Chapter 11 - Cell Signalling

Question 1

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What are the synonyms of cellular communication?

Answer 1

Cell to Cell Signalling or Transduction

Question 2

What’s the basic definition of cell to cell signalling?

Answer 2

The basics are that signalling molecules are sent out of cells and are picked up by neighbouring cells’s receptor proteins

Question 3

How do bacteria cells communicate?

Answer 3

Through quorum sensing. In quorum sensing, neighbouring cells can sense the messenger molecules and pick them up.

Question 4

Signalling messengers between cells are basically ________ messengers

Answer 4

Chemical

Question 5

How animal and plant cells directly communicate?

Answer 5

Through the cell junctions between two adjacent cells (plasmodesmata / gap junctions). Here molecules transfer directly from one cell to another.

Question 6

How exactly does cell communication happen in animal cells?

Answer 6

Through either direct contact or cell to cell recognization

Question 7

Signalling molecules are typically of what characteristics?

Answer 7

They are typically small, organic, are often proteins

Question 8

What occurs in cell-cell recognition?

Answer 8

Cells bump into each other so one molecule on the surface can interact with another molecule on the surface and recognize it.

Question 9

Are there other ways cells send signals to others locally?

Answer 9

Yes through paracrine and synaptic signalling.

Question 10

What occurs in paracrine and synaptic signalling?

Answer 10

In paracrine signalling - small molecules are released in vesicles by the cell which are meant to be picked up by another cell

In synaptic signalling - neurotransmitters are released into the synapse which causes the local nerve cells to pick it up.

Question 11

What’s a giveaway that a signal is being transported over long distance?

Answer 11

When the signalling molecule enters the bloodstream, it’s ALWAYS performing long distance signalling.

Question 12

What are long distance cell signalling reffered to as?

Answer 12

Endocrine/Hormonal signalling

Question 13

what are the three main components of cell signalling?

Answer 13

1. Receiving - Reception
2. Translating - Transduction
3. Cell Response

Question 14

Describe the process of cell signalling briefly.

Answer 14

A signalling molecule binds to the receptor located typically in a cell’s membrane.

The signalling molecule triggers a bunch of enzymatic chain reactions in the cell.

The enzymatic chain reactions activate a cellular response in the nucleus.

Question 15

What’s the most commonly occuring cellular response during cell signalling?

Answer 15

Typically, cells change gene expression aka turn a gene on or off in most cases.

Question 16

Do signalling molecules typically enter another cell to give a chemical message?

Answer 16

No, they just bind to the receptor on the surface/membrane 85% of the times.

Question 17

What are some examples of cellular signalling where the molecule doesn’t enter inside?

Answer 17

GCPR,
RT (receptor tyrosine),
Ligand gated Ion Channels

Question 18

Which types of molecules typically enter INSIDE of the cell to communicate?

Answer 18

Hormones, hydrophobic molecules,

Question 19

Full form of GCPR?

Answer 19

G Protein Coupled receptor family

Question 20

What does the receptor of GCPR look like?

Answer 20

Multiple Alpha helixes embedded into the membrane with a receptor at exterior end of the surface.
In the inner membrane region, GCPR is binded with a G Protein.

Question 21

What’s the entire process of GCPR like?

Answer 21

A signalling molecule binds to the receptor

When the signalling molecule interacts, a molecule called GDP that’s attached to G protein is attracted to the GCPR.

GDP binds to GCPR turning it into GTP (inactive into active)

GTP binds with an inactive enzyme and activates it and starts signal transduction

Question 22

How common are GCPRs?

Answer 22

In about 20-30% cases of cell signalling, they are GCPRs.
They are the most commonly used target molecules

Question 23

What’s the full form of RT

Answer 23

Receptor Tyrosine kinase proteins

Question 24

What’s the structure of RT like?

Answer 24

It has TWO ligand binding sites on the surface of the membrane. On the inner membrane region, tyrosines are attached to the protein ON EITHER SIDES in monomer form.

Question 25

Describe the process of cell signalling in RT proteins?

Answer 25

When a signalling molecule binds, the monomor structure inside the membrane turns into a dimer structure. (it comes together and becomes one unit)

Question 26

What happens when the RT dimerizes?

