B.Tech. DEGREE EXAMINATION, JUNE 2023
21BTB102T - INTRODUCTION TO COMPUTATIONAL BIOLOGY

Detailed Solution:
Step 1: Cell division consists of two main stages: the division of the nucleus (karyokinesis, such as mitosis or meiosis) and the division of the cytoplasm.
Step 2: Cytokinesis is the specific biological term for the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells.
Step 3: Interphase and Prophase are phases of the cell cycle/mitosis, not the division of the cytoplasm itself.

Detailed Solution:
Step 1: A nucleoid (meaning nucleus-like) is an irregularly shaped region within the cell of a prokaryote that contains all or most of the genetic material.
Step 2: Unlike a true nucleus, it is not surrounded by a nuclear membrane.
Step 3: Plants, Animals, and Yeast are all eukaryotes and have true membrane-bound nuclei. Bacteria are prokaryotes and thus have a nucleoid region.

Detailed Solution:
Step 1: In 1665, the English scientist Robert Hooke examined a thin slice of cork under a primitive microscope.
Step 2: He observed a multitude of tiny, empty compartments that reminded him of the small rooms (cells) inhabited by monks in a monastery.
Step 3: He consequently coined the biological term "Cell" in his book Micrographia.

Detailed Solution:
Step 1: In biological literature, proteins are universally referred to as the "workhorses of the cell" because they perform almost all operational functions (enzymes, structural support, transport).
Step 2: However, "Protein" is not an option. Mitochondria are the "powerhouses," not the workhorses.
Step 3: Ribosomes are the cellular machines responsible for manufacturing these workhorses (proteins) through translation. In the context of the given choices, Ribosome is the most appropriate functional answer (alternatively, the question might have intended a different phrasing, but Ribosome stands out functionally over nucleotides).

Detailed Solution:
Step 1: Protein synthesis (translation) occurs at the ribosome.
Step 2: To build a protein, specific amino acids must be brought to the ribosome matching the sequence of codons on the messenger RNA (mRNA).
Step 3: Transfer RNA (tRNA) is the specific adapter molecule that binds to a specific amino acid and "transports" it to the ribosome, pairing its anticodon with the mRNA codon.

Detailed Solution:
Step 1: A zygote (fertilized cell) is a single cell.
Step 2: As the zygote divides (cleavage), it forms an 8-cell stage, then a solid ball of cells called a morula.
Step 3: Further division and fluid accumulation create a hollow, multicellular stage called the blastocyst (consisting of the inner cell mass and trophoblast), which implants into the uterine wall.

Detailed Solution:
Step 1: In the DNA double helix, the two strands are held together by hydrogen bonds between complementary nitrogenous bases.
Step 2: According to Watson-Crick base pairing rules, Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs with Cytosine (C).
Step 3: There are exactly two (2) hydrogen bonds between A and T, whereas there are three (3) hydrogen bonds between G and C.

Detailed Solution:
Step 1: The BLAST (Basic Local Alignment Search Tool) suite has different programs based on query and database types.
Step 2: BLASTN compares nucleotide to nucleotide. BLASTP compares protein to protein.
Step 3: BLASTX takes a nucleotide query sequence, translates it in all six reading frames, and compares it against a protein database. TBLASTX compares a translated nucleotide query against a translated nucleotide database.

Detailed Solution:
Step 1: In the standard genetic code, there are 64 codons. Three of these do not code for any amino acid.
Step 2: These three codons are UAA, UAG, and UGA.
Step 3: They are known as stop codons (or termination codons). When the ribosome encounters UGA on the mRNA during protein synthesis, a release factor binds instead of a tRNA, causing translation to stop and the newly synthesized polypeptide to be released.

Detailed Solution:
Step 1: Amino acids are the monomeric building blocks of a specific class of macromolecules.
Step 2: When multiple amino acids are joined together by peptide bonds, they form a long chain called a polypeptide.
Step 3: One or more polypeptides folded into a functional 3D shape form a Protein. (DNA and RNA are made of nucleotides; carbohydrates are made of monosaccharides).

