Test: Genetic material -DNA & RNA (December 12) - NEET MCQ

Sugar component of a nucleotide may be ribose or deoxyribose.

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.

A nucleoside is composed of a base and a sugar.

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.

A nucleotide is composed of a base, a sugar and a phosphate.

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. 

In DNA and RNA, the phosphodiester bond is the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another, deoxyribose in DNA and ribose in RNA

Ribose or deoxyribose is a 5 carbon sugar.

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.

Purines have two rings in their structure, but pyrimidine bases have only one ring is true.

Purines and pyrimidines are two types of nitrogenous bases that are found in DNA and RNA. Purines have a larger, more complex structure than pyrimidines and contain two rings of atoms in their structure. Pyrimidines, on the other hand, have a simpler structure and contain only one ring of atoms.

Statements 1: They are hydrophobic and relatively insoluble in water at the near-neutral pH of the cell and 2: At acidic or alkaline pH the bases become charged and their solubility in water decreases are both false. Purines and pyrimidines are polar molecules and are generally soluble in water. They are not hydrophobic and do not become less soluble in water at acidic or alkaline pH.

Statement 3: At acidic or alkaline pH the bases become charged and their solubility in water increases is also false. As mentioned above, purines and pyrimidines are polar molecules that are generally soluble in water. They do not become more soluble in water at acidic or alkaline pH.

Therefore, the correct answer is statement 4: Purines have two rings in their structure, but pyrimidine bases have only one ring.