Microbial Genetic diversity and mutation Pt 3

Question 1

Why is it not beneficial for microbes to prevent all mutations and genetic change?

Answer 1

Because they lack the ability to create genetic diversity and evolve using sexual reproduction.

Question 2

What is genomic stability?

Answer 2

The ability to accurately and completely transfer genetic info, proteins and cellular systems to the next generation of cells.

Question 3

What is genomic plasticity?

Answer 3

The ability to evolve adaptations to their proteins and cellular systems in response to changing environmental conditions.

Question 4

In bacteria and Archaea, what are the 2 major groups of processes that create genomic plasticity?

Answer 4

1. Genetic rescue systems which permit microbial cells to replicate chromosomal DNA that has become extensively damaged.
2. Genetic transfer systems which permit microbial cells to acquire DNA from the environment or from other microbial cells.

Question 5

What is the main system of genetic rescue in bacteria and what does it consist of?

Answer 5

The SOS repair system which consists of a group of 40 genes called the SOS regulon.

Question 6

Transcription of each gene in the SOS regulon is under the control of ___________________________ called __________.

Answer 6

A repressor protein
LexA

Question 7

Each gene has an operator box called the ____________. Dimers of LexA protein bind to the ________ and repress __________________ of SOS genes.

Answer 7

SOS box
SOS box
Transcription

Question 8

What is RecA activation? What is the abbreviation for activated RecA?

Answer 8

When microbial DNA becomes heavily damaged and the loss of proper base pairing results in large sections of ssDNA during DNA replication. Binding of the RecA to these regions causes it to form long chains that act as a protease.

RecA*

Question 9

What does the activated RecA protease do?

Answer 9

Cuts LexA proteins so that they can no longer stick/bind to the operator. this releases the repression of the SOS regulon and allows transcription of the SOS genes.

Question 10

SOS responses are divided into early and late responses. Explain each. What do the genes umuC, umuD and dinB encode for?

Answer 10

1. Early responses: result in increased transcription of genes for recombination repair and nucleotide excision repair. The cell attempts to increase its ability to repair DNA first.
2. Late responses activate transcription of polymerases that can replicate through damage. The genes umuC and umuD encode the protein DNA polymerase 5. The gene dinB encodes the protein DNA polymerase 4.

Question 11

What do DNA polymerases 4 and 5 now have the ability to do? What can they do? What are the 2 mechanisms together called?

Answer 11

Do not have the ability to proofread.
DNA polymerase 5 can replicate over damaged areas by inserting random bases.
DNA polymerase 4 can break replication stalls by “looping out” the damaged DNA.
Together they are called translesion DNA synthesis.