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biosci > Cell communication > Flashcards

Cell communication Flashcards

1
Q

Why do cells communicate

A

Need to be able to respond to a cell, and as part of a whole tissue

Respond to signals from other cells and from the environment

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2
Q

What are the two subtypes of cell signalling?

A

Local or long distance

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3
Q

What is local signalling

A

Signals act on nearby cells

Growth factors such as fibroblast growth factor
Neurotransmitters such as acetylcholine - ACh

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4
Q

What is panacrine signalling

A

Cells release signals that act on nearby cells, producing local effects

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5
Q

What is synaptic signalling

A

Hormones released from endocrine cells travel via the cardiovascular system to act on specific distant cells

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6
Q

What are the two subtypes of local signalling

A

Panacrine and synaptic

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7
Q

What is long distance signalling

A

Signals act from a distance

Hormones produced by specialised cells travel via circulatory system to act on specific cells
e.g insulin from pancreas bind to insulin receptors initiating a cascade resulting in glucose uptake

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8
Q

What are the three main steps of cell signalling

A

Reception
Transduction
Response

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9
Q

What happens in reception of cell signalling

A

Signalling protein (primary messenger) binds to a receptor protein. Results in shape and/or chemical change in the receptor protein

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10
Q

What happens in transduction of cell signalling

A

Altered receptor activates another protein. The activated protein (often enzyme) may cause a relay of changes.
Relay molecules (second messengers) e.g cAMP and IP3.
Multiple other proteins may be activated

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11
Q

What happens to each activated protein in transduction

A

Each activated protein causes a series of changes, this is often via phosphorylation, known as a phosphorylation cascade

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12
Q

What happens in response in cell signalling

A

All of the activated proteins cause one or more functions to occur in the cell. This is where the cell actually does something

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13
Q

How are receptors specific

A

The human body simultaneously sends out different chemicals and molecules which are all aimed at eliciting specific responses BUT only the target receptor on the target cell will interact with that signal and use it to activate signal transduction pathways.

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14
Q

Where does the specificity of receptors come from

A

3D molecule shape of the proteins involved

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15
Q

How is the cell receptor specifically created

A

Created through 3D shape of the receptor (lock and key

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16
Q

How is exquisite control of receptors possible?

A

Only certain cells at certain times will have particular receptors, meaning that while the signal may be widespread the transmission of the signal occurs only where it is needed

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17
Q

What are the two main types of receptors

A

Intracellular and Membrane bound/cell surface receptors

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18
Q

What are intracellular receptors

A

A primary messenger that is generally hydrophobic and/or small - lipid soluble, can enter the cell.

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19
Q

What kind of signalling uses intracellular receptors?

A

Sex hormone signalling such as testosterone, progesterone, oestrogen.

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20
Q

What are membrane-bound/cell surface receptors?

A

Primary messengers that is generally hydrophilic and/or large

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21
Q

Are membrane bound receptors polar or non polar

A

polar

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22
Q

Which is the most common method of cell signalling?

A

Membrane-bound/cell-surface receptors

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23
Q

What are the two types of membrane bound receptors

A

GPCR’s, receptor tyrosine kinase, and ligand gated ion channels

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24
Q

G proteins are molecular switches, what does this mean?

A

The molecular switches of the G protein are either on and off depending on whether GDP (inactive) or GTP (active) is bound

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25
Q

How many times do G protein receptors (GPCRs) span the plasma membrane

A

7 times

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26
Q

How many different GPCR’s are there and what are their function(s)

A

Hundreds of different GPCRs exist each with different ligands with diverse functions e.g development, sensory reception

27
Q

What is the first step of the GPCRs process

A

1) At rest, receptor is unbound and G Protein is bound to GDP. The enzyme is in an inactive state.

28
Q

What is the second step of the process of GPCRs

A

2) Ligand binds receptor, and binds the G protein. GTP displaces GDP. The enzyme is still inactive

29
Q

What is the third step of the process of GPCRs

A

Activated G protein dissociates from receptor. Enzyme is activated to elicit a cellular response

30
Q

What is the fourth step of the process of GPCRs

A

G protein has GTPase activity, promoting its release from enzyme, reverting back to resting state.

31
Q

What are ligand gated ion channels/receptors?

A

Channel receptors that contain a ‘gate’.

Binding of ligand at specific site on receptor elicits a change in shape.

The channel opens/closes as the receptor changes shape

Ions can pass through channel

32
Q

What is a ligand

A

A signalling molecule that binds specifically to another protein

33
Q

What is an ion channel receptor

A

Membrane protein through which specific ions can travel, in response to ligand binding (aka ionotropic receptors)

34
Q

What are steps in ligand gated ion channels

A

At rest, ligand is unbound and gate is closed.

Upon ligand binding, gate opens, specific ions can flow into cell.

