DNA fingerprinting relies on identifying differences in specific regions called:
- Repetitive DNA
- Promoter regions
- Coding DNA
- Intron sequences
Explanation: DNA fingerprinting works by isolating and identifying polymorphic repetitive DNA sequences that are highly variable among individuals.
What percentage of the DNA nucleotide sequence is identical in all human beings?
- Ninety-five percent
- 99.9 percent identical
- Ninety-eight percent
- Ninety percent
Explanation: The Human Genome Project revealed that nucleotide sequences are exactly the same in all people for 99.9% of the genome.
A typical nucleosome contains approximately how many base pairs of DNA helix?
- Hundred base pairs
- Fifty base pairs
- Four hundred pairs
- Two hundred pairs
Explanation: The negatively charged DNA wraps around the positively charged histone octamer, creating a nucleosome that contains roughly 200 base pairs of DNA.
Termination of the transcription process in prokaryotes is facilitated by the:
- Sigma factor
- Rho factor
- Omega factor
- Delta factor
Explanation: The Rho factor ($\rho$) associates with the RNA polymerase to terminate transcription when it reaches the terminator region.
The linkage between a nitrogenous base and the pentose sugar in a nucleotide is called a:
- N-glycosidic linkage
- Hydrogen bond
- Phosphodiester bond
- Peptide bond
Explanation: A nitrogenous base is linked to the pentose sugar through an N-glycosidic linkage to form a nucleoside.
The histone octamer, around which DNA wraps to form a nucleosome, carries which electrical charge?
- Neutral charge
- Variable charge
- Highly positive
- Highly negative
Explanation: Histones are basic proteins that carry a strong positive charge, which allows them to tightly bind the negatively charged DNA molecule.
Which specific nitrogenous base is present in RNA but absent in DNA?
- Adenine
- Thymine
- Uracil
- Guanine
Explanation: RNA contains uracil (a pyrimidine) in place of thymine (5-methyl uracil) which is found exclusively in DNA.
For initiation, the RNA polymerase core enzyme requires binding with which transient factor?
- Sigma factor
- Rho factor
- Beta subunit
- Alpha subunit
Explanation: The Sigma factor ($\sigma$) transiently binds to RNA polymerase to initiate transcription specifically at the promoter region.
The backbone of a polynucleotide chain is structurally formed by:
- Nitrogenous bases only
- Phosphate and pyrimidines
- Sugar and purines
- Sugar and phosphate
Explanation: The alternating sugar and phosphate groups form the backbone of the DNA/RNA chain, with nitrogenous bases projecting perpendicularly from it.
The poly-A tail added during mRNA post-transcriptional processing consists of:
- Cytidylate residues
- Adenylate residues
- Guanylate residues
- Uridylate residues
Explanation: During tailing, about 200-300 adenylate residues are added to the 3' end of the hnRNA in a template-independent manner.
The enzyme 'peptidyl transferase' responsible for peptide bond formation is fundamentally a:
- Ribozyme
- Lipid molecule
- Carbohydrate complex
- Protein enzyme
Explanation: Peptidyl transferase is an RNA enzyme (a ribozyme, specifically the 23S rRNA in bacteria), not a protein-based enzyme.
In eukaryotes, the spliceosome machinery is responsible for the precise removal of:
- Promoters
- Introns
- Exons
- Terminators
Explanation: Splicing involves the removal of non-coding sequences called introns and the joining of coding sequences called exons.
Which heavy isotope was utilized in the Meselson-Stahl experiment?
- Carbon fourteen
- Oxygen eighteen
- Phosphorus thirty-two
- Nitrogen fifteen
Explanation: They used Nitrogen-15 ($^{15}N$), a heavy isotope of nitrogen, to label the DNA and distinguish it from normal DNA using density gradient centrifugation.
DNA polymerase inherently catalyzes polymerization exclusively in which chemical direction?
- 5' to 3'
- 3' to 5'
- Random direction
- Both directions
Explanation: DNA polymerase can only add nucleotides to the free 3'-OH end of a growing strand, meaning polymerization always occurs in the 5' to 3' direction.
Erwin Chargaff's rule regarding base pairing ratios applies specifically to:
- Single stranded RNA
- Double stranded DNA
- Double stranded RNA
- Single stranded DNA
Explanation: Chargaff's rule states that the ratio of adenine to thymine and guanine to cytosine is constant and equals one, which only applies to double-stranded DNA.
