Communication between cells

Question 1

What are the basic principles of cell signalling?

Answer 1

Conversion of a message (signal transduction)
Target cells have receptors for signalling molecules
Most cells both generate and receive signals

Question 2

What are the different categories of signal?

Answer 2

Endocrine
Paracrine
Neuronal
Contact-dependent

Question 3

How many responses can a signal trigger?

Answer 3

Many

Varying responses in different cell types

Question 4

What determines the response triggered?

Answer 4

The target cells interpretation of the signal

Question 5

What are the two types of receptor?

Answer 5

Cell surface

Intracellular

Question 6

What is an intracellular signalling pathway?

Answer 6

Extracellular signal binds to transmembrane receptor

Triggers an intracellular signal molecule

Question 7

What is relay?

Answer 7

Spreading the signal through the cell

Question 8

What is amplification?

Answer 8

Making the signal stronger so that a few extracellular signals trigger a large intracellular response

Question 9

What is integrating?

Answer 9

Receiving more than one signalling input and generating appropriate output

Question 10

What is distributing?

Answer 10

Passing on the signal to more than one pathway

Question 11

What role do kinases play in cell signalling?

Answer 11

Phosphorylate serine, threonine and tyrosine residues
Alter conformation and activity
Recruitment of effector proteins

Question 12

What are the categories of cell surface receptors?

Answer 12

Ion-channel coupled receptors
G-protein coupled receptors
Enzyme-coupled receptors

Question 13

How do ion channel coupled receptors work?

Answer 13

Open or close in response to a signalling molecule
Changes in membrane potential
Chemical signal becomes an electrical signal

Question 14

How do G-proten coupled receptors work?

Answer 14

Activated by proteins, peptides, amino acid derivatives and fatty acids
Binding ligand induces conformation change activating a G-protein on intracellular side of the membrane
Activated G-proteins activate enzymes or ion channels

Question 15

How do enzyme-coupled receptors work?

Answer 15

Tyrosine kinases

Question 16

Describe the structure of a G-protein coupled receptor

Answer 16

Single polypetide

7 pass transmembrane protein

Question 17

Describe the structure of a G-protein

Answer 17

Alpha, beta and gamma subunit

Question 18

What happens when a signal molecule binds to a G-protein coupled receptor?

Answer 18

Conformational changes result in exchange of GDP for GTP
Alpha subunit dissociates
Activated subunits activate downstream signals
Switched off when GTP is hydrolysed to GDP

Question 19

What increases in response to GPCR activation?

Answer 19

cAMP

Question 20

What does cyclic AMP do?

Answer 20

Activates phospholipase C

Question 21

What does phospholipase do?

Answer 21

Generates diacylglycerol and inositol trisphosphate

Question 22

What does inositol trisphosphase do?

Answer 22

Increase intracellular calcium

Question 23

How is cyclic AMP generated?

Answer 23

Generated from ATP by the enzyme adenylyl cyclase

Activated by G alpha subunit

Question 24

What switches off cyclic AMP?

Answer 24

Cyclic AMP phosphodiesterase

Question 25

What does cAMP act through?

Answer 25

Protein kinase A

Question 26

What is protein kinase A responsible for?

Answer 26

Transcription factors and gene expression Hormone synthesis Protein production in long term memory

Question 27

What happens if cell growth is disregulated?

Answer 27

Cancer

Question 28

How are receptor tyrosine kinases activated?

Answer 28

By dimerisation

Question 29

What does the signal molecule trigger in tyrosine kinases?

Answer 29

Receptor dimerisation Activation of intracellular kinase domains Trans-phosphorylation of tyrosine residues Recruitment of signalling proteins

Question 30

What does Grb2 trigger?

Answer 30

Recruits the Ras activating protein which exchanges GDP for GTP Conformational changes in Ras activates downstream proteins

Question 31

Why is Ras a molecular switch?

Answer 31

GTPases cycle Ras between active GTP bound and inactive GDP bound form

Question 32

What is the most commonly mutated oncogene?

Answer 32

Ras | Prevention of GTP hydrolysis causes it to be permanently switched on

Question 33

Describe MAP kinase signalling

Answer 33

Activated Ras protein activates Raf Raf activates Mek Mek activates Erk Erk targets transcription factors

Question 34

What drives cells into the G1 phase of the cell cycle?

Answer 34

Receptor tyrosine kinases

Question 35

What is the effect of inositol triphosphate activation?

Answer 35

Raises Ca2+ levels in the cell | Ca2+ interacts with Ca2+ responsive proteins

Question 36

What properties do transformed cells express?

Answer 36

``` Immortalisation Loss of contact inhibition High saturation density Altered morphology Anchorage independent growth ```