Cell Structure and General Anatomy

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Cell Structure — Key Facts for NEET PG

• Cell: Basic unit of life — all cells arise from pre-existing cells
• Plasma Membrane: Fluid Mosaic Model — phospholipid bilayer with embedded proteins
• Nucleus: Contains DNA, controls cell activities; nuclear envelope with pores
• Mitochondria: Powerhouse — ATP synthesis via oxidative phosphorylation
• ⚡ Exam tip: Mitochondria have their own DNA and ribosomes (evidence for endosymbiotic theory)

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Cell Structure and General Anatomy — NEET PG Study Guide

Cell Theory

1. All living organisms are composed of cells
2. Cell is the basic unit of life
3. All cells arise from pre-existing cells (Rudolf Virchow, 1855)

Exceptions to Cell Theory: Viruses — acellular, but living entities

Types of Cells

Prokaryotic Cells:

• No membrane-bound nucleus (nucleoid region)
• No membrane-bound organelles
• Examples: Bacteria, Archaea
• Size: 0.2-2 μm diameter

Eukaryotic Cells:

• Membrane-bound nucleus
• Membrane-bound organelles
• Examples: Plant, Animal, Fungal cells
• Size: 10-100 μm diameter

Plasma Membrane

Structure — Fluid Mosaic Model (Singer and Nicolson, 1972):

• Phospholipid bilayer (hydrophilic heads outward, hydrophobic tails inward)
• Proteins embedded or attached:
  • Integral proteins: Span the membrane
  • Peripheral proteins: Attached to surface
• Cholesterol (in animal cells) — stabilizes membrane
• Carbohydrates: Glycoproteins and glycolipids (cell recognition)

Functions:

• Selective permeability
• Transport (channels, carriers, pumps)
• Cell signaling
• Cell adhesion
• Cytoplasmic membrane framework

Cell Organelles

Nucleus:

• Nuclear envelope: Double membrane with nuclear pores
• Nucleolus: Site of rRNA synthesis
• Chromatin: DNA + histones (forming chromosomes)
• Nucleoplasm: Gel-like matrix

Mitochondria:

• Double membrane: Outer smooth, inner with cristae
• Matrix: Contains mitochondrial DNA, ribosomes, Krebs cycle enzymes
• ATP synthesis: 36 ATP per glucose (eukaryotes)
• Semi-autonomous organelle

Endoplasmic Reticulum (ER):

• Rough ER: Ribosomes attached, protein synthesis
• Smooth ER: No ribosomes, lipid synthesis, detoxification

Golgi Apparatus:

• Cis face (receiving) and trans face (shipping)
• Modifies, packages, and routes proteins

Lysosomes:

• Contain hydrolytic enzymes
• Acidic interior (pH 4.5-5)
• Autophagy, cell digestion

Ribosomes:

• rRNA + proteins
• 70S (prokaryotes) / 80S (eukaryotes)
• Site of protein synthesis (translation)

NCE Exam Pattern

Common question types:

1. Cell organelle functions
2. Membrane structure and transport
3. Differences between prokaryotic and eukaryotic cells
4. Cell cycle and division
5. DNA structure and replication

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Cell Structure and General Anatomy — Comprehensive NEET PG Notes

Detailed Theory

1. Plasma Membrane Transport

Passive Transport (no energy required):

• Simple diffusion: Small non-polar molecules (O₂, CO₂)
• Facilitated diffusion: Via channels or carriers (ions, glucose)
• Osmosis: Water across semipermeable membrane

Active Transport (energy required):

• Primary active transport: Direct ATP hydrolysis (Na⁺/K⁺ ATPase)
• Secondary active transport: Coupled transport (SGLT — sodium-glucose cotransporter)
• Vesicular transport: Endocytosis (phagocytosis, pinocytosis, receptor-mediated)

Sodium-Potassium Pump:

• 3 Na⁺ out, 2 K⁺ in per cycle
• Maintains resting membrane potential (-70mV)
• ATP-dependent

2. Cytoskeleton

Microfilaments (Actin):

• 7nm diameter
• Muscle contraction, cell movement, cytokinesis
• G-actin monomers → F-actin filaments

Intermediate Filaments:

• 10nm diameter
• Mechanical strength
• Types: Keratins (epithelial), Vimentin (mesenchymal), Neurofilaments (neurons)

Microtubules:

