DNA repair/Transcriptional regulation Flashcards
What causes damage to DNA?
Single base changes
Alkylation
Base removed causes Covalent bonding
How do you deal with the damage?
Direct repair Tolerance system Retrieval system Mismatch repair Excision repair
Describe types of direct repair
Photolyase enzyme attaches to thymine dimer and uses light energy to break structure.
Uracil DNA glycosylace removes uracil leaving binding site for AP endonuclease which breaks the backbone same side to the damage.
DNA POL I binds to break and add new DNA which is sealed by ligase.
mut system see’s mismatch in hemi-methylated DNA and binds with help of MutL, complex activated by MutH. Complex then nicks strand opposite methyl group.
Describe excision repair
uvrABC cut both sides of damage and helicase 2 removes, DNA POL I replaces, ligase seals
What is the tolerance system?
Recombination, mainly for UV repair. Replication can continue through damage.
What is the retrieval system?
Swaps DNA from one molecule to another via recombination
What is the SOS response?
Controlling expression of gene to fix damage.
To keep the response switched off while the cell is healthy and the other, RecA, to turn it on when DNA damage occurs.
In normal healthy cells the LexA protein binds to a certain section of the bacterial DNA called the ‘SOS box’ which codes for over 50 genes while RecA floats around the cell looking for damaged DNA. If it finds any, it binds to it and stimulates the breaking of the LexA protein. The SOS box genes are therefore released and the proteins that deal with DNA damage can be made.
What is constitutive expression?
When genes are always expressed
What is an operon?
Genes transcribed from a single promoter
What are repressors?
They prevent transcription
What are inducers?
activate activators, repress repressors
What are regulons?
Genes with same function on different operons may be encoded by regulon
What is global regulation?
When mass regulation from one environmental factor e.g. SOS response
What makes up the Lac operon?
Operator Repressor lacY lacA LacI LacZ
What does the Lac operon do?
The genes in the operon encode proteins that allow the bacteria to use lactose as an energy source as glucose preferred source of carbon in E.coli.
When glucose is present the repressor interferes with the promoter so RNA POL cannot attach.
When there is no glucose Repressor produces allolactose which stops repressor binding to operon.
