ISC Class 12 Biotechnology Board Exam Question Paper 2017 with Solutions

ISC Class 12 Biotechnology Board Exam Question Paper with Solutions 2017

PART - I (20 Marks)

Question 1.

(a) Mention any one significant difference between each of the following : [5]
(i) Reducing sugar and non-reducing sugar.
(ii) Triploids and haploids.
(iii) Lac operon and Trp operon
(iv) Blunt end and sticky end
(v) Spectroscopy and colorimetry

Answer:
(i) Reducing sugar possess a free aldehyde (-CHO) or ketone (-C = O) group while non-reducing sugars have no free aldehyde or ketone group.
(ii) Plants produced from pollen grains or egg cells of ovules are haploid plants, whereas plants produced from endosperm are triploid plants.
(iii) Lac-operon is under negative gene control, while Trp-operon is under positive gene control.
(iv) Blunt ends are formed when restriction enzymes cut both strands of a DNA molecule at the same site leaving flush ends, whereas sticky ends are produced by staggered cuts generating protruding single-stranded ends.
(v) Spectroscopy is the broader study of the interaction between matter and electromagnetic radiation, whereas colorimetry involves the estimation of the concentration of a colored substance by comparing its color intensity with a standard solution using visible light.

Teacher's Note:
a) Ensure clear chemical and biological distinctions are mentioned for full credit.
b) Do not confuse operon regulation mechanisms or end-product structural definitions.

(b) Answer the following questions : [5]
(i) Who developed the microbe called super bug, which was designed to degrade spilled oil ?
(ii) Name any two growth regulators used in a culture medium.
(iii) What is an apoenzyme ?
(iv) How is the disease albinism caused ?
(v) State any one limitation of gynogenesis.

Answer:
(i) Ananda Mohan Chakrabarty engineered the super bug (Pseudomonas bacteria) in 1971.
(ii) Auxin (Indole-3-acetic acid) and Cytokinin (6-benzylaminopurine).
(iii) An apoenzyme is the protein part of an enzyme that requires a coenzyme to become catalytically active.
(iv) Albinism is caused by the inheritance of recessive alleles resulting in the non-conversion of tyrosine into melanin.
(v) The frequency of responding ovules is quite low (typically 1 to 5 percent).

Teacher's Note:
a) Direct factual recall is required for these sub-parts.
b) Mention the correct scientific names and enzyme definitions clearly.

(c) Write the full form of each of the following : [5]
(i) AFLP
(ii) SSBs
(iii) BAC
(iv) CIMAP
(v) PAGE

Answer:
(i) AFLP: Amplified Fragment Length Polymorphism.
(ii) SSBs: Single-Strand DNA Binding Proteins.
(iii) BAC: Bacterial Artificial Chromosome.
(iv) CIMAP: Central Institute of Medicinal and Aromatic Plants.
(v) PAGE: Polyacrylamide Gel Electrophoresis.

Teacher's Note:
a) Spelling of acronym expansions must be precise to secure marks.
b) Common abbreviations in biotechnology frequently appear in board exams.

(d) Explain briefly : [5]
(i) Polyadenylation
(ii) Lock and key model of enzyme action
(iii) Edible vaccine
(iv) Vascular differentiation
(v) Seedless crops

Answer:
(i) Polyadenylation is the addition of a poly(A) tail to the 3' end of a messenger RNA transcript during eukaryotic post-transcriptional processing.
(ii) The lock and key model, proposed by Emil Fischer, states that the active site of an enzyme has a rigid, specific shape complementary to the substrate, fitting together like a lock and key.
(iii) Edible vaccines are antigenic proteins expressed in transgenic crop plants that induce mucosal and systemic immunity when eaten.
(iv) Vascular differentiation involves identifying and cloning transcripts produced in differentiating vascular tissues to study gene function through insertional mutagenesis.
(v) Seedless crops are fruits developed without mature seeds, achieved through parthenocarpy or stenospermocarpy, providing commercial convenience.

Teacher's Note:
a) Provide concise scientific definitions with biological significance for each term.
b) Ensure key historical names like Emil Fischer are included where relevant.

PART - II (50 Marks)

Question 2.
(a) Briefly explain the structure of tRNA. Write its function in protein synthesis. [4]

Answer:
1. Transfer RNA (tRNA) is the smallest RNA, consisting of 70 to 85 nucleotides with a sedimentation coefficient of 4S.
2. In two dimensions, it exhibits a clover-leaf structure, and in three dimensions, it folds into an L-shaped tertiary structure stabilized by base pairing.
3. Key structural regions include the amino acid binding site (3' end with CCA-OH), anticodon loop for codon recognition, T psi C loop for ribosome attachment, and DHU loop for aminoacyl synthetase binding.
4. Function: tRNA acts as an adapter molecule that decodes mRNA codons and transfers specific amino acids to the growing polypeptide chain during translation.

