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Practice each question, then open the answer or worked solution.
The human chromosomes with the highest and least number of genes in them are respectively:
Ans: (c) Chromosome 1 and $Y$
There are 2968 genes on chromosome 1 and 231 genes on chromosome Y.
Who amongst the following scientists had no contribution in the development of the double-helix model for the structure of DNA?
Ans: (d) Meselson and Stahl
The X-ray diffraction data of DNA was created by Rosalind Franklin and Maurice Wilkins, and Erwin Chargaff presented two rules based on thorough experimentation that helped lead to the discovery of the double helix structure of DNA, known as the Chargaff rules. Meselson and Stahl were not involved in the creation of the double helix, but they were involved in the testing of the semi-conservative character of DNA replication.
DNA is a polymer of nucleotides that are linked to each other by a \[3^{\prime}-5^{\prime}\] phosphodiester bond. To prevent polymerization of nucleotides, which of the following modifications would you choose?
Ans: (b) Remove/Replace \[3^{\prime} \mathrm{OH}\] group in deoxyribose
If the \[3 \mathrm{OH}\] group in deoxyribose is deleted or replaced, no phosphodiester linkages are formed, and so nucleotide polymerization is blocked.
Discontinuous synthesis of DNA occurs in one strand, because:
Ans: (b) DNA dependent DNA polymerase catalyzes polymerization only in one direction (5' \[\rightarrow 3^{\prime}\] )
Polymerization is only catalyzed in one direction by DNA-dependent DNA polymerases, which is $53 .$ At the replicating fork, this adds a layer of complexity. As a result, replication is continuous on one strand (the template with polarity 3 5) but discontinuous on the other (the template with polarity 53 ). The enzyme DNA ligase joins the fragments that are synthesizing intermittently.
Which of the following steps in transcription is catalyzed by RNA polymerase?
Ans: (d) All of the above
In bacteria, a single DNA-dependent RNA polymerase catalyzes the transcription of all kinds of RNA. The promoter is bound by RNA polymerase, which starts transcription (Initiation). It polymerizes in a template-dependent manner using nucleoside triphosphates as a substrate, following the complementarity rule. It also aids in the opening of the helix and promotes elongation. Only a little portion of the RNA is still linked to the enzyme. The nascent RNA and the RNA polymerase both fall off once the polymerases reach the terminator region. Transcription is halted as a result of this. Only the elongation phase can be catalyzed by the RNA polymerase. It forms transitory associations with initiation-factor () and termination-factor () to start and stop transcription, respectively. The RNA polymerase's selectivity to initiate or terminate is altered when it interacts with certain factors.
Control of gene expression takes place at the level of:
Ans: (b) Transcription
The initial stage in gene expression is transcription. A specific region of DNA is transcribed into mRNA during this process. As a result, it regulates gene expression.
Regulatory proteins are the accessory proteins that interact with RNA polymerase and affect its role in transcription. Which of the following statements is correct about regulatory protein?
Ans: (d) They can act both as activators and as repressors
Regulatory proteins have an impact on RNA's ability to recognize initiation sites. Both negative (repressor) and positive (activator) roles are played by regulatory proteins.
Which was the last human chromosome to be completely sequenced:
Ans: (a) Chromosome 1
The Human Genome Project was a megaproject that began in 1990 with the goal of sequencing all \[3 \times 10^{9}\] base pairs of the human genome. Because chromosome 1 has the most genes \[(2968)\], it was the last human chromosome to be sequenced entirely.
Which of the following are the functions of RNA?
Ans: (d) All of the above.
mRNA transports genetic information from DNA to ribosomes for polypeptide chain synthesis. Amino acids are carried by tRNA to mRNA for translation. Ribosomes require rRNA to function properly.
While analyzing 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 Chargaff's rule, it can be concluded that:
Ans: (b) It is single-stranded DNA
According to Chargaff's guidelines, DNA from any cell of any organism should have a 1:1 ratio of pyrimidine and purine bases (base Pair Rule). This means that the amounts of guanine and cytosine are equal, and the amounts of adenine and thymine are equal. This pattern can be found on both DNA strands. The percentages of adenine and guanine are not equal in this example, and the same is true for cytosine and thymine. As a result, it's single-stranded DNA.