Cell signalling and interactions

Question 1

What 4 ways can cells receive cell signals?

Answer 1

Endorcrine, paracrine, neuronal and contact-dependent

Question 2

What are endrocrine cells?

Answer 2

Cells that secrete hormones into the bloodstream in an inactive state until they reach their receptors in the target cell.

Question 3

What are paracrine cells?

Answer 3

Cells that secrete hormones which affect cells in the immediate vicinity. Hormones are released into the extracellular matrix.

Question 4

How do hydrophobic and hydrophilic signal molecules work?

Answer 4

Hyrdophobic molecules diffuse through the membrane in order to bind to intracellular receptors in the nucleus.(They have to be small hydrophobic molecules obviously)

Hyrdophilic molecules bind to receptors on the cell surface membrane causing secondary messengers within the cytoplasm to activate.

Question 5

What are the ‘major membrane receptor families’?

Answer 5

Ion-channel coupled receptors
G protein coupled receptors (GPCRs)
Enzyme-linked receptors
Intracellular receptors

Question 6

how do ion-channel coupled receptors work?

Answer 6

Ligand molecules bind to the ion channel, causing a change in the shape and allowing the channel to become permeable to the ion allowing the ion to diffuse down concentration gradient.

Question 7

What is the structure of G protein coupled receptors?

Answer 7

https://www.cusabio.com/manage/upload/201812/1545900446.png

‘loop’ between the 5th and 6th α-helix is the ‘interaction domain’.

Question 8

How does the G protein coupled receptors work?

Answer 8

Signal binds to receptor at the N-terminus region of the GPCR.
Heterotrimetric G protein associates with receptor (Gα-GDP)
GDP/GTP exchange occurs
G proteins dissociates into Gα-GTP and Gβγ subunits
Gα-GTP activate effector enzyme (adenylyl cyclase)
Effector enzyme produces cAMP (secondary messenger) from ATP
Gα subunit hydrolyses GTP to GDP and Gαβγ ressociates, which is the end of the signal.

Question 9

What is cAMP?

What is its structure?

Answer 9

google image of cAMP in comparison to AMP

cAMP stands for cyclic adenosine monophosphate. Its produced from ATP by adenylyl cyclase which removes two phosphate groups from the ATP.

Question 10

What activate protein kinase A and what does it do?

Answer 10

Protein kinase A (PKA) is activate by cAMP
It signals for protein phosphorylation (serine, threonine and tyrosine amino acids are the ones which are phosphorylated).

Question 11

What is the ‘fight or flight’ response in muscles cells, triggered by adrenaline?

Answer 11

Adrenaline activates β-adrenergic receptors in muscles, which increases cAMP and subsequently increases PKA.

PKA causes glycogen phosphorylase kinase to be stimulated, glycogen phosphorylase is stimulated and there is an increased glycogen degradation, to produce more glucose.
Additionally, PKA causes glycogen synthase inhibition, which decreases glycogen synthesis.

Question 12

How is protein kinase C activated?

Answer 12

GPCR is activated by signal molecule -> Activated Gα subunit activates phospholipase C -> inositol phospholipid splits into diacylglycerol and IP3 (inositol 1,4,5 triphosphate) by the enzyme phospholipase C

IP3 acts as a ligand for Ca2+ channel and so releases Ca2+. The released Ca2+ in addition to the diacylglycerol activates PKC

Question 13

Which receptor activates the Gs protein?

Which receptor activates the Gq protein?

Answer 13

Gs is activated by the β-adrenergic receptor

Gq is activated by α1-adrenergic receptor

Question 14

What are the secondary messengers for Gs protein ans Gq proteins?

Answer 14

Gs: cAMP
Gq: DAG (diacylglycerol), IP3 (inositol 1,4,5 triphosphate) -> Ca2+

Question 15

Why are there so many proteins involved activated in the EGF pathway?

Answer 15

One protein can activate multiple proteins, so having many proteins in the pathway allows the signal to be greatly amplified.

Question 16

What are ways endocytosis can occur?

Answer 16

Macropinocytosis, phagocytosis, clathrin-coated vesicles, non-coated vesicles, caveolae

Question 17

Why does phagocytosis occur?

Answer 17

Phagocytosis occurs to rid the body of pathogens or foreign molecules that are in the body.

Question 18

What is the ‘ER postcode’?

Answer 18

When the polypeptide chain is growing in the ribosome, there is an ER signal sequence. A signal recognition particle (SRP) is bound to signal sequence and transports the ribosome along with the mRNA and unfinished polypeptide chain to SRP receptor on the ER membrane.

The ‘ER postcode’ is the signal sequence on the polypeptide chain that allows the ribosome to be transported to the ER.

Question 19

Once ribosome is transported to the ER, what happens to the unfinished polypeptide chain?

Answer 19

EITHER:
The protein finishes being translated and ends up in the lumen of the ER where is is folded and packaged so it can transported further or secreted from the cell.

OR:
The protein finishes being translated and ends up embedded in the membrane.

Question 20

How does the vesicle and the target membrane ‘fuse’?

Answer 20

The vesicle has ‘v-snares’ and the target has ‘t-snares’. These snares bind and allow docking and fusion of the membrane and vesicle.

Question 21

What doe the Golgi actually do?

Answer 21

Forms disulphide bonds between Cys-Cys
Folds proteins (using chaperones)
Adds sugars to the proteins (glycosylation) using glycosyltransferase enzyme

Question 22

Where is the ER signal sequence located on the protein?

Answer 22

N-terminus region

Question 23

What is the ‘lysosome postcode’?

Answer 23

Mannose-6-phosphate (M6P) is added in Golgi which allows the secretory vesicles from to travel to the lysosome.

Question 24

What is I-cell disease?

Answer 24

Mutations in GNPTAB
Proteins that are supposed to go to the lysosome are secreted out of the cell instead
This causes developmental defects

Question 25

What is the mechanism of phagocytosis?

Answer 25

Receptors that bind bacteria become activated. Signal cascade occurs that activates actin skeleton, which pushes membrane out and around the bacteria to engulf bacteria
Phagosome is sealed off, transported into the cell and fuses with lysosomes.

Question 26

Lecture 15

Answer 26

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