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BSEH SS Biotechnology study materials
BSEH SS Biotechnology study resources

BSEH SS Biotechnology practice questions

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Question 1Biotechnology: An Introduction and Scope

Which discovery is most directly credited with launching the modern era of biotechnology by enabling transfer of specific genes between organisms?

  1. The description of the DNA double helix by Watson and Crick
  2. The development of the first monoclonal antibody hybridoma technique
  3. The construction of recombinant DNA molecules using restriction enzymes and plasmids Correct answer.
  4. The invention of the polymerase chain reaction for amplifying DNA

Explanation

Recombinant DNA technology, developed in the early 1970s, allowed scientists to cut DNA with restriction enzymes and insert fragments into plasmid vectors, creating the first genetically engineered molecules. This capability to move defined genes between organisms is the foundation on which modern biotechnology applications rest.

Question 2Biotechnology: An Introduction and Scope

A company uses microbial fermentation to produce citric acid for the food industry. This process is best classified as which area of biotechnology?

  1. Medical biotechnology
  2. Industrial biotechnology Correct answer.
  3. Agricultural biotechnology
  4. Environmental biotechnology

Explanation

Industrial biotechnology (often called white biotechnology) uses microorganisms and enzymes in large-scale fermentation and biocatalysis to manufacture chemicals, food additives, and fuels. Producing citric acid in fermenters is a classic example of a bulk product made by microbial metabolism.

Question 3Biotechnology: An Introduction and Scope

Which statement best describes the traditional use of biotechnology that predates knowledge of genes and microorganisms?

  1. Producing insulin in engineered bacteria
  2. Editing plant genomes with CRISPR systems
  3. Sequencing the human genome
  4. Using yeast to leaven bread and ferment beverages Correct answer.

Explanation

Long before genetics existed as a science, people used microorganisms empirically to make bread, beer, wine, cheese, and yogurt. These traditional fermentation practices are recognized as early biotechnology because they exploit living organisms to produce useful products.

Question 4Biotechnology: An Introduction and Scope

In the context of biotechnology, what does the term 'bioinformatics' primarily refer to?

  1. The engineering of bioreactors for large-scale cell culture
  2. The regulatory framework governing release of genetically modified organisms
  3. The use of computational tools to store, analyze, and interpret biological data Correct answer.
  4. The study of ethical issues arising from genetic testing

Explanation

Bioinformatics applies computer science, statistics, and information technology to biological datasets such as DNA, RNA, and protein sequences. It is essential for assembling genomes, comparing sequences, and predicting gene function in modern biotechnological research.

Question 5Biotechnology: An Introduction and Scope

Which of the following is an example of a biotechnology product obtained through genetic engineering rather than through traditional selective breeding?

  1. A seedless grape variety propagated by cuttings
  2. A disease-resistant wheat line selected over many generations
  3. Human insulin synthesized by bacteria carrying the human insulin gene Correct answer.
  4. A high-yielding hybrid maize variety produced by crossing inbred lines

Explanation

Human insulin produced by recombinant bacteria is a genetically engineered product: the human gene is inserted into a microbial host that then expresses the protein. Selective breeding and hybridization, by contrast, recombine existing traits without direct gene transfer.

Question 6Biotechnology: An Introduction and Scope

A researcher wants to insert a human gene into a bacterial plasmid so the bacterium will express the encoded protein. Which combination of elements is essential for the plasmid to function as an expression vector in bacteria?

  1. A centromere and a pair of homologous recombination arms
  2. Reverse transcriptase and integrase genes
  3. A eukaryotic nuclear localization signal and telomeres
  4. A promoter active in bacteria, a ribosome-binding site, and an origin of replication Correct answer.

Explanation

For bacterial expression, the plasmid must replicate, which requires an origin of replication, and the inserted gene must be transcribed and translated, which requires a bacterial promoter and a ribosome-binding site upstream of the coding sequence. These elements together allow the host to produce the foreign protein.

Question 7Biotechnology: An Introduction and Scope

Why is the enzyme Taq DNA polymerase particularly useful in the polymerase chain reaction?

