ASSIGNMENT

Biology - Assignment

[Writer's Initials]

Assignment

SECTION - C

Describe the process of nucleotide excision repair in E. coil. Why are bacteria with mutation in the enzymes involved in this pathway so sensitive to UV light?

In the NER which is the short form for Nucleotide Excision Repair, within a string of nucleotide, the bases that are damages are cut out and replace with the directed DNA by the temple strand (undamaged). For the removal of dimmers, the repair system is used and formed by radiations (Ultra violet) as well as the modified nucleotide by the adducts bulky chemical. By nucleotide excision, the known feature of damage is mended and the modified nucleotide causes a distortion so significant in the DNA helix. In all the examined organisms, NER occurs.

The enzymes which catalyzed this process are the best characterized and are call UvrABC excinuclease and in the E. coli the UvrD helicase. The encoding genes repairs the discovered function as the mutants that are sensitive to the UV damage, As show in fig, at the extensive and high dose of UV radiations the E. coli wile type are killed. Sensitive to UV radiation, mutant strains can be known and recognized, needed for UV resistance commonly known as uvr, these are flaws in the operation and functions. The complementation genes, proteins that play chief rules in NER are four mentioned as, uvrA, uvrB, uvrC and uvrD.

 

Explain, with examples, how DNA binding proteins can determine DNA sequence without disrupting the double-helix structure DNA.

Proteins that see and know a particular DNA sequence do this because of the area of the protein is much tight with the particular area (surface) features of the region of the double helix, depending on the nucleotide, these features vary and in this case different protein will know the different sequence of the nucleotide. In most of the cases, in the major groove of the DNA helix the protein inserts and makes a molecular contact with the series of base pairs. The hydrogen bonds, and ionic bonds are formed by the protein, and hydrophobic contact with the bases edges usually hydrogen bonds disrupting that together holds the base pairs. Although it is a weak individual contact, at the protein about 20 or so contacts are formed typically. It is made sure by the DNA interface combination so that the relation and interaction is very strong and specific. In biology, the interaction of DNA among the most specific and tightest molecular interactions. The DNA in the examples is known that it is unique in details, and through several structural motifs, many of the protein are responsible for the regulation of gene recognizes the DNA. In the major groove, these fit into the DNA double helix and form an association tightly with DNA base pair short stretch.

What are the roles of topoisomerases in a eukaryotic cell? Explain class I topoisomerases function.

There is a covalent bond with the DNA enzyme intermediate in the middle of the 5'-phosphoryl end of the tyrosine residue and nicked DNA in the inset ...