Detailed Solution:
Step 1: Many enzymes require non-protein "helper" molecules to function catalytically.
Step 2: If this helper molecule is an organic molecule (like those derived from vitamins), it is specifically called a coenzyme.
Step 3: If the helper molecule is an inorganic substance, typically a metal ion (like $Mg^{2+}, Zn^{2+}, Fe^{2+}$), it is broadly and appropriately termed a cofactor.

Detailed Solution:
Step 1: To study the 3D structures of biomacromolecules (like proteins downloaded from the PDB), specific graphics software is required.
Step 2: BLAST is a sequence alignment tool. NCBI is a database portal.
Step 3: PyMOL is an open-source, user-sponsored, molecular visualization system created by Warren Lyford DeLano, widely used to produce high-quality 3D images of small molecules and biological macromolecules.

Detailed Solution:
Step 1: Glial cells are support cells in the central nervous system.
Step 2: Astrocytes derive their name from the Greek word "astron" meaning star, due to their characteristic star-shaped morphology with many radiating processes.
Step 3: They are the most abundant glial cells in the brain and are responsible for regulating blood flow, maintaining the blood-brain barrier, and providing nutrients to neurons.

Detailed Solution:
Step 1: The synapse is the microscopic gap between two communicating neurons.
Step 2: When an action potential reaches the end of the presynaptic neuron (axon terminal), it triggers synaptic vesicles to fuse with the membrane.
Step 3: This fusion releases chemical messengers called Neurotransmitters (e.g., dopamine, serotonin, acetylcholine) into the synaptic cleft to transmit the signal to the postsynaptic cell.

Detailed Solution:
Step 1: An Artificial Neural Network (ANN) is a mathematical/computational model inspired by the biological brain.
Step 2: Biological neurons contain physical structures like Dendrites (receivers), Axons (transmitters), and Synapses (connections).
Step 3: ANNs contain mathematical equivalents: Input nodes (simulating dendrites), output nodes (simulating axons), and numerical weights (simulating synapses). Therefore, an ANN technically does NOT contain actual Axons, Dendrites, or Synapses. This question is poorly phrased, but (D) 'N' population is the most nonsensical term in both fields, while A, B, and C are biological terms specifically excluded from the *artificial* software architecture.

Detailed Solution:
Step 1: Alzheimer's disease is a neurodegenerative disorder characterized by severe memory loss.
Step 2: The primary pathological hallmarks observed in the brains of Alzheimer's patients are the extracellular accumulation of amyloid-beta peptides.
Step 3: These accumulations clump together to form amyloid plaques (along with intracellular neurofibrillary tangles of tau protein), which disrupt cell function and lead to neuronal death. (Note: Dopamine related neuron loss causes Parkinson's).

Detailed Solution:
Step 1: While blood contains white blood cells, it is predominantly composed of red blood cells and plasma.
Step 2: The lymphatic system is explicitly dedicated to immune defense.
Step 3: Lymph is a fluid that circulates through the lymphatic system. It is exceptionally rich in immune cells, specifically lymphocytes (B cells and T cells) and macrophages, especially as it passes through lymph nodes where these cells congregate to fight infections.

Detailed Solution:
Step 1: There are two main types of polio vaccines: IPV (Inactivated Polio Vaccine) given via injection, and OPV (Oral Polio Vaccine) given as drops.
Step 2: OPV (the "polio drops" formulated by Albert Sabin) contains viruses that are still alive but have been weakened (attenuated) in the lab.
Step 3: Because they are weakened, they replicate in the gut to induce a strong immune response (producing mucosal immunity) without causing the disease, making them a Live attenuated vaccine.

Detailed Solution:
Step 1: An immune response is triggered by foreign substances entering the body, collectively known as antigens.
Step 2: However, antibodies and T-cell receptors do not recognize the entire large antigen molecule at once.
Step 3: They recognize and bind to a specific, small structural sequence or 3D shape on the surface of the antigen. This specific target region present on the Antigen is called an Epitope (or antigenic determinant). The corresponding binding site on the antibody is the paratope.

