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GMC > Block 3 - environmental perception > Flashcards

Block 3 - environmental perception Flashcards

1
Q

why is environmental perception particularly important in plants

A

because they cant move

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2
Q

describe autocrine signalling

A

cells detect a signal they produce e.g. metabolite

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3
Q

describe juxtacrine signalling

A

where adjacent cells initiate responses by direct contact

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4
Q

describe paracrine signalling

A

cells detect local signal from neighbouring cell e.g. neurotransmitters

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5
Q

describe endocrine signalling

A

cells detect a signal secreted by distant cells e.g. hormones

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6
Q

what connects stimuli reception to responses

A

signal transduction

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7
Q

what is a stimuli

A

something that initiates a response through signalling e.g. physical, adjacent cells, external chemicals, internal metabolites or hormones, small molecules, peptides, gases etc

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8
Q

why do we need a range of stimulus receptors

A

because there is a range of stimuli

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9
Q

give examples of some responses to stimuli

A

physical movement
physiological and behavioural changes
differential gene expression

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10
Q

some receptors require a cofactor, give an example

A

chromophore for light detection - the cofactor detects the light stimulus

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11
Q

some receptors associate with the PM in order to regulate ………… ……………. activity which can change ion concentration and activate downstream proteins

A

ion channel

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12
Q

receptors activation can stimulate enzymes associated with the receptor. in what 2 ways can a kinase for example be associated with a receptor

A

it can either be an intrinsic kinase or an independent kinase that is recruited to the receptor

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13
Q

signalling often amplifies the response level relative to the ………. ……………

A

stimulus magnitude

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14
Q

describe protein kinase cascades

A

phosphorylate numerous target proteins and amplify the response. massive amplification

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15
Q

what is desensitization

A

it enables cells to avoid excessive responses. receptor activation may lead to negative feedback that switches off the receptor or removes it from the cell. a signalling component feeds back onto the receptor

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16
Q

why would continual response to a stimulus be a problem

A

it can damage the cell and it uses valuable resources

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17
Q

give an examples of how responses to stimuli are prioritised

A

priority may be given to pathogen stimulus

there is crosstalk between signalling pathways

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18
Q

the activity of one receptor can change the activity of another …………..

A

receptor

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19
Q

give some outcomes of defects in reception or signalling

A

impair metabolism or development

cause disease e.g. cancer, diabetes, endocrine diseases

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20
Q

how does reception and signalling have application in drug design

A

in making inhibitors/activators and modifying pathways and in synthetic biology e.g. optogenetics

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21
Q

give 2 examples of a receptor where stimulation activates ion channels that give rise to a response

A

channelrohodopsin activated by light or the nicotinic acetylcholine receptor involved in neural transmission

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22
Q

describe channelrohodopsin main function

A

it is a light activated ion channel that functions in phototaxis of unicellular green algae e.g. Chlamydomonas

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23
Q

describe channelrhodopsin structure

A

it has one subunit and is a 7 TM protein (7+M spanning helices) that forms an ion channel in the PM. it is the photoreceptor and the ion channel

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24
Q

how do Chlamydomonas respond to a light stimulus

A

they move towards it to increase photosynthesis

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25
Q

how many channelrohodopsins does Chlamydomonas have

A

it has 2 - they are both non specific cation channels and have slightly different ion specificities

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26
Q

what is channelrhodopsin gated by

A

light

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27
Q

what s the channelrohdopsin chromophore (cofactor that detects light) called

A

retinal

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28
Q

what happens when retinal of channelrhodopsin is excited by light

A

it generates a conformational change in the channel due to isomerisation of retinal resulting in an influx of ions
retinal changes from all trans to 13 cis retinal

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29
Q

what is the maximal absorption for retinal in channelrhodopsin

A

480nm

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30
Q

after opening of channelrhodospsin the channel quickly closes, what causes this

A

retinal returns to its all trans form

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31
Q

channelrhodopsin is similar to rhodopsin used in visual photoperception but what is a key difference between them

A

rhodopsin isn’t an ion channel

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32
Q

describe the structure of the nicotinic acetylcholine receptor

A

it has 5 subunits - beta, gamma, sigma and 2 alpha that bind acetylcholine
each subunit has 4 membrane spanning helices
the ligand binding sites are in the extracellular face of the subunit
the 5 subunits are arranged around a central channel

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33
Q

what is the ligand for the nicotinic acetylcholine receptor

A

acetylcholine or nicotine

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34
Q

what happens when the ligand binds to the nicotinic acetylcholine receptor

A

there is a conformational change that opens the channel to Na and Ca

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35
Q

what happens to the nicotinic acetylcholine receptor experiences prolonged ligand exposure

A

there is a conformational change that prevents ligand binding and channel opening - desensitisation

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36
Q

what do neurotoxins do to the nicotinic acetylcholine receptor

A

they cause receptor inactivation and hence paralysis

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37
Q

give 3 examples of receptors that have enzymatic activity (protein kinase activity that is activated on receptor activation)

A
  • bacterial-2-component histidine kinase
  • mammalian growth factor TGF beta signalling and its ser/thr kinase receptor
  • tyrosine kinase signalling - insulin receptor
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38
Q

how do bacteria move toward or away from a stimulus

A

they use their flagella

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39
Q

what are 2 component systems

A

they comprise a receptor histidine kinase that detects the stimulus and a response regulator that initiates the response

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40
Q

describe the receptor histidine kinase of the bacterial 2 component system

A

it is located on the cell membrane and has a ligand binding domain on the external surface which binds e.g. sugars or amino acids

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41
Q

what happens to the bacterial 2 component system when the ligand binds

A

the kinase activity is activated in an internal domain of the receptor causing autophosphorylation of a histidine amino acid. the receptor histidine kinase relays the phosphoryl group onto an aspartate amino acid of the second component, a cytosolic protein called the response regulator which then initiates the response e.g. regulates flagella movement or gene expression

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42
Q

why does phosphatase need to dephosphorylate the response regulator of the bacterial 2 component system

A

so that it is ready to activate again in response to a new stimulus

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43
Q

2 component systems are common in prokaryotes and less common in yeast. what is the exception to this

A

plants and yeast

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44
Q

what is TGF beta

A

a type of cytokine. it is part of a super family of related proteins with diverse and important functions including regulating growth, regulating cell division, immunosuppression, cell differentiation, dorsal/ventral specification etc

