B.Tech. / M.Tech (Integrated) DEGREE EXAMINATION, JANUARY 2023
21BTB102T - INTRODUCTION TO COMPUTATIONAL BIOLOGY

Detailed Solution:
Step 1: Cell division in eukaryotes occurs in two primary ways: Mitosis and Meiosis.
Step 2: Meiosis is strictly for sexual reproduction (creating gametes).
Step 3: Mitosis produces two identical somatic cells from a single parent cell. This process is essential for the growth of the organism and the maintenance/repair of tissues.

Detailed Solution:
Step 1: Prokaryotes (bacteria and archaea) lack a membrane-bound true nucleus.
Step 2: Instead, their primary genetic material (the main circular DNA chromosome) is concentrated in an irregularly shaped region within the cytoplasm.
Step 3: This region is called the Nucleoid. (While plasmids are also genetic material, they are small, accessory, extra-chromosomal rings, not the primary genetic material).

Detailed Solution:
Step 1: In 1665, the English scientist Robert Hooke examined a thin slice of cork under a primitive compound microscope.
Step 2: He observed box-like pores that reminded him of the small rooms (cellula) inhabited by monks in a monastery.
Step 3: Because of this resemblance, he coined the biological term "Cell" in his book Micrographia.

Detailed Solution:
Step 1: Organelles are often given nicknames based on their function. Mitochondria are the "power house" and Lysosomes are the "suicide bags."
Step 2: Ribosomes are the cellular machinery responsible for translating mRNA into amino acid chains (polypeptides).
Step 3: Because they manufacture all the proteins for the cell, they are aptly nicknamed the Protein factory.

Detailed Solution:
Step 1: In all living cellular organisms, the permanent blueprint containing the hereditary instructions for growth, development, and reproduction must be highly stable.
Step 2: Deoxyribonucleic Acid (DNA), with its double-helix structure and lack of a 2'-OH group, is chemically much more stable than RNA.
Step 3: Therefore, genetic information is stored long-term in the form of DNA, while RNA acts mostly as a temporary messenger or structural molecule.

Detailed Solution:
Step 1: After fertilization, a zygote divides into a solid ball of cells (morula).
Step 2: Around day 5 of mammalian development, a fluid-filled cavity forms inside, creating a hollow structure consisting of an inner cell mass and an outer trophoblast layer.
Step 3: This specific developmental structure is called the blastocyst, which is definitively an early stage of the embryo just prior to implantation in the uterus.

Detailed Solution:
Step 1: The two antiparallel strands of a DNA double helix are held together by hydrogen bonds between the complementary nitrogenous bases (A=T, C≡G).
Step 2: A hydrogen bond is an electrostatic dipole-dipole attraction. It does not involve the sharing (covalent) or complete transfer (ionic) of electrons.
Step 3: In biophysics, hydrogen bonds, along with Van der Waals forces and hydrophobic effects, are classified collectively as non-bonded interactions (or non-covalent interactions).

Detailed Solution:
Step 1: The BLAST (Basic Local Alignment Search Tool) suite has different variants depending on the input and target database.
Step 2: To compare a protein (amino acid) query directly against a protein database, the appropriate algorithm is BLASTp (p stands for protein).
Step 3: BLASTn is for nucleotide vs nucleotide. BLASTx translates a nucleotide query into protein and compares it to a protein database.

Detailed Solution:
Step 1: During translation, the ribosome reads mRNA in triplets (codons). When it hits a termination signal, synthesis stops.
Step 2: There are exactly three universal stop codons in the genetic code: UAA (Ochre), UAG (Amber), and UGA (Opal).
Step 3: Among the options, only UGA is a stop codon. (AUG is the start codon).

Detailed Solution:
Step 1: The process of assembling amino acids into a polypeptide chain is called translation.
Step 2: mRNA carries the instructions, and tRNA brings the amino acids, but the physical location where the peptide bonds are actually catalyzed is the Ribosome.
Step 3: The ribosome acts as the cellular workbench and enzyme (ribozyme) that physically assembles the protein.

