All eukaryotic genes contain two kinds of base sequences. Which of the following plays role in protein synthesis?

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The gene of a Eukaryotic organism contains two kinds of base sequences. These sequences are known as Intron or intragenic region and Exon.

The intron is a part of a gene that is removed during mRNA maturation by a process called RNA splicing. Therefore, the intron sequence is a noncoding part of the gene that does not code for any protein sequence. Most of the eukaryotic genes are broken up by one or more introns. On the other hand, exons are the parts of the eukaryotic gene sequence that are expressed in the protein.

During RNA processing introns are removed by RNA splicing, and exons are joined covalently to one another generating the mature mRNA. Therefore, the exon of the eukaryotic gene plays an important role in protein synthesis. 

Which of the following statement is true regarding the double helical structure of DNA and Nobel Prized received by Watson and Crick?

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The double helix structure is formed by two strands of nucleic acids such as DNA. The two strands are joined together by hydrogen bonds between the nucleotides (A-T and G-C) of two strands that run in anti-parallel (5′-3′ and 3′-5′) direction. The B-DNA is a is right-handed double-helix DNA with about 10 base pairs present per turn.

British X-ray crystallographer Rosalind Franklin along with American molecular biologist James Dewey Watson, British molecular biologist Francis Harry Compton Crick, and British biophysicist Maurice Hugh Frederick Wilkins played important roles in deciphering the double-helical structure of the DNA. The double-helical structure of DNA was published in the journal Nature in 1953.

For their discoveries concerning the molecular structure of DNA Watson, Crick and Wilkins received the Nobel Prize in Physiology and Medicine in 1962.

Which of the following RNA contains a dihydrouridine arm?

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The dihydrouridine arm or the D-arm is present in the tRNA or the transfer RNA. Dihydrouridine is a modified pyrimidine base found in the tRNAs of the prokaryotes, eukaryotes, and in some archaea. The formation of dihydrouridine is catalyzed by the enzyme Dihydrouridine synthase. The modified base is formed by the reduction of the uracil (C=C double bond at positions 5 and 6) with flavin mononucleotide as a cofactor. 

The dihydrouridine is mostly found in the D-loop of tRNAs. The D-loop of the tRNA is named due to the modified dihydrouridine base. The numbers of dihydrouridines is varying in different tRNAs. The Dihydrouridine base on the D-loop forms a hairpin structure in the tRNA. The hairpin structure plays an important role in the folding and stability of tRNA.

Which one of the following pair of nitrogenous bases of nucleic acids, is wrongly matched with the category mentioned against it?

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DNA and RNA are genetic materials chemically known as nucleic acids. DNA and RNA are polymers of nucleotides. A nucleotide is made up of a nitrogenous base, a pentose sugar, and a phosphoric acid. The nitrogenous bases present in DNA are Adenine, Guanine, Thymine, and Cytosine and for RNA are Adenine, Guanine, Uracil, and Cytosine.

The nitrogenous bases are divided into two types (i) purine and (ii) pyrimidines. Purines are heterocyclic compounds with two rings. On the other hand, pyrimidines are single-ring compounds. Examples of purines are Adenine and Guanine. Examples of pyrimidines are thymine, cytosine, uracil.

Therefore (D) Adenine, Thymine – Purines is wrong.

Who coined the term gene?

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A gene is a sequence of nucleotides in the DNA or the chromosome of an organism. Gene is the basic unit of heredity. It inherits from the parents to the offspring. The gene contains the information for a specific trait. The gene is responsible for the synthesis of gene products. The gene products may be RNA (tRNA, rRNA, miRNA) or protein through mRNA.

The term gene was coined by Danish plant biologist and geneticist Wilhelm Johannsen. He introduce the term gene in 1909. He also coined the terms phenotype and genotype.

The number of protein-coding genes present in humans is 20,000-25,000, mice 30,000, C. elegans 18000, Trichomonas vaginalis 60,000, Drosophila melanogaster 14000, Plasmodium falciparum 5000 etc.

Deoxy position of deoxyribose in DNA is

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The sugar present in DNA is a Pentose sugar that contains five carbon atoms. The numbering of the carbon atoms is given in clockwise position as 1st as (1′), 2nd as (2′), 3rd as (3′), 4th as (4′), and 5th as (5′). In ribose sugar, the number of hydroxyls (-OH) groups are present at the Carbon position 1st, 2nd, 3rd, and 5th. On the other hand, the number of hydroxyls (-OH) groups is present at the Carbon position 1st, 3rd, and 5th in deoxyribose sugar.