Which type of RNA constitutes the highest percentage of total cellular RNA?
- Ribosomal RNA
- Messenger RNA
- Transfer RNA
- Micro RNA
Explanation: Ribosomal RNA (rRNA) is the most abundant RNA in a cell, making up about 80% of the total cellular RNA.
The specific DNA sequence where the RNA polymerase binds to initiate transcription is the:
- Promoter region
- Structural gene
- Operator region
- Terminator region
Explanation: The promoter is a DNA sequence located towards the 5' end of the structural gene that provides a binding site for RNA polymerase.
During replication, Okazaki fragments are discontinuously synthesized on the:
- Continuous strand
- Lagging strand
- Leading strand
- Non-template strand
Explanation: Because the lagging strand template runs 5' to 3', synthesis must occur discontinuously in short segments called Okazaki fragments.
Which ribosomal subunit binds to mRNA first during the initiation of translation?
- Small subunit
- Large subunit
- Peptidyl transferase
- Whole ribosome
Explanation: During the initiation of translation, the small ribosomal subunit first binds to the mRNA before the large subunit joins to form the complete translation complex.
Which RNA molecule acts as the physical adapter translating codons into amino acids?
- Ribosomal RNA
- Messenger RNA
- Small nuclear RNA
- Transfer RNA
Explanation: tRNA acts as an adapter molecule that reads the genetic code on mRNA on one end and binds to specific amino acids on the other.
Which organism was used by Meselson and Stahl to prove the semi-conservative nature of DNA replication?
- Streptococcus pneumoniae
- Escherichia coli
- Neurospora crassa
- Drosophila melanogaster
Explanation: Matthew Meselson and Franklin Stahl used the bacterium E. coli grown in heavy nitrogen to prove semi-conservative replication.
In the lac operon, the repressor protein binds to which specific region?
- Inducer binding site
- Operator region
- Promoter region
- Structural gene
Explanation: The repressor protein tightly binds to the operator region, physically blocking RNA polymerase from transcribing the downstream structural genes.
The unequivocal proof that DNA is the genetic material came from the:
- Avery's experiment
- Meselson Stahl experiment
- Griffith's experiment
- Hershey Chase experiment
Explanation: Alfred Hershey and Martha Chase (1952) provided unequivocal proof by using radioactive phosphorus and sulfur to show that DNA, not protein, enters the bacteria from bacteriophages.
In the lac operon, the 'z' gene codes for which specific enzyme?
- Repressor protein
- Transacetylase enzyme
- Permease enzyme
- Beta-galactosidase
Explanation: The 'z' structural gene encodes $\beta$-galactosidase, which cleaves lactose into its monomeric units, galactose and glucose.
In eukaryotes, RNA polymerase II is specifically responsible for transcribing:
- Precursor mRNA
- Ribosomal RNA
- Transfer RNA
- Small nuclear RNA
Explanation: RNA polymerase II transcribes the precursor of messenger RNA (mRNA), which is known as heterogeneous nuclear RNA (hnRNA).
The Human Genome Project aimed to sequence approximately how many base pairs?
- Thirty billion
- Three trillion
- Three million
- Three billion
Explanation: The Human Genome Project (HGP) aimed to determine the sequence of the estimated 3 billion ($3 \times 10^9$) base pairs that make up human DNA.
Out of the 64 possible triplet codons, how many actually code for amino acids?
- Three
- Sixty four
- Twenty
- Sixty one
Explanation: 61 codons code for the 20 amino acids, while the remaining 3 act as stop or termination codons.
Which of the following acts as a chemical mutagen causing frameshift mutations?
- X-ray radiation
- Ultraviolet rays
- Acridine dyes
- Alpha particles
Explanation: Acridine dyes intercalate between DNA bases, causing additions or deletions of base pairs, which leads to frameshift mutations.
The charging of tRNA with an amino acid requires the hydrolysis of:
- ADP molecule
- AMP molecule
- ATP molecule
- GTP molecule
Explanation: Aminoacylation of tRNA (charging) is an energy-dependent process that uses ATP to link the amino acid to its corresponding tRNA.
Which process serves as a notable exception to the classic Central Dogma?
- DNA replication
- Reverse transcription
- Translation process
- Transcription process
Explanation: Retroviruses use reverse transcriptase to synthesize DNA from an RNA template, reversing the typical DNA-to-RNA flow.
