1. कोशिका का परिचय — Introduction to Cell

कोशिका क्या है?

Cell जीवन की मूलभूत संरचनात्मक एवं क्रियात्मक इकाई (basic structural and functional unit of life) है।

• सभी living organisms एक या अधिक कोशिकाओं से बने होते हैं।
• कोशिका में जीवन की आवश्यक क्रियाएँ होती हैं।
• एककोशिकीय organisms में एक ही cell सभी आवश्यक life functions करता है।
• बहुकोशिकीय organisms में अलग-अलग cells specialised functions करते हैं।

Examples:

• Amoeba → एककोशिकीय
• Bacteria → एककोशिकीय
• Human → बहुकोशिकीय
• Mango plant → बहुकोशिकीय

Cell size

अधिकांश cells microscopic होते हैं।

• सबसे छोटी ज्ञात free-living cells → Mycoplasma
• सबसे बड़ी single cell का सामान्य उदाहरण → Ostrich egg
• Human RBC → लगभग 7–8 µm diameter
• सामान्य bacterial cell → लगभग 0.5–5 µm

---

2. Cell Theory — कोशिका सिद्धांत

Cell theory मुख्यतः Schleiden और Schwann ने प्रस्तावित किया।

प्रमुख वैज्ञानिक

Scientist	Contribution
Robert Hooke	1665 में cork में cells देखे और “cell” शब्द का प्रयोग किया
Anton van Leeuwenhoek	Living cells/microorganisms को देखा
Matthias Schleiden	Plants are made of cells
Theodor Schwann	Animals are made of cells
Rudolf Virchow	“Omnis cellula e cellula” — new cells arise from pre-existing cells

Modern Cell Theory

1. सभी living organisms cells और cell products से बने होते हैं।
2. Cell जीवन की basic structural and functional unit है।
3. सभी cells pre-existing cells से बनते हैं।
4. Genetic information cells में होती है और daughter cells को transfer होती है।
5. Energy flow/metabolism cells के अंदर होता है।

NEET Point

“Omnis cellula e cellula” → Rudolf Virchow

अर्थ:

Every cell arises from a pre-existing cell.

---

3. Types of Cells

Cells को मुख्यतः दो प्रकारों में बाँटा जाता है:

1. Prokaryotic cell
2. Eukaryotic cell

---

---

6. Eukaryotic Cell

Eukaryotic cells अधिक complex होती हैं।

Characteristics

• True nucleus present
• Nuclear membrane present
• Membrane-bound organelles present
• Linear chromosomes
• 80S cytoplasmic ribosomes
• Cytoskeleton well developed
• Generally larger than prokaryotic cells

Examples

• Protists
• Fungi
• Plants
• Animals

---

7. Prokaryotic vs Eukaryotic Cell

Feature	Prokaryotic	Eukaryotic
Size	Generally smaller	Generally larger
True nucleus	Absent	Present
Nuclear membrane	Absent	Present
DNA	Usually circular	Usually linear chromosomes
Membrane-bound organelles	Absent	Present
Ribosome	70S	80S in cytoplasm
Cell division	Binary fission	Mitosis/Meiosis
Example	Bacteria	Plant/Animal cell

Important Exception

Eukaryotic cells के mitochondria और chloroplasts में 70S ribosomes पाए जाते हैं।

---

8. (पादप एवं जन्तु कोशिका)Plant Cell and Animal Cell

(पादप कोशिका)Plant Cell

Plant cells में सामान्यतः:

• Cell wall
• Plasma membrane
• Plastids
• Large central vacuole
• Nucleus
• Mitochondria
• ER
• Golgi apparatus
• Ribosomes

होते हैं।

(जन्तु कोशिका)Animal Cell

Animal cells में सामान्यतः:

• Plasma membrane
• Nucleus
• Mitochondria
• ER
• Golgi apparatus
• Lysosomes
• Ribosomes
• Centrioles
• Small vacuoles

होते हैं।

---

9. (पादप एवं जन्तु कोशिका में अंतर)Plant Cell vs Animal Cell

Feature	Plant Cell	Animal Cell
Cell wall	Present	Absent
Plastids	Present	Absent
Large central vacuole	Usually present	Usually absent
Centrioles	Generally absent in higher plants	Usually present
Lysosomes	Less prominent/functional equivalents present	Prominent
Shape	Often fixed	Often flexible/variable
Nutrition	Mainly autotrophic	Heterotrophic

NEET Caution

Plant cells में cell wall और plastids major identifying features हैं।

---

10. Cell Envelope

Cell envelope mainly refers to the layers surrounding a cell.

In bacteria, it may include:

1. Glycocalyx
2. Cell wall
3. Plasma membrane

Functions

• Protection
• Shape maintenance
• Transport regulation
• Interaction with environment

---

11. Plasma Membrane — Cell Membrane

Plasma membrane cell की outer living boundary है।

यह selectively permeable होती है।

Chemical composition

मुख्यतः:

• Lipids
• Proteins
• Carbohydrates

से बनी होती है।

---

12. Fluid Mosaic Model

Singer and Nicolson (1972) ने fluid mosaic model प्रस्तावित किया।

Model की मुख्य बातें

• Lipid bilayer basic framework बनाती है।
• Proteins lipid bilayer में embedded या associated होती हैं।
• Membrane dynamic/fluid nature की होती है।
• Carbohydrates proteins/lipids से जुड़े हो सकते हैं।

Lipids

मुख्यतः:

• Phospholipids
• Cholesterol

Phospholipid structure

Phospholipid में:

