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BM211 microbiology > Block A 2 > Flashcards

Block A 2 Flashcards

1
Q

what is supercoiled DNA

A

when DNA is further twisted to save space

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2
Q

negative supercoiling

A

double helix is underwound

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3
Q

positive supercoiling

A

double helix is overwound

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4
Q

relaxed DNA

A

DNA has number of turns predicted by number of base pairs

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5
Q

where is negative supercoiling predominately found

A

in nature

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6
Q

what catalyses DNA supercoiling

A

DNA gyrase

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7
Q

difference between RNA and DNA genomes

A

linear or circular
single or double stranded

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8
Q

how do plasmids replicate

A

separately from chromosome

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9
Q

what does pNDM plasmid encode and confer

A

new dehli beta lactamase
resistance to beta lactam antibiotics

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10
Q

what is a chromosome

A

large, encodes all essential genes and more

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11
Q

what are plasmids

A

small, many copies, non essential but advantageous genes (antibiotic resistance)

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12
Q

what are transposable elements

A

segment of DNA that can move from one site to another site on the same or different DNA mol

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13
Q

3 main types of transposable elements

A

insertion sequences
transposons
special viruses

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14
Q

what do sigma factors recognise

A

two highly conserved regions of promoter

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15
Q

what are the 2 conserved regions

A

pribnow box- 10 bases before start of transcription (-10 region)
-35 region- -35 bases upstream of transcription

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16
Q

how do sigma factors govern promoter recogniton

A

RNAP

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17
Q

what is a unit of transcription

A

unit of chr bounded by sites where transcription of DNA to RNA is initiated and terminated

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18
Q

3 types of rRNA

A

16S
23S
5S

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19
Q

half life of mRNAs

A

short
(few mins)

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20
Q

polycistronic mRNA

A

an mRNA encoding group of cotranscribed genes

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21
Q

operon

A

group of related genes cotranscribed on a polycistronic mRNA
allows for expression of multiple genes to be coordinated

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22
Q

homodimeric proteins

A

proteins composed of 2 identical proteins

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23
Q

why do mRNA transcripts have a short half life

A

prevents production of unneeded proteins

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24
Q

what do protein dimers interact with on DNA

A

inverted repeats

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25
Q

DNA binding proteins interact with DNA is a sequence-specific manner, how is specificity achieved

A

by interactions between aa side chains and chem groups on bases and sugar phosphate backbone

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26
Q

what is the main site of protein binding

A

major groove of DNA

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27
Q

3 possible outcomes after DNA binding

A

-DNA binding protein may catalyse a specific reaction on the DNA mol
-negative regulation
-positive regulation

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28
Q

what is negative regulation

A

binding event can block transcription

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29
Q

what is positive regulation

A

binding event can activate transcription

30
Q

inducer

A

substance that induces enzyme synthesis

31
Q

corepressor

A

substance that represses enzyme synthesis

32
Q

effectors

A

collective term for inducers and repressors
affect transcription indirectly by binding to specific DNA binding proteins

33
Q

what do repressor molecules bind to

A

allosteric repressor protein

34
Q

once allosteric repressor becomes active where does it bind

A

region of DNA near promoter
operator

35
Q

operon

A

cluster of genes arranged in a linear fashion whose expression is under control of a cingle operator

36
Q

what is physically blocked when repressor binds to operator

A

transcription

37
Q

what else can be controlled by a repressor

A

enzyme induction

38
Q

what is negative control

A

a regulatory mechanism that stops transcription

39
Q

what is repression

A

preventing synthesis of an enzyme in response to a signal

40
Q

what type of enzyme does repression normally affect

A

anabolic enzymes
eg arginine biosynthesis

41
Q

what is positive control

A

regulator protein activates binding of RNA polymerase to DNA

42
Q

what is the DNA sequence that activator proteins bind to called

A

activator binding site

43
Q

what must first occur so maltose activator protein can bind to DNA

A

must first bind maltose

44
Q

binding strength of promoters of positively controlled operons to RNA pol

A

weak

45
Q

what does activator protein help RNA pol do

A

recognise promoter

46
Q

what can be said about distance of activator binding site and promoter

A

may be close or several hundred base pairs away

47
Q

name given to multiple operons controlled by the same regulatory protein

A

regulon

48
Q

what are global control systems

A

regulate expression of many different genes simultaneously

49
Q

example of global control

A

catabolite repression

50
Q

what is diauxic growth

A

2 exponential growth phases

51
Q

what is the activator protein used to control transcription in catabolite repression

A

cyclic AMP receptor protein (CRP)

52
Q

what is a key mol in many metabolic control systems (regulatory nucleotide)

A

cyclic AMP

53
Q

what other genes also controlled by catabolite repression

A

flagellar genes
(no need to swim in search of nutrients)

54
Q

prokaryotes regulate cellular metabolism in response to

A

environmental fluctuations

55
Q

what is signal transduction

A

external signal detected by senor and transmitted to regulatory machinery

56
Q

what are the 2 components in the 2 component regulatory system

A

sensor kinases
response regulator

57
Q

what and where is sensor kinases

A

in cytoplasmic membrane
detects environmental signal and autophosphorylates

58
Q

what is where is response regulator

A

in cytoplasm
DNA binding protein that regulates transcription

59
Q

chemotaxis used to

A

sense temporal changes in attractants or repellants
regulate flagellar rotation

60
Q

3 main steps of chemotaxi regulation

A

response to signal
controlling flagellar rotation
adaptation

61
Q

what do MCPs do in response to signal (chemotaxi)

A

bind attractant or repellant and initate flagellar rotation

62
Q

what is flagellar rotation controlled by (chemotaxi)

A

CheY protein

63
Q

what method of adaptation used (chemotaxi)

A

feedback loop

64
Q

phototaxis

A

movement toward light
light sensors replace MCPs

65
Q

aerotaxis

A

movement toward oxygen
redox protein monitors oxygen level

66
Q

what is quorum sensing

A

mechanism by which bacteria assess their pop. density

67
Q

what does each species of bacterium produce

A

specific autoinducer

68
Q

what do autoinducers do

A

bind to specific activator protein and triggers transcription of specific genes

69
Q

what was first autoinducer identified

A

AHL
acyl homoserine lactone

70
Q

what encodes bioluminescence

A

lux operon

71
Q

examples of quorum sensing

A

virulence factors
switching from free living to growing as biofilm

BM211 microbiology (14 decks)

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