Tag: zoology

B-DNA is physiologically the most important form of DNA. The double helical secondary structure model of DNA described by Watson and Crick was the B-DNA. As per the original model, it contains 10 bp per turn but later measurements showed that it contains 10.5 base pairs per turn. Z DNA is the zigzag DNA. It is left handed helix. There are 12 base pair per turn, with a rise of 0.38 nm per base pair.
So, the correct answer is option B.

• DNA replication goes in the 5' to 3' direction because DNA polymerase acts on the 3'-oh of the existing strand for adding free nucleotides.
• Histones are rich in the basic amino acid residues lysines and arginines and forms histone octamer.
• Catalytic converters, having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing the emission of poisonous gases.
• As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.
• Fermentation of idli or dosa batter is carried out largely by lactic acid bacteria, the same class of microorganisms that are found in ‘curd.’
  
• So the correct answer is " Template with 5′⟶3′ polarity shows continuous DNA replication ".

DNA is a macromolecule of high molecular weight made up of repeating units called nucleotides. Each nucleotide is made up of

DNA replication, is the process of producing two identical replicas from one original DNA molecule. This biological process, occurs in all living organisms and forms the basis for biological inheritance. DNA is made up of two strands and each strand of the original DNA molecule serves as a template for the production of the complementary strand, a process referred to as semiconservative replication.

The purine & pyrimidine pairs of complementry strands of DNA are held together by hydrogen bonds. A set of five nitrogenous bases is used in the construction of nucleotides, which in turn build up the nucleic acids like DNA and RNA.

Purines and pyrimidines, make up the two groups of nitrogenous base which plays on important role in structural backbone of DNA. Adenine and guanine are purines, while cytosine and thymine are pyrimidines. Purines pairs with pyrimidines, by formation of H-bonds. Adenine attaches to thymine, by two hydrogen bonds, while cytosine and guanine forms three hydrogen between them.

If DNA is subjected to high temperature, the hydrogen bonds between the nitrogenous bases break down and the two strands separate. This process is called as melting of DNA. More the content of guanine (G) and cytosine (C) in the DNA, higher will be the melting temperature because G forms three hydrogen bonds with C as against adenine (A) and thymine (T) which form two hydrogen bonds.
So, the correct answer is option A.

The C$ _1$ of pentose sugar in nucleotides is linked to the N1 or N9 position of pyrimidine or purine bases through a glycosidic bond. The syn and anti conformations, are the two conformational forms of nucleotides around this bond. The two forms are interconvertible by rotating the glycosidic bond without a need to break the bond.
So, the correct answer is option B.

The DNA duplex of Watson and Crick is right handed helix and is called the B-DNA. There are five more models (A-DNA, C-DNA, D-DNA, E-DNA and Z-DNA) have been proposed. The Z-DNA is left handed double helix which contains zigzag back and 12 base pairs per turn.
So, the correct answer is option A.

The base pairing confers a unique property to the polynucleotide chains. The chains are complimentary to each other, such that if the sequence of one strand is known then the sequence of other strand can be predicted. Also if each strand of DNA acts as a template, for the synthesis of a new strand, the two double stranded DNA molecule thus produced would be identical to the parent molecule. The bases in the two strands of a double stranded DNA molecule are paired through hydrogen bonds forming base pairs (bp). Adenine forms two hydrogen bonds with thymine from opposite strand and vice versa. Similarly cytosine is bonded with guanine from three H bonds. As a result, always a purine comes opposite to a pyrimidine. This generated approximately, equal distance between the two strands. If base order in one chain of DNA is "ATCGA" then the number of H bonds will be 2, 2, 3, 3 and 2 respectively for the given nucleotides to base pair. Thus, the total number of hydrogen bonds will be 12.