Molecular Biology and Genetics

DNA replication is semiconservative, and because the two strands are antiparallel, one strand (leading) is synthesized continuously while the other (lagging) is synthesized discontinuously in Okazaki fragments.

Meselson and Stahl used heavy nitrogen (15N) and light nitrogen (14N) isotopes to distinguish between old and new DNA strands in their experiment.

The bond energy of a DNA molecule is 1 eV, so this will be the energy required to break the bond

 A mutation is a permanent change in the sequence of DNA. Mutations can be caused by external (exogenous) or endogenous (native) factors, or they may be caused by errors in the cellular machinery. Physical or chemical agents that induce mutations in DNA are called mutagens and are said to be mutagenic. Exogenous factors: environmental factors such as sunlight, radiation, and smoking can cause mutations. Endogenous factors: errors during DNA replication can lead to genetic changes as can toxic by-products of cellular metabolism.

Eukaryotic genes are characterized by split gene organization, meaning they contain non-coding intervening sequences called introns that are removed during RNA processing. Prokaryotic genomes generally lack these introns.

The prokaryotic genetic system does not have a nucleus in their cell but the genome in a prokaryote is held within a DNA in the cytosol called nucleoid.

Two polynucleotide chains of DNA are wound around the same axis and are held together by complementary base pairing between nitrogenous bases of two strands in the same plane. Adenine of one strand forms two hydrogen bonds with thymine of other strand and guanine forms three hydrogen bonds with cytosine.  The two bases forming hydrogen bonds to joins the polynucleotide strands together are present in the same plane. Thus, the correct answer is A.

As per Watson and Crick standard base pairing rules, adenine forms double hydrogen bond with thymine and guanine forms triple hydrogen bond with cytosine. Hence, content of adenine is equal to content of thymine and content of guanine is equal to content of cytosine.

Nucleotides are organic molecules that serve as the monomers, or subunits, of nucleic acids like DNA and RNA. The building blocks of nucleic acids, nucleotides are composed of a nitrogenous base, a five-carbon sugar-ribose or deoxyribose, and at least one phosphate group. Thus, a nucleoside plus a phosphate group yields a nucleotide. The distance between two nucleotide pairs in DNA is 0.34nm.

RNA and DNA are genetic materials. Cytosine, Thymine, Guanine, and Uracil are all nitrogenous bases. They are present in RNA. Uracil is replaced by adenine in DNA. Arginine is an amino acid which is basic in nature. It is the building block of protein. 

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.

Genetic information is carried in the linear sequence of nucleotides in DNA. Each molecule of DNA is a double helix formed from two complementary strands of nucleotides held together by hydrogen bonds between G-C and A-T base pairs.

According to the Watson Crick double helical model of DNA, the diameter of DNA molecule is 20 angstrom. Hence, the distance between two DNA strand is 20 angstroms.
So, the correct answer is option A.

DNA is acidic. For its compaction, it requires basic (histone) proteins. The histone proteins, are positively charged and occupy the major grooves of DNA at an angle of 30° to helix axis.