🔬 Biology — Cell Biology
1. Biology: An Introduction
BASIC FACTS
- Biology: Study of living organisms (plants and animals)
- Father of Biology: Aristotle
- Term 'Biology' coined by: Lamarck and Treviranus (1802)
- Father of Botany: Theophrastus (wrote Historia Plantarum)
- Father of Zoology & Embryology: Aristotle (wrote Historia Animalium)
- Father of Medicine: Hippocrates
BRANCHES OF BOTANY
| Branch | Study of |
|---|---|
| Agronomy | Crops |
| Mycology | Fungi |
| Phycology | Algae |
| Dendrology | Trees and shrubs |
| Pomology | Fruits |
| Spermology | Seeds |
BRANCHES OF ZOOLOGY
| Branch | Study of |
|---|---|
| Entomology | Insects |
| Ichthyology | Fishes |
| Ornithology | Birds |
| Herpetology | Reptiles & Amphibians |
| Haematology | Blood and its diseases |
| Osteology | Bones |
MISUSE OF BIOLOGY
- Amniocentesis: Detects foetal abnormalities; misused for sex determination
- Bioweapons: Antibiotic-resistant microorganisms used as weapons of bioterrorism
2. Characteristics of Living Beings
KEY CHARACTERISTICS
- Cellular structure: Basic unit of life
- Metabolism: Sum total of all chemical reactions
- Anabolism: Constructive phase (protein synthesis, photosynthesis)
- Catabolism: Destructive phase (breakdown, energy release)
- Nutrition: Intake of food for energy and growth
- Growth & Development: From cell to complete organism
- Reproduction: Continuity of life
- Sensitivity: Response to environmental changes
- Adaptation: Adjustment to environmental changes
3. The Cell
DISCOVERY
- Robert Hooke (1665): Observed cell-like chambers in cork
- Cell = Fundamental structural and functional unit of life
- Unicellular (single cell) vs Multicellular (many cells)
CELL STRUCTURE
- Plasma membrane: Outer covering of lipids and proteins
- Cytoplasm: Fluid-like substance containing organelles
- Nucleus: Bears genetic material (DNA)
- Protoplasm: Cytoplasm + Nucleoplasm (physical basis of life)
- Deutoplasm: Non-living inclusions
CELL THEORY
- Formulated by: M. Schleiden (Botanist) and T. Schwann (Zoologist)
- Contributed by: Rudolf Virchow
- Principles:
- All living organisms are composed of cells
- All cells arise from pre-existing cells (Omnis cellula e cellula)
- Cells are basic building units of life
- Viruses do not follow cell theory
PROKARYOTIC vs EUKARYOTIC CELLS
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | Without nuclear membrane | With nuclear membrane |
| Membrane-bound organelles | Absent | Present |
| Ribosomes | 70S only | 80S and 70S |
| Vacuole | Generally absent | Generally present |
4. Chromosome and Genes
CHROMOSOME
- Condensed form of DNA with histone proteins
- Centromere: Point where chromatids are held together
- Telomere: Ends of chromosome
- Types based on centromere position:
- Metacentric (centre)
- Submetacentric (little away from centre)
- Acrocentric (close to end)
- Telocentric (terminal)
- Lampbrush chromosome: Discovered by Balbiani (1882)
- Polytene chromosome: Discovered by Balbiani (1881) in salivary gland of Chironomus larvae
GENES & KARYOTYPE
- Gene: Unit of inheritance; controls transfer of genetic information
- Karyotype: Number and appearance of chromosomes
- Idiogram: Diagrammatic representation of chromosomes
5. Cell Cycle and Division
CELL CYCLE STAGES
- G₁ phase: Gap 1 — cell growth
- S phase: Synthesis — DNA replication
- G₂ phase: Gap 2 — preparation for division
- M phase: Mitosis/Meiosis — division
- G₀ phase: Quiescent stage (cells that do not divide)
MITOSIS vs MEIOSIS
| Feature | Mitosis | Meiosis |
|---|---|---|
| Cell type | Somatic cells | Gamete cells |
| Number of divisions | 1 | 2 |
| Daughter cells | 2 (diploid) | 4 (haploid) |
| Crossing over | Absent | Present |
| DNA exchange | No | Yes |
| Genotype | Identical to parent | Different from parent |
TRANSCRIPTOME
- Full range of messenger RNA molecules expressed by an organism
- Describes array of mRNA transcripts in a particular cell or tissue
6. Biomolecules
MONOMER → POLYMER
- Monosaccharide → Polysaccharide
- Amino acid → Polypeptide (Protein)
- Nucleotide → Nucleic acid (DNA & RNA)
LIPIDS
- Fats, oils, steroids, waxes — hydrophobic
