Test: DNA, RNA & Experiments on Genetic Material - NEET MCQ

Meselson and Stahl prove experimentally semi conservation of DNA replication not say but structure of DNA.

Avery, MacLeod and Mcarty conclude DNA is heridatary material first time while Griffith show transforming principal.

Transformation was discovered in Streptococcus pneumoniae in 1928 by Frederick Griffith; in 1944, Oswald T. Avery, Colin M. MacLeod, and Maclyn McCarty demonstrated that the “transforming principle” was DNA. Both results are milestones in the elucidation of the molecular nature of genes.

Nucleobases, also known as nitrogenous bases  are nitrogen-containing biological compounds that form nucleosides, which in turn are components of nucleotides, with all of these monomersconstituting the basic building blocks of nucleic acids. The ability of nucleobases to form base pairs and to stack one upon another leads directly to long-chain helical structures such as ribonucleic acid (RNA) and deoxyribonucleic acid (DNA)....

According to Chargaff’s rule in all cellular DNA, regardless of the species, number of adenosine residues is equal to the number of thymidine residues which means that A = T and the number of guanosine residues is equal to the number of cytidine residues; G = C . Hence, that the sum of the purine residues equals the sum of the pyrimidine residues; i.e., A + G = T + C.

In Hershey and Chase experiment, some bacteriophage viruses where grown in a medium which contained radioactive phosphorus(32P) and some in radioactive sulphur(35S) medium. Viruses grown under radioactive (32P) contained radioactive DNA and Viruses grown under radioactive (35S) contained radioactive protein. When infected in E.coli separately, bacterial cells were gently agitated in blender to remove viralcoats from the bacteria. Culture was also centrifuged. Radioactive 32P was found to be associated with the bacterial cell whereas Radioactive 35S was found in the surrounding medium. Hence, the process resulted in viral DNA. 

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 and at least one phosphate group.

mRNA carries genetic information from DNA to ribosomes for synthesising polypeptide chains. tRNA carries amino acids to mRNA for translation. rRNA is a vital component of ribosomes.

 In the DNA of an organism a total number of 5386 nucleotides were found out of which the proportion of different bases were: Adenine = 29%, Guanine = 17%, Cytosine = 32%, Thymine = 17%. Considering the Chargaff’s rule it can be concluded that it is a single stranded DNA.

Answer:
The nitrogenous bases present in DNA are:
- Adenine: It pairs with thymine (T) in DNA. Adenine is a purine base, meaning it has a double-ring structure.
- Guanine: It pairs with cytosine (C) in DNA. Guanine is also a purine base.
- Cytosine: It pairs with guanine (G) in DNA. Cytosine is a pyrimidine base, meaning it has a single-ring structure.
- Thymine: It pairs with adenine (A) in DNA. Thymine is a pyrimidine base.
The correct option is A, which includes all four nitrogenous bases found in DNA: adenine, guanine, cytosine, and thymine.
Explanation:
DNA (deoxyribonucleic acid) is a molecule that carries the genetic information in living organisms. It is composed of two strands that are twisted together to form a double helix structure. Each strand is made up of a series of nucleotides, which are the building blocks of DNA.
A nucleotide consists of three components: a nitrogenous base, a sugar molecule (deoxyribose), and a phosphate group. There are four different nitrogenous bases found in DNA, and they are responsible for carrying the genetic code. The arrangement of these bases along the DNA molecule determines the instructions for the formation and functioning of an organism.
Adenine, guanine, cytosine, and thymine are the four nitrogenous bases found in DNA. Adenine always pairs with thymine, and guanine always pairs with cytosine. These base pairs are held together by hydrogen bonds, forming the rungs of the DNA ladder.
Uracil (U) is not present in DNA; it is found in RNA (ribonucleic acid) instead. RNA is a single-stranded molecule that plays a role in protein synthesis.
In summary, the correct answer is A: Adenine, guanine, cytosine, and thymine are the nitrogenous bases present in DNA.

Beadle and Tatum proposed their one gene one enzyme hypothesis on the basis of biochemical genetics in Neurospora crassa. Beadle and Tatum showed that each kind of mutant bread mould lacke a specific enzyme. Their experiments demonstrated that genes carry information for making proteins.

Nucleosomes can be said when the DNA is wrapped around the histone protein, so this structure is called nucleosome and it has 200 base pairs of the DNA helix.

• Alfred Hershey and Martha Chase wanted to figure out whether it was the protein from the bacteriophage that was entering into the bacteria or if it was the DNA.
• So, they cultured the bacteriophage in a medium containing radioactive phosphorous.
• In this medium they observed that the radioactive DNA was present in the virus but not the radioactive protein.
• This is because, protein doesn’t contain phosphorous but on the contrary, the DNA does.

In the DNA molecule:
A: There are two strands which run parallel in the 5'-3' direction.
- The DNA molecule is composed of two strands that are arranged in a double helix structure.
- These two strands run parallel to each other.
- The numbering of the DNA strands is based on the carbon atoms in the sugar molecule of the nucleotides.
- The 5' end of one strand is connected to the 3' end of the other strand.
B: The total amount of purine nucleotides and pyrimidine nucleotides is not always equal.
- Purine nucleotides include adenine (A) and guanine (G), which have a double-ring structure.
- Pyrimidine nucleotides include thymine (T) and cytosine (C), which have a single-ring structure.
- In a DNA molecule, the total number of purine nucleotides is always equal to the total number of pyrimidine nucleotides.
- However, the specific sequence of nucleotides can vary, resulting in variations in the proportions of different purines and pyrimidines.
C: Proportion of adenine in relation to thymine varies with the organism.
- Adenine (A) always pairs with thymine (T) in a DNA molecule.
- The proportion of adenine in relation to thymine can vary between different organisms.
- In some organisms, the proportion of adenine may be higher than thymine, while in others, it may be lower.
- These variations in nucleotide composition contribute to the genetic diversity among different species.
D: There are two strands which run antiparallel - one in 5'-3' direction and the other in 3'-5' direction.
- The two strands of the DNA molecule run in opposite directions, which is known as antiparallel.
- One strand runs in the 5'-3' direction, while the other runs in the 3'-5' direction.
- This antiparallel arrangement allows for complementary base pairing between the two strands, where adenine pairs with thymine and guanine pairs with cytosine.
- The antiparallel arrangement is essential for DNA replication and transcription processes.
In summary, the correct statement is D: There are two strands which run antiparallel - one in 5'-3' direction and the other in 3'-5' direction.