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PMP-101 > Cell communication and signalling > Flashcards

Cell communication and signalling Flashcards

1
Q

Cell communication

A

It governs basic cellular functions and coordinates activities within and among tissues/organs of multicellular organisms, in response to external changes

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2
Q

Cell signalling

A

Cells communicate through physical interactions or sending/receiving signalling molecules

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3
Q

Examples of cell communication:

A
  1. Plant bending toward light
  2. Fight or flight ( cheetah running after antelope)
  3. Sweating/Shivering in hot/cold conditions
  4. Bacteria cell aggregate
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4
Q

Cell-cell interactions - physical communication

A

> Required for cell adhesion within a tissue
- Controlling the shape and function of cells
- organisation of cells into tissues (e.g Epithelia)

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5
Q

What is the space between cells composed of meshwork of proteins and polysaccharides secreted by cells called?

A

The Extra Cellular Matrix or ECM - required for anchoring cell

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6
Q

Three types of junctions:

A
  1. gap junctions
  2. anchoring junctions
  3. tight junctions
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7
Q

Gap junctions structure:

A
  • Consists of 2 cylindrical channels (connexons composed of 6 connexin proteins each
  • Plasma membrane of adjacent cells that are joined together to form a PORE
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8
Q

Gap junctions role:

A

> Allowing direct and bidirectional exchange of molecules. ions between 2 neighbour cells
- e.g Heart (cardiac muscle) to pass the signal to contract

  • No effect in cell-ECM adhesions
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9
Q

ONLY gap junctions…

A

provide direct communication or material exchange between cells

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10
Q

Types of cell signalling:

A

a) Contact-dependent
b) Paracrine
c) Synaptic
d) Endocrine

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11
Q

The signal cell produces a…

A

type of extracellular signal molecule that id detected by the target cell (specific receptors)

HUGE variety of signal molecules

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12
Q

What are Receptors?

A

target cells that specifically recognise the signal molecules

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13
Q

What range can signals act over?

A

long or short range

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14
Q

CONTACT-DEPENDENT signalling

A
  • a signal molecule binds to receptor on an interacting cell
    (interactions between immune cells - induce an immune response)
  • signals exchange via GAP junctions
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15
Q

ENDOCRINE signalling

A
  • Releases signals called HORMONES that travel through the bloodstream and act on receptors of target cells at distant body sites
    (insulin, produced by pancreatic B-cells, promotes the adsorption of glucose into liver, fat and skeletal muscle cells)
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16
Q

PARACRINE signalling

A

(act locally - short distance)
- released by cells into the extracellular fluid in their neighbourhood

(Nitric Oxide (NO), acts by relaxing smooth muscle cells around blood vessels, resulting in increased blood flow

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17
Q

SYNAPTIC signalling

A

-Specific signal’s (neurotransmitters) at specialised junctions (synapses) between nerve cells
-Neuronal signals are transmitted electrically along a nerve cell axon
-electrical signals into the synaptic space to reach receptors on adjacent target cells

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18
Q

AUTOCRINE signalling

A

Signals that act back on the secreting cell

-signalling cells secrete and extracellular signal that binds to receptors on the same cell (target cell)
- usually associated to a feedback response to self-regulate certain cellular processes (e.g protein secretion)

> CANCER cells, produce extracellular signals that stimulate their own survival and proliferation

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19
Q

Signal - receptor interaction

A
  • Receptors are proteins that recognise specific ligands (complementary shape) and medicate a response (cell changes/modifies activity)
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20
Q

What is a receptors role?

A
  • to respond to signal = cells need to possess a receptor for that signal
  • each receptor is usually activated by only one type (or a few) of signals
  • some signal molecules act a the cell surface whilst other inside the cell (steroids)
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21
Q

Types of receptors:

A
  1. Cell-surface receptors
  2. Intracellular receptors
22
Q

1-signal-receptor binding

A

Receptor is on target cell and the extracellular signal molecule binds with the receptor on the other side of the cytosol (bc the membrane is the cytosol’s membrane)

23
Q

What are intracellular receptors?

A
  • some receptor proteins are intracellular found in cytosol OR nucleus of target cells
24
Q

Intracellular receptor structure:

A

Small/hydrophobic signal molecules can readily cross the membrane and activate receptors

25
Q

Examples of intracellular receptors

A
  • steroids (cortisol, testosterone)
  • thyroid hormones (thyroxine)
26
Q

Type of membrane receptors:

A
  1. Ion channel-coupled receptors
  2. G portein-coupled receptors (GPCRs)
  3. Enzyme-coupled receptors
27
Q

Signal- receptor interaction ALWAYS induces…

A

conformational change of the receptor, that leads to the transmission of an intracellular signal

28
Q

Ion channel-coupled receptors

A
  • the receptor conformational change after binding to the signal activities an ion channel action as a gate for specific ions, changing the intracellular charge
  • converts chemical signals into electrical ones (nerve impulse conduction)
29
Q

G-proteins-coupled receptors (GPCRs) structue:

A
  • G proteins-linked receptors have a common structure = 2 components
30
Q

Which receptor is the largest class of cell-surface receptor?