Answer 26

They start a process called autophosphorylation where each of the tyrosine kinase proteins have a phosphate added to them.

Question 27

How do RT system start the transduction process?

Answer 27

When the monomers come together as dimers and autophosphorylation occurs, other enzymes are attracted to the phosphorylated kinase proteins and attach to it. This triggers the transduction process.

Question 28

What’s the third major type of receptor protein called?

Answer 28

Ligand gated Ion channel

Question 29

What’s the process when a signalling molecule binds to a Ligand gated ion channel?

Answer 29

The gated ion channel is typically closed from letting ions in.
When a signalling molecule comes in, the gate opens due to a chemical reaction.
The ions are allowed in and trigger the transduction cascade.

Question 30

Do ligand gated channel ions let in any types of ions?

Answer 30

No, each gated ion channel has a specific type of ion that it is controlling from entering the cell.

Question 31

Do all signalling molecules bind to the receptors on the outside?

Answer 31

No, some types of molecules are exceptions to that case.
Hydrophobhic signalling molecules (typically hormones) are one of them.

Question 32

How do hydrophobic molecules or hormones send signals to the cell?

Answer 32

Hydrophobic molecules typically bind to a hormone receptor complex inside the cytosol. The complex then transports to the nucleus where the message is delivered.

Question 33

What’s another name for signal transduction?

Answer 33

Phosphorylation cascade

Question 34

What typically occurs in a phosphorylation cascade?

Answer 34

When the signalling molecule activates a relay protein. It’s the relay protein’s job to trigger the phosphorylation cascade.
During the cascade, the relay protein either adds or removes a phosphate causing the rest of the kinases/phosphorylates to add/remove phosphates like a chain reaction.
(in respective order)

Question 35

What’s the difference between secondary messengers? What’s their function?

Answer 35

The primary messengers bind to the receptors on the outside. The secondary messengers are molecules that further relay the primary messenger’s signal INSIDE THE CELL

Question 36

What’s the most common secondary messenger?

Answer 36

Cyclic AMP or cAMP

Question 37

how does cAMP function with a GCPR?

Answer 37

When a signalling molecule activates GCPR and thus attracts a G Protein, the G protein activates Adenylyl cyclase. The Adenylyl cyclase creates cAMP.

Then cAMP starts activates the first protein kinase in signal transduction.

Question 38

What’s the 2nd most common second messenger?

Answer 38

Calcium

Question 39

How is calcium used a secondary messenger in a signalling pathway?

Answer 39

Suppose the signalling pathway uses a GCPR. The activated G Protein inside the cell **activates Phospholipase **C which creates IP3 or inositol triphosphate.

Then IP3 binds to calcium channels in the ER. Then calcium TURNS ON the first protein for signal transduction.

Question 40

What’s the transition step between signal transduction and cellular response?

Answer 40

The last kinase protein that becomes activates turns on the transcriptor factor that makes a cellular response (typically in the nucleus)

Question 41

What’s the main purpose of a signal transduction?

Answer 41

The main function of a signal transduction is to amplify the signal.
This is done by activating more and more proteins/molecules in each step.

Question 42

What’s another purpose of signal transduction?

Answer 42

Signal tranduction can control the amount of times a signal is amplified which gives the signal transduction process a power to alter cellular response.

Question 43

Can two signalling molecule interfere with each other’s signalling pathway?

Answer 43

yes, sometimes, two different signalling molecules bind to different receptors which causes one of the signal molecule to **inhibit/enhance **the other signal molecule’s message.
That is called cross talk

Question 44

Could a signalling molecule bind to a receptor and cause multiple cellular responses to occur?

Answer 44

Yes

Question 45

Could a specific signalling molecule bind to another receptor to initiate another cellular response?

Answer 45

Yes, one signalling molecule can bind to many.

Question 46

What do scaffolding proteins do?

Answer 46

Hold protein kinases that work in a phosphorylation together and ensures that the kinases are activated orderly and efficiently.

Question 47

Can cells signal other cells to die? What is the process called?

Answer 47

Yes they can. The process is called programmed cell death or apoptosis.

Question 48

What enzymes are involved in apoptosis?

Answer 48

When a cell has to undergo through programmed cell death, an enzyme family called capsaicin.