Genomic instability and mutations

Question 1

mention 3 types of chromosomal mutations

Answer 1

• Inversion
• Translocation ( reciprocal translocation, changing of the information, nothing is lost)
• Euploid & aneuploid - during cell division trisomy and monosomy can occur and very common in cancer cells

Question 2

How does DNA polymerase prevent DNA mutation

Answer 2

• DNA polymerase is quit precise, making very few mistakes
• If mistakes occur it proofreads
• If mistake have happened it can “mismatch repair”, changing to right nucleotide

Question 3

What is Mismatch repair (MMR)

Answer 3

Single nucleotide mismatch

MutS and MutL protein recognize mismatch and recruit MutH, which make a nick at 5’ end. Exonuclease degrade the strand beyond the mismatch and polymerase fills the gap. Parent strand is recognize on its methylation.

Lack of MMR genes cause cancer

Question 4

What is Necleotide excision repair (NER)

Answer 4

Disorted strand, caused by UV

Distortions are recognized by XP proteins that makes two nicks and the polymerase fills the gap

Question 5

What is a double strand break (DSB) and how is it repaired

Answer 5

Non-homologous end-joining –> just ligation of the two double strands together with the help of proteins, this is error prone

Homologous recombination –> The ligation is made by copying of the other sister chromatid.

If BRCA is involved in DSB repair, if its dysfunctional NHEJ is preferred and thereby more mutations occur