Detailed Solution:
Step 1: Many enzymes are conjugated proteins, meaning the protein portion (apoenzyme) is inactive by itself.
Step 2: To become catalytically active (a holoenzyme), they require the binding of a non-protein chemical component.
Step 3: This essential non-proteinaceous "helper" molecule is broadly termed a Cofactor. (If it is an organic molecule, it is specifically called a coenzyme; if inorganic, like a metal ion, it remains a cofactor).

Detailed Solution:
Step 1: In bioinformatics, a PDB file contains the XYZ atomic coordinates of a protein.
Step 2: PyMOL is a proprietary, open-source molecular graphics system created by Warren Lyford DeLano.
Step 3: Its primary and most famous purpose is as a 3D molecular visualization tool used to render high-quality images and animations of protein structures.

Detailed Solution:
Step 1: The central nervous system contains various supporting glial cells.
Step 2: The most abundant type of macroglial cell has numerous branching processes radiating from its central soma.
Step 3: This gives the cell a distinct, highly irregular star shape, which is why they were named Astrocytes (from the Greek astron, meaning star).

Detailed Solution:
Step 1: Synaptic signaling is a highly specialized form of paracrine signaling that occurs exclusively between neurons or between a neuron and a target cell (like a muscle).
Step 2: An action potential triggers the presynaptic neuron to release chemical messengers into the synaptic cleft.
Step 3: These specific chemical messengers, which bind to receptors on the postsynaptic cell, are called Neurotransmitters (e.g., dopamine, serotonin, acetylcholine).

Detailed Solution:
Step 1: In Artificial Neural Networks (ANN), the connection between two artificial nodes has a mathematical "weight" ($w$). This weight determines the strength of the signal passed to the next node.
Step 2: In a biological neuron, the connection point where a signal is passed from one cell to another is the Synapse.
Step 3: Biological learning occurs by strengthening or weakening synaptic connections (synaptic plasticity). Therefore, the adjustable weights in an ANN perfectly correspond to the strength of a biological Synapse.

Detailed Solution:
Step 1: Amyloid plaques and neurofibrillary tangles are the hallmarks of Alzheimer's disease. Spongiform refers to prion diseases.
Step 2: Parkinson's disease is a progressive motor system disorder characterized by tremors and rigidity.
Step 3: It is primarily caused by the death or degeneration of dopamine-producing (dopaminergic) neurons in a specific region of the midbrain called the substantia nigra.

Detailed Solution:
Step 1: The lymphatic system is a network of tissues and vessels that helps maintain fluid balance and defends against infections.
Step 2: As blood circulates, plasma leaks out of capillaries into tissues, becoming interstitial fluid.
Step 3: When this interstitial fluid is absorbed into the lymphatic vessels, it is officially called Lymph. It is a clear, plasma-like liquid containing white blood cells (lymphocytes).

Detailed Solution:
Step 1: Polio drops are the Oral Polio Vaccine (OPV), which contains a live attenuated (weakened) form of the poliovirus.
Step 2: Like all vaccines, the purpose is not related to RBCs, digestion, or bone marrow correction.
Step 3: The vaccine safely mimics an infection, stimulating the infant's adaptive immune system (specifically B-cells) to produce neutralizing antibodies and memory cells against the poliovirus, providing long-term immunity.

Detailed Solution:
Step 1: T-lymphocytes are broadly divided into two main effector subtypes based on their surface glycoproteins and functions: $CD4^+$ and $CD8^+$ cells.
Step 2: The $CD4^+$ cells are Helper T cells (Th).
Step 3: The $CD8^+$ cells, denoted biologically as $T_c$ cells, are Cytotoxic T cells. Their function is to directly kill virally infected host cells and cancer cells by inducing apoptosis.

Detailed Solution:
Step 1: An epitope is the specific part of an antigen that an antibody or B-cell receptor binds to.
Step 2: While T-cells only recognize continuous, linear peptide sequences presented by MHC, B-cells can recognize free-floating 3D antigens in their native state.
Step 3: Approximately 90% of B-cell epitopes are conformational (discontinuous), meaning they consist of amino acids that are far apart in the linear sequence but brought close together in 3D space when the protein folds. Therefore, advanced B-cell epitope prediction algorithms must primarily account for 3D conformational structure.

