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Flashcards in Cell Signalling - Gray Deck (32):

define 1st messenger

signal that goes between cells


when does a signal molecule become a ligand?

when the signal binds the receptor it becomes a ligand


what is the structural effect on a receptor when a ligand binds?

the receptor undergoes a conformational change


describe the endocrine pathways

uses hormones as signalling molecules which are distributed by the bloodstream in animals. involved in long distance 'communication'


describe the paracrine pathways

GFs/controllers of development/histamines/neurotransmitters – diffuse out affecting surrounding cells, have short half-life. involved in short distance 'communication'


which endocrine molecule does the adrenal gland use? what type of molecule is it? what are it's effects?

its a derivative of tyrosine (catecholamine hormone but you don't need to know this)
Increases blood pressure, heart rate and metabolism


which endocrine molecule does the pancreas use? what type of molecule is it? what are it's effects?

insulin is a protein
it stimulates glucose uptake. protein and lipid synthesis in liver cells


which endocrine molecule do the testes/ovaries use? what type of molecule is it? what are it's effects?

Steroid (derivative of cholesterol) (steroids often used for long-term maintenance)
Induces and maintains secondary male/female sexual characteristics


which cells does NO act upon? how does it travel around the body? is it paracrine or endocrine molecule? what are its effects?

acts upon cells lining blood vessels
travels as a dissolved gas
paracrine molecule
causes smooth muscles to relax


which cells does GFs act upon? what type of molecule are they? are they paracrine or endocrine molecules? what are their effects?

acts upon various cells
it is a protein
paracrine molecule
stimulates cells to proliferate


describe the effects of acetylcholine interacting with:
1) a heart muscle cells
2) a salivary gland cell
3) skeletal muscle cell

1) a heart muscle cells: decreased frequency of contraction
2) a salivary gland cell: secretion of saliva
3) skeletal muscle cell: contraction


describe the signal transduction sequence

1) ligand (primary messenger) bind receptor
2) signal transduction via second messengers
3) cellular responses
4) changes in gene expression


what type of molecule is a receptor?



define a signal transducer

a receptor protein - with the ability to detect small amounts of signal and convert them into another signal


what kind of bonding occurs between a receptor and a ligand



what type of receptor do hydrophobic/charged molecules bind to?

diffuse through the membrane and bind intracellular receptors


what types of receptors do ligands bind to?

G protein coupled receptors


where do hydrophilic signals bind their receptors?

cell surface


give an example of an intracellular receptor-ligand interaction with enzyme activity

NO gas binding to enzyme:
Activated enzyme catalyses synthesis of cyclic GMP (from GTP)
Relaxes smooth muscle surrounding blood vessels
Blood vessels expand, increasing blood flow
NO release by nerve terminals in penis causes local blood-vessel dilation (erection) – Viagra interferes with this by not breaking down cGMP


give an example of a intracellular receptor-ligand interaction which regulate gene expression

steroid hormone receptors
- Steroid binds to site on receptor
- Activated receptor complex enters nucleus
- Binds to DNA to alter gene expression (eg secondary sexual characteristics)


name the 3 major classes of cell-surface receptors

- Ligand gated ion channels
- Receptors with enzyme activity
- G-protein linked receptors


describe a ligand gated ion channel. give an example of a neurotransmitter that uses one and describe how it works

Transmembrane protein forms a pore which ions can pass through
Opens/closes when signal binds to receptor protein
- Has 2 binding sites
- When ligand bound, the pore opens (Na+ enters)
- Important in research – Alzheimer’s


describe a receptor with enzyme activity and give an example of one

Has cytoplasmic domain in the cell
Must act as dimer – conformational change isn’t transmissible in a single molecule
Single pass transmembrane proteins
Most are protein kinases – add phosphate groups to proteins (adds -ve charge)


describe how protein kinases work and the type of ligand used

Ligand binds to extracellular domain
Brings each half of the dimer (an intracellular kinase domain) closer together
Each monomer phosphorylates the other (phosphorylation occurs on specific amino acids)
This phosphorylation occurs again in multiple places
Kinases can activate other kinases
- Causes protein kinase cascades
Ligands are often peptide hormones eg insulin/GFs


name 2 common protein kinase pathways

1) Ras pathway
2) PLC pathway


describe the Ras GTPase switch, what is the effect of this pathway, what happens when Ras is mutated?

receptor activation causes Ras to bind GTP (turns it on)
Ras-GTP activates specific kinases which lead to cell proliferation
Ras GTPase activity hydrolyses GTP to GDP (turns it off)
Mutant Ras that can bind GTP but not hydrolyse it, found in many human tumours


describe the PLC pathway

Phospholipase C is activated by a receptor (either receptor kinase or G-protein coupled)
PLC generates 2nd messenger IP¬3
- PLC cleaves PIP2 (a membrane phospholipid)
- Produces inositol trisphosphate (IP3) and diacylglycerol (DAG) – two 2nd messengers
- IP3 soluble and diffuses away from membrane
- IP3 causes release of Ca2+ from intracellular stores eg ER
- Ca2+ changes cell’s activity


how many g-protein coupled receptor genes are there?



what do g-protein coupled receptors do?

mediate diverse responses to hormones, neurotransmitters and local mediators (paracrine signals)


why are G-protein coupled receptors called 7 pass receptors?

they pass through the membrane 7 times


describe the activation of a g protein-coupled receptor

- Ligand binding activates receptor-associated G-protein by causing it to bind GTP (not GDP)
- G-protein relays the signal – it moves along surface of membrane and binds to effector enzyme
- Effector enzymes:
i. Adenylate cyclase (catalyses the production of cAMP – cAMP is 2nd messenger)
ii. PLC (catalyses the production of IP3)


describe the mechanism of cAMP mediated responses

Ligand + receptor --> activated receptor --> activated G-protein --> activated adenylate cyclase --> increased [cAMP] --> activates (downstream) effectors