L5: Translation 2 (Mutations) Flashcards
What happens if the genomic DNA or mRNA sequence is altered?
At what point is there the highest chance of the genomic DNA sequence being changed?
During DNA replication
What can happen to the DNA sequence if it is altered?
The DNA sequence can be altered or permanently altered so the mutations are inherited into the next cell generation
What can happen to the DNA nucleotides in mutation?
Normal nucleotides can undergo a proton shift, whereby a rare form of the nucleotides will be produced. This will impact the complementary base pairing between nucleotides
What can happen to the DNA double helix if there are rare forms of the nucleotides (caused by mutations) binding with the normal nucleotides?
- Changes the distance between bases in the hydrogen bonding
- Changes the stability of the hydrogen bonding and will take up a different spatial place within the nucleus
- Can change the genomic DNA sequence
What term is used to describe the reduction in stability of the DNA double helix?
Strand slippage caused by a wobble in the bases of the nucleotides
How many mistakes will the DNA polymerase make, without the wobble?
A mistake approximately every 100 000 nucleotides
How many mistakes would the DNA polymerase make for the human genome, with 6 billion base pairs in each diploid cell?
Amount to 120 000 mistakes every time a cell divides
What does DNA polymerase do to prevent so many mistakes?
Has a proof reading ability
Fixes around 99% of errors
What direction does DNA polymerase normally run in?
5’ to 3’ direction
Which forms of DNA polymerase are able to run in the 3’ to 5’ direction and have exonuclease activity?
Gamma and delta polymerase
Why is it so important that gamma polymerase has a proof reading ability?
Only one that functions in the mitochondria
Has to do both functions and still give a replicated daughter cell which has a high fidelity to the parent cell
What term is used to describe corrections after replication?
Mismatch repairs
Define a mismatch repair
When an incorrect nucleotide is added to the growing strand, replication is STALLED by the fact that the nucleotide’s exposed 3’-OH group is in the “wrong” position
Cannot form the 3’5’ phosphodiester bond
Why does replication take 8 hours to complete?
DNA polymerase has to come in a fix any replication errors, like mismatch repairs, before it allows the cell to divide
What happens to incorrectly paired nucleotides that still remain following mismatch repairs?
Become PERMANENT mutations after the next cell division. This is because once a mistake is established in the gene, the cell no longer recognises them as errors. Recognised as the parent
When can these permanent mutations occur?
- When a rare mutation in the nucleotide base occurs, and these complementary base pair with a normal nucleotide base
- Wobble induced replication errors that can lead to strand slippage
What two scenarios can occur if mutations from rare nucleotides occurs in the next cell division?
1) Newly synthesised DNA can loop out and remain there, with one nucleotide added to the new DNA strand - one extra nucleotide
2) The template strand can loop out and come back again, leading to the deletion of one base on the new strand - missing one nucleotide
Key sentence to remember about changes in the genomic DNA through rare mutations
We can get permanent changes in the genomic DNA due to wobble induced replication errors that leads to strand slippage