If histones are depleted from a metaphase chromosome and viewed under a transmission electron microscope shows SCAFFOLD. Which is almost 8% of wt

TLS Online TPP Program

#Id: 3348

#Unit 3. Fundamental Processes

Direct repair of alkylated bases by AlkB

TLS Online TPP Program

#Id: 3349

#Unit 3. Fundamental Processes

The AlkB protein is an alpa-ketoglutarate-Fe2+ dependent hydroxylase. It catalyzes the oxidative demethylation of 1-methyladenine and 3-methylcytosine residues

TLS Online TPP Program

#Id: 3350

#Unit 3. Fundamental Processes

Methyltransferase catalyzes the transfer of the methyl group on O6 -methylguanine to a cysteine residue on the enzyme, thereby restoring the normal G in DNA.

TLS Online TPP Program

#Id: 3352

#Unit 3. Fundamental Processes

Photoreactivation directly reverses the formation of pyrimidine dimers that result from ultraviolet irradiation.

TLS Online TPP Program

#Id: 3354

#Unit 3. Fundamental Processes

In photoreactivation, the enzyme DNA photolyase captures energy from light and uses it to break the covalent bonds linking adjacent pyrimidines.

TLS Online TPP Program

#Id: 3359

#Unit 3. Fundamental Processes

Another example of direct reversal is the removal of the methyl group from the methylated base O6 –methylguanine  In this case, a methyltransferase removes the methyl group from the guanine residue by transferring it to one of its own cysteine residues. This is costly to the cell because the methyltransferase is not catalytic; having once accepted a methyl group, it cannot be used again.