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45
Q

how many TGF beta isotypes are there in animals

A

3

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46
Q

by what type of signalling does TGF beta act

A

through paracrine signalling

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47
Q

describe TGF beta synthesis and secretion

A
  1. protein synthesised with a signal peptide and the N terminus which targets it to the ER, and is removed by proteolytic cleavage during translation and translocation into the ER
  2. the protein is secreted as a proprotein - the propeptide domain blocks ligand activity (ligand is never released in its active form inside the cell)
  3. the propepetide is removed by proteolytic cleavage outside the cell releaseing mature TGF beta ligand
  4. the mature ligand is able to initiate signalling by binding to adjacent cells expressing a TGF beta receptor on their surface
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48
Q

describe the TGF beta receptor structure

A

it is a TM protein with ser/thr kinase
it is a heterotetramer - made from 2x type 1 and type 2 receptor
type 1 has ser/thr kinase activity
type 1 molecules become phosphorylated by type 2
the receptor can bind 2 TGF beta molecules

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49
Q

what happens to the TGF beta receptor when TGF beta binds

A

binding of extracellular dimeric TGF beta ligand to a type II receptor causes it to bind to and phosphorylate a type I receptor, activating it

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50
Q

what are the detailed steps in TGF beta signalling

A
  1. TGF beat binding causes type II receptor to phosphorylate type I
  2. phosphorylated TGF beta type I receptor recruits and phosphorylates SMAD2 or SAMD3 proteins which are signalling proteins and TFs for TGF beta signalling
  3. phosphorylated SMAD2 or 3 dissociates from the receptor and binds to SMAD4. get heterodimer of SMAD4 with SMAD 2 or 3
  4. the SMAD2/3 - SMAD4 complex activates transcription of target genes in the nucleus. it translocates to the nucleus and recruits other proteins that together promote transcription
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51
Q

why are TGF beta recpetor mutations common in cancer

A

many tumours contain inactivating mutations in TGF beta receptors or SMAD proteins making them resistant to TGF beat growth inhibition

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52
Q

name a signalling pathway that recruits a kinase that then initiates a signalling pathway

A

JAK/STAT signalling

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53
Q

what is the role of JAK/STAT signalling

A

it is involved in the regulation of transcription by regulatory cytokines e.g. RBC formation stimulation by cytokine EPO

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54
Q

when and where is EPO secreted

A

it is secreted by the kidney in response to hypoxia in the cellular environment

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55
Q

what happens when EPO binds to its PM receptor

A

it causes the receptor to dimerise. the receptor then binds the soluble protein kinase JAK. JAK is activated and phosphorylates tyrosine amino acids on the cytoplasmic domain of the receptor. STAT TFs bind to the p-tyr residues of the receptor via the SH2 domain (part of STAT). STAT is now positioned to be phosphorylated on tyrosine amino acids by JAK. phosphorylated STAT is released from the receptor, forms dimers and translocates to the nucleus where it binds to regulatory sequences to stimulate transcription of genes required for RBC maturation

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56
Q

give an examples where ligand/receptor binding activates transcription

A

steroid hormone signalling e.g. estradiol

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57
Q

what is estradiol

A

it is an estrogen steroid hormone that regulates reproductive cycle and development. it is mainly produced in the follicles of the ovaries. estradiol levels change during the menstrual cycle and get lower after menopause. the levels peak prior to ovulation

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58
Q

what is estradiol synthesised from

A

it is synthesised from cholesterol

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59
Q

why is estradiol carried in serum bound to a carrier protein e.g. serum albumin

A

it is relatively insoluble due to being a lipophilic molecule.

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60
Q

estradiol can pass through the membrane due to being small and …………. ………..

A

lipid soluble

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61
Q

describe the estradiol receptor and its role

A

it is an intracellular estrogen receptor which binds estradiol in the cytosol then dimerises and is translocated to the nucleus, activating as a TF

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62
Q

describe the estradiol receptor structure and what happens to the structure when it binds estradiol

A

there are 2 estrogen receptor proteins, alpha and beta, and each binds a molecule of estradiol. the receptor can be a homodimer or a heterodimer and they have different effects on transcription
the dimer/estradiol complex is specific to a DNA sequence, the estrogen response element, to initiate transcription.

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63
Q

what happens when estradiol binds to the estrogen receptor

A

estradiol binding –> receptor conformation change –> association with cofactor proteins and binding to regulatory sequences of target genes

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64
Q

what are many of the genes regulated by estradiol involved in

A

cell growth and division

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65
Q

why do different cell types respond differently to estradiol

A

because cells differ in the type of receptor and level of expression. the coactivators required can also be differently expressed

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66
Q

why is the estradiol signalling pathway relevant to breast cancer

A

estrogen regulates breast cell proliferation. many tumours have increased estrogen receptor expression and proliferate rapidly in the presence of estradiol. tamoxifen blocks estrogen receptors

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67
Q

how does tamoxifen work

A

it is a competitive inhibitor of estradiol binding. it causes an allosteric change which makes the receptor non functional. helix 12 conformation changes such that the receptor becomes inactivated

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68
Q

give 2 examples where a receptor functions in conjunction with a G protein (GPCR)

A

adenylate cyclase/cAMP signalling

vision

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69
Q

give an example where direct interaction between adjacent cells via surface components initiates signalling

A

delta/notch signalling

integrins

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70
Q

do tidal and circadian rhythms persist in constant lab conditions and explain

A

yes - they are driven endogenous clock mechanisms, not external environment changes. the rhythms are thought to be Darwinian fitness benefits

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71
Q

annual rhythms result from interplay between the …………… …………. and ….. …… that affect reproductive hormones

A

circadian clock

day length

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72
Q

what are some circadian rhythm properties

A

persist in constant conditions, period - 24h, phase can be reset by zeitgebers (light, temperature) which ensures synchronisation with the solar day, show temperature compensation (not affected by temperature)

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73
Q

clocks are found in all eukaryotes/prokaryotes and some eukaryotes/prokaryotes

A

all eukaryotes

some prokaryotes

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74
Q

what is entrainment

A

the process by which an oscillator is synchronised to an environmental rhythm such as light/dark or warm/cold cycles

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75
Q

give examples of things that can be used to monitor rhythms

A

wheel running

promoter-reporter fusion

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76
Q

what methods can we use to identify clock components

A

mutagenesis - isolation of mutants with altered circadian period etc
cloning of relevant genes

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77
Q

what is an actogram

A

a plot of mouse activity

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78
Q

describe the process of promoter-reporter fusions

A

promoter - DNA sequence upstream of the genes that controls the gene’s expression
- fuse promoter to reporter (e.g. luciferase) then introduce to cell or organism. luciferase protein is synthesised rhythmically and emits flashes of light

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79
Q

using promoter-reporter fusions what has been identified about the perception of time in Arabidopsis