  1. It remains active at the high temperatures used to denature DNA Correct answer.
  2. It cuts DNA at specific recognition sequences
  3. It joins DNA fragments by forming phosphodiester bonds between blunt ends
  4. It proofreads newly synthesized DNA with very high fidelity

Explanation

PCR repeatedly heats samples to near 95 degrees Celsius to separate DNA strands, so a thermostable polymerase is needed. Taq polymerase, from a thermophilic bacterium, survives these denaturation steps and can extend primers during the cooler synthesis phases.

Question 8Biotechnology: An Introduction and Scope

In a bioprocess for producing a recombinant protein, what is the main purpose of the downstream processing stage?

  1. To introduce the expression plasmid into the host cells
  2. To purify and concentrate the product from the fermentation broth Correct answer.
  3. To sterilize the bioreactor before inoculation
  4. To optimize the growth medium composition for maximum cell yield

Explanation

Downstream processing covers all operations after fermentation, including cell harvesting, disruption, chromatography, and concentration, whose goal is to recover a pure product. Upstream steps such as medium design and inoculation come before it.

Question 9Biotechnology: An Introduction and Scope

Which application best illustrates the use of biotechnology in environmental management?

  1. Using monoclonal antibodies in a pregnancy test kit
  2. Using bacteria to degrade oil spills in contaminated marine environments Correct answer.
  3. Using tissue culture to propagate virus-free banana plantlets
  4. Using immobilized enzymes to convert starch into high-fructose syrup

Explanation

Bioremediation harnesses microorganisms or their enzymes to break down pollutants such as petroleum hydrocarbons, restoring contaminated environments. This is a defining application of environmental biotechnology.

Question 10Biotechnology: An Introduction and Scope

A patient with diabetes is prescribed human insulin produced by recombinant bacteria. Compared with insulin extracted from animal pancreases, what is the principal advantage of this recombinant product?

  1. It can be taken orally without degradation in the stomach
  2. It has an identical amino acid sequence to human insulin, reducing immune reactions Correct answer.
  3. It is cheaper because bacteria grow without any nutrient requirements
  4. It does not require any purification before use

Explanation

Recombinant human insulin matches the human hormone's sequence, which lowers the risk of immune responses that can occur with animal-derived insulin. It also offers a more reliable supply independent of animal availability.

Question 11Biotechnology: An Introduction and Scope

Which feature distinguishes a genomic DNA library from a cDNA library made from the same organism?

  1. A genomic library can only be made from bacteria, whereas a cDNA library requires a viral vector
  2. A genomic library contains only sequences that are actively transcribed, whereas a cDNA library contains all sequences
  3. A genomic library is constructed from RNA, whereas a cDNA library is constructed from DNA
  4. A genomic library contains introns and regulatory sequences, whereas a cDNA library contains only expressed coding sequences Correct answer.

Explanation

A genomic library is built by fragmenting total chromosomal DNA, so it includes introns, promoters, and noncoding regions. A cDNA library is derived by reverse transcription of mRNA and therefore represents only genes expressed in the sampled tissue, without introns.

Question 12Biotechnology: An Introduction and Scope

Which technique would be most appropriate for detecting a specific DNA sequence in a sample without amplifying it?

  1. Enzyme-linked immunosorbent assay
  2. SDS-PAGE followed by Coomassie staining
  3. Southern blotting with a labeled complementary probe Correct answer.
  4. Gas chromatography of the nucleic acid extract

Explanation

Southern blotting separates DNA fragments by electrophoresis, transfers them to a membrane, and detects a target sequence by hybridization with a labeled complementary probe. It identifies specific DNA sequences directly, without the exponential amplification used in PCR.

Question 13Biotechnology: An Introduction and Scope

A company claims its new enzyme preparation will improve juice clarification. Which experimental design best provides evidence that the enzyme, rather than another factor, causes the observed effect?

  1. Compare enzyme-treated juice with juice treated by a different company's product
  2. Treat juice with increasing enzyme doses and report the highest clarity obtained
  3. Treat juice with the enzyme and compare clarity with untreated juice processed identically Correct answer.
  4. Treat juice with the enzyme and also heat it, then measure clarity

Explanation

A controlled comparison in which only the enzyme treatment differs isolates its effect from confounding variables such as temperature, time, and handling. Including an untreated control processed identically is the key feature of a valid efficacy test.

