Gray (Cell signalling and communication) Flashcards
1
Q
Do all cells communicate?
A
- all communicate w/ each other
2
Q
What signals do cells send and receive?
A
- send and receive chem signals
- receive signal from env
3
Q
Why do cells communicate?
A
- coord activities to behave as group
4
Q
How many cells in human body
A
- 100 trillion
5
Q
What is the pathway taken from signal to response?
A
- signal
- reception (and amplification)
- transduction
- response
6
Q
What is signal transduction?
A
- info converted from 1 form to another
7
Q
What signalling molecules do cells use and why?
A
- use variety (usually not involved in metabolic pathway)
- eg. proteins, mod AAs, lipids
- as quick to make and destroy
8
Q
How are signalling molecules released from signalling cell?
A
- diffusion or exocytosis
9
Q
What are the types of 1st messengers or ligands?
A
- hormones (long distance)
- local mediators
- neurotransmitters
- contact dependent signals
10
Q
What chemical signals do cells respond to?
A
- 1st messengers or ligands
11
Q
What is a signalling molecule/ligand?
A
- small molecule that binds to site on macromolecule surface by intermolecular forces
12
Q
What happens when ligand binds to receptor molecule?
A
- changes specific receptor molecule
13
Q
Types of intercellular signalling
A
- endocrine
- paracrine
- neuronal (specific type of paracrine)
- contact dependent signals
14
Q
How does endocrine signalling work?
A
- signal molecule released (hormones)
- collected and distributed via blood in animals
- only cells w/ receptors respond
- response depends on cell
15
Q
Examples of endocrine signalling (hormone, released from, type of molecule, effects)
A
- adrenaline, released from adrenal gland, Tyr derivative. increases blood pressure, heart rate and metabolism
- insulin, pancreas, protein, stimulates glucose uptake and synthesis of proteins and lipids
- testosterone/oestrogen, testes/ovaries, steroid, induces and maintains 2º male/female sexual characteristics
16
Q
How does paracrine signalling work?
A
- molecules released and responded to by neighbouring cells
17
Q
Examples of paracrine signalling (hormone, released from, type of molecule, effects)
A
- epidermal growth factor, various cells, protein, stimulates epidermal and many other cell types to proliferate
- histamine, mast cells, His derivative, blood vessel dilation and become leaky, helping cause inflammation
- NO, cells lining blood vessels, dissolved gas, causes smooth muscle cells to relax
18
Q
How does neuronal signalling work?
A
- neurons prod and release neurotransmitters into synapse, close to target cells
19
Q
Example of neuronal signalling (hormone, released from, type of molecule, effects)
A
- ACh, nerve terminals, choline derivative, neurotransmitter at many nerve-muscle synapses and in CNS
20
Q
Example of how the same signalling molecule can induce diff responses in diff target cells?
A
- ACh
- decrease freq contraction in cardiac muscle cells
- secretion in salivary gland cells
- contraction of skeletal muscle cells
21
Q
How does contact dependent signalling work?
A
- molecules of plasma membrane bind in specific ways
- eg. cell interactions in early dev
22
Q
Example of contact dependent signalling (hormone, released from, type of molecule, effects)
A
- delta, prospective neurons and various other embryonic cell types, transmembrane protein, inhibits neighbouring cell from becoming specialised in same way as signalling cell
23
Q
What is the flow of info during cell signalling?
A
- receptor-ligand binding
- signal transduction (via 2nd messenger)
- cellular responses
- changes in gene expression
24
Q
How can receptor proteins only respond to subset of signals surrounding them?
A
- receptor-ligand interactions specific
- signals cell can respond to determined by receptor proteins it has
- ignore signals it doesn’t have receptor for
25
Are all receptors enzymes?
- all are proteins
- some have enzyme activities
- some affect enzymes indirectly
- some affect gene expression
26
What are receptor molecules?
- signal transducers
| - 3D shape
27
What type of interaction occurs between receptor and ligands?
- non-covalent
28
What can receptor-ligand interactions cause?
- may induce shape change in receptor protein
| - results in intracellular response
29
Do receptor molecules need to be high affinity and why?
- yes as many concs are v low
30
How are receptor protein genes grouped?
- many grouped into families
31
What is an orphan receptor protein gene?
- when function is unknown
32
In what way do cell surface receptors convert signals and how?