• 25nm diameter
• Hollow tubes of tubulin dimers
• Form centrioles, cilia, flagella
• Intracellular transport (kinesin, dynein)

Centrosome:

• Microtubule organizing center
• Contains centrioles (9+0 triplet pattern)
• Important in cell division

3. Cell Adhesion Molecules

Selectins: Bind carbohydrates on other cells (leukocyte rolling)

Integrins: Connect cytoskeleton to extracellular matrix

Cadherins: Calcium-dependent cell-cell adhesion

Tight Junctions: Seal epithelial cells (paracellular barrier)

Gap Junctions: Allow direct cell-cell communication (connexons)

4. Cell Cycle

Interphase (90% of cell cycle):

• G1: Cell growth, protein synthesis
• S: DNA replication (each chromosome becomes two chromatids)
• G2: Further growth, preparation for division

M Phase (Mitosis + Cytokinesis):

• Prophase: Chromatin condenses, nuclear envelope breaks
• Metaphase: Chromosomes align at equator (metaphase plate)
• Anaphase: Sister chromatids separate, move to poles
• Telophase: Nuclear envelopes reform, chromosomes decondense
• Cytokinesis: Cytoplasm divides (cleavage furrow in animals, cell plate in plants)

Checkpoints:

• G1 checkpoint: Restriction point — commits to division
• G2 checkpoint: Ensures complete DNA replication
• M checkpoint: Ensures proper chromosome attachment

Regulation — Cyclins and CDKs:

• Cyclins: Regulatory subunits (levels rise and fall)
• CDKs: Catalytic subunits (always present)
• Complex → Phosphorylates target proteins → Cell cycle progression

5. Apoptosis vs. Necrosis

Apoptosis (Programmed Cell Death):

• Physiological and pathological
• Cell shrinkage, chromatin condensation
• Membrane blebbing, apoptotic bodies
• Phagocytosis by macrophages
• No inflammation

Necrosis (Pathological Cell Death):

• Due to injury, toxins, ischemia
• Cell swelling, membrane rupture
• Release of cellular contents
• Inflammation

Extrinsic Pathway: Fas-FasL, TNF receptors Intrinsic Pathway: Mitochondrial (cytochrome c release), Bcl-2 family

6. Stem Cells

Totipotent: Can form entire organism (zygote) Pluripotent: Can form any tissue (embryonic stem cells) Multipotent: Can form multiple related tissues (adult stem cells)

Therapeutic Applications: Regenerative medicine, hematopoietic stem cell transplantation

7. Cell Signaling

Types of Signaling:

• Autocrine: Self-signaling
• Paracrine: Local signaling
• Endocrine: Hormone signaling (long distance)
• Neurotransmitter: Synaptic signaling

Receptor Types:

• Membrane receptors: Peptide hormones, catecholamines
• Intracellular receptors: Steroid hormones, thyroid hormone

Second Messengers:

• cAMP (G-protein coupled receptors)
• IP₃/DAG pathway
• Calcium signaling

8. Extracellular Matrix

Components:

• Collagen: Tensile strength (most abundant protein in body)
• Elastin: Elasticity
• Proteoglycans: Hydration, resistance to compression
• Fibronectin: Cell adhesion
• Laminin: Basement membrane component

Functions:

• Structural support
• Cell adhesion
• Migration
• Tissue repair

9. Specializations for Cell Functions

Cell Types with High Mitochondria: Hepatocytes, cardiac muscle, proximal tubule cells

Cells with High Ribosome Content: Pancreatic acinar cells (protein secretion), plasma cells (antibody production)

Cells with Abundant Lysosomes: Macrophages, neutrophils (phagocytosis)

Cells with Well-Developed Golgi: Secretary cells (mucous cells, plasma cells)

10. Clinical Correlations

Cancer:

• Loss of cell cycle control
• Defects in apoptosis (p53 mutation)
• Telomerase activation
• Metastatic potential

Genetic Disorders:

• Cystic fibrosis: CFTR chloride channel defect
• Muscular dystrophy: Dystrophin protein defect
• Mitochondrial disorders: Mitochondrial DNA mutations

Practice Questions for NEET PG

1. Which organelle is the major site of ATP synthesis in a cell?
2. Describe the structure of the fluid mosaic model of the plasma membrane.
3. Explain the stages of mitosis.
4. What is the difference between apoptosis and necrosis?
5. Discuss the role of the cytoskeleton in cell function.

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