Question 14Biotechnology: An Introduction and Scope

Which regulatory and ethical consideration is most specific to field release of a genetically modified crop, as opposed to contained laboratory research?

  1. The work must be done under a laminar flow hood
  2. The DNA must be sequenced before any experiment
  3. The researcher must obtain informed consent from human volunteers
  4. Approval requires assessment of gene flow to wild relatives and effects on nontarget organisms Correct answer.

Explanation

Open-environment release raises ecological questions that contained work does not, notably whether the transgene can spread to wild relatives and whether nontarget species are harmed. Risk assessment and regulatory approval therefore focus on environmental fate and ecological impact.

Question 15Biotechnology: An Introduction and Scope

A gene encoding a human glycoprotein is expressed in Escherichia coli, but the product lacks the correct carbohydrate modifications and is inactive. Which explanation best accounts for this outcome?

  1. Bacterial ribosomes cannot translate codons used in human genes
  2. Bacteria cannot perform the N-linked glycosylation typical of eukaryotic secretory pathways Correct answer.
  3. Bacterial promoters cannot initiate transcription of human genes
  4. Plasmids are lost from bacteria whenever a foreign gene is inserted

Explanation

Glycosylation is carried out by enzymes of the eukaryotic endoplasmic reticulum and Golgi apparatus, which bacteria lack. A human glycoprotein therefore requires a eukaryotic expression host such as yeast or mammalian cells to acquire the correct carbohydrate structures.

Question 16Biotechnology: An Introduction and Scope

In a directed evolution experiment, a researcher introduces random mutations into an enzyme gene, expresses variants in bacteria, and selects those with improved activity at high temperature. Which statement best explains why this iterative approach can yield enzymes not found in nature?

  1. Selection acts on randomly generated variation, allowing accumulation of beneficial mutations over successive rounds Correct answer.
  2. The bacteria deliberately mutate the gene in response to heat stress to improve survival
  3. The selection pressure guarantees that every possible amino acid substitution is tested
  4. Random mutagenesis always produces a single defined variant that can be characterized

Explanation

Directed evolution mimics natural selection in the laboratory: diversity is generated randomly, and screening or selection enriches beneficial variants, which are then used as templates for further rounds. Repeated cycles allow multiple advantageous mutations to accumulate beyond what natural evolution produced.

Question 17Cell Biology and Biomolecules

Which organelle is the principal site of ATP synthesis by oxidative phosphorylation in a eukaryotic cell?

  1. Golgi apparatus
  2. Lysosome
  3. Smooth endoplasmic reticulum
  4. Mitochondrion Correct answer.

Explanation

The inner mitochondrial membrane carries the electron transport chain and ATP synthase, so oxidative phosphorylation occurs there. The other listed organelles perform sorting, degradation, or lipid synthesis rather than bulk ATP production.

Question 18Cell Biology and Biomolecules

A protein destined for secretion is synthesized on ribosomes attached to the rough endoplasmic reticulum. Which sequence best describes its subsequent route?

  1. Cytosol → smooth ER → nucleus → secretory vesicle
  2. Golgi → rough ER → lysosome → plasma membrane
  3. Rough ER → mitochondrion → Golgi → plasma membrane
  4. Rough ER → Golgi → secretory vesicle → plasma membrane Correct answer.

Explanation

Secretory proteins enter the ER lumen, are transported by vesicles to the Golgi for modification and sorting, then leave in secretory vesicles that fuse with the plasma membrane. This is the classical secretory pathway established by pulse-chase experiments.

Question 19Cell Biology and Biomolecules

Which structural feature distinguishes prokaryotic cells from eukaryotic cells?

  1. Absence of a membrane-bound nucleus Correct answer.
  2. Presence of ribosomes
  3. Presence of chromosomal DNA
  4. Presence of a plasma membrane

Explanation

Prokaryotes keep their genetic material in a nucleoid region without a nuclear envelope, whereas eukaryotes enclose chromosomes in a double membrane. The other features listed are shared by both cell types.

Question 20Cell Biology and Biomolecules

Which bond links two monosaccharides in a disaccharide such as sucrose?