Detailed Solution:
Step 1: In immunoinformatics, various computational tools predict where immune cells will bind to antigens.
Step 2: NetChop, ProPred, and NetMHCpan are all well-known algorithms designed to predict MHC binding and cleavage sites specifically for T-cell epitopes.
Step 3: Bcepred stands for "B-cell epitope prediction." It is designed to predict continuous B-cell epitopes based on physico-chemical properties. Thus, it is the odd one out as it relates to B-cells, not T-cells.

1. Introduction:
Plant cells are eukaryotic cells. While they share many organelles with animal cells (like the nucleus, mitochondria, and ER), they possess specialized organelles adapted for their autotrophic (self-feeding) and sedentary lifestyle.

2. Unique Plant Cell Organelles:

• Chloroplasts (Plastids):
  Structure: Double-membrane bound organelle containing stacks of thylakoid discs (grana) suspended in a fluid called stroma. Contains the green pigment chlorophyll.
  Function: The site of Photosynthesis. They capture light energy and convert it into chemical energy (glucose) using carbon dioxide and water.


• Large Central Vacuole:
  Structure: A massive, membrane-bound sac (the membrane is called the tonoplast) that can occupy up to 90% of the cell's volume.
  Function: - Turgor Pressure: It fills with water to push against the cell wall, keeping the plant upright and rigid. - Storage: Stores nutrients, waste products, and sometimes toxic byproducts to deter herbivores.


• Cell Wall (Extracellular structure, but crucial):
  Structure: A rigid outer layer composed primarily of cellulose microfibrils, hemicellulose, and pectin, located outside the plasma membrane.
  Function: Provides immense structural support, shape, and protection against mechanical stress and osmotic bursting.

3. Shared Eukaryotic Organelles (Briefly):

• Nucleus: Stores DNA and controls cellular activities.
• Mitochondria: Performs cellular respiration to generate ATP (breaking down the glucose made by chloroplasts).
• Endoplasmic Reticulum (Rough & Smooth): Synthesizes proteins (Rough) and lipids (Smooth).
• Golgi Apparatus (Dictyosomes in plants): Modifies, sorts, and packages proteins and synthesizes complex polysaccharides for the cell wall.

1. Introduction:
Nucleic acids are large, complex biological macromolecules essential for all known forms of life. They function as the primary information-carrying molecules in cells, directing the process of protein synthesis and determining the inherited characteristics of every living thing.

2. Structure (The Monomers):
Nucleic acids are polymers made of repeating monomer units called nucleotides. Every nucleotide consists of three covalently bonded components:

• A 5-carbon (pentose) sugar.
• A phosphate group ($PO_4^{3-}$).
• A nitrogenous base (a ring structure containing nitrogen).

The nucleotides are joined together by phosphodiester bonds forming a strong sugar-phosphate backbone.

3. Types of Nucleic Acids:
There are two main classes of nucleic acids: DNA and RNA.

A. Deoxyribonucleic Acid (DNA):

• Sugar: Deoxyribose (lacks an oxygen atom on the 2' carbon).
• Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
• Structure: Double-stranded double helix. The two strands are antiparallel and held together by hydrogen bonds between complementary bases (A=T, G≡C).
• Function: Long-term, stable storage of genetic information (the blueprint).

B. Ribonucleic Acid (RNA):

• Sugar: Ribose.
• Bases: Adenine (A), Uracil (U) (replaces Thymine), Cytosine (C), Guanine (G).
• Structure: Typically single-stranded, though it can fold onto itself to form complex 3D shapes (like tRNA).
• Function: Acts as a messenger and machinery for translating the DNA blueprint into actual proteins. Exists in forms like mRNA (messenger), tRNA (transfer), and rRNA (ribosomal).

1. Introduction:
Secondary structure prediction involves determining whether a given segment of an amino acid sequence will coil into an Alpha-helix, fold into a Beta-sheet, or remain a random Coil (loop). This is a crucial intermediate step before predicting full 3D tertiary structure.

2. Methods of Prediction:

• Statistical / Propensity Methods (First Generation):
  Method: e.g., The Chou-Fasman method. It relies on calculating the statistical probability of specific amino acids appearing in a helix or sheet, based on previously solved crystal structures (e.g., Proline is a "helix breaker", while Alanine strongly prefers helices).
  Limitation: Low accuracy (~50-60%) because they ignore the influence of neighboring residues.