A

G-proteins-coupled receptors (GPCRs)

31
Q

G protein-coupled receptors: structure broken down…

A
  1. trans-membrane receptor
  2. G protein (acts as an on/off switch)
32
Q

Trans-membrane receptor

A
  • crosses 7 times the plasma membrane
    -ligand binding site is on the extracellular
33
Q

G protein (acts like an on/off switch)

A
  1. On the cytosolic side of the plasma membrane
  2. 3 protein subunits-a,b,y
  3. a subunit is associated with GDP (inactive state)
  4. Ligand binding activities a subunit that exchanges GDP fro GTP (active state)
34
Q

GDP

A

Guanosine diphosphate

35
Q

GTP

A

Guanosine-5’-triphosphate

36
Q

GPCRs activation

A
  1. signal binds to receptor, which undergoes a conformational change
  2. This change attracts and activates a G-protein and its a subunit exchanges its GDP for GTP
  3. This allows the dissociation of the a subunit and By (beta/gama) complex
37
Q

GPCRs effect and inactivation

A

> Cell response
- Both a subunit and By (beta/gama) complex can interact and activate ion channels or membrane-bound enzymes involved in signal transduction

> Inactivation
- Hydrolysis of GTP by the a subunit inactivates the subunit and causes it to dissociate from the target protein

-inactive a subunit reassembles with By complex to re-form an inactive G protein

38
Q

Enzyme-coupled receptors

A

Similar to GPCRs, but the receptor cytoplasmic part either:

  1. acts as an enzyme itself (receptor tyrosine kinases, RTKs)
  2. or forms a complex with an enzyme
39
Q

RTKs

A
  • membrane receptors that attach phosphates to tyrosine amino
  • can trigger multiple signal transduction pathways at once

-stimulating cell growth and cell survival

-abnormal functioning of RTKs is associated with many types of cancers

40
Q

Enzyme-coupled receptors - how the work step-by-step:

A
  1. Ligand binding induces the pairing of 2 receptors (dimerisation)
  2. Intracellular receptor (kinases) phosphorylate each other’s specific tyrosines
  3. Phosphorylated tyrosine recruit different intracellular signalling proteins
  4. some become phosphorylated and activated (signal transductions) a process required to trigger and complex response such as cell proliferation or differentiation
41
Q

How is the effect reversed?

A

Phosphates removes the phosphates from the tyrosines

42
Q

2-Transduction step:

A
  • Multisteps to amplify a signal
  • Multistep pathways provide more opportunities for coordination and regulation
  • Different transaction strategies (phosphorylation cascade or 2nd messengers) for different pathways
43
Q

2- Protein phosphorylation cascade

A
  1. in many pathways, signal is transduced by a protein phosphorylation cascade
  2. This phosphorylation (by kinases) and dephosphoylation( by phosphates) system acts as a molecular switch, turning activities on and off
44
Q

2- Small molecules and ion as 2nd messangers

A

> The binding of an extracellular signal molecule to the membrane receptor activates enzymes, which is a pathway’s “first messenger”

> 2nd messengers can readily spread through cells to amplify the signal

45
Q

Composition/ structure of 2nd messengers:

A
  1. small, nonprotein, water-soluble molecules or ions
    >cAMP (cyclic AMP), cGMP (cyclic GMP), lipids, Ca^2+, NO (Nitrogen monoxside)
46
Q

What pathways do 2nd messengers participate:

A

Pathways initiated by:
- GPCR
- RTK

47
Q
  1. Example of 2nd messengers in GPCRs
A
  • Activation of some G-protein-linked receptors can activate a membrane-bound enzyme called ‘adenylyl’ cyclase that converts ATP to GMP

-cAMP exerts most of its effects by activating the enzyme cyclic-AMP-dependant protein kinase (PKA)

  • Activated PKA catalyses the phosphorylation of patricular PKA serines/threonines on specific target proteins (e,.g involved in the glycogen breakdown)
48
Q
  1. Example of 2nd messengers in GPCRs
A
  • Another membrane-bound enzyme associated to GPCRs in phospholipase C. Once activated, it cleave a lipid generating 2 small molecules called inositol triphosphate (IP3)
  • IP3, opens Ca^2+ channels in the endoplasmic reticulum to release Ca^2+ (2nd messenger in the cytosol

Ca^2+ activates many proteins triggering many biological processes

49
Q
  1. Cellular response
A
  • Cell signalling leads to regulation of one or more cellular activities
  • Regulation of gene expression (turning transcription of specific genes on or off) is a common outcome
50
Q

Different steps in cellular response:

A
  1. Reception = signalling molecule binds with receptor in the extracellular fluid
  2. Transduction = Relay molecules in transduction pathway
  3. Response = Activation of cellular response
51
Q

Examples of cell response:

A

a) CELL SURVIVAL

b) CELL DIVISION

c) CELL DIFFERENTIATION

d) CELL DEATH

PMP-101 (53 decks)

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