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Question 1

What are three ways in which cells can communicate?

Answer 1

ParacrineEndocrineSynaptic

Question 2

What is paracrine communication?

Answer 2

Adjacent cells are effected within a tissue by local chemical mediators

Question 3

What is endocrine communication?

Answer 3

Message released into bloodstream and affects a distant cell

Question 4

What is synaptic communication?

Answer 4

Neurotransmitter crosses a synaptic cleft and binds to receptors on the post synaptic membrane of the target cell

Question 5

What kind of molecule do cell surface receptors bind?

Answer 5

Hydrophillic, such as insulin and glucagon

Question 6

What kind of molecule do intracellular receptors bind?

Answer 6

Small hydrophobic signalling molecules (bound to a carrier in blood) bind to intracellular recptors in nucleus or cytoplasm. (Thyroid and steroid hormones)

Question 7

What is a ligand?

Answer 7

Any small molecule that binds to a receptor site.

Question 8

What is a ligand called if it produces a response in a receptor?

Answer 8

An agonist

Question 9

What is an antagonist?

Answer 9

A ligand which binds to a receptor without causing any activation.

Question 10

What is an agonist which stimulates a receptor but are unable to elicit the maximum cell response called?

Answer 10

Partial agonists

Question 11

What is the definition of a receptor?

Answer 11

A molecule which specifically recognises a ligand or family of ligands and which, in response to ligand binding brings about regulation of a cellular process. In the unbound state, a receptor is functionally silent.

Question 12

What are the 8 roles of receptors?

Answer 12

1. Signalling by hormones/ local chemical mediators2. Neurotransmission3. Cellular delivery4. Control of gene expression5. Cell adhesion6. Modulation of the immune response7. Sorting of intracellular proteins8. Release of intracellular calcium stores

Question 13

What is an acceptor?

Answer 13

A molecule whos basic function can be carried out without the interaction of a ligand.

Question 14

What are the two types of acetylcholine receptors?

Answer 14

Nicotinic and muscarinic

Question 15

What are the three muscarinic receptors, and their antagonists?

Answer 15

M1 PirenzipineM2 GallamineM3 Hexahydrosiladiphenol

Question 16

What is a ligand?

Answer 16

Definition: any molecule that binds specifically to a receptor site

Question 17

What are receptors classified according to?

Answer 17

Which specific physiological signalling molecule (agonist) recognised

Question 18

How are receptors subclassified?

Answer 18

By its affinity to a series of antagonists

Question 19

What are the similarities between receptor binding and active and regulatory sites of enzymes?

Answer 19

• Specific binding- Specificity shape related- Specificity of binding confers specificity to the regulation of processes by ligand binding- Binding reversible- Ligand binding to a receptor and regulator binding to enzyme allosteric sites induce a conformational change in activity- No chemical modification of ligand in receptor binding sites or enzyme regulatory sites

Question 20

What are the differences between receptor binding and active and regulatory sites of enzymes?

Answer 20

• The affinity of ligand binding > binding of substrate and regulators to enzyme sites * Ligand bound to a receptor site is not modified chemically whereas substrate is converted to product by an enzyme

Question 21

Explain how membrane bound receptors with intergral ion channels have an effect

Answer 21

• Agonist binds to ligand-gated ion channels > conformational change > gated channel opens > permits flow of ions down an electrochemical gradient > signal transduced into an electrical event

Question 22

What is the subunit structure of a classical ligand gates ion channel family?

Answer 22

• Similar pentameric subunit structures* E.g. nicotinic acetylcholine receptors (nAChR), GABA receptors, glycine receptors (GlyR)* Subunits have four transmembrane domains – M2 forms the lining to the channel pore

Question 23

Describe the activation of membrane bound receptors with intergral enzyme activity

Answer 23

• Agonist binds to extracellular domain > conformational change > activation of intrinsic enzyme e.g. tyrosine kinase-linked receptors

Question 24

How are tyrosine kinase linked receptors operated?

Answer 24

• Binding of hormone to extracellular domain > activation of protein kinase activity in the cytoplasmic domain of the receptor protein kinase activity

Question 25

What is the effect of tyrosine kinase linked receptor activation?

Answer 25

Autophosphorylates tyrosine residues on the cytoplasmic domain of the adjacent receptor

Question 26

What are phosphorylated tyrosine residues recognised by?

Answer 26

o Transducing proteinso Directly by enzymes containing phosphotyrosine recognition sites

Question 27

How is does phosphorylated tyrosine activate shizzle?

Answer 27

* On association with receptor or transducing protein > effector enzymes become activated allosterically > transduce message into an intracellular event

Question 28

Describe structure of membrane-bound receptors which couple to effectors through transducing proteins

Answer 28

* Seven transmembrane domains receptors (7TMDR) couple to effector molecules via G-proteins

Question 29

What are the effectors of membrane-bound receptors which couple to effectors through transducing proteins

Answer 29

o Adenyl cyclase (ATP > cyclic AMP)o Ion channels e.g. Ca2+ and K+ channels

Question 30

What are membrane-bound receptors which couple to effectors through transducing proteins used by? (4)

Answer 30

o Muscarinic receptorso Dopamine receptorso Peptide receptorso Purine receptors e.g. ATP

Question 31

Describe the four roles of intracellular receptors

Answer 31

* Hydrophobic ligands e.g. steroid and thyroid hormones* Bind to monomeric receptors in the cytoplasm or nucleus* Receptors stabilised in resting state by association with heat shock or chaperone proteins* Activated receptors dissociates from the chaperone proteins and translocates to the nucleus > regulates gene expression

Question 32

Define amplification

Answer 32

* Cascade event* Binding of a chemical signal molecule to a single receptor can cause the modification of hundreds or thousands of substrate molecules

Question 33

Define cellular activation and inhibition

Answer 33

* Responses to receptor activations can lead to either cellular activation or inhibition

Question 34

Give an example of cellular inhibitionv

Answer 34

o E.g. noradrenaline binding to B1 adrenoreceptors in cardiac pacemaker cells > increased heart rate / ACh acting on M2 > decreased heart rate