  1. Phosphodiester bond
  2. Peptide bond
  3. Ester bond
  4. Glycosidic bond Correct answer.

Explanation

Monosaccharides join through a condensation reaction between anomeric hydroxyl groups, forming a glycosidic bond with loss of water. Peptide bonds join amino acids, phosphodiester bonds join nucleotides, and ester bonds link fatty acids to glycerol.

Question 21Cell Biology and Biomolecules

Which property of the phospholipid bilayer directly explains why small nonpolar molecules cross membranes faster than small ions?

  1. The hydrophobic core excludes charged and polar solutes Correct answer.
  2. The hydrophilic tails face the aqueous exterior
  3. Membrane proteins actively pump nonpolar molecules
  4. The bilayer is rigid and impermeable to all solutes

Explanation

The interior of the bilayer is hydrophobic, so nonpolar gases and lipids dissolve and diffuse through it readily. Ions are charged and strongly hydrated, so they require channels or transporters.

Question 22Cell Biology and Biomolecules

Which nitrogenous base is found in RNA but not in DNA?

  1. Adenine
  2. Uracil Correct answer.
  3. Guanine
  4. Thymine

Explanation

RNA uses uracil in place of the thymine found in DNA. Adenine and guanine are purines present in both nucleic acids.

Question 23Cell Biology and Biomolecules

Which level of protein structure is defined by the linear order of amino acids joined by peptide bonds?

  1. Primary structure Correct answer.
  2. Secondary structure
  3. Quaternary structure
  4. Tertiary structure

Explanation

Primary structure is the sequence of residues in the polypeptide chain. Secondary structure refers to local folds such as alpha helices, tertiary to the overall 3D fold, and quaternary to assembly of multiple subunits.

Question 24Cell Biology and Biomolecules

A liver cell is placed in a hypotonic solution. What is the expected immediate osmotic response?

  1. No net water movement occurs
  2. Solute moves out until equilibrium is reached
  3. Water leaves the cell and it shrinks
  4. Water enters the cell and it swells Correct answer.

Explanation

In a hypotonic medium the external solute concentration is lower, so the water potential outside is higher and water moves inward by osmosis. Animal cells without a wall swell and may eventually lyse.

Question 25Cell Biology and Biomolecules

In an enzyme-catalyzed reaction, a competitive inhibitor is added at a concentration far below the substrate concentration. Which kinetic change is expected?

  1. Both Km and Vmax increase
  2. Both Km and Vmax decrease
  3. Apparent Km increases while Vmax is unchanged Correct answer.
  4. Vmax decreases while Km is unchanged

Explanation

A competitive inhibitor binds the free enzyme active site and can be outcompeted by high substrate, so the apparent Km rises but Vmax is reached at saturating substrate. Noncompetitive inhibition instead lowers Vmax without changing Km.

Question 26Cell Biology and Biomolecules

Why does a triglyceride yield more energy per gram than a carbohydrate?

  1. It contains more oxygen per carbon than a carbohydrate
  2. It is more readily hydrated in the cytosol
  3. Its fatty acid chains are highly reduced and store more energy per carbon Correct answer.
  4. It is catabolized without any requirement for oxygen

Explanation

Fatty acids are largely hydrocarbon and highly reduced, so their oxidation releases more energy per carbon than the partially oxidized carbons of sugars. The greater energy density per gram reflects this lower oxygen content and higher proportion of C–H bonds.

Question 27Cell Biology and Biomolecules

During glycolysis, one molecule of glucose is converted to two molecules of pyruvate. What is the net yield of ATP and NADH per glucose?

  1. 4 ATP and 4 NADH
  2. 2 ATP and 2 NADH Correct answer.
  3. 4 ATP and 2 NADH
  4. 2 ATP and 4 NADH

Explanation

Glycolysis consumes 2 ATP in the investment phase and produces 4 ATP in the payoff phase, giving a net of 2 ATP. Two NAD+ are reduced to NADH when glyceraldehyde-3-phosphate is oxidized.

Question 28Cell Biology and Biomolecules

A mutation changes a single base in a codon from UAC to UAA. What is the most likely consequence for the polypeptide?

