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Biology
Molecular Basis of Inheritance
200 questions from 38 papers, each with its answer.
- 200 questions
- 38 papers
- 5.67% of Biology
Transcription in Eukaryotes
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What is the role of RNA polymerase III in the process of transcription in Eukaryotes?
RNA polymerase III transcribes tRNA, 5S rRNA and snRNAs.
In eukaryotes, the RNA polymerase I transcribes rRNAs (28S, 18S and 5.8S), whereas the RNA polymerase III is responsible for transcription of tRNA, 5S rRNA and snRNAs (small nuclear RNAs). The RNA polymerase II transcribes precursor of mRNA, the heterogeneous nuclear RNA (hnRNA).
Human Genome Project – Methodologies
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Expressed Sequence Tags (ESTs) refers to
ESTs identify all the genes that are expressed as RNA.
All the genes that are expressed as RNA are referred to as Expressed Sequence Tags (EST); the EST approach focuses on identifying all the genes that are expressed as RNA.
The DNA – Search for Genetic Material
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Unequivocal proof that DNA is the genetic material was first proposed by
Hershey and Chase (1952) gave unequivocal proof using bacteriophages.
The unequivocal proof that DNA is the genetic material came from the experiments of Alfred Hershey and Martha Chase (1952). They worked with viruses that infect bacteria called bacteriophages.
Translation – Ribosome
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How many different proteins does the ribosome consist of?
The ribosome consists of structural RNAs and about 80 different proteins.
The cellular factory responsible for synthesising proteins is the ribosome. The ribosome consists of structural RNAs and about 80 different proteins.
The Genetic Material – RNA World
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Given below are two statements: Statement I: RNA mutates at a faster rate. Statement II: Viruses having RNA genome and shorter life span mutate and evolve faster. In the light of the above statements, choose the correct answer from the options given below:
RNA is unstable and mutates faster, so RNA viruses with short life spans evolve faster.
RNA mutates at a faster rate because it is unstable. Therefore, viruses having RNA genome and shorter life span mutate and evolve at faster rates.
Regulation of Gene Expression – The Lac Operon
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Match List-I with List-II.
Pick the matching item from Column II for each row.
Column I
- A. Gene 'a'
- B. Gene 'y'
- C. Gene 'i'
- D. Gene 'z'
Column II
- I. $\beta$-galactosidase
- II. Transacetylase
- III. Permease
- IV. Repressor protein
Correct answer: A → II, B → III, C → IV, D → I
Gene a codes for transacetylase, y for permease, i for repressor and z for beta-galactosidase.
The lac operon consists of one regulatory gene (the $i$ gene – here the term $i$ does not refer to inducer, rather it is derived from the word inhibitor) and three structural genes ($z$, $y$ and $a$). The $i$ gene codes for the repressor of the lac operon. The $z$ gene codes for beta-galactosidase ($\beta$-gal), which is primarily responsible for the hydrolysis of the disaccharide lactose into its monomeric units, galactose and glucose. The $y$ gene codes for permease, which increases permeability of the cell to $\beta$-galactosides. The $a$ gene encodes a transacetylase.
The Structure of DNA and Packaging of DNA Helix
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Given below are two statements: Statement I: In prokaryotes, the positively charged DNA is held with some negatively charged proteins in a region called nucleoid. Statement II: In eukaryotes, the negatively charged DNA is wrapped around the positively charged histone octamer to form nucleosome. In the light of the above statements, choose the correct answer from the options given below:
DNA is negatively charged and is held by positively charged proteins, so Statement I is incorrect.
In prokaryotes, such as E. coli, though they do not have a defined nucleus, the DNA is not scattered throughout the cell. DNA (being negatively charged) is held with some proteins (that have positive charges) in a region termed as 'nucleoid'. The DNA in nucleoid is organised in large loops held by proteins.
Transcription – Coding Strand and Template Strand
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Which one of the following is the sequence on corresponding coding strand, if the sequence on mRNA formed is as follows: $5'$-AUCGAUCGAUCGAUCGAUCGAUCGAUCG-$3'$?
The coding strand has the same sequence as the mRNA (T in place of U) and the same 5'→3' polarity.
The two strands have opposite polarity and the DNA-dependent RNA polymerase also catalyses the polymerisation in only one direction, i.e., $5'\rightarrow3'$. The strand that has the polarity $3'\rightarrow5'$ acts as a template, and is also referred to as template strand. The other strand which has polarity ($5'\rightarrow3'$) and the sequence same as RNA (except thymine at the place of uracil), is displaced during transcription. This strand is referred to as coding strand.
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