Major Eukaryotic Cell Organelles:
1. Nucleus:
Structure: The largest organelle, surrounded by a double membrane (nuclear envelope) punctuated by nuclear pores. Contains chromatin (DNA) and a dense nucleolus.
Function: The control center of the cell. Stores genetic information and orchestrates DNA replication and RNA transcription.

2. Mitochondria:
Structure: Double-membraned. The inner membrane is heavily folded into structures called cristae, enclosing a fluid matrix.
Function: The "powerhouse" of the cell. The site of aerobic cellular respiration, generating the vast majority of the cell's ATP (energy).

3. Endoplasmic Reticulum (ER):
Structure: A continuous network of membranous tubules and flattened sacs (cisternae) extending from the nuclear envelope.
Function: - Rough ER (studded with ribosomes) synthesizes and modifies proteins. - Smooth ER (no ribosomes) synthesizes lipids, metabolizes carbohydrates, and detoxifies poisons.

4. Golgi Apparatus:
Structure: A stack of flattened, unconnected membranous sacs.
Function: The cell's "post office." Modifies, sorts, packages, and tags proteins and lipids received from the ER for transport to their final destinations.

5. Lysosomes:
Structure: Small, membrane-bound vesicles containing highly acidic hydrolytic enzymes.
Function: The cell's "garbage disposal." Digests macromolecules, old organelles (autophagy), and engulfed foreign pathogens.

6. Chloroplasts (Plant Cells Only):
Structure: Double-membraned organelle containing stacks of thylakoids (grana) surrounded by a fluid stroma. Contains the green pigment chlorophyll.
Function: The site of photosynthesis, converting solar light energy into chemical energy (glucose).

1. Introduction to Nucleic Acids:
DNA and RNA are the two main classes of nucleic acids, which are large biological macromolecules essential for all known forms of life. They are polymers composed of repeating monomer units called nucleotides. Every nucleotide contains a 5-carbon sugar, a phosphate group, and a nitrogenous base.

2. DNA (Deoxyribonucleic Acid):
Description: DNA is the master blueprint of life. It contains all the genetic instructions necessary for the development, functioning, growth, and reproduction of an organism.
Structure:

• It is a double-stranded molecule twisted into a right-handed double helix.
• The 5-carbon sugar is Deoxyribose (lacking an oxygen on the 2' carbon, making it highly stable).
• It uses four nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
• The two strands are held together by complementary base pairing (A=T with two hydrogen bonds, C≡G with three hydrogen bonds).

Function: Long-term, secure storage and transmission of hereditary genetic information.

3. RNA (Ribonucleic Acid):
Description: RNA is the versatile messenger and catalytic molecule that executes the instructions stored in the DNA to build proteins.
Structure:

• It is generally a single-stranded molecule, though it can fold onto itself to form complex 3D structures.
• The 5-carbon sugar is Ribose (contains a hydroxyl -OH group on the 2' carbon, making it more reactive and less stable than DNA).
• It uses four bases, but substitutes Uracil (U) in place of Thymine (so A pairs with U).

Function: Comes in three main types: - mRNA (messenger RNA): Carries the genetic code from DNA to the ribosome. - tRNA (transfer RNA): Brings specific amino acids to the ribosome during translation. - rRNA (ribosomal RNA): The structural and catalytic core of the ribosome.

1. Introduction to Secondary Structure Prediction:
Protein secondary structure refers to the local folded structures that form within a polypeptide due to hydrogen bonding between the backbone amide and carbonyl groups. The two main types are the Alpha-helix and the Beta-pleated sheet. Predicting secondary structure from a 1D amino acid sequence is a crucial intermediate step toward predicting the full 3D tertiary structure.

2. Types/Generations of Secondary Structure Prediction Tools:
These computational tools evolved through three main generations, improving in accuracy over time.
A. First Generation (Statistical / Propensity-Based Methods):
These early tools were based purely on the statistical likelihood of a single amino acid being found in a helix, sheet, or coil, derived from early known protein structures.

• Example - Chou-Fasman Algorithm: Calculates "conformational parameters" for each amino acid. E.g., Glutamate strongly prefers alpha-helices, while Proline acts as a helix breaker.
• Example - GOR (Garnier-Osguthorpe-Robson): An improvement over Chou-Fasman; instead of looking at single amino acids, it looks at a "sliding window" of 17 amino acids, considering the influence of neighboring residues. Max accuracy was ~65%.

