DNA REPAIR, DNA RECOMBINATION

Question 1

what does “direct repair” mean, in regards to DNA?

Answer 1

Direct repair refers to the specific systems or enzymes that have been created for specific DNA repairs. These involve no removal of base or nucleotides. Include methyaltion, pyrinidine dimers

Question 2

What enzyme repairs UV induced pyrimindine dimer damage? Explain UV induced damage and how enzyme repairs it

Answer 2

photolyase. UV light causes the double bonds of one pyrimidine nucleotide to connect to another, forming a cyclobutyl ring. Photolyase has a MTHFpolyGlu in its active site, which, absorbs a blue light photon, using UV light to restore UV damage. The electron then transfers to FADH, becoming FADH-. From FADH-, the electrons go to the pyrimindine dimer to break/destabilze the cyclobutyl ring and reverting to FADH Rearrangement happens to restore the monomers and electron goes back to FADH to become FADH-

Question 3

What is the enzyme AlkB?

Answer 3

direct repair enzyme that repairs methlaytion of 1-methyladenine and 3-methylcytosine. Uses OH of a-ketoglutarate (citric acid cycle) to become succinate (TCA cycle). The result is the correct nucleotide and formaldehyde (H2C=O) and H+

Question 4

What is a consequence of unrepaired DNA?

Answer 4

Mutation that affects the types of nucleotides hydrogen bonding to eachother. For example, methyl guanine will hydrogen bond with thymine, rather than a cytosine

Question 5

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What enzyme repairs a O6 - Methylguanine nucleotide?How does it do it?

Answer 5

methyltransferase. It uses an active protein (Cys-SH) and inactivates it (Cys-S-CH3). Energy costsly, put worth it for cell. ONly for this guanine

Question 6

What is DNA recombination?

Answer 6

It is when DNA rearranges its location. This can be within a chromsome or from one chromo to another

Question 7

What is homologous or general recombination?

Answer 7

This is when 2 similar DNA sequences exchange DNA

Question 8

What is DNA transposition?

Answer 8

It is when short DNA moves from one chromosome to another. Called jumping genes

Question 9

What is site-specific recombination?

Answer 9

It is when DNA exchange happens only at a particular sequence

Question 10

What are the 3 functions of homologous recombination?

Answer 10

1. It assists in DNA repair
2. It links sister chromosomes to properly segregte them between self and daughter cells
3. Source of DNA exchange and therefore genetic diversity

Question 11

When does recombination occur in meiosis?

Answer 11

In first meiotic division