Introduction to Receptors and Signal Transduction Pathways

Question 1

in terms of receptors, state what it is meant by the key term ‘receptor’

Answer 1

a receptor is a specific protein, either in the plasma membrane or the interior of a target cell, that a chemical messenger binds to invoking a biologically relevant response in that cell

Question 2

in terms of receptors, state what it is meant by the key term ‘specificity’

Answer 2

specificity refers to the ability of a receptor to bind only to one type, or a number of structurally similar chemical messengers

Question 3

in terms of receptors, state what it is meant by the key term ‘saturation’

Answer 3

saturation refers to the degree to the proportion of receptors bound to chemical messengers

Question 4

in terms of receptors, state what it is meant by the key term ‘affinity’

Answer 4

affinity refers to the strength at which a chemical messenger binds to a receptor

Question 5

in terms of receptors, state what it is meant by the key term ‘competition’

Answer 5

competition refers to the ability of different molecules to compete with a ligand for a receptor. receptors are generally similar in shape to the natural ligand

Question 6

in terms of receptors, state what it is meant by the key term ‘antagonist’

Answer 6

an antagonist is a molecule that competes with a ligand for binding to it’s receptor but does not activate signalling normally associated with the natural ligand. therefore, an antagonist prevents the actions of a natural ligand

Question 7

in terms of receptors, state what it is meant by the key term ‘agonist’

Answer 7

an agonist refers to a chemical messenger that binds to a receptor and triggers it’s response

Question 8

in terms of receptors, state what it is meant by the key term ‘down-regulation’

Answer 8

down-regulation refers to a decrease in the total number of target cell receptors for a given messenger; may occur in response to a chronic high extracellular concentration of a messenger

Question 9

in terms of receptors, state what it is meant by the key term ‘up-regulation’

Answer 9

up-regulation refers to a decrease in the total number of target cell receptors for a given messenger; may occur in response to a chronic low extracellular concentration of the messenger

Question 10

in terms of receptors, state what it is meant by the key term ‘increased sensitivity’

Answer 10

increased sensitivity refers to the increased responsiveness of a target cell to a given messenger

Question 11

state what it is meant by the key term ‘receptor activation’

Answer 11

receptor activation is when a messenger binds to a receptor and causes a conformational change in the shape of the receptor

Question 12

state the 5 changes caused by the initial response of a messenger

Answer 12

1. changes the permeability, transport properties or electrical state of the plasma membrane
2. metabolism
3. secretary activity
4. rate of proliferation and differentiation
5. contractile or other properties

Question 13

state what it is meant by the key term ‘signal transduction pathways’

Answer 13

signal transduction pathways refers to the diverse sequence of events that link the receptor activation to the response of the cell

Question 14

state what the two transduction pathways are

Answer 14

1. pathway initiated by lipid-soluble messengers

2. pathway initiated by water-soluble messengers

Question 15

state 3 basic facts about the transduction pathways initiated by lipid-soluble messengers

Answer 15

1. usually act on cells by binding to intracellular receptor proteins
2. lipid-soluble messengers include all steroid hormones and the thyroid hormones
3. are all hydrophobic

Question 16

explain the transduction pathway initiated by lipid-soluble messengers (5 steps)

Answer 16

1. messenger diffuses out plasma into intistitual fluid
2. diffuses accrocs plasma membrane + nuclear envelope into nucleus to bind to receptor
3. activated receptor complex acts as a transcription factor
4. the hormone receptor complex binds to DNA at a gene regulatory region
5. changes cellular concentration of protein and secretion in response to messenger

Question 17

state 3 basic facts about transduction pathways initiated by water-soluble messengers

Answer 17

1. cannot enter cell via diffusion across membrane
2. binds to extracellular portion of receptor proteins embedded in plasma membrane
3. most peptide hormones, neurotransmitters and paracrine-autocrine compounds

Question 18

explain the transduction pathway initiated by water-soluble messengers

Answer 18

1. messenger binds to primary messenger
2. second messenger enter, or generated by, cytoplasm
3. second messagers diffuse through cell acting as chemical relays from plasma membrane to biochemical machinery in cell
4. protein kinase activated/deactivated via phosphorylation, then catalyses phosphorylation of another protein kinase…
5. at end of sequence, phosphorylation of key transporters underline biochemical response to primary messenger

Question 19

state the major way that signal transduction pathway activation ceases

Answer 19

a decrease in concentration of the first messenger molecules in the region of the receptor. this occurs as enzymes in the vicinity metabolise the messenger and the messenger is taken up by adjacent cells or it diffuses away

Question 20

state and explain 3 other ways in which receptors can be inactivated

Answer 20

1. receptor chemically altered via phosphorylation reducing affinity for first messenger so first messenger is released
2. phosphorylation of receptor prevents further G-protein binding to the receptor
3. receptors removed from CSM via endocytosis

Question 21

state the 5 second messengers you need to know about in this chapter

Answer 21

1. Ca2+
2. Cyclic AMP (cAMP)
3. Cyclic GMP (cGMP)
4. Diacylglycerol (DAG)
5. Inositol triphosphate (IP3)

Question 22

what is the source and effect of CA2+ as a second messenger

Answer 22

1. enters cell via PM ion channels or released from ER
2. activates CA2+ calmodulin and other CA2+ binding proteins: calcium-calmodulin activates calmodulin-dependant protein kinases and protein Kinase C

Question 23

what is the source and effect of Cyclic AMO (cAMP)

Answer 23

1. a G protein activates PM adenylyl cyclase which catalyses cAMP formation from ATP
2. activates cAMP-dependent protein kinase (protein kinase A)

Question 24

what is the source and effect of Cyclic GMP (cGMP)

Answer 24

1. generated from guanosine triphosphate in reaction catalysed by a PM receptor with guanylyl cyclase activity
2. activates cGMP-dependent protein kinase (protein kinase G)

Question 25

what is the source and effect of Diacylglycerol (DAG)

Answer 25

1. a G protein activates PM phospholipase C which catalyses generation on DAG and IP3 from PM phosphatidylinositol bisphosphate (PIP2)
2. activates protein kinase C

Question 26

what is the source and effect of triphosphate (IP3)

Answer 26

1 .a G protein activates PM phospholipase C which catalyses generation on DAG and IP3 from PM phosphatidylinositol bisphosphate (PIP2)
2. releases CA2+ from ER