A

perception of time is transferred from mother to daughter cells

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80
Q

describe the central oscillator principle: negative feedback with a delay

A
  • component inhibits its own formation after a delay to get a rhythm
  • component must turn over rapidly so that it disappears by the end of the oscillation
  • there must be machinery to kickstart formations of the component again after it has disappeared
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81
Q

anything involved in a circadian rhythm needs to have a half life of less than a day - why

A

so that it can be formed and disappear in one day

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82
Q

describe gene expression negative feedback loops

A

protein A inhibits its own synthesis by inhibiting a positive TF. rate of destruction of protein A and its mRNA must be fast
the time to get transcription regulation represents the delay

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83
Q

which gene has been found to be one of the most important in controlling the circadian rhythm

A

period gene

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84
Q

how have most circadian clock genes been identified

A

using sequence similarities with drosophila genes

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85
Q

what is the role of the per and cry genes

A

they produce per and cry proteins. per and cry mRNA oscillates and so do the proteins, they are all short lived. the per/cry complex forms in the cytosol and moves into the nucleus after a delay o inhibit expression of per and cry genes

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86
Q

what does the clk/bmal1 complex do

A

it can restart expression of per and cry. it is a TF that binds to the Ebox and E’box which are found in the promoters of per and cry and other genes. binding at these sites promotes transcription by changing chromatin structure

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87
Q

how does ckl1 control per

A

it controls accumulation of cytosolic per during the day by phosphorylating it . this leads to destruction of per (marked by ubiquitin and destroyed by the proteasome)

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88
Q

name 5 circadian clock genes and their corresponding proteins

A 
period - per 
clock - clk
cryptochrome - cry
BMAL1 - bmal1
CK1E - ck1
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89
Q

describe the mouse circadian clock in a flow chart

A

dawn –> per/cry complex in cytosol and mRNA levels peak –> per/cry entering nucleus and mRNAs falling –> per/cry all in nucleus - mRNAs absent –> dusk –> per/cry being destroyed –> per/cry low –> per, cry mRNA synthesis started by CLK/BMAL1

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90
Q

what is CLK

A

it is a histone acetyl transferase that acetylates histones in nucleosomes

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91
Q

what happens when the per/cry complex interacts with the ckl/bmal complex

A

it blocks transcription by recruiting a histone deacetylase

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92
Q

why are many of the clock controlled genes transcription activated by clk/bmal1

A

because they have E or E’ boxes in their promoters

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93
Q

mammals have a master clock - what is this and what is the evidence

A

it is located in the brain suprachiasmatic nucleus (SCN)

SCN transplant changes the period to that of the donor in mice

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94
Q

major organs have the same clock genes, usually running in the same ………….

A

phase

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95
Q

describe how some of the clock outputs are particular to specific tissues

A

heart - diurnal variations in cardiac electrical properties and metabolism
skin - skin cells boost DNA repair and do DNA synthesis of growth cycle at night

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96
Q

how can rhythms in the liver be reset

A

by feeding

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97
Q

what can circadian misalignment cause

A

many issues including metabolic diseases

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98
Q

how can light interrupt the phase in light sensitive animals

A

for animals in a light dark cycle, a pulse of light in the early night results in a phase delay. a light pulse in the late night gives a phase advance

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99
Q

how is the eye connected to the SCN

A

by the retinohypothalmic tract

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100
Q

light activates the expression of ……. genes. the photoreceptor (…………….) absorbs light in intrinsically photosensitive retinal …………… cells and sends signal to the SCN which leads to creb ………… and clock regulation

A

per
melanopsin
ganglion
phosphorylation

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101
Q

why are blue light filters important

A

exposure to blue light in the evening will increase per expression and delay sleep (phase delay). exposure later in the night enhances the rise (phase advance

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102
Q

the clock and day length control flowering by the level of ..………… protein

A

constance

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103
Q

describe 4 plant activities which are controlled by the circadian clock

A
  • leaf movements - optimizes light capture - low in the morning/night and raised in the middle of the day
  • stomatal opening and closing - allows gas exchange during the day but not at night generally
  • expression of genes encoding light harvesting proteins - need to be expressed late at night every day
  • hypocotyl extension
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104
Q

name 2 circadian associated processes in plants

A

photoperiodic flowering in plants and tuberisation in potatoes

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105
Q

what is the Linnaeus flower clock

A

schematic showing that different plants open at different times of the day

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106
Q

what are the key genes/proteins in the Arabidopsis circadian clock

A
  • CCA1 and LHY are a both dawn expressed TFs that bind to the evening element which can inhibit expression of some genes and activate others
  • pseudo response regulators - DNA binding proteins expressed between morning and evening
  • the evening complex (ELF3, ELF4 and LUX) expressed at dusk and early night
  • GI (gigantean) - drives expression of CO which is an output gene that controls flowering
  • CRY1 and CRY2 (cryptochromes) absorb blue light - they are not part of the clock itself but are part of the input pathway by which the light absorbed affects the clock
  • a gene expressed in the evening or at night is repressed by CCA1 and LHY during the day
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107
Q

the Arabidopsis clock is more complex than the mammalian clock but has the same principle which is

A

feedback with delay

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108
Q

what does the fact that the Arabidopsis and mammalian clock components are different tell us

A

that they evolved separately

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109
Q

describe how the plant clock is involved in flowering

A

LHY and CCA1 go up and inhibit EC expression, the EC therefore goes down so PRR expression goes up. PRRs inhibit CCA1 and LHY so we get overall negative feedback (look at triangle diagram in notes)

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110
Q

what 3 types of plants do we get in terms of flowering time

A

long day, short day and day neutral

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111
Q

chyrsantheums and rice are long/short day plants

A

short

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112
Q

under long days, chrysanthemums grow ………. then they are grown in short days just before they are needed and they will ……………..

A

vegetatively

blossom

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113
Q

in flowering, ……… protein is produced in leaves in response to CO and acts at the ………. ………. ……………

A

FT

apical shoot meristem

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114
Q

list some factors that affect flowering time

A 
clock 
temperature
environmental factors 
sugars
endogenous factors 
GA etc
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115
Q

is Arabidopsis a long day or short day plant

A

long day

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116
Q

plants sense the length of the light/dark period using the circadian clock

A

dark

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117
Q

what is vernalisation

A

when some plants need a cold period before they flower

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118
Q

what is the GI mutant

A

a late flowering plant mutant - grows much larger than WT before flowering

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119
Q

how is FT expression controlled

A

it is controlled by the level of CO protein via the circadian clock and also by vernalisation via FLC