  1. Premature termination of translation Correct answer.
  2. Substitution of one amino acid for another
  3. A shift in the reading frame downstream
  4. No change because the genetic code is degenerate

Explanation

UAA is a stop codon, so the ribosome will terminate translation at that position and release a truncated polypeptide. A missense change would require the new codon to specify another amino acid.

Question 29Cell Biology and Biomolecules

Which statement correctly describes the role of the sodium-potassium pump in maintaining the resting membrane potential of a neuron?

  1. It transports only K+ ions down their concentration gradient
  2. It moves equal numbers of Na+ and K+ in each cycle
  3. It exports three Na+ and imports two K+ per ATP, leaving the interior negative Correct answer.
  4. It imports three Na+ and exports two K+ per ATP, leaving the interior positive

Explanation

The pump hydrolyzes one ATP to move three Na+ out and two K+ in, creating an electrogenic net export of positive charge. This contributes to the negative resting potential and maintains the ion gradients used during action potentials.

Question 30Cell Biology and Biomolecules

Which feature of the fluid mosaic model best accounts for the ability of membrane proteins to move laterally within the bilayer?

  1. Absence of hydrophobic regions in membrane proteins
  2. Covalent anchoring of proteins to the cytoskeleton
  3. Presence of a rigid cholesterol crystal lattice
  4. Weak noncovalent interactions between lipids and proteins Correct answer.

Explanation

Lipids and integral proteins associate mainly through hydrophobic and van der Waals interactions rather than covalent bonds, allowing lateral diffusion. Cholesterol modulates fluidity but does not form a rigid lattice that immobilizes proteins.

Question 31Cell Biology and Biomolecules

A cell is treated with a drug that blocks the function of the mitotic spindle. At which stage would chromosome segregation most directly fail?

  1. S phase
  2. G1 phase
  3. Anaphase Correct answer.
  4. Prophase

Explanation

Spindle microtubules attach to kinetochores and pull sister chromatids apart during anaphase. Without a functional spindle, congression and separation of chromatids cannot occur.

Question 32Cell Biology and Biomolecules

In a cell that has a mutation eliminating telomerase activity, what happens to chromosome ends over successive divisions?

  1. They progressively shorten Correct answer.
  2. They fuse into circular chromosomes
  3. They remain unchanged
  4. They progressively lengthen

Explanation

DNA polymerase cannot fully replicate the extreme 5' end of the lagging strand, so telomeres shorten each round of replication unless telomerase extends them. Loss of telomerase therefore leads to progressive shortening and eventual replicative senescence.

Question 33Cell Biology and Biomolecules

Which interaction is chiefly responsible for stabilizing the alpha-helix and beta-sheet conformations of a polypeptide?

  1. Hydrophobic clustering of aromatic side chains
  2. Ionic bonds between charged side chains
  3. Hydrogen bonding between backbone amide and carbonyl groups Correct answer.
  4. Disulfide bonds between cysteine side chains

Explanation

Secondary structure is stabilized by regular hydrogen bonds between the backbone C=O and N–H groups, running parallel to the helix axis or between adjacent beta strands. Side-chain interactions instead contribute mainly to tertiary structure.

Question 34Cell Biology and Biomolecules

A DNA sample contains 30% adenine. According to Chargaff's rules, what percentage of its bases is guanine?

  1. 30%
  2. 40%
  3. 70%
  4. 20% Correct answer.

Explanation

If adenine is 30%, thymine is also 30%, leaving 40% shared equally by guanine and cytosine. Each of G and C therefore accounts for 20% of the bases.

Question 35Cell Biology and Biomolecules

Which property of water allows it to absorb considerable heat with only a small rise in temperature?

  1. Its high specific heat capacity from extensive hydrogen bonding Correct answer.
  2. Its nonpolar covalent bonds
  3. Its low molecular mass
  4. Its ability to evaporate rapidly

Explanation

Hydrogen bonds between water molecules must be broken to raise kinetic energy, so a large amount of heat produces a modest temperature change. This high specific heat buffers cells against thermal fluctuations.

Question 36Cell Biology and Biomolecules

An enzyme's active site contains a glutamate residue with a pKa of 4.5. At pH 7.0, what is the predominant state of this side chain, and how does it affect catalysis?