• Information Theory / Window Methods (Second Generation):
  Method: e.g., The GOR (Garnier-Osguthorpe-Robson) method. It doesn't just look at a single amino acid, but utilizes a "sliding window" (typically 17 residues long) to calculate how neighboring amino acids influence the folding state of the central residue.
  Accuracy: Slightly better (~65%).


• Machine Learning & Evolutionary Profiles (Third Generation):
  Method: This is the modern standard. It uses Artificial Neural Networks (ANNs) or Support Vector Machines (SVMs). Instead of just looking at one sequence, it uses PSI-BLAST to generate a Multiple Sequence Alignment (MSA). By observing evolutionary conservation across species, the algorithm makes highly accurate predictions.
  Accuracy: High (>80%).

3. Prominent Computational Tools:

• PSIPRED: Uses a highly accurate neural network approach utilizing Position-Specific Scoring Matrices (PSSMs) generated by PSI-BLAST. It is one of the most widely used and accurate web servers.
• Jpred 4: Uses the Jnet algorithm (neural networks) trained on representations of multiple sequence alignments and Hidden Markov Models (HMMs).
• PHDsec: A pioneering neural network-based tool that uses evolutionary information to predict secondary structure.

1. Introduction:
Machine Learning (ML), a subset of Artificial Intelligence, involves training algorithms on large datasets so they can identify patterns and make predictions without being explicitly programmed. With the explosion of "Big Data" in biology (genomics, proteomics), ML has become indispensable.

2. Key Uses in Biology:

• Genomics and DNA Sequencing:
  ML algorithms (like Hidden Markov Models and deep learning) are used to annotate genomes. They can accurately identify the locations of genes (gene prediction), detect splice sites, find regulatory promoter regions, and classify non-coding DNA. They also help in identifying disease-causing genetic mutations (SNPs) from sequencing data.


• Protein Structure Prediction:
  Predicting a 3D protein structure from a 1D amino acid sequence is notoriously difficult. Deep learning ML models, specifically DeepMind's AlphaFold, have revolutionized biology by predicting protein structures with near-experimental accuracy, accelerating enzyme design and structural biology.


• Drug Discovery and Design:
  ML drastically cuts down R&D time in pharmacology. Algorithms can screen millions of virtual chemical compounds to predict which ones will effectively bind to a disease target (like a viral receptor). ML also predicts the toxicity (ADMET properties) and efficacy of a drug before it ever enters a physical lab.


• Medical Imaging and Diagnostics:
  Convolutional Neural Networks (CNNs) are trained on thousands of medical images. They can detect subtle anomalies in MRI scans, X-rays, or tissue biopsies (like distinguishing between benign and malignant cancer cells) faster and sometimes more accurately than human pathologists.


• Systems Biology and Biomarker Discovery:
  By integrating data from transcriptomics (RNA-seq) and proteomics, ML models can uncover complex biological networks and identify novel biomarkers for diseases like Alzheimer's or cancer, paving the way for personalized medicine.

1. Introduction:
The Humoral Immune Response is the branch of the adaptive immune system mediated by macromolecules found in extracellular fluids ("humors"), specifically the production of Antibodies by B-Lymphocytes (B-cells). It is primarily directed against extracellular pathogens (like bacteria, fungi, and freely circulating viruses) and their toxins.

2. Step-by-Step Illustration of the Process:

• Step 1: Antigen Recognition (Activation)
  A circulating naive B-cell encounters an extracellular pathogen. The B-cell's surface receptor (BCR) binds specifically to a matching epitope on the pathogen's antigen. The B-cell internalizes the pathogen via receptor-mediated endocytosis, degrades it, and presents fragments of it on its surface using an MHC Class II molecule.


• Step 2: Helper T-cell Interaction (Co-stimulation)
  For a full response, the B-cell usually requires confirmation. A mature Helper T-cell ($T_H$ cell), which has been independently activated by a dendritic cell presenting the same antigen, recognizes the MHC-II-antigen complex on the B-cell. The $T_H$ cell binds to the B-cell and releases chemical signals called cytokines (like Interleukin-4).


