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(b) phosphodiester bonds
A dinucleotide is made up of two nucleotides joined together by a \(3^{\prime} 5^{\prime}\) phosphodiester bond. To construct a polynucleotide chain, more nucleotides are connected in a similar way.
A nucleoside differs from a nucleotide. It lacks the:
(c) phosphate group
A pento is linked to a purine or pyrimidine base. A nucleoside is a sugar that is either ribose or deoxyribose.
A nucleotide is a sugar that has one or more phosphate groups connected to it.
Both deoxyribose and ribose belong to a class of sugars called:
(c) pentoses
Both deoxyribose and ribose belong to the Pentoses sugar family. The sugar molecule pentose has five carbons.
The fact that a purine base is always paired through hydrogen bonds with a pyrimidine base leads to, in the DNA double helix:
(c) uniform width throughout DNA
Purine always couples with pyrimidine to provide stability to the DNA strand. Because the sizes of the two bases differ, the arrangement is such that the bigger base forms a bond with a smaller base, making DNA 2 nm thick and providing a uniform width to DNA throughout its length.
The net electric charge on DNA and histones is:
(c) negative and positive, respectively
A nucleosome is formed when negatively charged DNA is wrapped around positively charged histone. This explains the nucleus’s ability to pack so much DNA into such a compact region.
The promoter site and the terminator site for transcription are located at:
Option (b) is the answer.
Which of the following statements is the most appropriate for sickle cell anaemia?
(d) All of the above
Because sickle cell anemia is an inherited condition, iron supplementation will not help. In persons with sickle cell anemia, the altered structure of RBCs confers malaria resistance.
One of the following is true with respect to AUG
(d) All of the above
The initiation code is the first codon of a messenger RNA (mRNA) transcript translated by a ribosome, and it is one of the genetic codes. The start codon is ubiquitous and codes for methionine, an amino acid, in both prokaryotes and eukaryotes.
The first genetic material could be:
(d) RNA
There are numerous convincing pieces of evidence that RNA was the earliest genetic substance. However, as a catalyst, RNA proved reactive and unstable. As a result, DNA became a genetic material in the living world.
With regard to mature mRNA in eukaryotes:
(b) exons appear but introns do not appear in the mature RNA
Introns, also known as intervening sequences or noncoding sequences, are additional regions found in eukaryotic transcripts. They aren’t found in either mature or processed RNA. Exons are the functional coding sequences. Splicing is the process of removing introns and joining exons to create functional RNAs.
The human chromosomes with the highest and least number of genes in them are respectively:
(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 doublehelix model for the structure of DNA?
(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?
(b) Remove/Replace \(3^{\prime} \mathrm{OH}\) group in deoxyribose
If the 3 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:
(b) DNA dependent DNA polymerase catalyzes polymerization only in one direction ( \(5^{\prime} \rightarrow 3^{\prime}\) ) Polymerization is only catalyzed in one direction by DNA-dependent DNA polymerases, which is 5 3 . 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?
(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 templatedependent 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:
(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?
(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:
(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?
(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:
(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.
In some viruses, DNA is synthesized by using RNA as a template. Such a DNA is called:
(c) C DNA
In a synthesis catalyzed by the enzyme reverse transcriptase, complementary DNA (cDNA) is doublestranded 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:
(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.
If the sequence of nitrogen bases of the coding strand of DNA in a transcription unit is: \(5^{\prime}-\) ATGAATG \(-3^{\prime}\) the sequence of bases in its RNA transcript would be;
(a) \(5^{\prime}-\mathrm{A} \cup \mathrm{GAA} \cup \mathrm{G}-3^{\prime}\)
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:
(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:
(b) \(5^{\prime}-\mathrm{CAU}-3^{\prime}\)
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:
\((b) 3^{\prime}\) – 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:
(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:
(a) lactose is present and it binds to the repressor
Lactose is a stimulant. It attaches to the repressor protein and activates the operon.
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