  1. Neutral and unable to participate in acid-base catalysis
  2. Deprotonated and negatively charged, available to stabilize a positive transition state Correct answer.
  3. Protonated and positively charged, available to donate a proton
  4. Protonated and negatively charged, acting as a nucleophile

Explanation

At pH 7.0, well above the pKa of 4.5, the carboxyl group is mostly deprotonated and carries a negative charge. Such a carboxylate can stabilize developing positive charge or act as a general base during catalysis.

Question 37Cell Biology and Biomolecules

In the electron transport chain, cyanide binds tightly to cytochrome c oxidase. Which immediate consequence is expected?

  1. Glycolysis stops immediately because glucose cannot be phosphorylated
  2. ATP synthase reverses to hydrolyze ATP without any change in proton gradient
  3. Electron transfer to oxygen stops, halting proton pumping and ATP synthesis Correct answer.
  4. The Krebs cycle accelerates to compensate for the block

Explanation

Cytochrome c oxidase carries electrons to oxygen, so its inhibition blocks the terminal step and the proton gradient collapses. Oxidative phosphorylation ceases, though glycolysis can continue briefly using substrate-level phosphorylation.

Question 38Cell Biology and Biomolecules

A frameshift mutation arises from insertion of two nucleotides near the start of a coding sequence. Why is the resulting protein usually nonfunctional?

  1. Transcription is completely abolished
  2. Only one amino acid is substituted at the insertion site
  3. Every downstream codon is read out of register, altering the amino acid sequence Correct answer.
  4. The mRNA becomes immediately degraded by the ribosome

Explanation

Insertions that are not multiples of three shift the reading frame, so all codons downstream of the lesion specify different amino acids. This usually introduces a premature stop codon and destroys protein function.

Question 39Cell Biology and Biomolecules

A researcher measures enzyme activity at increasing substrate concentrations and finds that a noncompetitive inhibitor lowers Vmax without changing Km. Which interpretation is most consistent with these data?

  1. The inhibitor competes directly with substrate for the active site
  2. The inhibitor increases the affinity of the enzyme for substrate
  3. The inhibitor is a reversible substrate analog that can be outcompeted
  4. The inhibitor binds a site distinct from the active site and reduces the fraction of functional enzyme Correct answer.

Explanation

Unchanged Km indicates substrate binding affinity is unaffected, while reduced Vmax indicates less active enzyme is available. This fits inhibitor binding at an allosteric or alternative site that does not prevent substrate binding.

Question 40Cell Biology and Biomolecules

Which observation would most directly support the endosymbiotic origin of mitochondria?

  1. Mitochondria are enclosed by a single membrane
  2. Mitochondria possess their own circular DNA and 70S ribosomes Correct answer.
  3. Mitochondria synthesize all their own proteins
  4. Mitochondria divide only during mitosis of the host cell

Explanation

Circular genomes and bacterial-type 70S ribosomes resemble prokaryotic features and support an endosymbiotic ancestry. The double membrane and import of most proteins from the nucleus are consistent with progressive gene transfer to the host.

Question 41Genetics and Molecular Biology

In the Meselson–Stahl experiment, cells grown in 15N medium were transferred to 14N medium, and DNA sampled after one generation formed a single band of intermediate density. Which conclusion does this result support?

  1. DNA replication is semiconservative Correct answer.
  2. DNA replication proceeds bidirectionally
  3. DNA replication is conservative
  4. DNA replication is dispersive

Explanation

A single hybrid band after one generation means each daughter duplex contains one old 15N strand and one newly synthesised 14N strand, which is the definition of semiconservative replication. Conservative replication would have produced two bands (fully heavy and fully light), and dispersive replication would have produced one band of density intermediate between the two but with fragmented strands.

Question 42Genetics and Molecular Biology

Which enzyme removes the RNA primer and replaces it with DNA during bacterial chromosomal replication?

  1. Primase
  2. DNA ligase
  3. DNA polymerase I Correct answer.
  4. Helicase

Explanation

DNA polymerase I has 5'→3' exonuclease activity that excises the RNA primer while its polymerase domain fills the gap with deoxynucleotides. Ligase then seals the remaining nick between the new DNA and the adjacent Okazaki fragment.