• Hydrophilic head
• Hydrophobic tail

होती है।

इसलिए phospholipids bilayer बनाते हैं।

Important

Hydrophilic heads → बाहर की aqueous environment की ओर

Hydrophobic tails → अंदर की ओर

---

13. Membrane Proteins

Membrane proteins मुख्यतः दो प्रकार से वर्णित की जाती हैं:

Integral proteins

• Membrane में deeply embedded
• कुछ पूरी membrane को cross करती हैं।
• Transport/receptor functions में महत्वपूर्ण

Peripheral proteins

• Membrane surface से loosely associated
• आसानी से अलग की जा सकती हैं।

---

14. Functions of Plasma Membrane

• Cell को boundary प्रदान करना
• Selective transport
• Cell signalling
• Cell recognition
• Cell adhesion
• Endocytosis
• Exocytosis

---

15. Transport Across Plasma Membrane

15.1 Simple Diffusion

Molecules higher concentration से lower concentration की ओर move करते हैं।

• Energy required नहीं
• Concentration gradient के along

Example: O₂ और CO₂ का movement

---

15.2 Osmosis

Water का movement:

Higher water potential → Lower water potential

या dilute solution से concentrated solution की ओर, semipermeable membrane के माध्यम से।

---

15.3 Facilitated Diffusion

• Concentration gradient के along
• ATP directly required नहीं
• Transport proteins involved

---

15.4 Active Transport

• Concentration gradient के विरुद्ध
• Energy required
• Transport proteins involved

Example: Na⁺/K⁺ pump

---

15.5 Endocytosis

Cell membrane बाहर से material को अंदर लेती है।

Types:

• Phagocytosis → cell eating
• Pinocytosis → cell drinking
• Receptor-mediated endocytosis

---

15.6 Exocytosis

Cell vesicles के माध्यम से material को बाहर release करती है।

Example: secretion of hormones, enzymes आदि।

---

16. Cell Wall

Plant cell की plasma membrane के बाहर rigid non-living layer को cell wall कहते हैं।

Main components

Plant cell wall मुख्यतः:

• Cellulose
• Hemicellulose
• Pectin

से बनी होती है।

---

17. Plant Cell Wall Layers

Middle Lamella

• Adjacent plant cells को जोड़ती है।
• Mainly calcium pectate से बनी होती है।

Primary Cell Wall

• Young cells में बनती है।
• Relatively thin और flexible होती है।

Secondary Cell Wall

• कुछ mature cells में primary wall के अंदर बनती है।
• अधिक thick और rigid हो सकती है।
• Lignin इसमें पाया जा सकता है।

---

18. Plasmodesmata

Adjacent plant cells के बीच cytoplasmic connections को plasmodesmata कहते हैं।

Functions

• Cell-to-cell communication
• Cytoplasmic exchange
• पदार्थों के intercellular movement में सहायता

---

19. Endomembrane System

Endomembrane system में मुख्यतः:

• Endoplasmic reticulum
• Golgi apparatus
• Lysosomes
• Vacuoles

शामिल हैं।

Important

Mitochondria और chloroplast endomembrane system का हिस्सा नहीं हैं।

---

20. Endoplasmic Reticulum — ER

ER एक membrane-bound network है जो cytoplasm में फैला होता है।

दो प्रकार:

1. Rough ER
2. Smooth ER

---

21. Rough Endoplasmic Reticulum — RER

RER की surface पर ribosomes attached होते हैं।

Functions

• Protein synthesis
• Protein folding/modification
• Membrane protein production
• Secretory proteins का transport

Example

Pancreatic cells में RER abundant होता है क्योंकि वे digestive enzymes जैसे proteins बनाते हैं।

---

22. Smooth Endoplasmic Reticulum — SER

SER की surface पर ribosomes नहीं होते।

Functions

• Lipid synthesis
• Steroid synthesis
• Detoxification
• Carbohydrate metabolism
• Calcium storage

Example

Liver cells में SER detoxification में महत्वपूर्ण है।

Muscle cells में specialised SER को sarcoplasmic reticulum कहते हैं।

---

23. Golgi Apparatus

Golgi apparatus को Camillo Golgi ने खोजा।

यह flattened membrane-bound sacs की stack होती है जिन्हें cisternae कहते हैं।

Golgi के दो faces

Cis face

• Receiving face
• ER से vesicles receive करता है।

Trans face

• Shipping/dispatching face
• Modified products को विभिन्न destinations पर भेजता है।

---

24. Functions of Golgi Apparatus

• Modification of proteins
• Packaging
• Sorting
• Secretion
• Lysosome formation
• Cell wall components synthesis में भूमिका
• Glycoprotein/glycolipid formation

Example

ER द्वारा बनाए proteins → Golgi में modification → vesicles → destination.

