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MCBM Exam 4 Kat > Mutations and Repair > Flashcards

Flashcards in Mutations and Repair Deck (35):
1

What usually results in mutation?

Failure to repair/repair accurately lesions to the DNA.

2

Do mutations permanently alter the sequence of bases in a gene?

Yes

3

What happens where there are mutations in prokaryotes?

The mutation affects only one copy of the genetic information and if the organism survives it will be passed on to the next generation.

4

Can mutations in germ cells in multicellular organisms be transmitted?

Yes they can to subsequent generations. (I.e. cancer)

5

What are somatic mutations?

They are mutations that affect tissues (cancer) but are not heritable.

6

How do eukaryotic cells react when there is damage to DNA?

The cell cycle arrests until repairs are completed. If too extensive apoptosis may be triggered. Tissue damage safer than risk of cancer.

7

How do prokaryotes react to DNA damage?

Cell cycle arrests and is followed by emergency repair via SOS systems. Many cells die but some mutants survive because cannot afford to lose entire population.

8

When are somatic mutations harmful?

If they result in a substantial clone of mutant cells (i.e. tumor or mutation in embryogenesis at progenitor cells)

9

Why do we get cancer?

Some mutations increase mutation rate
Some mutations enhance cell proliferation

10

What are the four major types of mutation?

Substitution
Deletion
Insertion
Rearrangement

11

Do mutations tend to occur together or apart?

Deletion, Insertion and Rearrangements tend to occur together (i.e. radiation)

12

What are the types of substitution mutations?

Silent
Missense
Nonsense
Frameshift

13

Transition vs. Transversion Substitutions

Transition = purine for purine/pyrimidine for pyrimidine
Transversion = purine for pyrimidine/pyrimidine for purine

14

What is the most common mutation in cystic fibrosis?

Deletion of one codon (Phe out 1480)

15

What are 4 causes of mutations?

1) Errors during DNA replication (substitutions)
2) Chemical modification (substitutions)
3) Intercalation of certain chemical mutagens between cases (insertions and deletions)
4) Double stranded breakage and "emergency repair" (rearrangements and deletions)

16

What is intercalation?

Distorts helix which can block DNA replication and RNA transcription
Believed to interfere with any ongoing repair

17

How does radiation cause mutations?

X-ray exposure causes double stand breaks in DNA resulting in rearrangements and deletions

UV exposure causes thymine dimers that interfere with replication

18

What does mismatch repair do?

Repairs mismatches

19

What does base-excision repair do?

Repairs abnormal bases, alkylated bases and pyrimidine dimers

20

What does nucleotide-excision repair?

DNA lesions that cause large structural changes

21

What does direct repair repair?

Pyrimidine dimers

22

How is the correct strand chosen in mismatch repair?

In prokaryotes DNA is methylated at GATC sites which provides a temporary tag for parent strand as replication fork passes through
This guide excision of the daughter instead of the parent strand

23

What do mismatch repair defects lead too?

Leads to a strong predisposition to cancer (i.e. hereditary nonpolyopsis colorectal cancer)

24

What enzyme do all cells have that remove abnormal bases in a DNA strand?

DNA glycosylases

25

How does base excision repair work?

Enzymes remove base but leave sugar intact creating an AP site > specific AP endonuclease cuts sugar out > repair system fills in gap

26

How does nucleotide excision repair work?

Bulky distortions (thymine dimers) are removed (by ABC exonuclease in E. coli) then repair system fills the gap

27

What happens in nucleotide excision repair defects?

Leads to an autosomal recessive disease Xeroderma pigmentosum

28

What are the symptoms of xeroderma pigmentosum?

High sensitivity to skin damage by UV light
Strong predisposition to skin cancer

29

What happens in infancy with xeroderma pigmentosum?

Skin becomes dry and dermis atrophies
Keratoses form, eyelids scar and cornea ulcerates
Multiple skin tumors form and many patients die before the age of 30 from metastasis

30

How does direct repair work?

Repair without removing a base or nucleotide
Energetically expensive (dealkylating alkylated bases)

31

Example of low energy cost direct repair

Pyrimidine dimers can be repaired by light induced reverse reaction catalyzed by photolyases (less cost, no chance for more mistakes)

32

What alkylation agent should you know?

Mustard gas

33

What is the phenotype of Hereditary nonpolyopsis colorectal cancer?

Colon cancer

34

What repair process is affected in hereditary nonpolyopsis colorectal cancer?

Mismatch repair

35

What repair process is affected in zeroderma pigmentosum?

Nucleotide excision-repair