B. Second Generation (Machine Learning & Neural Networks):
These tools moved away from simple statistics and began using Artificial Neural Networks (ANNs) trained on databases of known structures.

• Example - PHD (Profile network from HeiDelberg): Utilized neural networks and sliding windows. Accuracy improved significantly over first-generation tools, hitting ~70%.

C. Third Generation (Evolutionary Profiles / Hidden Markov Models):
The massive leap in accuracy came when tools started incorporating evolutionary information. Before feeding the sequence into the neural network, they run a BLAST search to find all related proteins across different species, creating an MSA (Multiple Sequence Alignment) profile.

• Example - PSIPRED (Position-Specific Scoring Matrix based PREdiction): Uses two feed-forward neural networks and PSI-BLAST profiles. It achieves over 80% accuracy and is highly reliable.
• Example - Jpred: A popular web server that uses Jnet, a neural network predicting secondary structure based on Hidden Markov Models (HMM) and PSI-BLAST profiles.

1. What is Machine Learning (ML)?
Machine Learning is a subset of Artificial Intelligence (AI) rooted in statistics and computer science. Instead of programmers writing explicit, step-by-step rules (e.g., "if X happens, do Y"), machine learning algorithms are designed to mathematically "learn" patterns directly from massive datasets. By iteratively processing data, calculating errors, and updating internal parameters (weights), the model improves its accuracy over time, enabling it to classify new data, make predictions, or discover hidden structures.

2. Main Paradigms of Machine Learning:

• Supervised Learning: The algorithm is trained on labeled data (e.g., images labeled as "cancer" or "healthy"). It learns the boundary between the classes.
• Unsupervised Learning: The algorithm is given unlabeled data and must find inherent patterns, such as clustering similar genes together.
• Deep Learning: Uses complex, multi-layered Artificial Neural Networks to analyze highly unstructured data (like images or long genomic sequences).

3. Uses and Applications of Machine Learning in Biology:
Modern biology generates petabytes of data (from Next-Generation Sequencing, microarrays, and cryo-EM). ML is essential to make sense of this "Big Data."

• Genomics and Sequence Analysis: ML models, specifically Hidden Markov Models (HMMs), are used for Gene Prediction. They scan newly sequenced raw DNA and predict exactly where the protein-coding genes, promoters, and splice sites are located.
• Protein Structure Prediction: Predicting a protein's 3D structure from its 1D sequence was computationally impossible for 50 years. DeepMind's AlphaFold (a deep learning neural network) solved this by learning the complex spatial relationships of amino acids from the entire PDB database.
• Medical Diagnostics and Imaging: Convolutional Neural Networks (CNNs) are trained on millions of medical images (X-rays, MRIs, histology slides). They can now diagnose diseases like diabetic retinopathy or skin melanoma with accuracy rivaling top human specialists.
• Drug Discovery (Cheminformatics): Developing a new drug takes 10+ years and billions of dollars. ML algorithms can virtually screen millions of chemical compounds in a database to predict which ones will successfully dock with a disease target (like a viral enzyme) and predict their toxicity, drastically reducing lab time.

1. Introduction to Cell-Mediated Immunity:
Unlike humoral immunity (which uses antibodies to attack free-floating pathogens), cell-mediated immunity does not involve antibodies. It is an immune response driven by T-lymphocytes (T-cells) that is specifically designed to target and destroy intracellular pathogens (viruses hiding inside host cells) or mutated host cells (cancer).

2. Mechanism of Cell-Mediated Immunity:

• Infection & Antigen Presentation: When a virus infects a normal body cell, the cell breaks down viral proteins and presents the viral antigens on its surface using an MHC Class I molecule. This acts as a distress flag saying, "I am infected."
• Recognition: A circulating naive Cytotoxic T-Cell (CD8+ Tc cell) whose specific T-Cell Receptor (TCR) matches the viral antigen binds to the MHC-I complex.
• Activation & Clonal Expansion: Simultaneous chemical signals (cytokines like IL-2) from a Helper T-Cell (Th1) fully activate the Cytotoxic T-Cell, causing it to rapidly multiply into an army of identical clones.
• Lethal Action (Cytotoxicity): The cloned active Cytotoxic T-cells travel to the site of infection. They bind tightly to other infected cells and release lethal proteins:
  • Perforins: Punch holes (pores) in the infected cell's membrane.
  • Granzymes: Enter through the pores and trigger apoptosis (programmed cell death).
• Memory: Some cloned T-cells become Memory T-Cells, remaining dormant to provide rapid protection against future infections by the same virus.

