Bacterial growth and cell division L4 Flashcards
what are the events required for cell division
- DNA replication
- Transcription of genes and production of new proteins
- Septation and synthesis of a new cell wall
- Cell separation
Events occur in a set order, can be divided into distinct periods of cell cycle
what is the integrated cellular machine
Energy can be generated in many ways – biochemical generation
Need to generate energy – all processes need energy to drive them
what is the bacterial chromosome structure of DNA
DNA supercoiled, not uniformly associated with proteins – compared with Eukaryotic chromatin structure
what is supercoiling
over winding of DNA - DNA has a natural structure it forms with a natural structure and amount of twisting – B form DNA
what causes the cell to be wound tighter and what is natural DNA like
Enzymes in cell either wind it tighter or under wind it - natural state DNA is tighter wound
what happens to DNA when start winding up
DNA up cannot unwind – physical thing that happens
where does DNA get energy and what is it used for
DNA has energy – wants to unwind back to relaxed state, energy helps transcription
Supercoiling energising DNA molecules
what other proteins are bound to DNA
- RNA polymerase
- Transcriptional regulators
- small DNA binding proteins
how many chromosomes do bacteria have
not all have one
what chromosomes do bacteria have
not all have circular some have linear
do bacteria require plasmids
cell can lose plasmid and still live
if bacteria lose this they die
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
where does DNA polymerase ‘work’
DNA polymerase can only add bases to 3’ end of a primer
- once DNA is extended from primer DNA Pol I removes RNA
what does cell need to recognise needs to be replicated
origin of replication
where does DNA replication start
OriC on chromosome DnaA (initiator protein) binds to OriC
what does primase synthesis do
make RNA primer
what carries out DNA replication
DNA polymerase III (used for bacteria)
which way does DNA replication occur
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
what is the DNA polymerase I function
- 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
how does a DNA replication fork in bacteria form
Helicase unwinds dsDNA ahead of replication fork
SSB = keeps unwound strands apart
what is the DNA elongation rate
Proceeds at a constant rate irrespective of growth conditions
where does DNA elongation occur in the cell
at cell centre by a complex of proteins = Replisome
when does termination occur in DNA replication
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
what is partitioning
separate chromosomes into two daughter cells