---

25. Lysosomes

Lysosomes membrane-bound organelles हैं जिनमें hydrolytic enzymes होते हैं।

इन्हें कभी-कभी suicidal bags कहा जाता है, लेकिन यह term descriptive है और lysosome के कई सामान्य cellular functions होते हैं।

Enzymes

• Proteases
• Lipases
• Nucleases
• Carbohydrases आदि

Functions

• Intracellular digestion
• Worn-out organelles का breakdown
• Foreign material का digestion
• Autophagy
• Cellular waste processing

---

26. Vacuoles

Vacuoles membrane-bound sacs होते हैं।

Plant cells में vacuole सामान्यतः बहुत बड़ा होता है।

Tonoplast

Vacuole की membrane को tonoplast कहते हैं।

Cell sap

Vacuole में उपस्थित fluid को cell sap कहते हैं।

इसमें हो सकते हैं:

• Water
• Sugars
• Amino acids
• Ions
• Pigments
• Waste products

---

27. Functions of Vacuoles

• Storage
• Osmoregulation
• Maintaining turgor pressure
• Waste storage
• Cell volume regulation

Example

Plant cell का large vacuole cell को turgidity बनाए रखने में मदद करता है।

---

28. Mitochondria

Mitochondria को cell का major powerhouse कहा जाता है क्योंकि aerobic respiration से ATP production में इसकी प्रमुख भूमिका है।

Structure

Mitochondrion double membrane-bound organelle है।

Outer membrane

• Relatively smooth
• Permeable to many small molecules through porins

Inner membrane

• Highly folded
• Folds को cristae कहते हैं।

Matrix

Inner membrane के अंदर का region matrix कहलाता है।

इसमें:

• Enzymes
• Circular DNA
• 70S ribosomes
• RNA

पाए जाते हैं।

---

29. Functions of Mitochondria

• Aerobic respiration
• ATP production
• TCA/Krebs cycle
• Oxidative phosphorylation
• Fatty acid oxidation
• Some metabolic pathways

NEET Facts

• Mitochondria are semi-autonomous organelles.
• इनमें अपना DNA और ribosomes होते हैं।
• Mitochondrial DNA generally circular होता है।
• Inner membrane पर electron transport chain होती है।
• ATP synthesis में F₀–F₁ particles/ATP synthase involved होता है।

---

30. Ribosomes

Ribosomes non-membranous structures हैं।

Function

Protein synthesis

Eukaryotic cytoplasm

80S

• 60S large subunit
• 40S small subunit

Prokaryotes

70S

• 50S large subunit
• 30S small subunit

Important

Mitochondria और chloroplasts में 70S ribosomes होते हैं।

---

31. Plastids

Plastids plant cells और कुछ algae में पाए जाने वाले double membrane-bound organelles हैं।

मुख्य प्रकार:

1. Chloroplast
2. Chromoplast
3. Leucoplast

---

32. Chloroplast

Chloroplast photosynthesis का प्रमुख organelle है।

Structure

Double membrane के अंदर:

• Stroma
• Thylakoids
• Grana
• Stroma lamellae

होते हैं।

Grana

Thylakoids की stacked structures को grana कहते हैं।

Stroma

Chloroplast का fluid-filled internal matrix stroma कहलाता है।

इसमें:

• Enzymes
• DNA
• Ribosomes
• Starch grains

आदि पाए जा सकते हैं।

---

33. Chloroplast Functions

• Photosynthesis
• Light reactions
• Carbon fixation
• Formation of carbohydrates
• कुछ biosynthetic pathways

Location of major reactions

Process	Location
Light reaction	Thylakoid membrane
Calvin cycle	Stroma

---

34. Chromoplast

Chromoplast में coloured pigments पाए जाते हैं।

Function

Plants के विभिन्न parts को yellow, orange, red आदि colours देने में सहायता।

Example

• Tomato
• Carrot
• Some flowers

---

35. Leucoplast

Leucoplast colourless plastids हैं।

मुख्य प्रकार:

• Amyloplast → starch storage
• Elaioplast → oil storage
• Aleuroplast/Proteinoplast → protein storage

---

36. Microbodies

Microbodies छोटे single membrane-bound organelles हैं जिनमें specialised enzymes होते हैं।

Examples:

• Peroxisomes
• Glyoxysomes

---

37. Peroxisomes

Peroxisomes में oxidative enzymes पाए जाते हैं।

Important enzyme

Catalase

यह hydrogen peroxide को break करती है:

2H₂O₂ → 2H₂O + O₂

Functions

• Detoxification
• Hydrogen peroxide metabolism
• Fatty acid oxidation
• Photorespiration में भूमिका

---

38. Glyoxysomes

Glyoxysomes विशेषकर germinating oil seeds में पाए जाते हैं।

Function

Stored fats को carbohydrates में convert करने के pathway में महत्वपूर्ण।

Example

Germinating:

• Castor
• Groundnut
• Other oil-rich seeds

---

39. Cytoskeleton

Cytoskeleton cell के अंदर protein filaments का dynamic network है।

मुख्य components:

1. Microtubules
2. Microfilaments
3. Intermediate filaments

---

40. Microtubules

Microtubules tubulin protein से बने hollow structures हैं।

Functions

• Cell shape
• Intracellular transport
• Chromosome movement
• Cilia/flagella structure
• Spindle formation

---

41. Microfilaments

Microfilaments मुख्यतः actin protein से बने होते हैं।

Functions

• Cell shape
• Cell movement
• Cytoplasmic streaming
• Muscle contraction
• Cytokinesis में भूमिका

---

42. Intermediate Filaments

ये मजबूत protein fibres होते हैं।

Functions

• Mechanical strength
• Structural support
• Cell integrity

---

43. Cilia and Flagella

Cilia और flagella cell movement या fluid movement में सहायता करते हैं।

Cilia

• Short
• Numerous
• Coordinated movement

Example: Respiratory tract में mucus movement.

Flagella

• Usually longer
• Fewer
• Cell locomotion में important

Example: Human sperm flagellum.

---

44. Ultrastructure of Cilia and Flagella

Typical eukaryotic cilia/flagella का axoneme:

9 + 2 arrangement

का होता है।

Arrangement

• Outer → 9 peripheral microtubule doublets
• Centre → 2 single microtubules

Important protein

Dynein

Dynein arms microtubule sliding में भूमिका निभाते हैं।

Movement

Microtubule sliding → bending → ciliary/flagellar movement.