Question 43Genetics and Molecular Biology

A mutation changes a codon from UAC to UAA. What is the consequence for the encoded polypeptide?

  1. The reading frame shifts downstream of the mutation
  2. Translation terminates prematurely at that codon Correct answer.
  3. A different amino acid is inserted at that position
  4. The codon becomes a start codon for translation

Explanation

UAA is one of the three stop codons (UAA, UAG, UGA), so the ribosome releases the nascent chain at that point. Because the change is a single base substitution within one codon, the reading frame of downstream codons is unaffected.

Question 44Genetics and Molecular Biology

Which structural feature distinguishes the two DNA strands in a double helix according to the Watson–Crick model?

  1. One strand contains uracil in place of thymine
  2. They are parallel, both running 5'→3' in the same direction
  3. They are antiparallel, with 5'→3' direction opposite to each other Correct answer.
  4. The two strands are joined by covalent bonds between bases

Explanation

The two strands of the duplex run in opposite orientations, one 5'→3' and the other 3'→5', which is why replication has leading and lagging strands. Base pairs are held by hydrogen bonds, not covalent bonds, and both DNA strands contain thymine.

Question 45Genetics and Molecular Biology

In eukaryotes, which enzyme is primarily responsible for transcribing messenger RNA from protein-coding genes?

  1. Reverse transcriptase
  2. RNA polymerase II Correct answer.
  3. RNA polymerase III
  4. RNA polymerase I

Explanation

RNA polymerase II transcribes mRNA precursors as well as many snRNAs. RNA polymerase I makes the large rRNA precursor and RNA polymerase III makes tRNA and 5S rRNA.

Question 46Genetics and Molecular Biology

A bacterial strain acquires a functional gene from a bacteriophage during transduction. Which term describes this process?

  1. Segregation
  2. Genetic drift
  3. Horizontal gene transfer Correct answer.
  4. Vertical gene transfer

Explanation

Transfer of genetic material between organisms that is not parent-to-offspring is horizontal (lateral) gene transfer; transduction, transformation, and conjugation are its classical mechanisms. Vertical transfer, by contrast, passes genes from parent cell to daughter cells during division.

Question 47Genetics and Molecular Biology

Which type of mutation most often produces a truncated, non-functional protein?

  1. Silent mutation
  2. Nonsense mutation Correct answer.
  3. Synonymous substitution
  4. Missense mutation

Explanation

A nonsense mutation converts a sense codon into a stop codon, causing premature termination and usually a shortened, unstable protein. Silent and synonymous changes leave the amino acid sequence unchanged, and missense changes substitute one residue without necessarily abolishing function.

Question 48Genetics and Molecular Biology

Which bond links two adjacent nucleotides within a single DNA strand?

  1. Glycosidic bond
  2. Peptide bond
  3. Phosphodiester bond Correct answer.
  4. Hydrogen bond

Explanation

The phosphate group of one nucleotide is joined to the 3' hydroxyl of the next sugar by a phosphodiester bond, forming the sugar-phosphate backbone. Hydrogen bonds instead connect complementary bases across the two strands.

Question 49Genetics and Molecular Biology

In the lac operon of E. coli, what is the effect of high glucose and low lactose on transcription of the lac genes?

  1. Transcription is very low because CAP is not activated and the repressor remains bound Correct answer.
  2. Transcription is maximal because both CAP and the repressor are active
  3. Transcription is constitutive because the repressor is inactivated by glucose
  4. Transcription is moderate because lactose relieves repression but glucose lowers cAMP

Explanation

Low lactose keeps the LacI repressor bound to the operator, and high glucose lowers cAMP so catabolite activator protein (CAP) does not stimulate the promoter. The combined effect is a very low basal transcription rate, illustrating dual negative and positive control.

Question 50Genetics and Molecular Biology

A restriction enzyme recognises the palindromic sequence 5'-GAATTC-3' and cuts between G and A. How many fragments result from cutting a linear DNA molecule that contains exactly two such sites?

  1. Two
  2. Four
  3. Three Correct answer.
  4. One

Explanation

Each cut in a linear molecule increases the number of fragments by one, so two cuts yield three fragments. A circular molecule with two sites would instead yield two fragments.