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120
Q

what is the action of CO in long day plants

A
  • CO is stabilised by light and activates FT expression
  • CO is antagonised by FLC, hence FLC inhibits flowering
  • exposure to cold reduces expression of FLC and allows flowering
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121
Q

what is the action of CO in short day plants

A

CO inhibits FT production instead of activating it

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122
Q

what are the steps in controlling flowering time in Arabidopsis

A
  • the circadian clock drives expression of G1 in the evening/night which drives coexpression –> FT production and flowering
  • in a plant that requires vernalisation, FLC levels are high until the plant is exposed to cold. FLC can block the effect of CO on FT expression but vernalisation will reduce FLC expression so flowering is allowed
  • sunlight is required by CRY2 to stabilise CO - without CO expression we don’t get flowering
    (see extended triangle diagram)
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123
Q

why do CO and FT only accumulate in long days and what does this mean for flowering

A

because CO is stabilised by light - if they only accumulate in longs days we will only see flowering in long days
CO rises towards Zt 10 or 12, reaches its peak then falls again

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124
Q

at critical night length why don’t short day plants flower and why are long day plants different

A

only get CO message in dark and as a result we get no CO protein because it is unstable in the dark
no FT and no flowering
in long day plants the CO message occurs when it is still light so CO is stabilised and we get FT and flowering

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125
Q

describe the sheep annual reproductive rhythm

A

sheep become fertile in autumn and lambs are born in spring due to the melatonin peak being much longer in short days than long days
long duration of melatonin reduces cAMP which affects the expression of circadian clock genes
per and cry expression overlaps in summer but in winter one is expressed earlier than the other (qualitative and quantitative differences in the transcriptome in winter vs. summer)
the gene for TSH is expressed more in spring/summer than autumn/winter –> seasonal hormone changes –> reproduction control

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126
Q

list some human implications of the circadian clock

A
  • shift work - circadian misalignment - associated with increased BMI, T2D, metabolic syndrome (can be rescued with restricted feeding time in mice), stroke, heart attack risk increased
  • sleep disorders
  • ageing - clock becomes less robust with age
  • social jetlag - weekend behaviour patterns
  • clock controls DNA repair - shift work has been described as a carcinogen
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127
Q

describe the sleep disorder FASPs

A

familial advanced sleep phase syndrome results from mutations that alter phosphorylation of hPER2 which affects hPER2 turnover rate and can shorten circadian period. in normal diurnal conditions, a short circadian period leads to a phase advance - the clock is reset by light every dawn but gets to the end of the cycle before the next dawn
one with FASPS is active in the first part of the day but sleeps very early and wakes up at 2am - very short circadian period

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128
Q

what are the 2 types of mutations that cause FASPS

A
  1. hPER2 - ser662 –> glycine (cant be phosphorylated)
  2. CKI gene (controls phosphorylation). thr44 needs phosphorylated to be active but is mutated to alanine which is not phosphorylated –>CKI inactive –> PER not phosphorylated –> FASPS
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129
Q

what is the chronotype

A

mid time of sleep on free days with no social interaction

130
Q

younger people have higher/lower chronotypes than older people

A

higher - why we don’t like 9ams

131
Q

the further east the higher/lower the chronotype

A

lower

132
Q

how does sildenafil work in jetlag

A

it accelerates re-entrainment of circadian rhythms after advancing light schedules

133
Q

how does sildenafil work in penile function

A

it is the same as Viagra. it inhibits cGMP phosphodiesterase and therefore elevates the level of cGMP in target tissues –> smooth muscle relaxation –> increased blood flow –> erection enabled

134
Q

does sildenafil work for a phase delay

A

no it only works for a phase advance - it elevates cGMP in the SCN allowing re-entrainment

135
Q

CO drives flowering in long/short days plants but prevents it in long/short day plants

A

long

short

136
Q

Ca exerts ……… regulatory effects on many enzymes and proteins

A

allosteric

137
Q

what is the resting Ca concentration in the cytosol and how does this compare to the extracellular concentration

A

100nm

much lower than the extracellular concentration

138
Q

what is meant by an allosteric affect

A

binding –> conformational change –> change in activity

139
Q

name some processes dependent on Ca

A

muscle contraction
neuron transmission
cell motility
fertilization etc

140
Q

describe the plasma membrane Ca ATPase (PMCA)

A

ATP dependent pump which actively pumps Ca out of the cell

141
Q

apart from PMCA how else can ATP be moved out of the cell

A

by coupling it to the downhill movement of Na. Ca moves against the gradient and Na moves in the direction of the gradient

142
Q

define symport and antiport transport

A

symport - molecules go in the same direction

antiport - molecules go in the opposite direction

143
Q

describe the ER

A

it forms an interconnected network of flattened, membrane enclosed sacs or tube like structures known as cisternae. it is continuous with the outer nuclear membrane

144
Q

in plants where else can Ca be stored other than the ER

A

the vacuole

145
Q

Ca is pumped in from the cytosol to the ER by ………….., an ATPase

A

SERCA

146
Q

what happens when Ca enters the ER

A

it binds storage proteins (calsequestrin) so that high Ca concentrations can be achieved. each protein binds ~40 Ca allowing for high concentration in the ER which enables steep [Ca] gradients

147
Q

what is the function of Ca channels

A

they allow for rapid concentration change (many ions can flow through in a short period) due to steep gradients

148
Q

what is faster, Ca channels or antiporters

A

channels - Ca is pumped out more slowly than it is allowed in

149
Q

some GPCRs trigger elevations in Ca, what is this mediated by

A

it is mediated by causing transient opening of a Ca channel in the ER

150
Q

Ca signalling can be activated by ……….. …………. …….

A

protein kinase C

151
Q

describe the key features of GPCR signalling

A

a key feature is activation by phospholipase C by a GTP-binding protein (G protein).
the signal is received by GPCR and the activated G protein subunit activates phospholipase C triggering amplification. phospholipase c breaks down phosphatidylinositol 4,5 bisphosphate into DAG and inositol 1,4,5 trisphosphate (IP3) which activates PKC. due to the conformational change by allosteric modification IP3 opens the ion channel in the ER. the released Ca into the cytosol binds to and activates PKC. Ca and DAG activate PKC

152
Q

what is the difference between tri and tris phosphate

A

tri - 3 phosphates arranged in series

tris - 3 phosphates arranged different

153
Q

describe the basic structure of the PKC family

A

regulatory domain - N terminal, pseudo substrate domain, C1A and C1B, C2, V3 hinge
catalytic domain - kinase domain, C terminal

154
Q

what happens when Ca and DAG bind to the PKC

A

they induce conformational changes that activate the kinase domain leading to signal transmission

155
Q

what does Ca do to PKC

A

it binds to C2 and changes the PKC shape and encourages its binding to the PM by linking the negatively charged lipid-phosphatidylserine

