Lecture 13 and 14

Question 1

what are examples of substances that activate and inhibit proteins

Answer 1

• antibiotics
• alcohol
• animal or insect venoms
• chemical compounds from fungi
• hormones
• neurotransmitters
• drugs or medicines

Question 2

what are the steps that cause protein activation or inhibition

Answer 2

• chemical substance = travels from its source
• chemical substance interacts with target protein = binding or reception
• binding event affects the protein = either activates or inhibits it
• leads to functional consequences that change the cellular response

Question 3

how many active sites do enzymes have compared to receptors

Answer 3

enzymes = one active site

receptors = can have several binding sites

Question 4

what do enzymes bind to compared to receptors

Answer 4

enzymes = bind to substrates

receptors = bind to ligands

Question 5

what do enzymes do compared to receptors

Answer 5

enzymes = change substrate into product

receptors = release ligands unchanged

Question 6

where can enzymes and receptors be found

Answer 6

both can be membrane bound or free in the cytosol

Question 7

what is signal transduction

Answer 7

messages passed on through the cell
- often multi step pathways, that provide opportunities for coordination and regulation of the cellular response

Question 8

what do second messengers do

Answer 8

they can transmit signals from a receptor to other relay molecules

Question 9

where are second messengers found

Answer 9

they are not attached to the membrane so free to move in the cell

Question 10

what can phosphorylation and de-phosphorylation do

Answer 10

can turn protein on and off or up and down as required

Question 11

what is phosphorylation

Answer 11

kinases transfer phosphates from ATP to protein (for regulating protein activity)

Question 12

what is dephosphorylation

Answer 12

protein phosphatases rapidly remove phosphates from proteins (to carefully control signal transduction)

Question 13

common mechanisms to control signal transduction

Answer 13

• ligand dissociation
• internalisation (receptor is removed from cell surface through endocytosis so it can no longer respond to ligand)
• phosphatases (removal of phosphate group?)

Question 14

why can the same receptor/ligand pairing have different effects in different cells

Answer 14

because they use different combinations of relay molecules for signal transduction

Question 15

what does different cells having different collections of receptors and relay molecules allow for

Answer 15

allows cells to detect and respond differently to different ligands

Question 16

what are the different classes of receptors

Answer 16

• ligand gated ion channels
• G protein coupled receptor
• receptor tyrosine kinase

Question 17

how do G protein-coupled receptors work

Answer 17

• use G protein to start signal transduction
• GPCR activates the G protein, which communicates with other proteins in the cell
• receptor activation causes G protein activation and further signal transduction events

Question 18

what are Gas G proteins

Answer 18

Gas = stimulatory G protein, which activates an enzyme called adenylate cyclase

Question 19

what are Gai G proteins

Answer 19

Gai - inhibitory G protein, decreases the activity of adenylate

Question 20

how do receptor tyrosine kinase work

Answer 20

• use phosphorylation of so called adaptor proteins to start signal transduction

Question 21

process of receptor tyrosine kinase

Answer 21

• agonist binds to ligand
• receptor changes conformation and becomes activated
  -receptor autophosphorylation occurs
• adaptor protein is phosphorylated
• adaptor proteins communicate with other proteins in the cell

Question 22

do all adaptor proteins have the same effect (receptor tyrosine kinase)

Answer 22

no, different types of adaptor proteins will have different effects

Question 23

how do ligand gated ion channels work and whats the BUT that makes them different

Answer 23

agonist that binds ligand causes conformational change to adaptive receptor

BUT

instead of ‘relay’ proteins like G coupled proteins or adaptors being used, ions flow directly through the channel to produce effects

Question 24

are ligand gated ion channels fast or slow signalling

Answer 24

compared to GPCR’s and RTK’s they are FAST signalling

Question 25

what is a receptor

Answer 25

a cellular protein(or assembly or proteins) that control chemical signalling between and within cells

Question 26

what is a ligand

Answer 26

chemical substance that specifically binds to a receptor

Question 27

what is an agonist

Answer 27

chemical substance (ligand) that binds to a receptor to activate it

Question 28

what is an antagonist

Answer 28

chemical substance (ligand) that binds to a receptor and prevents activation by an agonist

Question 29

what are endogenous ligands

Answer 29

ligands produced in the body

Question 30

what are exogenous ligands

Answer 30

like drugs and toxins

Question 31

what is important about the binding pocket of a receptor and a ligand

Answer 31

the size and shape of the ligand must match the binding pocket of the receptor for chemical interactions to occur

Question 32

what occurs when an agonist binds to receptor

Answer 32

activation occurs when the receptor undergoes conformational change

Question 33

what occurs when an antagonist binds to a receptor

Answer 33

the antagonist will bind and block the agonist from binding, the receptor will remain inactive

Question 34

what occurs after activation of a receptor

Answer 34

a chain of events will be passed on through the cell = signal transduction