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Physiology of Microbes > Bacterial growth and cell division > Flashcards

Bacterial growth and cell division Flashcards

1
Q

what is the structure of the bacterial chromosome like ?

A

Bacterial DNA is not structured its simple and not organised into chromatins or histones

  • DNA is supercoiled and not uniformly associated with proteins
  • circular DNA, no nuclease
  • DNA is organised into domains by scaffold proteins in nucleoid
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2
Q

what are scaffold proteins ?

A

non-uniform proteins

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3
Q

what are some of the other proteins that are bound to DNA ?

A
  • RNA polymerase
  • transcriptional regulators
  • small DNA binding proteins, H-NS, HU, IHF (and others)
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4
Q

how is DNA looped into hoops ?

A

by domain proteins

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5
Q

what does supercoiling do to the loops ?

A

it turns the open loops into wound up compact loops

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6
Q

how many kilo bases is the E. coli chromosome?

A

4.6 x 10^4 kilobases

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7
Q

what is the difference between a plasmid and a chromosome ?

A
  • chromosome is covered with protein where as plasmid is not
  • plasmids are used as gene carriers where as chromosomes are not
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8
Q

for a cell to recognise it has to be replicated, what does every DNA molecule need to have ?

A

an origin of replication = oriC

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9
Q

what is oriC ?

A

a gene that says this DNA needs to be copied

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10
Q

what binds to oriC ?

A

DnaA

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11
Q

what is DnaA ?

A

it is an initiating protein which then attracts other proteins required for DNA replication

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12
Q

what is the origin of replication called in plasmids ?

A

oriV

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13
Q

what is the role of primase in the initiation step of DNA replication ?

A

synthesises RNA primer

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14
Q

what enzyme is DNA replication carried out by ?

A

DNA polymerase III

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15
Q

what happens once DNA is extended from the primer ?

A

DNA Pol I removes RNA

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16
Q

in what direction does DNA replication proceed ?

A

5’ to 3’ direction on both strands

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17
Q

is leading strand DNA synthesis continuous or discontinuous ?

A

continuous

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18
Q

as leading strand DNA synthesis is continuous what enzyme is it carried out by ?

A

DNA polymerase III

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19
Q

is lagging strand continuous or discontinuous ?

A

it’s discontinuous

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20
Q

what enzyme are Okazaki fragments made by ?

A

DNA Pol III

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21
Q

what does DNA polymerase I do ?

A
  • extends ends of Okazaki fragments until adjacent RNA primer reached
  • 5’ to 3’ exonuclease activity of DNA pol I removes RNA primer
  • DNA pol I fills gaps between Okazaki and uses 3’ - 5’ exonuclease activity (proofreading function) to correct errors
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22
Q

what does DNA ligase do in the lagging strand during initiation ?

A

DNA ligase joins the fragments

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23
Q

what is the role of helices in the replication fork ?

A

helices unwinds the dsDNA ahead of the replication fork

it opens it out to help primases and DNA polymerases to get in

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24
Q

what is the role of SSB (single-stranded binding protein) ?

A

it keeps unwound strands apart

25
Q

DNA replication is bidirectional. what does this mean ?

A

it moves away from the centre

26
Q

what happens in the elongation step of DNA replication ?

A
  • DNA replication occurs at the centre of the cell by a complex of proteins = replisome
  • proceeds at a constant rate irrespective of growth conditions
  • once replication begins, it continues until the end and does not require additional protein synthesis
27
Q

what happens in the termination step of DNA replication ?

A
  • the two replication forks meet at the terminus (terC)
  • a termination protein (Tus) is bound to terC region
  • terC is flanked by DNA sequences that form structure that block progression of replication fork
28
Q

how does the ter structure slow the replication forks down ?

A

Ter has a special DNA sequence either side of it that form structures that slows the replication fork down

29
Q

where does all DNA replication occur ?

A

All DNA replication occurs at centre of cell = Replisome

30
Q

what is partitioning ?

A

partitioning separates chromosome into two daughter cells

31
Q

what is the Z-ring ?

A

it is the first ring of protein that starts the separation of the two cytoplasms

32
Q

what happens to the origin and terminus when DNA replication is initiated ?

A

the origin and terminus is in the centre

33
Q

what are the 6 protein subunits of the RNA polymerase holoenzyme ?

A
  • core enzyme (5 subunits)

- sigma factor

34
Q

where does the sigma factor bind and what does it do ?

A

the sigma factor binds to the -10 and -35 sequences in bacterial promoters and identifies the beginning of a gene

35
Q

what are the role of regulatory proteins ?

A

they control binding RNA Pol to promoters

36
Q

what does -10 refer to ?

A

-10 refers to 10 bases before transcription starts

37
Q

what are the 3 phases of translation in bacteria ?

A
  • initiation
  • elongation
  • termination
38
Q

what happens in initiation ?

A

binding of ribosome to mRNA

39
Q

what happens in elongation ?

A
  • movement of ribosome along mRNA

- synthesis of polypeptide

40
Q

what happens in termination?

A
  • release of mature polypeptide

- recycling of ribosome

41
Q

what are the two subunits of prokaryotic ribosomes ?

A

50S and 30S

42
Q

which ribosome subunit binds first ?

A

30s binds first

- IF3 (initiation factor 3) binds to 30s unit and prevents binding to 50s

43
Q

what is the name of the tRNA that can enter the P site ?

A

fmet-tRNAmet

44
Q

what does the fmet-tRNAmet do ?

A

it binds to 30s at p (peptidyl) site

- it requires IF-2 and GTP

45
Q

what is IF-1 (initiation factor 1) required for ?

A

it binds the 30s + fmet-tRNA stably to mRNA

46
Q

what are the 3 sites on the ribosome ?

A

exit site
peptidyl site
amino acyl site

47
Q

when does termination occur in prokaryotic protein synthesis ?

A

when STOP codon is in A site

- requires specific release factors to cause dissociation of ribosome complex

48
Q

what are the different stop codons recognised by protein RF (release factors) ?

A
  • UAA (ochre)
  • UAG (amber)
  • UGA (opal)
49
Q

what is the release factor that recognises UAA ?

A

RF1/RF2

50
Q

what is the release factor that recognises UAG ?

A

RF1

51
Q

what is the release factor that recognises UGA ?

A

RF2

52
Q

what is the strongest stop codon ?

A

UAA

53
Q

at what site on the ribosome do RFs act at ?

A

site A

54
Q

what is it called when multiple ribosomes bind to one transcript ?

A

polyribosome

- result in multiple copies of the new protein being produced from one RNA molecule

55
Q

what happens during cytokinesis ?

A

the nucleoid and cytoplasmic contents have to be divided between the two daughter cells

56
Q

what happens to FtsZ when GTP is bound to it ?

A

it forms straight filaments

straight chains fo FtsZ

57
Q

what happens when GTP is hydrolysed to GDP ?

A

introduces a curvature (curves)

58
Q

how do coccoid bacteria divide in comparison to rod shaped bacteria ?

A

coccoid bacteria can divide in one plane or many where as rod shaped bacteria can only divide in one plane

Physiology of Microbes (8 decks)

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