156
Q

what does DAG do to PKC

A

it binds to C1B causing further conformation change and the kinase then activates and is localised to the PM
it also pulls all the other domains away from kinase so it can performs its catalytic activity

157
Q

are both DAG and Ca required for PKC activation

A

yes

158
Q

why does the PKC kinase need to become membrane localised

A

because DAG is membrane localised

159
Q

what is the pseudo substrate peptide

A

it is a peptide that when sitting in the chain, the whole protein is inactive

160
Q

describe beta cell vesicle exocytosis

A

insulin vesicles are released in response to increased blood glucose
glucose entry changes the ATP/ADP ratio which closes an ATP sensitive channel leading to membrane depolarisation and opening of voltage gated Ca channels and an influx of Ca from the ER or extracellularly. this leads to fusion of the insulin vesicles with the PM and they release their con\tent

161
Q

describe how Ca channels are involved in neural transmission

A

Ca voltage gated channels are opened by depolarisation signal which is sent along the neuron causing the synaptic vesicles to fuse with the PM, releasing neurotransmitter. this results in a very quick response

162
Q

describe the molecular changes to the Ca channel on opening

A
  • in the closed state the molecules are twisted together

- upon opening there is a change from isoleucine –> glutamine which are negative, allowing Ca to pass through

163
Q

Ca channel blocker and ACE inhibitors are very common prescriptions for …………..

A

hypertension - they slow the heart beat so that the left ventricle fills completely. heart workload is reduced which reduces arterial constriction and lowers bp

164
Q

can drugs target selectively for particular Ca channels

A

yes

165
Q

how does verapanul act

A

plugs pore preventing Ca entry

166
Q

how does amlopdipine act

A

remodels channel from outside so Ca lodges inside and prevents conformation change and channel opening

167
Q

how can we monitor Ca changes

A

FRET

168
Q

describe FRET

A

we need 2 different fluorescent proteins - CFP (blue) and venus (yellow). CFP is excited at 405nm causing it to emit fluorescence at 447nm. the 2 proteins have spectral overlap. venus can be activated by light from CFP if within 10nm of each other. we can create a construct with 2 fluorescent proteins connected by a hinge molecule which can change its conformation dependent on a Ca signal. when Ca is present the proteins are brought together and we get FRET transfer –> yellow light emitted. we can calibrate the system to measure Ca concentration in cells

169
Q

explain the time differences between insulin secretion which only takes a few seconds and signalling via PKC to takes hours

A

PKC signalling results in a change in gene expression which takes longer

170
Q

what is phosphorylation

A

a type of reversible covalent modification involving the transfer of gamma P from ATP onto a protein

171
Q

what is the difference between motifs and domains

A

motifs tend to suggest functional characteristics and are found within domains. domains tend to relate more to structural units

172
Q

which kinases are the best studied

A

ser/thr and tyrosine kinases are best studied. there are also histidine kinases but these are rare

173
Q

how is kinase involved in blood glucose control

A

PKA phosphorylates glycogen synthase switching it off and glycogen phosphorylase switching it on in response to glucagon. we see a 3 kinase pathway. the first kinase activates the second, second activates the third which phosphorylates glycogen and breaks it down. we see huge amplification

174
Q

when the R2C2 complex dissociates is the catalytic subunit immediately active

A

no

175
Q

where in PKA does ATP sit

A

in the active site

176
Q

what is the kinase mechanism that is conserved across all kinases

A
  1. ATP binds the active site, substrate binds at the active sites
  2. gamma P is transferred from ATP to ser/thr/tyr
  3. substrate released from the kinase and so is ADP
177
Q

describe the kinase conserved sequence motifs and differences

A
  • most have GxGxxGx. they all have the gate keeper lysine and the DGF motif
  • some kinases have greater distance between motifs than others and motif position in linear sequence is not always indicative of 3D structure
  • DGF and gate keeper always end up in the same position in the active site maintain catalytic function
  • the substrate and binding site are particular to the target protein
178
Q

describe how kinases can be activated by removing the activation loop and unmasking the active site

A

the loop block access to the kinase active site so it is inactive (ATP can access but the substrate cant). when the loop is phosphorylated there is a conformational change which leads to the activation loop to move out of the active site. this is known as the priming event. loop sequences have a lot of phosphoacceptor sites. aspartate residues can be catalytic and often closely associated with the target peptide

179
Q

describe the effect of pseudo substrate domains on the kinase active site

A

the pseudo substrate domain is a small domain that mimics the substrate. it sits in the binding (catalytic) domain and masks it. it has no phosphoacceptor sites. DAG and C1 domain interaction pulls the pseudo substrate out of the active site, activating the kinase

180
Q

what are the different classes of PKC

A

there are 3 classes - c, n and a

181
Q

how can we predict other phosphoacceptor sites in other proteins

A

sequences around the substrate phosphoacceptor sites show similarity allowing prediction of other sites in other proteins using bioinformatics - can search for motifs and predict targets

182
Q

what 4 things can phosphorylation alter

A

change localisation, interactions, half-life and sensitivity to signal

183
Q

what are the 2 main functions of kinases

A

signal amplifiers and/or key control steps

184
Q

what is Herceptin

A

an Ab of the EGF tyrosine kinase

185
Q

insulin receptor has an intrinsic/extrinsic tyrosine kinase

A

intrinsic

186
Q

what is c-src

A

the first protooncogene - tyrosine kinase

187
Q

why are tyrosine kinases often involved in disease

A

dues to their function in cell signalling, growth/cell division, metabolism etc

188
Q

describe insulin receptor signalling

A

the receptor is an alpha2beta2 polypeptide held together by disulphide bonds. insulin binds to the alpha2 subunit inducing a conformational change which results in transmission of the signal to beta2 subunits which leads to the intrinsic kinase in the cytosolic domain being activated. the kinase phosphorylates receptor residues (autophosphorylation) and these residues recruit signalling molecules e.g. IRS-1 which is then also phosphorylated. this all forms a signalling complex

189
Q

describe ligand binding receptor activation

A

dimersation is key to receptor activation.
EGF, SCF and nerve growth factor exist as monomers then dimerise upon binding their ligand (sometimes required for signal transduction)
insulin receptor is unusual in that it is already a heterodimer

190
Q

it is difficult to get an X ray crystallography of a membrane protein, what can we do instead

A

we can use an artificial system and cryo EM to study the insulin receptor for example

191
Q

describe cryo EM

A

samples are frozen to maintain structures then normal EM is carried out

192
Q

what makes the autophosphorylation in the insulin receptor more likely

A

the huge conformation change brings the kinase domains of the receptor closer together

193
Q

all receptor tyrosine kinases exhibit ………. dependent activation of tyrosine kinase