---

45. Basal Body

Cilia/flagella का base basal body से जुड़ा होता है।

Typical basal body:

9 triplets of microtubules

और central pair absent होता है।

NEET Comparison

Feature	Axoneme	Basal body
Arrangement	9 + 2	9 triplets
Central microtubules	Present	Absent

---

46. Centrioles

Centrioles cylindrical structures हैं जो animal cells में centrosome का प्रमुख भाग होते हैं।

Structure

एक centriole में:

9 peripheral triplets of microtubules

होते हैं।

Functions

• Spindle organisation
• Basal bodies बनाने में भूमिका
• Cilia/flagella formation में भूमिका

Centrosome

Animal cells में centrosome सामान्यतः एक pair of centrioles से बना होता है।

दो centrioles:

• Mother centriole
• Daughter centriole

हो सकते हैं।

---

47. Nucleus

Nucleus eukaryotic cell का major genetic control centre है।

Main components

1. Nuclear envelope
2. Nucleoplasm
3. Chromatin
4. Nucleolus

---

48. Nuclear Envelope

Nucleus double membrane से घिरा होता है।

Outer membrane

• ER से continuous होती है।
• Ribosomes attached हो सकते हैं।

Inner membrane

Nuclear interior की ओर होती है।

Nuclear pores

Nuclear envelope में pores होते हैं।

Function

• Nucleus और cytoplasm के बीच controlled exchange

---

49. Chromatin

DNA + associated proteins का complex chromatin कहलाता है।

मुख्य proteins:

Histones

Types

Euchromatin

• Loosely packed
• Transcriptionally more active
• Light staining

Heterochromatin

• Condensed
• Generally less transcriptionally active
• Dark staining

---

50. Nucleolus

Nucleolus nucleus के अंदर dense, non-membranous region है।

Functions

• rRNA synthesis
• Ribosomal subunit assembly

Important

Nucleolus membrane-bound नहीं होता।

---

51. Chromosome

Cell division के समय chromatin highly condensed होकर chromosomes बनाता है।

Chromosome contains

• DNA
• Histone proteins
• Non-histone proteins
• Other associated molecules

Centromere

Chromosome का constricted region।

यह spindle attachment और chromosome movement में महत्वपूर्ण है।

---

52. Chemical Constituents of Living Cells

Living cells में मुख्य chemical components:

Inorganic components

• Water
• Mineral ions
• Gases

Organic biomolecules

1. Carbohydrates
2. Proteins
3. Lipids
4. Nucleic acids

---

53. Water

Water living cells का सबसे abundant inorganic component है।

Functions

• Solvent
• Transport medium
• Chemical reactions
• Temperature regulation
• Cell structure बनाए रखने में सहायता

---

54. Biomolecules

Biomolecules वे organic molecules हैं जो living organisms में पाए जाते हैं और life processes में महत्वपूर्ण भूमिका निभाते हैं।

मुख्य biomolecules:

• Carbohydrates
• Proteins
• Lipids
• Nucleic acids

---

55. Carbohydrates

Carbohydrates mainly:

C, H and O

से बने होते हैं।

सामान्य formula कई simple carbohydrates के लिए:

Cₙ(H₂O)ₙ

लेकिन यह सभी carbohydrates पर universally लागू नहीं होता।

Functions

• Energy source
• Energy storage
• Structural role
• Cell recognition

---

56. Monosaccharides

सबसे simple carbohydrates।

Examples:

• Glucose
• Fructose
• Ribose
• Deoxyribose

Glucose

Major cellular respiratory fuel।

Ribose

RNA में पाया जाता है।

Deoxyribose

DNA में पाया जाता है।

---

57. Disaccharides

दो monosaccharides के combination से बनते हैं।

Disaccharide	Components
Sucrose	Glucose + Fructose
Maltose	Glucose + Glucose
Lactose	Glucose + Galactose

Bond

Monosaccharides glycosidic bond द्वारा जुड़े होते हैं।

---

58. Polysaccharides

बहुत सारे monosaccharides के polymers।

Important examples

Starch

• Plants में storage carbohydrate
• Glucose polymer

Glycogen

• Animals में storage carbohydrate
• Highly branched

Cellulose

• Plant cell wall का major structural component
• β-glucose polymer

Chitin

• Fungal cell wall
• Arthropod exoskeleton

---

59. Carbohydrate Quick Table

Carbohydrate	Major role
Glucose	Immediate energy source
Starch	Plant storage
Glycogen	Animal storage
Cellulose	Plant cell wall
Chitin	Fungal wall/arthropod exoskeleton

---

60. Proteins

Proteins are polymers of amino acids.

Elements

Generally:

• C
• H
• O
• N

Some proteins also contain:

• S

---

61. Amino Acids

Amino acid contains:

• Amino group → –NH₂
• Carboxyl group → –COOH
• Hydrogen
• Variable R group
• Central α-carbon

General structure:

NH₂–CH(R)–COOH

Examples

• Glycine
• Alanine
• Lysine
• Valine

---

62. Peptide Bond

Two amino acids dehydration/condensation reaction द्वारा जुड़ते हैं।

Peptide bond → –CO–NH–

Important

Amino acids joined by peptide bonds form:

• Dipeptide
• Tripeptide
• Polypeptide
• Protein

---

63. Levels of Protein Structure

Primary structure

• Amino acid sequence
• Most fundamental level

Secondary structure

Mainly:

• α-helix
• β-pleated sheet

Tertiary structure

Complete 3D folding of a polypeptide chain.