Teacher's Note:
a) Mention both clover-leaf and L-shaped forms for complete credit.
b) Clearly explain the adapter function of tRNA in polypeptide synthesis.

(b) With reference to lipids, explain its :
(i) Building blocks.
(ii) Any two chemical properties. [4]

Answer:
(i) Building blocks: The building blocks of lipids include simple fatty acids, glycerol, sphingosine, and cholesterol.
(ii) Chemical properties:
- Hydrolysis: Fats break down into fatty acids and glycerol upon treatment with alkalis or lipolytic enzymes like lipases.
- Saponification: The alkaline hydrolysis of fats yields glycerol and soaps, which are salts of fatty acids.

Teacher's Note:
a) State both building blocks and chemical reactions clearly.
b) Distinguish clearly between general hydrolysis and saponification.

(c) What is DNA probe ? [2]

Answer:
1. A DNA probe is a single-stranded DNA or oligonucleotide segment labeled with a radioactive isotope or fluorescent marker.
2. It is used to detect and identify complementary DNA sequences in a sample via specific hybridization reactions.

Teacher's Note:
a) Emphasize that probes must be single-stranded and labeled.
b) Mention the role of complementary base pairing in hybridization.

Question 3.
(a) Explain the process involved in the transcription of DNA to mRNA. [4]

Answer:
1. Initiation: RNA polymerase binds to the promoter region on the DNA template strand and unwinds the double helix.
2. Elongation: RNA polymerase moves along the template strand in the 3' to 5' direction, synthesizing mRNA in the 5' to 3' direction by adding complementary ribonucleotides.
3. Termination: Upon reaching the termination sequence, transcription stops, the completed mRNA transcript is released, and RNA polymerase detaches.
4. Post-transcriptional modification: In eukaryotes, the pre-mRNA undergoes 5' capping with 7-methylguanosine and 3' polyadenylation before export.

Teacher's Note:
a) Specify the direction of transcription (5' to 3').
b) Include both transcriptional steps and post-transcriptional modifications.

(b) What are stem cells ? Explain the various types of stem cells. [4]

Answer:
1. Stem cells are unspecialized cells capable of self-renewal through mitotic division and differentiation into specialized cell types.
2. Totipotent cells: Can give rise to an entire organism and extra-embryonic tissues.
3. Pluripotent cells: Can give rise to most cell types necessary for fetal development, excluding extra-embryonic tissues.
4. Multipotent cells: Can differentiate into a limited number of specialized cell types within a specific lineage.
5. Unipotent cells: Can produce only a single cell type while retaining the ability of self-renewal.

Teacher's Note:
a) Define self-renewal clearly as a core property.
b) Categorize stem cells correctly based on developmental potency.

(c) Name any two chemicals used to determine the amino acid sequence in protein. [2]

Answer:
1. Sanger reagent (1-fluoro-2,4-dinitrobenzene).
2. Dansyl chloride (dansyl derivative).

Teacher's Note:
a) Provide exact chemical names for peptide sequencing reagents.
b) Commonly tested in biochemical techniques.

Question 4.
(a) Explain the following methods of selection of recombinant cells: [4]
(i) Insertional inactivation.
(ii) Blue white colony.

Answer:
(i) Insertional inactivation: A foreign DNA fragment is inserted into a marker gene (such as the tetracycline resistance gene in pBR322), inactivating it. Recombinants can thus be identified by the loss of that specific marker trait.
(ii) Blue-white screening: Relies on the inactivation of the lacZ gene encoding beta-galactosidase. In the presence of X-gal, non-recombinant colonies form blue spots, while recombinant colonies with disrupted lacZ genes appear white.

Teacher's Note:
a) Contrast selection markers for both techniques clearly.
b) Mention plasmid examples like pBR322 or pUC19 for complete credit.

(b) Enumerate the steps involved in regenerating a plant from a single cell [4]

Answer:
1. Preparation and sterilization of nutrient medium containing minerals, vitamins, sucrose, and hormones.
2. Selection and surface sterilization of explants (such as shoot tips).
3. Inoculation of the explant onto the sterile nutrient medium under aseptic conditions.
4. Incubation under controlled temperature, light, and humidity to form an unorganized mass of cells called callus, followed by organogenesis and plantlet hardening.

Teacher's Note:
a) Sequence the steps logically from medium preparation to hardening.
b) Mention callus formation and totipotency explicitly.