A

ligand dependent

194
Q

when the receptor is phosphorylated, the …………. ……………. changes shape so that the kinase domain can be accessed. when the ……… tyr residues are phosphorylated, the loop is flipped open and the active site is available

A

activation loop

3

195
Q

what is trans autophosphorylation

A

the dimeric receptor phosphorylates trans - chain A phosphorylates tyrosine in chain B and vice versa

196
Q

p tyr act as docking sites for signalling molecules - explain

A

they allow proteins like SH2 domain containing proteins to be recruited and dock allowing the assembly of signalling complexes

197
Q

different receptors recruit the same/different SH2 domain containing proteins

A

different

198
Q

why do all SH2 domains exhibit the same shape

A

because they all have the same arrangement of alpha helix and beta sheet

199
Q

how do SH2 domains show specificity

A

they all bind p-tyr but show specificity in the 2 pronged concept. they have a p-tyr pocket and a specificity pocket. the surrounding sequence dictates which SH2 domain containing proteins a receptor can bind

200
Q

describe overall signalling complex assembly

A

ligand binds receptor –> dimerization –> activation of tyrosine kinase domain by release of activation loop –> autophosphorylation –> SH2 domain containing proteins recruitment
- ligand dependent assembly of signalling molecules localised to the receptor and activated with precise spatial and temporal coordinates. different receptors assemble different protein complexes depending on which effectors are recruited.

201
Q

describe leptin signalling

A

leptin is a hormone that triggers a series of signalling events. the leptin receptor homodimerizes which results in recruitment of JAK2 tyrosine kinase which binds to the dimer a phosphorylates its tyrosines. p-tyr residues recruit STAT3 and allows dimerization and access to the nucleus to act on gene expression

202
Q

why is it important to control signalling pathways

A

to ensure they are only carried out at the correct time

203
Q

give 2 examples of SH2 domain containing proteins

A

Ras-GAP, PLCgamma

204
Q

describe PLCgamma activation by RTKs

A

PLCgamma is recruited via specific SH2 domain. this brings the PLCgamma into close proximity to the tyrosine kinase domain of the receptor

205
Q

what is Ras and what does it do

A

a g protein and Ras-GTP activates a signalling pathway

206
Q

what is the Ras-GTP/Ras-GDP balance controlled by

A

relative activity of Ras-GAP and SOS proteins. recruiting these to receptors via SH2 domains is a key control step

207
Q

ras is often mutated in certain …….. ……….

A

tumour types

208
Q

describe how ERK is produced

A

as a result of the EGF receptor signalling pathway through Ras –> Raf –> Mek –> Erk

209
Q

how can the distribution of Erk be studied

A

using immunofluorescence

210
Q

how many genes code for the GPCR receptor superfamily

A

791

211
Q

what is the beta-2-adrenoceptor the target for

A

beta blockers and anti-asthma medicines

212
Q

what are GLP-1 mediated functions regulated by

A

hormones and neurotransmitters

213
Q

where is GLP-1 found and why

A

in the cells of the gut so it can respond to food availability. it is also found in the pancreatic islets and regulates insulin release, beta cell proliferation and glucagon secretion

214
Q

where is the GLP-1 receptor found

A

they are found on the beta cells of the pancreas and on the neurons in the brain

215
Q

the GLP-1 receptor regulates systems in the brain, give 2 examples

A

satiety and control of gastric emptying

216
Q

targeting of the GLP-1 receptor is the basis of a number of treatments of ………

A

T2D

217
Q

GLP-1 is a peptide hormone and is destroyed rapidly by …….…., how can these be applied medicinally

A

DPP4

DPP4 inhibitors and GLP-1 analogues are used as a medicinal approach

218
Q

why is it a medical issue that many GPCRs are closely related and expressed in multiple tissues

A

it is associated with side effects and toxicity of treatments

219
Q

what is tiotropum

A

a muscarinic (acetylcholine) M3 receptor antagonist used to treat COPD but produces unwanted side effects on salvation and in the intestines

220
Q

what can be regulated using selective GPCR drugs

A

COPD, glucose homeostasis and insulin restriction, detrusor contractibility, smooth muscle contraction, emesis, insulin homeostasis, ageing and dementia

221
Q

what is meant by GPCRs being referred to as serpentine

A

they are 7 TM receptors - 2 predominantly hydrophobic TM parts
each section is a single polypeptide
serpentine structure is the tertiary structure

222
Q

why do mice have double the GPCRs compared to humans

A

many of their extra ones control their acute sense of smell. ours became pseudo genes when we became bipedal

223
Q

for signal transduction what must a GPCR interact with

A

heterotrimeric guanine nucleotide binding proteins

224
Q

how do agonists and inverse agonists affect GPCRs

A

the receptor is in an equilibrium of inactive and active states and the agonist changes the equilibrium. the agonist allows more active state and the inverse agonist induces the inactive state of the receptor

225
Q

GPCRs can form quaternary structure to control ………. …….…….

A

activity levels

226
Q

what does tagging a protein by ubiquination do

A

it targets it to the proteasome for degradation

227
Q

why are there less G proteins than receptors

A

a range of receptors send equivalent signals

228
Q

what are the 4 G protein groups and their functions

A

Gs - stimulate adenylyl cyclase and production of cAMP
Gi/o - inhibit adenylyl cyclase to lower cAMP and control ion channels
Gq/11 - stimulate phospholipase C and regulate Ca levels
G12/13 - regulate the cytoskeleton

229
Q

describe the G protein resting state

A

the G protein is a heterotrimer - 3 subunits - alpha, beta and gamma

230
Q

describe the active state of a G protein

A

the alpha subunit has GTP bound

231
Q

the ……….. promotes the off rate of GDP from the subunit. GDP is replaced by ……….. causing a physical dissociation of the …… subunit from the other 2

A

agonist
GTP
alpha

232
Q

to which subunit of the G protein do GDP/GTP bind

A

the alpha subunit

233
Q

the G protein activation cycle controls what

A

cAMP production

234
Q

the alpha subunit of the g proteins has an intrinsic ……..