Quaternary structure

Association of multiple polypeptide subunits.

Example: Haemoglobin has four polypeptide subunits.

---

64. Protein Functions

Function	Example
Enzyme	Amylase
Transport	Haemoglobin
Hormone	Insulin
Structural	Collagen
Defence	Antibodies
Movement	Actin, Myosin
Storage	Ferritin

---

65. Lipids

Lipids are mostly water-insoluble organic molecules.

Major elements:

• C
• H
• O

Some lipids also contain:

• P
• N

Functions

• Energy storage
• Membrane formation
• Hormone synthesis
• Insulation
• Protection

---

66. Fatty Acids

Fatty acid contains:

• Long hydrocarbon chain
• Carboxyl group

Types

Saturated fatty acids

No C=C double bond.

Example: Palmitic acid

Unsaturated fatty acids

One or more double bonds.

Example: Oleic acid

---

67. Triglycerides

A triglyceride contains:

Glycerol + 3 fatty acids

Fatty acids and glycerol are joined through ester bonds.

Function

Long-term energy storage.

---

68. Phospholipids

Phospholipids contain:

• Glycerol
• Fatty acids
• Phosphate-containing group

They are amphipathic.

Meaning

• Hydrophilic region
• Hydrophobic region

Importance

They form the basic lipid bilayer of biological membranes.

---

69. Steroids

Steroids have characteristic fused carbon-ring structures.

Examples

• Cholesterol
• Testosterone
• Estrogen
• Cortisol

Functions

• Membrane component
• Hormonal roles
• Precursor for steroid hormones

---

70. Nucleic Acids

Nucleic acids are polymers of nucleotides.

Two major types:

1. DNA
2. RNA

---

71. Nucleotide

A nucleotide contains:

Nitrogenous base + Pentose sugar + Phosphate

Nucleoside

Nitrogenous base + Sugar

Therefore:

Nucleoside + phosphate = Nucleotide

---

72. Nitrogenous Bases

Purines

• Adenine (A)
• Guanine (G)

Pyrimidines

• Cytosine (C)
• Thymine (T)
• Uracil (U)

DNA

A, G, C, T

RNA

A, G, C, U

---

73. DNA

DNA = Deoxyribonucleic acid

Main functions

• Genetic information storage
• Hereditary information transfer
• Template for RNA synthesis

Structure

• Usually double-stranded
• Antiparallel strands
• Sugar → deoxyribose
• Bases → A, T, G, C

Base pairing

A = T

G ≡ C

Hydrogen bonds:

• A–T → 2 hydrogen bonds
• G–C → 3 hydrogen bonds

---

74. RNA

RNA = Ribonucleic acid

Characteristics

• Usually single-stranded
• Sugar → ribose
• Bases → A, U, G, C

Major types

• mRNA
• tRNA
• rRNA

Functions

• Gene expression
• Protein synthesis
• Regulation
• In some viruses, RNA acts as genetic material.

---

75. DNA vs RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Pyrimidine	Thymine	Uracil
Strands	Usually double	Usually single
Main role	Genetic information storage	Gene expression/protein synthesis
Stability	Generally more stable	Generally less stable

---

76. Enzymes

Enzymes are biological catalysts that increase the rate of biochemical reactions without being permanently consumed.

Most enzymes are proteins.

Exception

Some RNA molecules can act as catalysts.

They are called ribozymes.

NEET Fact

All enzymes are not proteins because ribozymes are catalytic RNA molecules.

---

77. Properties of Enzymes

• Highly specific
• Increase reaction rate
• Required in small amounts
• Not consumed permanently
• Work under mild physiological conditions
• Have optimum temperature
• Have optimum pH
• May require cofactors

---

78. Enzyme and Activation Energy

For a chemical reaction to occur, reactants must reach an energy barrier called activation energy.

Enzymes lower the activation energy.

Important

Enzymes:

Lower activation energy

but do not change the overall equilibrium of a reaction.

---

79. Active Site

Enzyme molecule में वह specific region जहाँ substrate binds करता है, active site कहलाता है।

Substrate

जिस molecule पर enzyme act करता है उसे substrate कहते हैं।

Basic concept

Enzyme + Substrate → Enzyme-substrate complex → Product + Enzyme

---

80. Lock and Key Model

Emil Fischer ने lock-and-key model दिया।

इसके अनुसार:

• Enzyme active site → lock
• Substrate → key

Specific substrate specific active site में fit होता है।

---

81. Induced Fit Model

Koshland ने induced-fit concept दिया।

इस model के अनुसार substrate binding के समय enzyme active site में conformational change हो सकता है।

Comparison

Lock & Key	Induced Fit
Active site relatively rigid माना जाता है	Active site flexible माना जाता है
Exact fitting	Binding से conformational change
Fischer	Koshland

---

82. Factors Affecting Enzyme Activity

Temperature

• Temperature बढ़ने पर reaction rate initially बढ़ती है।
• Optimum temperature पर maximum activity।
• बहुत high temperature → enzyme denaturation।

Human enzymes का optimum temperature सामान्यतः लगभग:

37°C

के आसपास होता है।

---

pH

हर enzyme का optimum pH अलग हो सकता है।

Examples:

Enzyme	Approx. optimum pH
Pepsin	~2
Trypsin	~8

---

Substrate Concentration

Substrate concentration बढ़ने पर enzyme activity initially बढ़ती है।

एक point के बाद सभी active sites occupied होने लगते हैं और rate लगभग maximum पर पहुँच जाती है।

