Molecular Basis of Heredity Practice Questions
40 free Molecular Basis of Heredity practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
The molecular basis of heredity primarily involves the study of:
- A Membrane-bound cell organelles
- B Protein synthesis only
- C Structure and function of nucleic acids
- D Movement of chromosomes during cell division stages
Correct answer: Structure and function of nucleic acids
The molecular basis of heredity focuses on DNA and RNA as carriers of genetic information. It explains how this information is stored, replicated, and expressed.
Which molecule serves as the genetic material in most living organisms?
- A RNA
- B Protein
- C DNA
- D Lipid
Correct answer: DNA
DNA is the primary genetic material in most organisms. It stores hereditary information in the form of nucleotide sequences.
DNA is composed of repeating units called:
- A Amino acid residues
- B Nucleotides
- C Simple sugar molecules
- D Long-chain fatty acids
Correct answer: Nucleotides
DNA is a polymer made of nucleotide subunits. Each nucleotide consists of a sugar, phosphate group, and nitrogenous base.
Which nitrogenous base is found only in RNA?
- A Adenine
- B Guanine
- C Cytosine
- D Uracil
Correct answer: Uracil
RNA contains uracil instead of thymine. Uracil pairs with adenine during RNA base pairing.
The double helical structure of DNA was proposed by:
- A Mendel and Morgan
- B Watson and Crick
- C Hershey and Chase
- D Meselson and Stahl
Correct answer: Watson and Crick
Watson and Crick proposed the double helix model of DNA. Their model explained base pairing and replication.
In DNA, adenine pairs with:
- A Cytosine
- B Guanine
- C Thymine
- D Uracil
Correct answer: Thymine
Adenine pairs with thymine through two hydrogen bonds. This complementary base pairing maintains DNA structure.
Which bond links nucleotides together in a DNA strand?
- A Hydrogen bond between bases
- B Peptide bond
- C Phosphodiester bond
- D Glycosidic bond
Correct answer: Phosphodiester bond
Phosphodiester bonds connect nucleotides in a DNA strand. They link the sugar of one nucleotide to the phosphate of the next.
DNA replication is described as semi-conservative because:
- A DNA is fully conserved during transcription of genes
- B Each new DNA molecule contains one parental strand
- C Replication occurs only once
- D Only half the DNA is replicated
Correct answer: Each new DNA molecule contains one parental strand
In semi-conservative replication, each daughter DNA molecule contains one original strand and one newly synthesized strand. This was demonstrated by Meselson and Stahl.
Which enzyme is responsible for synthesizing new DNA strands?
- A RNA polymerase enzyme
- B DNA ligase that seals nicks
- C DNA polymerase
- D Helicase
Correct answer: DNA polymerase
DNA polymerase adds nucleotides to form a new DNA strand. It uses the parental strand as a template.
The enzyme helicase functions to:
- A Join adjacent Okazaki DNA fragments
- B Unwind the DNA double helix
- C Add RNA primers to the template
- D Correct replication errors
Correct answer: Unwind the DNA double helix
Helicase unwinds the DNA helix by breaking hydrogen bonds. This allows replication to proceed.
Short DNA fragments formed during lagging strand synthesis are called:
- A RNA primers on the leading strand
- B Protein-coding exons
- C Okazaki fragments
- D Non-coding introns
Correct answer: Okazaki fragments
Okazaki fragments are short DNA segments synthesized on the lagging strand. They are later joined by DNA ligase.
Which process converts genetic information from DNA to RNA?
- A Translation of mRNA into protein
- B Replication of the genome
- C Transcription
- D Spontaneous mutation
Correct answer: Transcription
Transcription involves synthesis of RNA from a DNA template. This step is essential for gene expression.
The enzyme involved in transcription is:
- A DNA polymerase enzyme
- B RNA polymerase
- C DNA ligase that joins fragments
- D Primase
Correct answer: RNA polymerase
RNA polymerase synthesizes RNA using DNA as a template. It binds to promoter regions of genes.
Which RNA carries amino acids to the ribosome during protein synthesis?
- A mRNA
- B rRNA
- C tRNA
- D snRNA
Correct answer: tRNA
tRNA transports specific amino acids to the ribosome. It matches amino acids with codons on mRNA.
The sequence of three nucleotides on mRNA that codes for an amino acid is called:
- A Anticodon
- B Codon
- C Gene
- D Exon
Correct answer: Codon
A codon is a triplet of nucleotides on mRNA. Each codon specifies a particular amino acid.
Translation occurs at the level of:
- A Nucleus
- B Chromosome
- C Ribosome
- D Mitochondria only
Correct answer: Ribosome
Translation takes place on ribosomes. Ribosomes read mRNA sequences to synthesize proteins.