A

ATPase

235
Q

what does GTPase do

A

it hydrolyses the last phosphate of GTP and restores GDP to the binding site. the speed of the enzyme process defines how long the 2nd messenger system is being regulated/activated

236
Q

what happens to the G protein upon GDP binding

A

it allows re-association of the subunits and the protein is ready for the next hormonal signal

237
Q

describe how g proteins are involved in cholera

A

GTP is not hydrolysed due to toxin inhibiting GTPase. cells continue to make cAMP even when they aren’t meant to. ion channels in intestinal cells have their g proteins continually active causing regulation of ion channels in cells causing water to be continually pumped out - diarrhoea

238
Q

how can one recover form cholera if its toxin is an irreversible inhibitor

A

the intestinal cells turn over quickly so dead cells are removed and new cells are healthy so long as clean water is consumed –> recovery

239
Q

what activates GTPases

A

guanin nucleotide exchange proteins - blocked in cholera

240
Q

what do adenylyl cyclases do

A

when they are active they convert ATP –> 3’5’ cyclic AMP

241
Q

where does the cyclase enzyme need to be in order to receive a signal and interact with the receptor

A

at the PM

242
Q

there are ………….. TM proteins that convert ATP to cAMP creating downstream responses (stimulates kinase cascades based on PKA)

A

12

243
Q

cAMP is polar/non-polar and charged/uncharged so will/wont diffuse out of the cell in a concentration dependent manner

A

polar
charged
wont

244
Q

what are needed to destroy cAMP

A

cAMP phosphodiesterases

245
Q

describe the structure of cyclic nucleotide phosphoesterases

A

N –> C : targeting, regulatory, catalytic, regulatory domains

246
Q

how does the cyclic nucleotide phosphoesterase know where to be active

A

we want different cAMP concentrations in different cells - there is a sequence in the enzyme that tell it the location to be active

247
Q

which site do all phosphodiesterases have

A

the catalytic site

248
Q

what is the 2nd messenger of G proteins

A

cAMP

249
Q

what are the basic steps in drug discovery and development

A

identify disease, isolate protein involved in disease, find effective drug agent against disease protein, preclinical testing, scale up, formulation, human clinical trials, approval - in total takes around 15 years

250
Q

what is the definition of a hormone

A

a chemical messenger released by one cell or tissue that, following transport through and aqueous system, alters physiology or response of a different cell or tissue

251
Q

the gut microbiome makes simple molecules from …….……..

A

dietary fibre

252
Q

what are FA

A

carboxylic acid with an aliphatic tail which can be saturated or unsaturated

253
Q

cancer, CVD and diabetes are 3 global big killers, what underpins them all

A

inflammation

254
Q

how does our diet affect the gut microbiome

A

balanced nutrition, high fibre diet leads to gut microbiota symbiosis and the person is healthy
high fat, processed carbs diet leads to gut microbiota dysbiosis and this can result in obesity/diabetes/inflammatory disorders

255
Q

how do gut microbiota produce large amounts of short chain FA

A

they ferment fibre and other poorly digested carbohydrates which produces large quantities SCFA

256
Q

how can we mimic good gut microbiota

A

approaches in humans - faecal transplants, pre/probiotics, antibiotics - all require long term lifestyle changes
beneficial microbial effects independent of microbiota - mimic actions of signalling molecules released by microbes

257
Q

what is photomorphogenesis

A

when light regulates plant development

258
Q

how do seedlings develop in the light

A

all resources go into leaf development and chloroplast development

259
Q

how do seedling develop in the dark

A

extension of hypocotyl

260
Q

how and what do plants detect about light

A

they sense light spectral quality, quantity, direction and duration using several photoreceptors. plants can detect far lower light intensity than humans

261
Q

what is the UVB photoreceptor

A

UVR8

262
Q

what are the UVA/blue photoreceptors

A

cryptochromes and Phototropins

263
Q

what are the red/far red photoreceptors

A

phytochromes

264
Q

how do photoreceptors detect light

A

they detect specific wavelengths of light using chromophores (small organic molecule) of various types bound to an apoprotein

265
Q

describe the UVR8 mutant and WT

A

the mutant is susceptible to damage by UVB radiation which is naturally present in sunlight. In WT UVR8 stimulates expression of genes that protect the plant against UV damage e.g. sun screen compound synthesis in the dermal layer. UVR8 also regulates developmental processes e.g. stem extension growth through regulation of gene expression. the mutant cannot suppress extension growth. UVR8 stimulates rapid extension of a TF called HY5 which stimulates genes in the UVR8 pathway e.g. expression of sunscreen proteins

266
Q

white light does not contain …………

A

UVB

267
Q

describe the role of HY5 and its mutant

A

its function is not restricted to UVR8
HY5 mutants have a long hypocotyl phenotype in all light qualities indicating that it acts downstream of several photoreceptors i.e. UVR8. cryptochrome, and phytochrome to control expression of many genes

268
Q

describe the role of phytochrome

A

it controls seed germination, stem extension, leaf development and flowering time

269
Q

the phytochrome apoprotein binds a chromophore called ……………….. that absorbs principally red and far red light

A

phytochromobilin

270
Q

what are the 2 photo-interconvertible forms of phytochrome

A

Pr and Pfr

271
Q

which of the 2 forms of phytochrome initiates the biological responses

A

Pfr

272
Q

phytochrome responses are ……….. ……… inducible

A

red light

273
Q

if far red light is given immediately after red light what happens to phytochrome

A

Pfr converts back to Pr before the response is formed

274
Q

what initiates phytochrome signal transduction

A

chromophore isomerises depending on the light quality. this causes a conformation change (twist) to the protein that initiates signal transduction and conversion between the active and inactive form

275
Q

what phenotype do phytochrome mutants have

A

they have long hypocotyls in red and/or far red light but normal short hypocotyls in other light qualities

276
Q

why cant the HY1 mutant make functional phytochrome and what is the effect of this on the phenotype

A

they cannot make functional phytochrome due to a defect in chromophore biosynthesis. this leads to the plants having long hypocotyl, less expanded leaves and impaired chloroplast development

277
Q

describe the steps in phytochrome signalling

A
  • after conversion to Pfr, Pfr moves from the cytoplasm to the nucleus
  • Pfr then associates with TFs called PIFs, causing their proteolytic destruction
  • PIFs repress transcription of genes involved in responses to light, so destruction of them allows stimulation of transcription of target genes
    overall: red light –> Pfr –> Pfr PIF –> PIF proteolysis –> transcription. phytochrome gets rid of the repressors allowing photomorphogenesis to occur
278
Q

explain why PIFs accumulate in shaded plants and what does this result in

A

vegetation absorbs red and blue light but reflects far red light. shaded plants experience lots of far red light (low red : far red) compared to unshaded plants. shaded plants have lower Pfr:Pr which allows PIFs to accumulate leading to the extension growth response due to auxin biosynthesis

279
Q

explain briefly how vertebrate vision works

A

light entering through the pupil is focussed on specialised light sensitive neurone in the retina: rods and cones. electric signals go into the optic nerve and into the brain

280
Q

describe rods in terms of light sensitivity and colour

A

high light sensitivity but no colour discrimination

281
Q

describe cones in terms of light sensitivity and colour

A

less sensitive to light but confer colour vision - they produce different photoreceptors