- Functions: Membrane structure, energy storage, insulation, hormone action
- Unsaturated fats: Liquid at room temperature; good for health
- Trans fats: Artificially produced unsaturated fats
CARBOHYDRATES
- Hydrates of carbon — (CH₂O)â‚™
- Monosaccharides: Single sugars
- Disaccharides: Two sugars linked
- Polysaccharides: Many sugars linked
- Functions: Energy storage, structural materials, cell signalling
PROTEINS
- Polymers of amino acids
- ~50% of biomolecule weight in cell (excluding water)
- PEM (Protein Energy Malnutrition): Kwashiorkor, Marasmus
- Functions: Enzymes, structural materials, carriers, contraction, signalling
NUCLEIC ACIDS
- Polymers of nucleotides (nitrogenous base + pentose sugar + phosphate)
- DNA: Stores genetic information; 5 types (A, B, C, D, Z — B-type in humans)
- RNA: Converts DNA information to proteins; types: t-RNA, r-RNA, m-RNA
- Ribozymes: RNA with catalytic ability
7. Enzymes
BASIC FACTS
- Biological catalysts; discovered by Buchner (1900) in yeast
- ~40,000 different enzymes in human cells
- Increase reaction rate by 10-12 times
- Holoenzyme: Complete active enzyme with cofactor
- Apoenzyme: Protein part without cofactor
- Active site: Small part where reaction takes place
FACTORS AFFECTING ENZYME REACTION
- Temperature: Optimum 35-40°C
- pH: Optimum 7-8
- Enzyme concentration: Rate increases linearly then constant
- Substrate concentration: Rate increases with substrate
- Inhibitors: Reduce enzyme activity
ENZYME REACTIONS
- Starch --Diastase→ Maltose
- Maltose --Maltase→ Glucose
- Glucose --Zymase→ Ethyl alcohol
- Sucrose --Invertase→ Glucose + Fructose
- Urea --Urease→ NH₃ + CO₂
HUMAN GENOME PROJECT-WRITE
- Announced on 2nd June, 2016
- 10-year extension of Human Genome Project
- Aims to synthesize the human genome
- Human genome = 3 billion DNA nucleotides
Summary: Cell Biology at a Glance
| Topic | Key Point |
|---|---|
| Father of Biology | Aristotle |
| Father of Botany | Theophrastus |
| Cell Discovered by | Robert Hooke (1665) |
| Cell Theory | Schleiden + Schwann + Virchow |
| Prokaryotic Ribosomes | 70S only |
| Eukaryotic Ribosomes | 80S and 70S |
| Mitosis | 2 daughter cells (diploid) |
| Meiosis | 4 daughter cells (haploid) |
KEY TAKEAWAYS FOR UPSC
- Father of Biology: Aristotle; Father of Botany: Theophrastus
- Cell: Discovered by Robert Hooke (1665)
- Cell Theory: Schleiden, Schwann, Virchow — "Omnis cellula e cellula"
- Prokaryotic: No nuclear membrane, 70S ribosomes
- Eukaryotic: Nuclear membrane, 80S + 70S ribosomes
- Chromosome types: Metacentric, Submetacentric, Acrocentric, Telocentric
- Mitosis: Somatic cells, 2 diploid daughter cells
- Meiosis: Gamete cells, 4 haploid daughter cells, crossing over
- Enzymes: Biocatalysts; optimum temp 35-40°C; optimum pH 7-8
- Nobel Prize 2016 (Physiology): Yoshinori Ohsumi — autophagy
High-Yield Interactive UPSC Quiz (Biology — Cell Biology)
Q1. Who is known as the Father of Biology?
Correct Answer: B. Aristotle is known as the Father of Biology.
Q2. Who discovered the cell?
Correct Answer: C. Robert Hooke discovered the cell in 1665 while observing cork.
Q3. Which type of ribosome is found in prokaryotic cells?
Correct Answer: B. Prokaryotic cells have only 70S ribosomes.
Q4. The cell theory was formulated by:
Correct Answer: C. The cell theory was formulated by M. Schleiden and T. Schwann.
Q5. During which phase of cell cycle does DNA replication occur?
Correct Answer: B. DNA replication occurs during the S (Synthesis) phase of the cell cycle.
Q6. How many daughter cells are produced in meiosis?
Correct Answer: D. Meiosis produces 4 haploid daughter cells.
Q7. Which biomolecule acts as a catalyst in living organisms?
Correct Answer: C. Enzymes are biological catalysts that speed up chemical reactions.
Q8. What is the optimum temperature range for enzyme activity?
Correct Answer: B. Enzymes have an optimum temperature range of 35-40°C.
Q9. Which chromosome has the centromere at the centre?
Correct Answer: B. Metacentric chromosomes have the centromere at the centre.
Q10. The term 'transcriptome' refers to:
Correct Answer: C. The transcriptome is the full range of messenger RNA molecules expressed by an organism.