The Central Dogma of molecular biology, explaining the directional flow of genetic information, was proposed by:
- Francis Crick
- Rosalind Franklin
- Marshall Nirenberg
- James Watson
Explanation: Francis Crick proposed the Central Dogma, stating that genetic information flows from DNA to RNA to Protein.
In the nucleus, the loosely packed and transcriptionally active region of chromatin is known as:
- Euchromatin
- Centromere
- Nucleolus
- Heterochromatin
Explanation: Euchromatin is loosely packed, lightly stained, and contains transcriptionally active genes, unlike the densely packed heterochromatin.
According to the Watson and Crick model, the pitch of the DNA double helix is:
- 3.4 nanometers
- 3.4 Angstroms
- 34 nanometers
- 0.34 nanometers
Explanation: The pitch (one full turn) of the B-DNA helix is 3.4 nm (34 Angstroms), containing roughly 10 base pairs.
The 'y' gene in the lac operon directly codes for which protein?
- Permease enzyme
- Transacetylase enzyme
- Lactose enzyme
- Beta-galactosidase
Explanation: The 'y' gene codes for permease, which increases the permeability of the bacterial cell to beta-galactosides (like lactose).
Less than what percentage of the human genome actually codes for proteins?
- Twenty percent
- Fifty percent
- Two percent
- Ten percent
Explanation: One of the surprising findings of the HGP was that less than 2% of the entire human genome sequence codes for proteins.
RNA is more reactive and less stable than DNA primarily due to its:
- Phosphodiester bonds
- Uracil base
- Single strandedness
- 2'-OH group
Explanation: The presence of a reactive 2'-hydroxyl (OH) group on the ribose sugar makes RNA easily degradable and catalytically active compared to DNA.
Which enzyme acts as a 'molecular glue' to join the Okazaki fragments together?
- DNA polymerase
- DNA ligase
- Topoisomerase enzyme
- DNA helicase
Explanation: DNA ligase facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond.
The codon AUG serves a dual function in translation. It acts as the:
- Terminator and Valine
- Start and Tryptophan
- Only for Methionine
- Initiator and Methionine
Explanation: AUG is the universal start codon (initiator) and also specifically codes for the amino acid Methionine.
The structural stability of the DNA double helix is provided by hydrogen bonds and:
- Peptide bonds
- Disulfide bridges
- Base stacking
- Glycosidic bonds
Explanation: In addition to hydrogen bonds between base pairs, the plane of one base pair stacks over the other, conferring additional stability to the helix.
VNTRs, used extensively in DNA fingerprinting, belong to a class of:
- Microsatellite DNA
- Plasmids
- Macrosatellite DNA
- Minisatellite DNA
Explanation: Variable Number of Tandem Repeats (VNTRs) are a type of minisatellite DNA where a short sequence is repeated many times in tandem.
In transcription, the DNA strand acting as the template inherently possesses which polarity?
- Variable polarity
- Neutral polarity
- 3' to 5'
- 5' to 3'
Explanation: Since RNA polymerase catalyzes synthesis in the 5' to 3' direction, the template strand must have the opposite 3' to 5' polarity.
In split eukaryotic genes, the coding sequences that appear in mature RNA are called:
- Mutons
- Exons
- Promoters
- Introns
Explanation: Exons are the expressed or coding sequences that are joined together after splicing out the non-coding introns to form the mature mRNA.
Which molecule acts as the inducer in the lac operon system?
- Lactose or allolactose
- Glucose molecule
- Galactose molecule
- Repressor protein
Explanation: Lactose (or its isomer allolactose) binds to the repressor protein, altering its shape and preventing it from binding to the operator, thus inducing transcription.
Which primary enzyme catalyzes the polymerization of deoxynucleotides during DNA replication?
- RNA primase
- Helicase enzyme
- DNA polymerase III
- DNA ligase
Explanation: DNA-dependent DNA polymerase (specifically Pol III in E. coli) is the main enzyme responsible for adding nucleotides during replication.
The 'Wobble hypothesis' explains the degeneracy of the genetic code at which position?
- First codon position
- Fourth codon position
- Second codon position
- Third codon position
Explanation: The wobble hypothesis states that the third base of a codon can tolerate non-standard base pairing, explaining why multiple codons can bind to a single tRNA.