282
Q

what is the function of ganglion neurons

A

they gather electrical information from the rods and cones and relay it to the brain via the optic nerve

283
Q

describe the structure of rods and cones

A

outer segment - membranous discs with rhodopsin photoreceptors
inner segment - nucleus and mitochondria that provide energy for photo-transduction
synaptic part connects to the optic nerve

284
Q

describe rod/cone ion channels

A

outer segment has an inward Na/Ca channel gated and opened by cGMP
the inner segment has an Na/K pump

285
Q

how does light perception affect the ion channels of rods/cones

A

it leads to a decrease in cGMP concentration in the cytoplasm which closes the Na/Ca channel causing a change in membrane potential which is transmitted through the neuron

286
Q

what is the visual photoreceptor

A

rhodopsin

287
Q

what is the structure of rhodopsin

A

consists of opsin protein with retinal chromophore. opsin has 7TM alpha helices

288
Q

what happens when retinal absorbs light

A

it undergoes isomerisation which causes conformational change to opsin

289
Q

why are there 2 photoisomers of rhodopsin

A

due to the rotation around the carbon atom

290
Q

what are the similarities between rhodopsin and channelrhodopsin

A

7 TM structure and retinal chromophore

291
Q

what are the differences between rhodopsin and channelrhodopsin

A

opsin doesn’t form an ion channel and retinal has different light induced isomerisation. rhodopsin: 11-cis –> all-trans isomerisation. channelrhodopsin: all trans –> 13 cis isomerisation

292
Q

rhodopsin is associated with g protein called …………..

A

transducin

293
Q

what are the steps in rhodopsin photoreception

A

photoreception causes exchange of GDP –> GTP on the transducing alpha subunit and dissociation of the alpha subunit
activated transducing alpha stimulates cGMP phosphodiesterase by removal of an inhibitory subunit.
this results in cGMP –> 5’-GMp lowering [cGMP]
this leads to closure of cGMP gated Na/Ca channels, causing a change in membrane potential from -40 –> -75mV in the light
this stimulates a signal through the optic nerve

294
Q

describe the desensitization that occurs after rhodopsin photoreception

A

continued illumination of rhodopsin exposes ser/thr amino acids that are phosphorylated by rhodopsin kinase. P-rhodopsin is bound by arrestin 1 which prevents further interaction with transducing and stops signalling.

295
Q

how does colour vision work

A

each type of cone expresses a different opsin, although they are all closely related in sequence. the retinal is in different molecular environments in the cone opsins, giving different absorption spectra

296
Q

what do mutations in opsins lead to

A

colour blindness

297
Q

what is melanopsin

A

the 3rd type of photoreceptive neuron in the retina, not involved in vision. intrinsically photosensitive retinal ganglion cells contain melanopsin as the photoreceptor. melanopsin binds retinal and is maximally sensitive to blue light. it activates a G protein by a different mechanism to transducin and resembles invertebrate opsins in structure and signalling. it functions in entrainment of circadian rhythms and behavioural responses to light

298
Q

what is low melanopsin associated with

A

seasonal affection disorder (SAD) - winter depression

299
Q

what is optogenetics

A

using light to understand complex signalling networks

300
Q

describe neurons

A

they are the basic unit of the nervous system. they send and receive signals, the cell body contains the nucleus, dendrites are the receiving part of the cell, axons send information on. cells are electrically excitable and vary in length

301
Q

describe the resting state of a neuron

A

the neural membrane is polarised - positive on the outside and negative on the inside

302
Q

describe the generation of an action potential (overall)

A

when neurons receive signals, protein channels open in the membrane resulting in localized influx of Na which leads to depolarisation (reduction of charge difference across the membrane) which activates neighbouring Na channels creating a wave of depolarisation

303
Q

what are the 5 steps in the action potential

A
  1. Na channels open
  2. more Na channels open
  3. Na channels close
  4. K channels open
  5. K channels close
304
Q

the wave of depolarisation starts at the ……. and moves towards the ………. ………… through the ………. to its terminal

A

dendrite
cell body
axon

305
Q

what happens at the synapse during neural transmission

A

depolarisation at the axon terminus/synapse triggers release of neurotransmitters which diffuse across the synapse and stimulate electrical excitation of the next cell.

306
Q

what do excitatory neurotransmitters do

A

they initiate depolarisation through opening of Na channels

307
Q

what doo inhibitory neurotransmitters do

A

they lead to opening of Cl channels and increase polarization, decreasing the chance of depolarisation

308
Q

why are negative ions inhibitory in neural transmission

A

because they cause the wrong charge change

309
Q

what can electrical stimulation be used to treat

A

Parkinson’s, depression etc but there are unwanted side effects due to the lack of specificity

310
Q

what is the disadvantage of chemical stimulation treatment compared to electrical stimulation

A

chemical stimulation takes longer

it also shows side effects

311
Q

why is optogenetics useful

A

light is easy to manipulate, can be delivered spatially and produces fast effects. we can use light sensitive proteins or photoreceptors which can be used to activate/inactivate neurons

312
Q

what is Chlamydomonas reinhardtii

A

it is a unicellular green algae that s reactive to sunlight. they grow in aquatic environments and move towards the light to maximise capture for photosynthesis. they have a light activated channel that is used to control movement

313
Q

is channelrhodopsin a GPCR

A

no - it is a blue light activated single component system that transports positive ions into the cell (primarily Na)

314
Q

why does channelrhodopsin respond to light

A

due to rhodopsin and channelrohodopsin cofactors in each of the 7 TM proteins.

315
Q

channelrhodopsin controls …………., it makes animal cells respond electrically to light (it is a light activated …….…. channel)

A

phototaxis

cation

316
Q

neurons can be made electrically responsive to blue light by using ………………. in optogenetics. the neurons recover in darkness

A

channelrhodopsin

317
Q

what is halorhodopsin

A

a light activated Cl pump found in algae and archaebacteria.

318
Q

what colour of light drive Cl influx by halorhodopsin and why

A

yellow - retinal absorbs yellow because of the changed protein environment

319
Q

opening of Cl channels increases polarization/depolarization and can activate/inhibit neural activity

A

polarization

inhibit

320
Q

how can we make a synthetic light activated GTPase to spatially control cell shape/proliferation

A

fuse DNA encoding photoreceptor domain, LOV flavin chromophore, DNA encoding animal GTPase.
LOV binds a flavin derived cofactor which absorbs UVA blue light. can take molecule out and fuse to protein of choice - it will hydrolyse GTP –> GDP creating an artificial photoreceptor system. in light GTPase is active and in dark it is disrupted.
light activated GTPase stimulates change in cell shape

GMC (4 decks)

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