Following ligand dissociation, gate closes back to resting

35
Q

How does ion gated channels work

A

Channel receptors contain a gate where the binding of a ligand elicits a conformational change so the channel opens and allows ions to pass through. When the ligand unbinds the shape of the receptor changes again and the channel closes

36
Q

What flows through ligand ion channels, and when?

A

Once a ligand binds to the receptor and causes a conformational change, ions such as Ca2+, Na+, K+ and Cl- can flow through

37
Q

Which body system relies heavily on ligand gated ion channels, and why

A

The nervous system
Released neurotransmitters bind as ligands to ion channels on target cells to propagate action potentials

38
Q

What are signal transduction pathways

A

Signals relayed from receptors to target molecules via a ‘cascade’ of molecular interactions

39
Q

What is a typical phosphorylation cascade

A

Enzymes that transfer a phosphate group from ATP to another (specific) protein. Typically, this activates the protein.

Series of protein kinases each adding a phosphate to the next kinase

40
Q

How is a phosphorylation cascade formed

A

Series of protein kinases each transfer a phosphate group from ATP to an inactive enzyme to activate it

41
Q

What are phosphatase in regards to the phosphorylation cascade

A

Phosphatase are enzymes that dephosphorylate (remove phosphate) rendering the protein inactive, but recyclable

42
Q

What are the typical residues (side chains) of proteins that are phosphorylated? what could this lead to

A

Serine or threonine residues
This means that mutations affecting these residues could be detrimental

43
Q

What are primary messengers

A

The original signal molecule (ligand) that binds to a receptor, useful in signal receptor

44
Q

What are second messengers

A

Intracellular molecules useful in signal transduction. They link the activated enzyme with the signalling cascade

45
Q

What are second messengers (cAMP)

A

Another small molecule that is included in the cascade that activates further pathways

46
Q

What does cAMP (second messengers) do and how is it made

A

When the G protein dissociates from the receptor and binds to an enzyme, it binds to adenylyl cyclase which catalyses the conversion of ATP to cAMP. cAMP acts as a second messenger by activating protein kinase A, which initiates a phosphorylation cascade

47
Q

What are the most common second messengers

A

cAMP, calcium and IP3

48
Q

Why is is calcium (second messengers) kept at low concentrations in the cell

A

To prevent cell damage - high Ca2+ can damage cells

49
Q

How is calcium kept at low concentrations in the cell?

A

Using calcium pumps to pump calcium out of the cell or into the mitochondria or ER

50
Q

What happens in CA2+ and IP3 in GPCR signalling

A

The activated protein phospholipase C hich then cleaves PIP2 (a phospholipid) into DAG and IP3

IP3 diffuses through cytosol and binds to gated channel in ER

Calcium ions flow out of ER down concentration gradient and activate other proteins toward a cellular response

51
Q

What is PIP2

A

A phospholipid embedded in the plasma membrane

52
Q

Why are there so many steps in signalling

A

Amplifies the response

Provides multiple control points

Allows for specifity of response and coordination with other signalling pathways

53
Q

Examples of a cellular response that includes activation or regulation of ___

A
  • Gene expression
  • Alteratation of protein function to gain or lose an activity
  • opening or closing of an ion channe;
  • alteration of cellular metabolism
  • regulation of cellular organelles or organisation
  • rearrangement/movement of cytoskeleton
  • a combo of any of these
54
Q

Elaborate on how signals are for a limited time

A

Because activation usually promotes the start of deactivation, so that signalling is of short period of time.

55
Q

Why is it important for signals to be for a short amount of time

A

To ensure homeostatic equilibrium so response is not execessive

56
Q

What is cAMP broken down by and what does this mean

A

By the enzyme phosphodiesterase (PDE), so will no longer continue to activate protein kinase

57
Q

Why is deactivation an important regulatory step?

A

Otherwise cascades can run rampant and cause problems or inappropriate activation of proteins

58
Q

Is deactivation automatic

A

Yes

59
Q

What is adrenaline stimulation of glycogen breakdown?

A
  • Adrenaline acts through a GPCR, activates cAMP and two protein kinases in a phosphorylation cascade
  • results in active glucogen phosphorylase which can convert glycogen to glucose 1-phosphate
60
Q

What does amplification in adrenaline stimulation result in

A

Means that 1 adrenaline molecule can result in 10^8 glucose 1-phosphat molecule

61
Q

What does glycogen breakdown result in, and what does this convert to

A

glucose 1-phosphate, which converts to glucose 6-phosphate which can then be used in glycolysis to generate ATP

62
Q

What is glycogen

A

A long term energy store in liver and skeletal muscle

63
Q

How does SARS-CoV-2 invade our respiratory tract?

A

ACE2 is the cellular receptor for the coronavirus

ACE2 in our respiratory tract is the lock and S protein on the virus is the key

biosci (28 decks)

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