules need surface receptors?

They cannot cross the hydrophobic lipid core of the plasma membrane on their own.

10
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Define a G-protein coupled receptor (GPCR).

A membrane receptor linked to an intracellular G-protein that triggers a cascade when activated by a ligand.

11
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What nucleotide switches a G-protein from inactive to active form?

GDP is exchanged or phosphorylated to GTP.

12
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Name two common second messengers generated through GPCR cascades.

Cyclic AMP (cAMP) and calcium ions (Ca²⁺).

13
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Which cholinergic receptor subtype is GPCR-linked?

Muscarinic receptors.

14
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What are the two broad categories of adrenergic receptors for norepinephrine/epinephrine?

Alpha (α) receptors and beta (β) receptors.

15
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Define receptor saturation.

The state in which all available receptors on a cell are occupied by ligand.

16
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What is receptor upregulation and when might it occur?

Insertion of additional receptors into the membrane; occurs when cells need more signaling (e.g., muscle during exercise).

17
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Explain receptor downregulation.

Removal or decrease of receptors when ligand levels are chronically high, reducing cellular response.

18
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How is type 2 diabetes related to receptor downregulation?

Chronic high insulin causes insulin-dependent cells to remove insulin receptors, diminishing glucose uptake.

19
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Why can uncontrolled diabetes impair brain glucose uptake?

The blood-brain barrier downregulates glucose transporters in response to prolonged high blood glucose, risking shortages when glucose later falls.

20
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Differentiate agonists and antagonists.

Agonists mimic the natural ligand and trigger the same response; antagonists bind but block receptor activation.

21
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How do some bacterial toxins (e.g., cholera, botulism) cause disease in relation to receptors?

They interfere with GPCR signaling, blocking or misregulating downstream events.

22
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Where are receptors for non-polar (lipophilic) signaling molecules typically located?

Inside the cell, in the cytoplasm or nucleus, because these molecules cross the membrane easily.

23
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What intermediate role does depolarization play in neurons and pancreatic β-cells?

In neurons it triggers neurotransmitter release; in β-cells it triggers insulin release.

24
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Why don’t circulating hormones activate every cell they encounter?

Only cells that express specific receptors for the hormone will respond.