Which of the following triplet sequences functions as a termination or stop codon?
Explanation: UAA, UAG, and UGA do not code for any amino acids and function as stop signals during translation.
Taylor et al. proved semi-conservative replication in Vicia faba chromosomes using radioactive:
- Adenosine
- Uridine
- Guanosine
- Thymidine
Explanation: In 1958, Taylor and colleagues used tritiated thymidine ($^3H$-thymidine) to demonstrate that DNA in chromosomes replicates semi-conservatively.
During post-transcriptional modification, capping of hnRNA involves the addition of:
- Adenylate residues
- Methyl guanosine triphosphate
- Poly-A tail
- Uracil residues
Explanation: Capping occurs at the 5' end of hnRNA, where an unusual nucleotide, methyl guanosine triphosphate, is added.
Some amino acids are coded by more than one codon, a property known as:
- Contiguous code
- Universal code
- Degenerate code
- Unambiguous code
Explanation: Because there are 61 coding codons and only 20 amino acids, most amino acids are specified by multiple codons; this is termed degeneracy.
Which is the largest known human gene discovered during the Human Genome Project?
- Insulin gene
- Dystrophin gene
- P53 gene
- Hemoglobin gene
Explanation: The dystrophin gene is the largest known human gene, comprising approximately 2.4 million base pairs.
Untranslated regions (UTRs) on a mature mRNA are typically located:
- After stop codon
- Before start codon
- Inside coding region
- Both ends
Explanation: UTRs are present at both the 5' end (before the start codon) and the 3' end (after the stop codon) and are necessary for efficient translation.
Which scientist conducted the experiment that led to the discovery of the 'transforming principle'?
- Avery MacLeod
- Frederick Griffith
- Hershey Chase
- Watson Crick
Explanation: Frederick Griffith conducted the transforming principle experiment in 1928 using Streptococcus pneumoniae, showing that a chemical substance could transform harmless bacteria into virulent ones.
DNA polymorphism is the fundamental basis of genetic mapping and which other technique?
- Gene cloning
- Polymerase chain reaction
- Recombinant DNA
- DNA fingerprinting
Explanation: Inheritable mutations observed in a population at high frequencies (polymorphism) serve as the basis for both genetic mapping and DNA fingerprinting.
The 'RNA World' hypothesis postulates that in the evolution of life:
- Lipids evolved first
- RNA evolved first
- Proteins evolved first
- DNA evolved first
Explanation: The hypothesis suggests that RNA was the first genetic material and could act as both a catalyst and a genetic template before DNA and proteins evolved.
Hershey and Chase used Radioactive Sulfur-35 specifically to label the viral:
- RNA molecules
- Lipid envelopes
- Protein coats
- DNA molecules
Explanation: Sulfur is found in proteins (in amino acids like cysteine and methionine) but not in DNA, so $^{35}S$ exclusively labeled the bacteriophage's protein coat.
Which RNA polymerase transcribes tRNA and 5S rRNA in eukaryotes?
- RNA polymerase I
- RNA polymerase III
- Primase enzyme
- RNA polymerase II
Explanation: RNA polymerase III is responsible for the transcription of transfer RNA (tRNA), 5S ribosomal RNA, and small nuclear RNAs (snRNAs).
The genetic code is 'unambiguous', meaning one codon codes for:
- Three amino acids
- Two amino acids
- Single amino acid
- Any amino acid
Explanation: Unambiguous nature of the code means that a specific codon will only ever code for one specific amino acid, preventing translation errors.
The 'i' gene in the lac operon is responsible for synthesizing the:
- Operator region
- Repressor protein
- Inducer molecule
- Promoter sequence
Explanation: The 'i' gene is a regulatory gene that constitutively synthesizes the repressor protein, which keeps the operon turned off in the absence of lactose.
Which two amino acids are abundantly present in histone proteins?
- Lysine and Arginine
- Glutamate and Aspartate
- Tryptophan and Tyrosine
- Valine and Leucine
Explanation: Histones are rich in the basic amino acid residues lysine and arginine, both of which carry positive charges in their side chains.
Which technique is used to transfer DNA fragments to a nitrocellulose membrane?
- Southern blotting
- Eastern blotting
- Western blotting
- Northern blotting
Explanation: Southern blotting is the technique used to transfer separated DNA fragments from an agarose gel to a synthetic membrane like nitrocellulose or nylon.