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Physiology of Microbes > Bacterial growth and cell division L4 > Flashcards

Bacterial growth and cell division L4 Flashcards

1
Q

what are the events required for cell division

A
  1. DNA replication
  2. Transcription of genes and production of new proteins
  3. Septation and synthesis of a new cell wall
  4. Cell separation
    Events occur in a set order, can be divided into distinct periods of cell cycle
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2
Q

what is the integrated cellular machine

A

Energy can be generated in many ways – biochemical generation
Need to generate energy – all processes need energy to drive them

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3
Q

what is the bacterial chromosome structure of DNA

A

DNA supercoiled, not uniformly associated with proteins – compared with Eukaryotic chromatin structure

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4
Q

what is supercoiling

A

over winding of DNA - DNA has a natural structure it forms with a natural structure and amount of twisting – B form DNA

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5
Q

what causes the cell to be wound tighter and what is natural DNA like

A

Enzymes in cell either wind it tighter or under wind it - natural state DNA is tighter wound

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6
Q

what happens to DNA when start winding up

A

DNA up cannot unwind – physical thing that happens

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7
Q

where does DNA get energy and what is it used for

A

DNA has energy – wants to unwind back to relaxed state, energy helps transcription
Supercoiling energising DNA molecules

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8
Q

what other proteins are bound to DNA

A
  • RNA polymerase
  • Transcriptional regulators
  • small DNA binding proteins
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9
Q

how many chromosomes do bacteria have

A

not all have one

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10
Q

what chromosomes do bacteria have

A

not all have circular some have linear

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11
Q

do bacteria require plasmids

A

cell can lose plasmid and still live

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12
Q

if bacteria lose this they die

A

If loose one of the circular molecules will die – as loose genetic information that is vital
Chromosomes – they have genes that cannot be lost from the cell

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13
Q

where does DNA polymerase ‘work’

A

DNA polymerase can only add bases to 3’ end of a primer

- once DNA is extended from primer DNA Pol I removes RNA

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14
Q

what does cell need to recognise needs to be replicated

A

origin of replication

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15
Q

where does DNA replication start

A

OriC on chromosome DnaA (initiator protein) binds to OriC

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16
Q

what does primase synthesis do

A

make RNA primer

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17
Q

what carries out DNA replication

A

DNA polymerase III (used for bacteria)

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18
Q

which way does DNA replication occur

A

5’ to 3’ direction on both strands
Leading strand DNA synthesis is continuous, carried out by DNA polymerase III
Lagging strand DNA synthesis is discontinuous
- Okazaki fragments are made by DNA Pol III

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19
Q

what is the DNA polymerase I function

A
  • Extends end of Okazaki fragment until adjacent RNA primer reached
  • 5’-3’ exonuclease activity of DNA pol I removes RNA primer
  • DNA pol I then fills gaps between Okazaki and uses 3’-5’ exonuclease activity (proofreading function) to correct errors
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20
Q

how does a DNA replication fork in bacteria form

A

Helicase unwinds dsDNA ahead of replication fork
SSB = keeps unwound strands apart

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21
Q

what is the DNA elongation rate

A

Proceeds at a constant rate irrespective of growth conditions

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22
Q

where does DNA elongation occur in the cell

A

at cell centre by a complex of proteins = Replisome

23
Q

when does termination occur in DNA replication

A

Two replication forks meet at terminus (terC)
A termination protein (Tus) is bound to terC region
terC is flanked by DNA sequences, form structure that block replication forks progression
Ter sequence has sequences either side of it, slow the DNA synthesis and replication down

24
Q

what is partitioning

A

separate chromosomes into two daughter cells

25
Q

how can DNA replication be imaged during partitioning

A

Fluorescent in situ hybridisation (FISH)
Uses Fluorescent probes specific for DNA sequences of oriC & terC
Cells viewed using fluorescent microscopy