- convert extracellular to intracellular signal
| - by inducing change in cyto
33
What are the 3 major classes of cell surface receptors?
- ligand gated ion channels
- receptors w/ enzyme activity
- G-protein coupled receptors
34
Where can receptors be located?
- intracellular
| - on cell surface
35
What is an intracellular response?
- signal passes through target cell plasma membrane
36
How does an intracellular receptor w/ enzyme activity work, using the example of NO(g)?
- NO binds to enzyme
- activated enzyme catalyses synthesis of cyclic GMP
- relaxes smooth muscle surrounding blood vessels
- blood vessels expand, increasing blood flow
- prod in endothelial cell lining blood vessel and diffuses into target cell
- NO release by nerve terminals causes erection
37
How does Viagra work?
- inhibits cGMP conversion to GMP
38
Example of an intracellular receptor regulating gene transcrip
- steroid hormone receptor family
- signal molecule binds to site on receptor
- activated receptor complex enters nucleus
- binds DNA and alters gene expression
39
How do ligand gated ion channels work?
- receptor is transmembrane protein
- winds across plasma membrane several times
- centre forms pore which ions can pass through
- opens and closes when ligand bind to protein
40
Example of a ligand gated ion channel
- ACh receptor
41
How do receptors w/ enzyme activity work?
- single pass transmembrane protein
- signal molecule binds outside cell, activating enzyme
- part w/ enzyme activity in cyto
42
What kind of enzyme are most receptors w/ enzyme activity, and what do they do?
- most protein kinases and add phosphates to proteins
- receptor kinases act as dimers
- phosphorylation of AA side chains affects enzyme activity
- can often activate other kinases --> cascade
43
How are receptor kinases activated?
- dimerisation and transphosphorylation
44
How do G-protein coupled receptors work?
- 7 pass receptors
- ligand binding activates G-protein, causing it to bind GTP
- activated G-protein diffuses away from receptor and affects activity of effector enzyme
45
What class of cell surface receptors are involved in half the mechanisms of medicines in use?
- G-protein coupled receptors
46
What do G-protein coupled receptors mediate responses to?
- diverse responses to hormones, local mediators and neurotransmitters
47
In what senses are G-protein coupled receptors found?
- odorant and vision receptors
48
How does the receptor kinase downstream signalling pathway work?
- ligand binding leads to receptor dimerisation
- phosphorylation of cytosolic Tyr residue
- other proteins recognise and bind Tyr
- activates intracellular signalling pathways, eg. kinase cascades, 2nd messenger release
49
What happens when the Ras GTPase switch is on?
- GTP bound
- receptor activation causes Ras to bind GTP
- Ras-GTP activates specific kinases which activate kinase cascades
- leading to cell proliferation
50
What happens when the Ras GTPase switch is off?
- GDP bound
- Ras GTPase activity hydrolyses GTP
- cascade req ATP
51
What do signalling cascades result in?
- amplification of response
52
What are intracellular responses a response to?
- receptor-ligand binding
| - inc protein phosphorylation, Ca release, cAMP
53
What do intracellular responses cause changes in?
- enzyme activity
- gene expression
- cytoskeleton
54
How does phospholipase C lead to release of Ca in intracellular response?
- phospholipase C (PLC) activated by receptor (either G-protein coupled or receptor kinase)
- phospholipase C cleaves membrane phospholipid to prod diacylglycerol (DAG) and inositol triphosphate (IP3)
- IP3 is 2nd messenger and binds to receptors on internal membranes and releases Ca
55
How does Ca2+ affect enzyme activity?
- rushes into cyto when Ca channels opened
- increasing conc affects Ca activated proteins, eg. calmodulin
- activated calmodulin activates other proteins, inc kinases
56
Why is Ca released on fertilisation?
- trigger egg activation
| - resumption of metabolic processes leading to embryo dev
57
How do G-protein coupled receptors activate effector enzymes that prod 2nd messengers?
- PLC catalyses IP3 prod
- adenylate cyclase catalyses cAMP prod
- PLC also activated by GPCRs, many GPCRs activate cAMP prod
58
What are cAMPs mediated responses?
- cAMP mainly acts by activating certain protein kinases
| - in most cells boosts energy release
59
What do signalling networks look like?
- pathways interact
| - not straight lines
60
What can mutant forms of Ras do, and where is this found?
- mutant forms of Ras can bind GTP but can't hydrolyse it
| - found in many human tumours
