Module 7: V1-V3

Question 1

Why do cells communicate?

Answer 1

survive
grow + divide
differentiate
die

Question 2

What is signal transduction?

Answer 2

movement of signal from the outside of a cell to the inside of a cell

Question 3

What are the different ways in which a signal is transmitted?

Answer 3

contact-dependent
paracrine
synaptic
endocrine

Question 4

What is specificity?

Answer 4

signal molecule fits binding site on its complementary receptor; other signals do not fit

Question 5

What is amplification?

Answer 5

when enzymes activate enzymes, the number of affected molecules increases geometrically in an enzyme cascade

Question 6

What is modularity?

Answer 6

proteins with multivalent affinities form diverse signaling complexes from interchangeable parts
phosphorylation provides reversible points of interaction

Question 7

Signalling molecules are usually expressed and degraded __________. (very fast / very slow)

Answer 7

very fast

Question 8

How are molecular switches turned on / off?

Answer 8

either signaling by phosphorylation or GTP-binding

Question 9

What are GPCRs associated with?

Answer 9

a guanine nucleotide-binding protein (G protein)

Question 10

What type of activity does the ɑ subunit of a G protein have?

Answer 10

GTPase activity as the ɑ subunit has a GDP-binding site

Question 11

What do the ɑ and ɣ subunits of a G protein have?

Answer 11

lipid molecules that insert into the membrane

Question 12

What does the activation of an enzyme by a G protein result in?

Answer 12

results in increased enzymatic activity and therefore an increased signal output

Question 13

How is a β-adrenergic receptor activated by adrenaline?

Answer 13

adrenaline binds -> G protein GDP is replaced by GTP = activation -> G protein activates adenylyl cyclase (AC) -> AC catalyses formation of cAMP -> cAMP activates PKA -> PKA phosphorylates cellular proteins = cellular response (>100,000 molecules liberated)

Question 14

What are receptor tyrosine kinases stimulated by?

Answer 14

growth factor

Question 15

What is the structure of a receptor tyrosine kinase?

Answer 15

a receptor coupled to an enzyme

Question 16

What does downstream signalling of receptor tyrosine kinase stimulate?

Answer 16

survival, growth and proliferation

issues with these receptors are linked to cancer

Question 17

What is cross-phosphorylation by activated kinase domains?

Answer 17

when one receptor by itself cannot become activated but once it is paired up with a partner it can

Question 18

What is dominant-negative inhibition by receptor tyrosine kinase?

Answer 18

if one receptor is mutated and has no activity then downstream signalling is not able to occur because it cannot pair up with a partner

Question 19

How to RTK signalling pathways progress?

Answer 19

activated receptor -> phosphorylates downstream target (e.g. transcription factor) which becomes a docking site for other signalling molecules -> amplification through multiple rounds of enzyme activation

Question 20

Cell signalling is often described like electric circuitry. What key features do you think they share that make this analogy a good one?

Answer 20

both allow for the movement of a signal from one place to another
as well as this circuits and cell signalling can both be switched on or off

Question 21

Does protein phosphorylation always activate a protein. Why, why not?

Answer 21

no, because sometimes phosphorylation results in inactivation of a protein

Question 22

Does ligand binding always need to cause receptor tyrosine kinases to dimerise? What does it need to cause?

Answer 22

no, the ligand must bind to the extracellular domain