26
Q

what does transcription require

A

RNA polymerase holoenzyme consists of six protein subunits

  • Core enzymes (five subunits)
  • Sigma factor
27
Q

where do sigma factors bind to for transcription

A

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

28
Q

how do regulatory proteins work to create RNA

A

Regulatory proteins control RNA pol binding to promoters

Any negative numbers not incorporated into RNA

29
Q

why dont bacterial mRNA undergo significant processing

A
  • Primary transcript synthesized by RNA pol is mature mRNA
    Transcription and translation both occur in same cell compartment
    Translation usually begins before transcription is complete
30
Q

what are the three phases of bacterial translation

A
  1. Initiation – binding of ribosomes to mRNA
  2. Elongation – movement of ribosomes along mRNA, synthesis of polypeptide
  3. Termination – release of mature polypeptide, recycling of ribosome
31
Q

what occurs during prokaryote initiation

A

ribosome binding site
Ribosomes usually bind to mRNA as separate subunits
- 30S binds first
- IF3 (initiation factor 3) binds to 30S unit & prevents binding to 50S
fmet-tRNAmet binds to 30S at P (peptidyl) site
- requires IF-2 (initiation factor 2) and GTP
- f-met tRNAmet is the only tRNA that can enter the P site
30S + fmet-tRNA binds stably to mRNA
- requires IF-1 (initiation factor 1)

32
Q

what does translation need to start

A

translation need methanonine that’s modified with formaldehyde
GTP energises the process
Only f-met tRNA can fit into P site – only tRNA that can start

33
Q

how and when does prokaryote translation termination occur

A

Termination occurs when STOP codon is in A site

Requires specific Release Factors to cause dissociation of ribosome complex

34
Q

what are examples of different stop codons recognised by protein release factors

A
  • UAA (Ochre) RF1/RF2
  • UAG (Amber) RF1
  • UGA (opal) RF2
  • stop codon P site must be occupied
  • RFs act at A site
35
Q

what are polyribosomes

A

Multiple ribosomes bind to one transcript

36
Q

polyribosome function

A

multiple copies of new protein being produced from one RNA molecules

37
Q

what happens in cytokinesis

A

Nucleoid and cytoplasmic contents divided between two daughter cells
Cell Envelope (cell wall plus cytoplasmic membrane) invaginate
Directional shift in growth of peptidoglycan occurs at a predetermined position by the in-growth of a septum
Cell membrane and cell wall – take part in slightly different things

38
Q

what is an essential protein for cells

A

FtsZ

39
Q

what is FtsZ and septum formation

A 
Boa constrictor 
FtsZ is polymerised into chain
GTP is hydolysed by unknown trigger
Protein chains begin to constrict cell
Cell wall shows elongated cells with rings present
40
Q

how is FtsZ imaged

A

using FISH for different cell components
FtsZ labelled green, located at replisome, know this as the DNA – nucleiod, is the dividing cell with a chain of FtsZ between it – one cell that’s been pinched and splitting into two daughters

41
Q

how is cell wall imaged

A

using fluroscent microscopy

42
Q

how does the nucleoid form from cell wall and FtsZ

A

FtsZ pinching off, finish cell separation need peptidoglycan making two cell walls

43
Q

how do cells grow and divide

A

binary fission

44
Q

how is the time course of helical and ring structures in peptidoglycan revealed

A

staining newly synthesised PG with fluorescently labelled Vancomycin (antibiotic than binds to new PG)
Bands of new peptidoglycan as it is growing, get helical rings

45
Q

what is formed depending on whether separation is complete or not

A

Separation may be complete (single cells released) or incomplete (chains or clumps produced)

46
Q

what forms if cell divides in same plane twice

A

chain

47
Q

what forms if cell divides in two different planes

A

tetra

48
Q

what causes the cell division in same or different planes

A

is genetically predetermined

49
Q

what replication occurs on plasmid

A

OriV

50
Q

what is a limiting factor in determining shortest generation time

A

DNA elongation

51
Q

what happens in prokaryote protein synthesis

A
  1. elongation
  2. aa-tRNA entry mediated by EF-Tu (elongation factor Tu)
    - forms 3° complex with GTP
    - delivers tRNA then leaves ribosome
    - hydrolysis of GTP to GDP occurs during release
    - EF-Tu is recycled by EF-Ts
  3. peptidyl transferase activity is located in 50S subunit
  4. peptide bond formed, ribosome changes conformation allow movement of tRNAs
  5. translocation moves tRNA to P site; uncharged tRNA leaves via E (exit) site
52
Q

how is prokaryote elongation acheived

A

further charged tRNA molecules entering the A site (aminoacyl site) & formation of peptide bond

53
Q

what does peptidyl transferase activity need

A

rRNA as part of catalytic site

54
Q

what does conformational change of ribosome in prokaryote protein synthesis require

A

requires GTP & EF-G (elongation factor G)

Physiology of Microbes (21 decks)

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