Therefore, the absence of the hydroxyl (-OH) group on the 2nd Carbon (2′) is denoted as the deoxy position in the deoxy-ribose sugar in DNA.

Which bond is present between the nucleotides of the DNA?

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Nucleotides are the basic unit of the genetic materials DNA and RNA. The bond present between two nucleotides of the DNA is a phosphodiester bond. A nucleotide in DNA is made up of nitrogen-containing nucleobase, deoxyribose sugar, and a phosphate group. The phosphodiester bond form by the sugar and the phosphate group between two nucleotides.

When a hydroxyl (OH) group of the phosphoric acid (H3PO4) reacts with the hydroxyl (OH) group on a different molecule an ester bond forms. In the case of DNA, the two hydroxyls (OH) groups of the phosphoric acid (H3PO4) reacts with two hydroxyls (OH) groups on different molecules, a phosphodiester bond forms. The phosphate and sugar form the phosphate-sugar backbone of the DNA molecule. Similarly, a phosphodiester bond is also present between the nucleotides of the RNA molecules.

Which of the following is not involved in eukaryotic translation?

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Eukaryotic translation requires ribosomes, messenger RNA (mRNA), and transfer RNA (tRNA) but does not require the spliceosome. The expression of genes in eukaryotes requires a mature mRNA.

During transcription, RNA polymerase II reads the gene sequence on DNA and transcribes the genes into a pre-mRNA. The pre-mRNA is large in size and contains some additional sequence that is not required in the protein. The coding sequence is called exon and the noncoding sequence is called introns. Therefore, the pre-mRNA undergoes processing to form the mature mRNA.

To remove the introns from the pre-mRNA a spliceosome is formed. The spliceosome needs many proteins called splicing factors. These splicing factors help to remove introns from pre-mRNA. After removal of introns through spliceosome, the mRNA comes out from the nucleus and the translation process starts.

The plasmid pBR322 has antibiotic resistance genes for:

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The plasmid pBR322 is a prokaryotic cloning vector. The pBR322 plasmid named as the p stands for “plasmid,” and the BR stands for the creator of the plasmid “Bolivar” and “Rodriguez” and the 322 stands for the transformed colonies used for sequencing. The length of plasmid pBR322 is 4361 base pairs.

The plasmid pBR322 has two antibiotic resistance genes. They are the bla gene and the tetA gene. The protein encoded by the bla gene is ampicillin resistance (AmpR) which provides resistance against antibiotic ampicillin. The protein encoded by the tetA gene is tetracycline resistance (TetR) which provides resistance against antibiotic tetracycline.

Both the antibiotic resistance genes act as selectable markers. Further, these two genes contain unique restriction sites for many restriction enzymes.

Several enzymes are involved in DNA repair pathways. Which one of the following enzymes is also referred to as a suicidal enzyme?

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The enzyme O-6-Methylguanine-DNA Methyltransferase (MGMT) (EC 2.1.1.63) encodes by the human MGMT gene. The gene is present on chromosome 10 at the q26.3 position. The enzyme is also known as O6-Methylguanine-DNA Methyltransferase, Methylated-DNA-Protein-Cysteine Methyltransferase, Methylguanine-DNA Methyltransferase, or DNA “suicide” repair enzyme.

Alkylating agents add an alkyl group (CH3) to the guanine (G) nitrogenous base of the DNA molecule. The methyl group on the nitrogenous base interferes with its binding with cytosine and mispair with thymine. This mispairing of guanine with thymine causes a point mutation (GC to AT transition mutations). Examples of alkylating agents are Nitrogen mustards (cyclophosphamide, mechlorethamine), busulfan, temozolomide, thiotepa, etc. Due to their mutagenic activity, alkylating agents are potent carcinogens. They can cause mutation and are associated with several types of cancer. Example: Lymphoma, glioblastoma, colorectal, and lung cancer.

The enzyme O-6-Methylguanine-DNA Methyltransferase (MGMT) is a DNA repair protein. The enzyme transfers the methyl groups (CH3) from O(6)-alkylguanine to its Cysteine molecule and repairs the mutation.  Thus O-6-Methylguanine-DNA Methyltransferase (MGMT ) avoiding mutation, cell death, and cancer caused due to the alkylating agents.

The Suicide Enzyme:

Unlike other enzymes, where the enzyme retains its activity at the end of the reaction, the MGMT lost its activity after catalyzing the enzymatic reaction. The enzyme O-6-Methylguanine-DNA Methyltransferase (MGMT) lost its activity after removing the methyl group from O(6)-alkylguanine. The enzyme transfer methyl group to one of its Cysteine amino acid that causes deactivation of the enzyme.