The genetic code is described as degenerate because:
- A It completely lacks defined start codons
- B A single codon codes for several different amino acids
- C Multiple codons can code for the same amino acid
- D It changes frequently
Correct answer: Multiple codons can code for the same amino acid
The genetic code is degenerate because more than one codon can specify the same amino acid. This provides tolerance against mutations.
A mutation is best defined as:
- A A change in protein structure only
- B A change in the total chromosome number
- C Permanent change in DNA sequence
- D Temporary gene expression change
Correct answer: Permanent change in DNA sequence
A mutation is a permanent alteration in the DNA sequence. It can create new alleles and genetic variation.
Which type of mutation involves substitution of a single nucleotide?
- A Frameshift mutation
- B Point mutation
- C Chromosomal mutation
- D Deletion mutation
Correct answer: Point mutation
Point mutations involve replacement of one nucleotide with another. They may or may not alter protein function.
The central dogma of molecular biology describes the flow of information from:
- A Protein to DNA and then to RNA
- B DNA to RNA to protein
- C RNA to DNA and then to protein
- D DNA to protein and then to RNA
Correct answer: DNA to RNA to protein
The central dogma states that genetic information flows from DNA to RNA to protein. This forms the basis of gene expression.
Which specific enzyme is responsible for relieving the torsional strain or 'overwinding' ahead of the replication fork?
- A Topoisomerase
- B DNA Ligase
- C Primase
- D DNA Polymerase I
Correct answer: Topoisomerase
As Helicase unwinds the DNA, the regions ahead of the fork become supercoiled. Topoisomerase cuts and reseals the DNA strands to release this tension, preventing the DNA from breaking.
The 'Beads-on-a-string' structure seen under an electron microscope represents DNA wrapped around which protein core?
- A Nucleosomes
- B Spliceosomes
- C Ribosomes
- D Transcription factors
Correct answer: Nucleosomes
Nucleosomes consist of DNA wrapped around an octamer of histone proteins. This is the fundamental unit of chromatin packaging in eukaryotic cells.
During DNA replication, which enzyme is required to lay down the short RNA sequence that gives DNA polymerase a free 3'-OH end to begin synthesis?
- A RNA Polymerase II
- B DNA Ligase
- C Telomerase
- D DNA Primase
Correct answer: DNA Primase
DNA polymerases cannot initiate a new strand from scratch; they require a 3'-OH group. Primase provides this by creating a short RNA sequence complementary to the template.
Which of the following describes the 'Antiparallel' nature of the DNA double helix?
- A The strands run in opposite directions
- B One strand is DNA and the other is RNA
- C The base pairs are held by ionic bonds
- D Both strands are synthesized continuously
Correct answer: The strands run in opposite directions
Antiparallel means the two sugar-phosphate backbones run in opposite directions. This orientation is essential for the formation of hydrogen bonds between complementary nitrogenous bases.
What is the role of the 'Sigma factor' in prokaryotic transcription?
- A To recognize the promoter sequence
- B To catalyze the elongation of the RNA chain
- C To terminate the transcription process
- D To add a poly-A tail to the mRNA
Correct answer: To recognize the promoter sequence
In bacteria, the RNA polymerase core enzyme requires the sigma factor to achieve specific binding at the promoter site. Once transcription initiates, the sigma factor is usually released.
The removal of non-coding introns and the joining of coding exons in eukaryotic pre-mRNA is catalyzed by:
- A The Spliceosome
- B The Ribosome
- C DNA Polymerase III
- D Reverse Transcriptase
Correct answer: The Spliceosome
Spliceosomes are large molecular complexes composed of snRNAs and proteins. They recognize specific sequences at the borders of introns to precisely remove them and ligate exons together.
In the genetic code, what is meant by the term 'Universal'?
- A A single codon is capable of coding for multiple different amino acids
- B The same codons specify the same amino acids in almost all organisms
- C All organisms possess exactly the same total number of chromosomes
- D DNA serves as the genetic material found in all known types of viruses
Correct answer: The same codons specify the same amino acids in almost all organisms
The genetic code is nearly universal, meaning a codon like UUU codes for Phenylalanine in bacteria, plants, and humans alike. This consistency is a strong indicator of a common evolutionary origin.
Which site on the ribosome holds the tRNA carrying the growing polypeptide chain during translation?
- A A site (Aminoacyl)
- B P site (Peptidyl)
- C E site (Exit)
- D O site (Origin)
Correct answer: P site (Peptidyl)
The P site holds the tRNA attached to the growing peptide chain. The incoming aminoacyl-tRNA enters at the A site, and the spent tRNA leaves via the E site.
A scientist finds that a DNA sample contains 20% Cytosine. According to Chargaff's rules, what is the percentage of Adenine?