• Step 3: Clonal Expansion (Proliferation)
  The cytokines stimulate the B-cell to rapidly divide (mitosis). This creates a massive army of identical clones that are all specific to that exact original antigen.


• Step 4: Differentiation
  The clones differentiate into two distinct populations:
  • Plasma Cells (Effector Cells): The vast majority become protein-factory cells. They lose their surface receptors and pump out millions of soluble, Y-shaped Antibodies directly into the bloodstream and lymph.
  • Memory B-Cells: A small fraction become long-lived memory cells. They remain dormant in the lymph nodes for years, ready to mount an immediate, massive response if the same pathogen ever invades again (the basis of vaccination).


• Step 5: Antibody Action (Effector Phase)
  The secreted antibodies circulate and bind to the pathogen. They neutralize toxins, clump pathogens together (agglutination), tag them for destruction by macrophages (opsonization), and activate the complement cascade to rupture the bacterial cell wall.

1. Characteristics of Stem Cells:
Stem cells are unique, unspecialized "master cells" of the body. They possess two defining characteristics that separate them from all other cell types:

• Self-Renewal: They have the ability to divide endlessly (mitosis) while remaining in an unspecialized, undifferentiated state, thereby maintaining the stem cell pool throughout life.
• Potency (Differentiation): Given the right biochemical signals, they can differentiate (specialize) into various functional cell types (e.g., muscle cells, neurons, red blood cells).
  Degrees of potency: Totipotent (can form an entire organism), Pluripotent (can form any body cell, e.g., Embryonic Stem Cells), and Multipotent (can form a limited range of cells in a specific tissue, e.g., Adult Stem Cells).

2. Uses and Applications of Stem Cells:
Because they can grow into any tissue, stem cells hold immense potential in regenerative medicine and research.

• Tissue Regeneration and Repair: The most direct application. For example, using hematopoietic (blood) stem cells from bone marrow to treat leukemia or immune deficiencies. In the future, they may be used to grow skin grafts for severe burns or patch damaged heart muscle after a heart attack.
• Treating Neurological Disorders: Stem cells offer hope for incurable neurodegenerative diseases. They could theoretically be guided to differentiate into dopamine-producing neurons to cure Parkinson's disease, or replace damaged motor neurons in spinal cord injuries.
• Disease Modeling: Scientists can take induced Pluripotent Stem Cells (iPSCs) derived from a patient with a genetic disease, grow them in a dish into affected tissues, and study the cellular pathology in real-time.
• Drug Testing and Toxicity Screening: Before testing new pharmaceutical drugs on animals or humans, they can be tested on human stem-cell-derived tissues (like heart or liver cells) in vitro. This safely and accurately assesses if the drug causes cellular toxicity.

1. The Principle of Vaccination:
Vaccination relies on immunological memory. By administering a harmless form of a pathogen (killed, live-attenuated, or subunit protein), a vaccine "tricks" the immune system into mounting a full primary immune response without the host suffering the actual severe disease.

2. Step-by-Step Biological Response:
Phase 1: Recognition and Uptake (Innate Immune Response)

• Upon injection, the vaccine introduces foreign antigens into the muscle or skin.
• Local innate immune cells, such as resident macrophages and Dendritic Cells (Professional Antigen-Presenting Cells or APCs), immediately recognize the antigens as foreign using Pattern Recognition Receptors (PRRs).
• The APCs engulf the vaccine antigens via phagocytosis, break them down into fragments, and display these peptide fragments on their cell surface bound to MHC molecules.
• The APCs then migrate through the lymphatic vessels to the nearest lymph node.

Phase 2: Activation of the Adaptive Immune System (T-Cells)

• In the lymph node, the APC presents the antigen to naive Helper T-cells ($CD4^+$).
• If a T-cell's receptor (TCR) perfectly matches the presented antigen, that specific T-cell is activated.
• The activated Helper T-cell proliferates and releases chemical messengers (cytokines) to orchestrate the rest of the immune response.