---

Enzyme Concentration

जब substrate पर्याप्त हो, enzyme concentration बढ़ाने पर reaction rate बढ़ सकती है।

---

83. Cofactors

कुछ enzymes को catalytic activity के लिए non-protein components की आवश्यकता होती है।

इन्हें cofactors कहते हैं।

Types

1. Prosthetic groups
2. Coenzymes
3. Metal ions

---

84. Coenzyme

Organic non-protein molecules जो enzymes की activity में सहायता करते हैं।

Examples:

• NAD⁺
• NADP⁺
• Coenzyme A
• FAD

---

85. Prosthetic Group

Cofactor जो enzyme से tightly bound होता है।

Example

कुछ enzymes में FAD tightly bound cofactor के रूप में कार्य कर सकता है।

---

86. Apoenzyme and Holoenzyme

Apoenzyme

Enzyme का protein component।

Holoenzyme

Apoenzyme + Cofactor = Holoenzyme

NEET Formula

Apoenzyme + Cofactor → Holoenzyme

---

87. Enzyme Classification

International classification में enzymes को reaction type के आधार पर classes में रखा जाता है।

परंपरागत रूप से 6 major classes:

1. Oxidoreductases
2. Transferases
3. Hydrolases
4. Lyases
5. Isomerases
6. Ligases

EC classification में बाद में Translocases को अलग class (EC 7) के रूप में जोड़ा गया है।

---

88. Oxidoreductases

Oxidation-reduction reactions catalyse करते हैं।

Example: Dehydrogenases, oxidases

---

89. Transferases

Functional groups को एक molecule से दूसरे molecule में transfer करते हैं।

Example: Kinases

---

90. Hydrolases

Water की सहायता से bonds को break करते हैं।

Example: Proteases, lipases, nucleases

---

91. Lyases

Hydrolysis या oxidation के बिना groups को remove/add करके double bonds बनाते या तोड़ते हैं।

Example: Decarboxylases

---

92. Isomerases

एक molecule के अंदर atoms/groups की rearrangement करते हैं।

Example: Phosphoglucose isomerase

---

93. Ligases

दो molecules को जोड़ने वाली reactions catalyse करते हैं, generally ATP/GTP energy का उपयोग होता है।

Example: DNA ligase

---

94. Cell Cycle

Cell cycle वह sequence है जिसमें cell:

Growth → DNA replication → Division

से गुजरती है।

Cell cycle के मुख्य phases:

1. Interphase
2. M phase

---

95. Interphase

Interphase को resting phase कहना पूरी तरह सही नहीं है क्योंकि इस दौरान cell metabolically active होती है।

Interphase में:

• Growth
• DNA replication
• Protein synthesis
• Organelle duplication
• Cell division की preparation

होती है।

Interphase के तीन मुख्य phases:

G₁ → S → G₂

---

96. G₁ Phase

G₁ = First gap phase

Events

• Cell growth
• RNA synthesis
• Protein synthesis
• Organelles की वृद्धि
• Normal metabolism

---

97. S Phase

S = Synthesis phase

Major event

DNA replication

Important

DNA amount double होता है, लेकिन chromosome number तुरंत double नहीं माना जाता क्योंकि प्रत्येक chromosome दो sister chromatids वाला हो जाता है।

Centrosome duplication भी S phase के दौरान शुरू/होती है।

---

98. G₂ Phase

Events

• Further growth
• Protein synthesis
• Spindle formation की तैयारी
• Mitosis के लिए final preparation

---

99. M Phase

M phase = Mitotic phase

इसमें:

1. Karyokinesis → nuclear division
2. Cytokinesis → cytoplasmic division

होती है।

---

100. G₀ Phase

कुछ differentiated cells cell cycle से बाहर निकलकर G₀ phase में जा सकती हैं।

Example

कुछ highly differentiated cells लंबे समय तक non-dividing state में रहती हैं।

---

101. Mitosis

Mitosis को equational division कहा जाता है।

इसमें chromosome number generally maintain रहता है।

Importance

• Growth
• Tissue repair
• Replacement of cells
• Asexual reproduction in some organisms
• Genetic stability

---

102. Stages of Mitosis

Mitosis:

Prophase → Metaphase → Anaphase → Telophase

याद रखें:

PMAT

---

103. Prophase

Events

• Chromatin condenses
• Chromosomes become visible
• Each chromosome has two sister chromatids
• Nucleolus disappears
• Nuclear envelope breaks down progressively
• Spindle formation begins

---

104. Metaphase

Events

• Chromosomes maximum condensation के करीब होते हैं।
• Chromosomes equatorial plate पर arrange होते हैं।
• Spindle fibres kinetochores से attach होते हैं।

NEET Point

Metaphase → chromosomes at equatorial plate

---

105. Anaphase

Major event

Centromeres divide.