(c) What is wobble effect ? [2]

Answer:
1. The wobble effect refers to the flexibility in pairing between the third base of an mRNA codon and the first base of a tRNA anticodon.
2. It explains why multiple codons can code for the same amino acid due to genetic code redundancy.

Teacher's Note:
a) Highlight the third position wobble base pairing.
b) Link it directly to genetic code redundancy.

Question 5.
(a) Discuss the working of PCR technique in detail. [4]

Answer:
1. Denaturation: Double-stranded DNA is heated to about \( 95^{\circ}\text{C} \) to separate the strands.
2. Annealing: The temperature is lowered to allow oligonucleotide primers to bind to complementary sequences on single-stranded templates.
3. Extension: Thermostable Taq DNA polymerase extends the primers in the 5' to 3' direction at approximately \( 70^{\circ}\text{C} \) using dNTPs and magnesium ions.
4. Amplification cycle: Repeating these thermal cycles exponentially amplifies the target DNA sequence by \( 2^n \).

Teacher's Note:
a) List all three temperature stages in correct order.
b) Mention Taq polymerase and exponential amplification.

(b) Explain the principle and any two applications of each of the following biochemical techniques:
(i) Iso-electric focusing.
(ii) Centrifugation. [4]

Answer:
(i) Iso-electric focusing: Proteins are separated in a gel along a pH gradient based on their isoelectric points (pI) where their net charge is zero.
(ii) Centrifugation: Particles and cells are separated based on differences in size, shape, and density under high rotational centrifugal force.

Teacher's Note:
a) Define the physical principle governing each separation technique.
b) State applications clearly for both protein and cellular separations.

(c) Where do we find the following carbohydrates:
(i) Glycogen
(ii) Chitin [2]

Answer:
(i) Glycogen is found in animals (as animal starch), fungi, and yeasts.
(ii) Chitin is found in the exoskeletons of arthropods (such as crabs and insects) and fungal cell walls.

Teacher's Note:
a) Give precise biological occurrences for both polysaccharides.
b) Mention animal starch and arthropod exoskeletons.

Question 6.
(a) Describe the procedure of sequencing of DNA by Sanger's method. [4]

Answer:
1. Single-stranded DNA template is mixed with normal deoxynucleotides (dNTPs) and fluorescently labeled dideoxynucleotides (ddNTPs) along with DNA polymerase.
2. Incorporation of a ddNTP terminates chain elongation prematurely, producing DNA fragments of varying lengths.
3. The resulting fragments are separated according to size by high-resolution gel electrophoresis.
4. An automated laser scanner detects the fluorescent dye on each terminal ddNTP to read the exact nucleotide sequence.

Teacher's Note:
a) Highlight the role of dideoxynucleotides in chain termination.
b) Mention size separation and laser fluorescence detection.

(b) Explain any two physical and any two chemical methods used to synchronize suspension cultures. [4]

Answer:
Physical methods:
1. Selection by volume: Cell aggregates are fractionated based on size using filtration or centrifugation.
2. Temperature shock: Low-temperature treatments combined with nutrient starvation induce synchronous cell cycle progression.
Chemical methods:
1. Starvation: Depriving cultures of essential nutrients arrests cells at a stationary phase, enabling synchronous resumption upon resupply.
2. Inhibition: Using metabolic inhibitors like hydroxyurea or excess thymidine temporarily arrests cells at specific cell cycle boundaries.

Teacher's Note:
a) Categorize methods correctly into physical and chemical.
b) Explain how cell cycle arrest and release achieve synchronization.

(c) Name any two industrial enzymes and give their uses. [2]

Answer:
1. Amylase: Used for producing sugars and high fructose corn syrup from starch.
2. Rennin: Used in cheese manufacturing to hydrolyze milk proteins.

Teacher's Note:
a) Provide standard industrial applications for enzymes.
b) Ensure correct spellings of Amylase and Rennin.

Question 7.
(a) Briefly explain the essential features of a vector. [4]

Answer:
1. Origin of replication (ori): A DNA sequence that initiates self-replication within the host cell.
2. Selectable marker: Genes (such as antibiotic resistance genes) that allow identification of transformed host cells.
3. Cloning sites: Unique recognition sites for restriction enzymes to insert foreign DNA.
4. Small size: Essential for easy uptake and stability within host cells.

Teacher's Note:
a) List all four standard vector characteristics.
b) Emphasize ori and selectable markers.