Phase 3: The Humoral Response (B-Cells and Antibodies)

• Simultaneously, circulating naive B-cells recognize the free-floating vaccine antigens.
• The activated Helper T-cells interact with these B-cells, providing the necessary co-stimulatory signals for them to activate fully.
• The B-cells undergo rapid clonal expansion and differentiate into Plasma Cells.
• Plasma cells secrete massive amounts of highly specific Y-shaped proteins called Antibodies into the bloodstream. These antibodies bind to, neutralize, and tag the vaccine antigens for destruction.

Phase 4: The Cell-Mediated Response (Cytotoxic T-Cells)

• If the vaccine is live-attenuated or a viral vector/mRNA vaccine, it enters host cells.
• Infected host cells display antigens on MHC-I, activating Cytotoxic T-cells ($CD8^+$). These cells are trained to seek out and destroy any host cell harboring the pathogen.

Phase 5: The Ultimate Goal - Immunological Memory

• Once the vaccine antigens are cleared, the active immune response subsides. Most of the plasma cells and effector T-cells undergo apoptosis (programmed cell death).
• However, a critical fraction of these cells transform into long-lived Memory B-cells and Memory T-cells.
• These memory cells circulate in the blood and reside in lymph nodes for years or decades.
• Result: If the actual, virulent pathogen infects the body in the future, the memory cells recognize it instantly. They mount a secondary immune response that is drastically faster, stronger, and more effective than the primary response, neutralizing the pathogen before it can cause disease symptoms.

1. Introduction to Parkinson's Disease:
Parkinson's Disease (PD) is a progressive, chronic neurodegenerative disorder of the central nervous system. It primarily affects the motor system, leading to severe disruptions in voluntary movement control. The disease is characterized by a highly specific, localized loss of a certain type of neuron deep within the brain.

2. The Cause: Neuronal Degeneration

• The Substantia Nigra: The primary pathology of Parkinson's involves the death of a very specific group of neurons located in a midbrain structure called the Substantia Nigra (specifically the pars compacta region).
• Dopaminergic Neurons: The neurons that are dying are dopaminergic neurons. Their sole biological function is to synthesize and release the neurotransmitter Dopamine.
• Lewy Bodies: While the exact trigger for why these cells die remains heavily researched (involving genetics and environmental toxins), a defining microscopic hallmark is the presence of Lewy bodies inside the dying neurons. Lewy bodies are abnormal, toxic clumps of a misfolded protein called alpha-synuclein, which disrupt normal cellular functions and trigger apoptosis (cell death).

3. The Physiological Effect: The Broken Circuit

• The Basal Ganglia Circuit: The substantia nigra is a critical component of a larger brain network called the basal ganglia. The basal ganglia's job is to smooth out and coordinate voluntary muscle movements initiated by the motor cortex.
• Loss of Dopamine: To communicate with the rest of the basal ganglia (specifically the striatum), the substantia nigra releases dopamine. Dopamine acts as a crucial chemical messenger that acts like a "lubricant" for the motor circuits.
• The Imbalance: When 60% to 80% of these dopaminergic neurons die, there is a severe deficit of dopamine in the striatum. This breaks the normal signaling loop. The basal ganglia can no longer send smooth, coordinated signals down the spinal cord to the muscles.

4. The Physical Effects (Clinical Symptoms):
Because the motor circuits are deprived of dopamine, patients experience classic motor symptoms (often remembered by the acronym TRAP):

• Tremor: A resting tremor, often beginning in the hands (pill-rolling tremor), which decreases with purposeful movement.
• Rigidity: Muscle stiffness and resistance to movement in the limbs and trunk, causing pain and a reduced range of motion.
• Akinesia / Bradykinesia: Slowness of movement. Patients find it incredibly difficult to initiate voluntary movements, resulting in a shuffling gait and a mask-like, expressionless face.
• Postural Instability: Loss of balance and coordination, leading to a stooped posture and frequent falls.

(Note: There is currently no cure, but treatments like Levodopa—a chemical precursor to dopamine—aim to artificially replenish dopamine levels in the brain to alleviate symptoms).