Important MCQs on Molecular Basis of Inheritance

Ans. (a) DNA Methylase

Explanation: In Mammals, DNA methylation is an epigenetic process that transfers the methyl group onto the cytosine’s C5 position to form 5-methylcytosine. DNA methylation tends to regulate gene expression as it recruits proteins that are involved in gene repression or as it inhibits the transcription factor(s)’ binding to DNA. When it is under development, the DNA methylation’s pattern in the genome changes due to dynamic processes involving both de novo DNA demethylation and methylation. So, differentiated cells build a unique and stable DNA methylation pattern that helps to regulate gene transcription that is tissue-specific. 

Ans. (b) Phosphodiester bonds

Explanation: The DNA is made up of the polynucleotide chain’s two strands both of which are attached with hydrogen bonds. A phosphodiester bond attaches one nucleotide to the other nucleotide. A Phosphodiester bond is made between the fifth carbon and the third carbon of two successive nucleotides. 

Ans. (c) Chromatin

Explanation: The Nucleosome is the repeating unit of chromatin in the nucleus. About six feet of DNA is filled in a nucleus that has a diameter less than the diameter of a human hair. One nucleosome has 150 base pairs of DNA sequences that are wrapped around histone proteins’ cores. Chromosomes are formed when these are repeatedly folded in themselves.

Also Read: Chromosomes and Genes

Ans. (a) Frederick Griffith

Explanation: Frederick Griffith was a bacteriologist. He conducted an experiment in the year 1928. This experiment was conducted on a Streptococcus Pneumoniae. He concluded that when the R II strain was injected into a healthy mouse, it continued to remain healthy. However, upon injecting the S III strain in the mouse, it died of Pneumonia. He once again injected the mouse with the heat-killed S III stain and the mouse remained healthy. When he injected the heat-killed S III strain in the living R II strain, the mouse still died of Pneumonia. He concluded that the heat-killed S III bacteria transformed the R II bacteria into S III bacteria.

Ans. (a) Operator

Explanation: The operator is a DNA sequence that is found between the first coding gene and the promoter region. This operator region functions as a binding site for repressor protein thus option A is correct. The regulator gene does the work of regulating the structural genes’ expression by its protein products that mostly tend to be transcription factors. These transcription repressors/factors tend to be bound to the operator region that is found in the binding site of the RNA polymerase. So, it prevents transcription and binding. The promoter is a DNA segment that initiates the transcription of a particular gene. The gene that tends to code for any protein product or RNA and it is not a regulatory protein is called a structural gene. 

Ans. (d) All of the above.

Explanation: RNA is unstable as a catalyst and is easily damaged by enzymes. By doubling itself and using deoxyribose sugar, a stable form of DNA was introduced with structural and chemical modifications. DNA damage can occur, like double-strand breaks or DNA cross-linkage, which can lead to tumours or cancer.

Ans. (c) both (a) and (b)

Explanation: The DNA replication was proved by conducting an experiment using two isotopes, namely, nitrogen-14 and nitrogen-15. When Nitrogen 14 was added to the heavy Nitogen15-Nitrogen15 DNA, a hybrid of Nitogen15-Nitrogen14 was found in the first generation. The hybrid remained after the second generation, but a light DNA of Nitrogen14-Nitrogen14 was seen too. This indicated that DNA has gone through replication. This type of DNA replication let each child strand be associated with its template strand.

Ans. (d) Transcription

Explanation: Transcription is when a segment of DNA is copied into RNA. The segments of DNA that are transcribed into RNA molecules that are able to encode proteins produce messenger RNA (mRNA). The Other segments of DNA that are copied into the RNA molecules are known as non-coding RNAs. 

Ans. (b) gene

Explanation: The segment of DNA molecules that are responsible for coding or specifying for one polypeptide chain is known as a gene. A gene is the basic functional and physical unit of heredity. Genes are made of DNA and they are instructions for making proteins.  They keep the information needed to maintain and build the cells of an organism and then pass those genetic characteristics to their offspring.

Also Read: Difference Between Gene and DNA

Ans. (c) Degenerate

Explanation: All amino acids (except methionine and tryptophan) are shown with more than one codon. Hence, they are known as degenerate. 64 combination of the four different nucleotides are possible in sets of three, there is a redundancy found in the system that means that more than the triplet can be used to code most amino acids.