- A 20%
- B 30%
- C 40%
- D 80%
Correct answer: 30%
If C is 20%, then G must also be 20% (total 40%). The remaining 60% must be split equally between A and T, resulting in 30% Adenine.
The process of 'Capping' at the 5' end of eukaryotic mRNA involves the addition of:
- A A long chain of adenine nucleotides
- B A 7-methylguanosine (m7G) residue
- C A sequence of thymine bases
- D A protein signaling factor complex
Correct answer: A 7-methylguanosine (m7G) residue
The 5' cap is added shortly after transcription begins. It protects the mRNA from degradation by exonucleases and helps the ribosome recognize the mRNA for translation.
Which enzyme has 5' to 3' exonuclease activity, allowing it to remove RNA primers and replace them with DNA?
- A DNA Polymerase I
- B DNA Polymerase III
- C RNA Polymerase
- D Ligase
Correct answer: DNA Polymerase I
DNA Polymerase I is unique because it can remove RNA primers (exonuclease activity) while simultaneously filling the gap with DNA nucleotides (polymerase activity).
In the Lac operon of E. coli, the repressor protein binds to which region to prevent transcription?
- A Promoter
- B Operator
- C Structural gene lacZ
- D Regulatory gene lacI
Correct answer: Operator
The operator is a DNA segment located between the promoter and the structural genes. When the repressor binds here, it physically blocks RNA polymerase from moving forward.
What kind of bond stabilizes the secondary structure (alpha-helices and beta-sheets) of the protein product of a gene?
- A Peptide bonds
- B Hydrogen bonds
- C Phosphodiester bonds
- D Glycosidic bonds
Correct answer: Hydrogen bonds
While peptide bonds link amino acids in the primary sequence, hydrogen bonds between the backbone atoms (oxygen and nitrogen) create the folding patterns known as secondary structure.
Which of the following is NOT a characteristic of DNA as described by Watson and Crick?
- A Right-handed helix
- B Sugar-phosphate backbone on the outside
- C Parallel strand orientation
- D Complementary base pairing
Correct answer: Parallel strand orientation
Watson and Crick's model explicitly described the strands as antiparallel, meaning they run in opposite directions. Parallel orientation would not allow the bases to pair correctly.
The 'Wobble Hypothesis' explains why:
- A DNA replication is prone to frequent errors
- B mRNA is degraded quickly by various cellular enzymes
- C The genetic code has multiple start codons
- D Some tRNAs can recognize more than one codon
Correct answer: Some tRNAs can recognize more than one codon
Proposed by Francis Crick, the wobble hypothesis suggests that base pairing rules are relaxed at the third position of the codon, allowing a single tRNA to pair with multiple synonymous codons.
In molecular biology, 'Reverse Transcription' refers to the synthesis of:
- A RNA from a DNA template
- B Protein from an RNA template
- C RNA from a protein template
- D DNA from an RNA template
Correct answer: DNA from an RNA template
Reverse transcription is carried out by the enzyme reverse transcriptase, commonly found in retroviruses like HIV. It converts the viral RNA genome into DNA that can integrate into the host genome.
Which molecule contains the anticodon loop?
- A mRNA
- B rRNA
- C tRNA
- D snRNA
Correct answer: tRNA
The tRNA (transfer RNA) contains an anticodon that is complementary to a specific mRNA codon. This ensures the correct amino acid is added to the growing polypeptide chain.
The initiation codon (AUG) in eukaryotes codes for which amino acid?
- A Valine
- B Leucine
- C Tryptophan
- D Methionine
Correct answer: Methionine
AUG is the universal start codon. In eukaryotes, it specifies the amino acid Methionine, while in prokaryotes, it specifies N-formylmethionine.
What provides the energy for the polymerization of nucleotides during DNA synthesis?
- A ATP hydrolysis taking place within the cytoplasm surrounding the nucleus
- B Heat energy from general cellular metabolic activity
- C GTP hydrolysis that occurs during the process of protein translation
- D The hydrolysis of pyrophosphate from deoxynucleoside triphosphates
Correct answer: The hydrolysis of pyrophosphate from deoxynucleoside triphosphates
Each incoming dNTP (like dATP or dCTP) carries three phosphate groups. When it is added to the strand, two phosphates (pyrophosphate) are released, providing the necessary energy for the bond formation.
Telomerase is an enzyme that is active in:
- A Bacterial cells to replicate their circular DNA molecules
- B Mature somatic cells to help prevent cellular aging
- C Certain viruses to help replicate their RNA genome material
- D Germ cells and cancer cells to maintain chromosome ends
Correct answer: Germ cells and cancer cells to maintain chromosome ends
Telomerase extends the repetitive DNA sequences at the ends of linear chromosomes (telomeres). It is highly active in cells that need to divide indefinitely, such as stem cells, germ cells, and unfortunately, many cancer cells.