Sister chromatids अलग होकर daughter chromosomes बन जाते हैं।

वे opposite poles की ओर move करते हैं।

NEET Point

Centromere division → Anaphase

---

106. Telophase

Events

• Chromosomes poles तक पहुँचते हैं।
• Chromosomes decondense होते हैं।
• Nuclear envelope पुनः बनता है।
• Nucleolus पुनः दिखाई देता है।
• Two daughter nuclei बनते हैं।

---

107. Cytokinesis

Cytokinesis में cytoplasm divide होता है।

Animal cells

Cleavage furrow बनता है।

Plant cells

Cell plate बनती है।

Important

Animal	Plant
Cleavage furrow	Cell plate
Outside → inward constriction	Centre → outward growth

---

108. Significance of Mitosis

• Growth
• Development
• Repair
• Cell replacement
• Maintenance of chromosome number
• Genetic continuity

---

109. Meiosis

Meiosis एक special type of cell division है जिसमें chromosome number half हो जाता है।

इसे reduction division कहते हैं।

Occurs in

Germ-line cells से gamete formation में।

Two successive divisions

1. Meiosis I
2. Meiosis II

DNA replication केवल एक बार होती है, जबकि nuclear division दो बार होती है।

---

110. Meiosis I

Meiosis I में homologous chromosomes अलग होते हैं।

Stages:

Prophase I → Metaphase I → Anaphase I → Telophase I

---

111. Prophase I

Prophase I meiosis का सबसे complex और longest phase है।

इसके पाँच sub-stages:

1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene
5. Diakinesis

Mnemonic:

Le-Zy-Pa-Di-Dia

---

112. Leptotene

• Chromosomes condensation शुरू
• Chromosomes thin threads जैसे दिखाई देते हैं।

---

113. Zygotene

Major event

Synapsis

Homologous chromosomes pair करते हैं।

Paired homologous chromosomes को bivalent कहते हैं।

---

114. Pachytene

Major event

Crossing over

Non-sister chromatids के बीच genetic material exchange होता है।

Crossing over genetic variation बढ़ाता है।

---

115. Diplotene

• Synaptonemal complex disappears
• Homologous chromosomes separate partially
• They remain attached at chiasmata

Chiasmata

Crossing-over के visible points को chiasmata कहते हैं।

---

116. Diakinesis

• Maximum chromosome condensation
• Chiasmata terminalisation
• Nuclear envelope disappears
• Spindle formation

---

117. Metaphase I

Homologous chromosome pairs/bivalents equatorial plate पर arrange होते हैं।

Important

Bivalents at equator

---

118. Anaphase I

Major event

Homologous chromosomes separate.

Important

Centromeres do not divide during normal Anaphase I.

इसलिए sister chromatids साथ रहते हैं।

---

119. Telophase I

• Chromosomes poles तक पहुँचते हैं।
• Nuclear membrane कुछ organisms में reform हो सकती है।
• Two haploid nuclei/cells बन सकते हैं।

इसके बाद interkinesis हो सकती है।

Important

Interkinesis में सामान्यतः DNA replication नहीं होती।

---

120. Meiosis II

Meiosis II mitosis जैसा दिखाई देता है।

Stages:

Prophase II → Metaphase II → Anaphase II → Telophase II

Anaphase II

इस stage में:

Centromeres divide

और sister chromatids अलग होते हैं।

---

121. Meiosis का Result

एक diploid parent cell से सामान्यतः:

4 haploid daughter cells

बनती हैं।

Importance

• Chromosome number आधा करना
• Gamete formation
• Genetic variation
• Sexual reproduction के लिए आवश्यक

---

122. Mitosis vs Meiosis

Feature	Mitosis	Meiosis
Divisions	1	2
DNA replication	1	1
Daughter cells	Usually 2	Usually 4
Chromosome number	Maintained	Reduced to half
Synapsis	Absent	Present in Prophase I
Crossing over	Normally absent	Present in Prophase I
Genetic similarity	Generally similar	Genetically variable
Main role	Growth/repair	Gamete formation
Homologous chromosomes separate	No pairing-based separation	Anaphase I
Centromere division	Anaphase	Anaphase II

---

123. Mitosis and Meiosis — High-Yield Differences

Mitosis

2n → 2n + 2n

Meiosis

2n → n + n + n + n

Remember

Mitosis = Maintain chromosome number

Meiosis = Make chromosome number half

---

124. Important Cell Organelles — One-Glance Table

Organelle	Membrane	Major function
Ribosome	Non-membranous	Protein synthesis
Nucleus	Double	Genetic control
Mitochondria	Double	ATP production
Chloroplast	Double	Photosynthesis
ER	Single	Protein/lipid synthesis
Golgi	Single	Modification & packaging
Lysosome	Single	Intracellular digestion
Vacuole	Single	Storage/turgor
Peroxisome	Single	Oxidative reactions
Centriole	Non-membranous	Spindle/basal body organisation

---

125. Double-Membrane Organelles

Important double-membrane organelles:

• Nucleus
• Mitochondria
• Plastids

Important

Mitochondria और chloroplasts have:

• Own DNA
• Own ribosomes
• Some degree of autonomy

इसलिए इन्हें semi-autonomous organelles कहा जाता है।

---

126. Single-Membrane Organelles

• Endoplasmic reticulum
• Golgi apparatus
• Lysosomes
• Vacuoles
• Peroxisomes
• Glyoxysomes

---

127. Non-Membranous Structures

• Ribosomes
• Centrioles
• Cytoskeleton
• Nucleolus
• Chromatin

---

128. Organelles with Their Own DNA

Mitochondria

→ mtDNA

Chloroplast

→ cpDNA

Important

दोनों में generally:

• Circular DNA
• 70S ribosomes

पाए जाते हैं।

---

129. Important “Who Discovered What?”

Scientist	Discovery/Contribution
Robert Hooke	Cell in cork
Leeuwenhoek	Living cells/microorganisms
Schleiden	Plant cell theory
Schwann	Animal cell theory
Virchow	Cells arise from pre-existing cells
Camillo Golgi	Golgi apparatus
Singer & Nicolson	Fluid mosaic model
Watson & Crick	DNA double helix model