(b) What is the principle of cryopreservation? Mention the steps of cryopreservation. [4]

Answer:
1. Principle: Cells and tissues are stored at ultra-low temperatures (using liquid nitrogen at \( -196^{\circ}\text{C} \)) to halt metabolic processes and prevent ice crystal damage.
2. Steps:
- Freezing: Cooling cells in the presence of cryoprotectants using controlled-rate freezers.
- Vitrification: Direct cooling into a glass-like solid state without ice crystal formation, suitable for sensitive plant cells.

Teacher's Note:
a) Mention liquid nitrogen and metabolic arrest in the principle.
b) Distinguish between conventional slow freezing and vitrification.

(c) What is the importance of pH and solidifying agents in cell cultures ? [2]

Answer:
1. pH: Regulates nutrient uptake and enzyme activity, with an optimum range of 5.0 to 6.0 required for plant tissue growth.
2. Solidifying agents: Agents like agar provide a stable solid support matrix for culture media without reacting chemically with nutrients.

Teacher's Note:
a) State the optimum pH range clearly.
b) Explain the supportive role of agar in media.

Question 8.
(a) Explain how DNA technology has been used to create the following: [4]
(i) Tomatoes with delayed ripening
(ii) Bt crops
(iii) Virus free crops
(iv) Biodegradable plastic.

Answer:
(i) Flavr Savr tomatoes: Engineered by introducing an antisense gene to inhibit polygalacturonase, delaying fruit softening and ripening.
(ii) Bt crops: Transgenic plants expressing insecticidal crystal proteins encoded by cry genes from Bacillus thuringiensis.
(iii) Virus-free crops: Produced through meristem tip culture coupled with antiviral transgenics.
(iv) Biodegradable plastic: Produced by expressing bacterial genes for polyhydroxybutyrate (PHB) synthesis in transgenic plants.

Teacher's Note:
a) Provide specific genetic modifications for each transgenic product.
b) Mention Bacillus thuringiensis for Bt crops and PHB for plastics.

(b) List the functions of the following bioinformatics tools: [4]
(i) GENSCAN
(ii) ENTREZ
(iii) FASTA
(iv) PIR

Answer:
(i) GENSCAN: Eukaryotic gene-finding algorithm used for ab initio gene prediction and sequence annotation.
(ii) ENTREZ: Integrated database retrieval system of NCBI used to access literature, nucleotide/protein sequences, and 3D structures.
(iii) FASTA: Software program used for performing database similarity searches and local sequence alignments.
(iv) PIR: Comprehensive protein sequence database providing annotated protein sequences and analytical tools.

Teacher's Note:
a) State distinct functional roles for each bioinformatics tool.
b) Associate ENTREZ and FASTA correctly with NCBI and sequence alignment.

(c) Name any two media used in plant tissue culture. [2]

Answer:
1. Murashige and Skoog (MS) medium.
2. Gamborg's (B5) medium.

Teacher's Note:
a) Name standard plant tissue culture media.
b) MS medium is the most widely used formulation.

Question 9.
(a) What are restriction enzymes? How do they work? What are the different types of restriction enzymes? [4]

Answer:
1. Restriction enzymes are endonucleases that cleave DNA molecules at specific palindromic recognition sequences.
2. Mechanism: They scan DNA for specific base sequences and hydrolyze phosphodiester bonds on both strands to generate blunt or sticky ends.
3. Types: Type I, Type II, and Type III restriction enzymes, with Type II being most commonly used in recombinant DNA technology due to its cleavage site specificity.

Teacher's Note:
a) Describe them as molecular scissors.
b) Differentiate between cleavage patterns and types.

(b) Define the term proteomics. Explain the various types of proteomics. [4]

Answer:
1. Proteomics is the large-scale identification, structural analysis, and quantification of the entire complement of proteins expressed by an organism.
2. Expression proteomics: Quantitative study of protein expression levels across different samples or experimental conditions.
3. Structural proteomics: Analysis of the 3D structures and interacting complexes of proteins within specific cellular organelles.
4. Functional proteomics: Investigation of large-scale protein functions, biochemical activities, and molecular interaction networks.

Teacher's Note:
a) Define proteomics as the study of the proteome.
b) Clearly distinguish the three functional branches of proteomics.

(c) Differentiate between the following: [2]
(i) Local alignment and Global alignment.
(ii) FST and STS.

Answer:
(i) Global alignment attempts to align every residue across the entire length of two sequences, whereas local alignment identifies regions of local similarity within longer sequences.
(ii) FST (Flanking Sequence Tag) is used for mapping insertion sites in mutagenesis studies, whereas STS (Sequence Tagged Site) is a unique short genomic DNA sequence identifiable by PCR.

Teacher's Note:
a) Highlight the scope difference between global and local alignments.
b) Define FST and STS clearly based on genomic mapping applications.