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Practice each question, then open the answer or worked solution.
In some viruses, DNA is synthesized by using RNA as a template. Such a DNA is called:
Ans: (c) C DNA
In a synthesis catalyzed by the enzyme reverse transcriptase, complementary DNA (cDNA) is double-stranded DNA generated from a messenger RNA (mRNA) template.
If Meselson and Stahl's experiment is continued for four generations in bacteria, the ratio of \[{ }^{15} \mathrm{~N} /{ }^{15} \mathrm{~N}:{ }^{15} \mathrm{~N}^{14} \mathrm{~N}:{ }^{14} \mathrm{~N}^{14} \mathrm{~N}\] containing DNA in the fourth generation would be:
Ans: (d) 0:1:7
In the following generation, the $15 \mathrm{~N} / 15 \mathrm{~N}$ ratio remains zero. The $15 \mathrm{~N} / 14 \mathrm{~N}$ ratio remains constant (one), whereas the $14 \mathrm{~N} / 14 \mathrm{~N}$ ratio rises. This is depicted in the diagram below.
If the sequence of nitrogen bases of the coding strand of DNA in a transcription unit is: \[5^{\prime}-\mathrm{A} \mathrm{T} \mathrm{G} \mathrm{A} \mathrm{A} \mathrm{T} \mathrm{G}-3^{\prime}\]
the sequence of bases in its RNA transcript would be;
Ans: (a) \[5^{\prime}-\mathrm{A} \cup \mathrm{G} \mathrm{A} \mathrm{A} \cup \mathrm{G}-3^{\prime}\]
The process of converting DNA to RNA is known as translation. It consists of coding and template strands of DNA, with the template strand becoming RNA and following the base-pairing rule except in the RNA strand, where uracil replaces thymine. We have coding strand-ATGAATG in the question.
So, the template strand is TACTTAC
As a result, the RNA strand-AUGAAUG
The RNA polymerase holoenzyme transcribes:
Ans: \[(d)\] the structural gene only
Transcription is divided into three stages: start, elongation, and termination. When the RNA. polymerase binds to the promoter, which is solely used as a binding site for the RNA polymerase and is not transcribed, initiation begins. Each gene has its own promoter region that directs the start of transcription. This is followed by a transcribed gene section (structural gene) and finally a terminator that stops transcription.
If the base sequence of a codon in mRNA is \[5^{\prime}-A U G-3^{\prime}\], the sequence of tRNA pairing with it must be:
Ans: (b) \[5^{\prime}-\] CAU \[-3^{\prime}\]
In the \[5^{\prime}-3^{\prime}\] direction, the first base of the anticodon binds to the third base of the codon (reading in the \[5^{\prime}-3^{\prime}\] direction). The complementary anticodon will be \[3^{\prime}-U A C-5^{\prime}\] or \[5^{\prime}-C A U-3^{\prime}\] if the nucleotide sequence in the mRNA codon is \[5^{\prime}-\mathrm{AUG}-3^{\prime}\].
The amino acid attaches to the tRNA at its:
Ans: \[(b) 3^{\prime}\] - end
The anticodon loop on tRNA has bases that are complementary to the coding, and the amino acid acceptor end binds to amino acids. In tRNAs, the site is located at the \[3^{\prime}\] end opposite the anticodon and is unique to each amino acid.
To initiate translation, the mRNA first binds to:
Ans: (a) The smaller ribosomal sub-unit
The ribosome is the cellular factory in charge of protein synthesis. The ribosome is made up of around 80 distinct proteins and structural RNAs. It has two subunits in its inactive state: a large subunit and a small subunit. When the small subunit comes into contact with an mRNA, the mRNA to protein translation process begins.
In E. coli, the lac operon gets switched on when:
Ans: (a) lactose is present and it binds to the repressor
Lactose is a stimulant. It attaches to the repressor protein and activates the operon.