3. Diagrammatic Representation:
(Note to student: You must draw this process clearly in your exam booklet)

[Virus infects Host Cell] ---> [Host Cell presents Viral Antigen on MHC Class I]
                                         |
                                         v
               [Naive Cytotoxic T-Cell (CD8+) binds via TCR to MHC-I]
                                         |
                                         | <--- (Cytokines from Helper T-Cell)
                                         v
                    (Activation and Clonal Expansion of Tc Cells)
                                         |
                       +-----------------+-----------------+
                       |                                   |
                       v                                   v
             [Active Cytotoxic T-Cells]              [Memory T-Cells]
                       |
                       v
         (Binds to other infected Host cells)
                       |
                       v
          (Releases Perforins & Granzymes)
                       |
                       v
           [Apoptosis (Death) of Infected Cell]
              

1. What are Stem Cells?
Stem cells are unique, unspecialized biological cells characterized by two defining traits: Self-renewal (they can divide and replicate indefinitely) and Potency (they can differentiate into various specialized cell types, such as muscle, brain, or red blood cells).

2. Types of Stem Cells (Classification by Potency/Origin):

• Embryonic Stem Cells (ESCs): Derived from the inner cell mass of a 5-day-old blastocyst. They are pluripotent, meaning they can become any of the ~200 cell types in the human body. They offer immense therapeutic potential but pose significant ethical debates regarding embryo destruction.
• Adult (Somatic) Stem Cells: Found in various mature tissues (like bone marrow, fat, or skin). They act as a repair system for the body. They are multipotent, meaning they can only differentiate into a limited, tissue-specific range of cells (e.g., hematopoietic stem cells only make blood cells).
• Induced Pluripotent Stem Cells (iPSCs): A revolutionary breakthrough (winning the 2012 Nobel Prize). Scientists take ordinary adult somatic cells (like a skin fibroblast) and genetically reprogram them back into an embryonic, pluripotent state using specific transcription factors (Yamanaka factors). They offer the power of ESCs without the ethical issues.

3. Overview of Stem Cell Technology Applications:
Stem cell technology is the cornerstone of modern regenerative medicine and biotechnology.

• Cell Replacement Therapy: The most immediate goal. Instead of treating symptoms with drugs, doctors can grow new, healthy tissue to replace diseased organs. E.g., implanting lab-grown neurons into patients with Parkinson's, or regenerating insulin-producing islet cells for Type 1 Diabetes.
• Bone Marrow Transplants: The most widely used, FDA-approved stem cell therapy currently. Used to replace a patient's hematopoietic system after intensive chemotherapy for leukemia.
• Personalized Drug Screening: By using iPSCs created from a specific patient's skin cells, scientists can grow the patient's own liver or heart tissue in a lab. They can then test thousands of experimental drugs on this tissue to see exactly how that specific patient will react, eliminating the risk of toxic side effects in humans.
• Disease Modeling: iPSCs from patients with complex genetic disorders (like Alzheimer's) can be grown into neurons in a dish, allowing scientists to study the molecular onset of the disease in real-time.

1. Introduction:
To predict and find similar sequences to a query protein sequence against a massive global database (like UniProt or GenBank), bioinformaticians do not use slow, exhaustive dynamic programming algorithms (like Smith-Waterman). Instead, they use a highly optimized heuristic algorithm called BLAST (Basic Local Alignment Search Tool), specifically the BLASTp variant for proteins.

2. The Fundamental Strategy of BLAST:
BLAST assumes that statistically significant similar sequences will almost certainly contain at least one short, highly conserved stretch of exact (or very highly scoring) amino acid matches. By rapidly scanning only for these short "words," BLAST skips comparing the vast majority of unrelated sequences, saving massive amounts of computational time.

3. The Three-Phase BLAST Algorithm (Step-by-Step):
Phase 1: Seeding (Word List Generation)

• The algorithm takes the user's query protein sequence and chops it into overlapping short segments called "words." For proteins, the default word length ($W$) is 3 amino acids.
• Example: If query is M K A Q E, the words are MKA, KAQ, and AQE.
• Next, BLAST uses a substitution matrix (like BLOSUM62) to generate a list of "synonymous" words that are chemically similar. Any synonymous word that scores above a specific threshold ($T$) is kept. This accounts for minor evolutionary mutations.

Phase 2: Scanning (Finding Hits in the Database)

• BLAST takes this compiled list of high-scoring words and rapidly scans the massive target database.
• It looks strictly for exact matches between the word list and sequences in the database.
• Because searching for short exact matches can be done using incredibly fast indexing (like a computer searching a dictionary), this step takes fractions of a second. Every exact match found is called a "Hit."

Phase 3: Extension (Local Alignment)

• Once a Hit is found, it acts as an anchor point between the query and the database sequence.
• The algorithm then attempts to extend the alignment bidirectionally (left and right) from the Hit, matching amino acid by amino acid.
• As it extends, it calculates a cumulative alignment score (adding points for matches, subtracting points for mismatches and gaps).
• The extension continues until the cumulative score drops below a certain drop-off value. The resulting segment is called a High-scoring Segment Pair (HSP).

4. Statistical Evaluation:
After finding HSPs, BLAST calculates the statistical significance of each match. It reports the E-value (Expect value), which estimates how many times a match of this quality would occur in the database purely by random chance. An E-value close to zero (e.g., $10^-50$) indicates a highly significant match, strongly predicting that the two protein sequences share common evolutionary ancestry and likely similar biological functions.

1. Introduction to the COVID-19 Vaccine Mechanism:
The most prominent COVID-19 vaccines (like Pfizer and Moderna) are mRNA vaccines. They do not contain the live or dead SARS-CoV-2 virus. Instead, they contain a synthetic strip of messenger RNA encased in a Lipid Nanoparticle (LNP). This mRNA acts as an instruction manual, teaching our immune system how to recognize and fight the virus without ever exposing us to the disease.

2. Step-by-Step Immune Process Post-Vaccination:
Step A: Injection and Cellular Entry
Upon injection into the arm muscle, the lipid nanoparticles fuse with the cell membranes of local muscle cells and resident antigen-presenting cells (APCs like Dendritic cells), releasing the mRNA into the cytoplasm.

Step B: Translation of the Spike Protein
The host cell's ribosomes read the viral mRNA and translate it into a harmless piece of the virus: the SARS-CoV-2 Spike Protein. Crucially, because it is only the spike protein and not the whole virus, it cannot replicate or cause COVID-19. The mRNA is then naturally degraded and destroyed by the cell.

Step C: Antigen Presentation
The cell transports these newly synthesized Spike Proteins to its surface. Dendritic cells (APCs) in the muscle also process the spike protein and display fragments of it on their surface using MHC Class II molecules. These APCs then migrate to nearby lymph nodes to sound the alarm.

Step D: Activation of the Adaptive Immune System
In the lymph node, the APCs present the Spike antigen to naive T-cells and B-cells.

• Helper T-Cells (CD4+): Recognize the antigen, become activated, and release cytokines. These chemical signals act as a massive amplifier for the rest of the immune system.
• B-Cell Activation (Humoral Immunity): Stimulated by the Helper T-cells, naive B-cells whose receptors match the Spike protein begin to clone themselves rapidly. They differentiate into Plasma cells, which act as factories pumping out massive amounts of specific, neutralizing Antibodies against the Spike protein.
• Cytotoxic T-Cells (CD8+): Stimulated by the cytokines, these cells are primed to seek out and destroy any host cell that becomes infected with the actual virus in the future.

Step E: Creation of Immunological Memory
Once the immune response subsides and the manufactured Spike proteins are cleared, the active plasma cells die off. However, a small fraction of the activated T-cells and B-cells remain in the body as long-lived Memory Cells.

3. Conclusion (The Result):
Months later, if the person is exposed to the real SARS-CoV-2 virus, the memory B and T cells immediately recognize the viral Spike protein. They mount a rapid, overwhelming secondary immune response—producing antibodies to neutralize the virus before it can enter lung cells and cause severe COVID-19.