---

130. High-Yield Biomolecule Table

Biomolecule	Basic unit/building block	Major function
Carbohydrate	Monosaccharide	Energy/structure
Protein	Amino acid	Enzyme/structure/transport
Lipid	Fatty acids + glycerol in many lipids	Energy/membrane
Nucleic acid	Nucleotide	Genetic information

---

131. Important Bonds

Bond	Found in
Glycosidic bond	Carbohydrates
Peptide bond	Proteins
Ester bond	Triglycerides
Phosphodiester bond	Nucleic acids
Hydrogen bond	DNA base pairing

---

132. NEET Enzyme Quick Table

Term	Meaning
Enzyme	Biological catalyst
Substrate	Molecule on which enzyme acts
Active site	Substrate-binding/catalytic region
Apoenzyme	Protein component
Cofactor	Non-protein helper
Holoenzyme	Apoenzyme + cofactor
Coenzyme	Organic cofactor
Ribozyme	Catalytic RNA
Activation energy	Energy barrier for reaction

---

133. Cell Cycle Quick Table

Phase	Major event
G₁	Growth
S	DNA replication
G₂	Preparation for division
M	Nuclear + cytoplasmic division
G₀	Non-dividing/quiescent state

Formula

Interphase = G₁ + S + G₂

Cell Cycle = Interphase + M phase

---

134. Mitosis Quick Table

Stage	Major event
Prophase	Chromosome condensation
Metaphase	Chromosomes at equator
Anaphase	Sister chromatids separate
Telophase	Daughter nuclei form
Cytokinesis	Cytoplasm divides

Trick

PMAT

---

135. Meiosis Prophase I

Stage	Key event
Leptotene	Condensation
Zygotene	Synapsis
Pachytene	Crossing over
Diplotene	Chiasmata visible
Diakinesis	Terminalisation + maximum condensation

Trick

Le-Zy-Pa-Di-Dia

---

136. Most Important NEET One-Liners

• Cell is the basic structural and functional unit of life.
• Hooke coined the term cell after observing cork.
• Schleiden + Schwann → Cell theory.
• Virchow → Cells arise from pre-existing cells.
• Prokaryotic cells lack a true nucleus.
• Prokaryotic ribosome → 70S.
• Eukaryotic cytoplasmic ribosome → 80S.
• Mitochondria and chloroplasts contain 70S ribosomes.
• Plasma membrane follows the fluid mosaic model.
• Fluid mosaic model → Singer and Nicolson.
• Plant cell wall is mainly made of cellulose, hemicellulose and pectin.
• Middle lamella is rich in calcium pectate.
• RER → protein synthesis.
• SER → lipid synthesis and detoxification.
• Golgi → modification, sorting and packaging.
• Lysosome → intracellular digestion.
• Tonoplast → vacuole membrane.
• Mitochondrial inner membrane forms cristae.
• Chloroplast thylakoids are stacked into grana.
• Light reaction → thylakoid membrane.
• Calvin cycle → stroma.
• Peroxisomes contain catalase.
• Glyoxysomes are important in germinating oil seeds.
• Cytoskeleton → microtubules + microfilaments + intermediate filaments.
• Microtubules → tubulin.
• Microfilaments → actin.
• Typical cilia/flagella axoneme → 9 + 2.
• Basal body/centriole → 9 triplets.
• Nucleolus → rRNA synthesis and ribosome assembly.
• Euchromatin → less condensed and transcriptionally active.
• Heterochromatin → more condensed and generally less active.
• Cell wall is non-living and rigid.
• Plasma membrane is living and selectively permeable.
• Starch → plant storage carbohydrate.
• Glycogen → animal storage carbohydrate.
• Cellulose → plant cell wall.
• Chitin → fungal cell wall and arthropod exoskeleton.
• Proteins are polymers of amino acids.
• Peptide bond joins amino acids.
• Triglyceride → glycerol + 3 fatty acids.
• Phospholipids are amphipathic.
• DNA contains thymine.
• RNA contains uracil.
• Purines → Adenine + Guanine.
• Pyrimidines → Cytosine + Thymine + Uracil.
• DNA A–T → 2 H-bonds.
• DNA G–C → 3 H-bonds.
• Enzymes lower activation energy.
• Ribozymes are catalytic RNA molecules.
• Apoenzyme + cofactor → holoenzyme.
• S phase → DNA replication.
• Mitosis → equational division.
• Meiosis → reduction division.
• Mitosis generally produces 2 daughter cells.
• Meiosis generally produces 4 haploid cells.
• Synapsis → Zygotene.
• Crossing over → Pachytene.
• Chiasmata become visible → Diplotene.
• Homologous chromosomes separate → Anaphase I.
• Sister chromatids separate → Anaphase of mitosis / Anaphase II of meiosis.
• Centromeres normally do not divide in Anaphase I.
• Centromeres divide in Anaphase II.
• Animal cytokinesis → cleavage furrow.
• Plant cytokinesis → cell plate.

---

137. NEET Ultra-Rapid Revision Map

Cell

Cell → Basic unit of life

↓

Cell Types

Prokaryotic → No true nucleus

Eukaryotic → True nucleus

↓

Cell Boundary

Glycocalyx → Cell wall → Plasma membrane

↓

Major Organelles

Nucleus → Genetic control

Ribosome → Protein synthesis

RER → Protein synthesis/transport

SER → Lipid synthesis/detoxification

Golgi → Modification/packaging

Lysosome → Digestion

Vacuole → Storage/turgor

Mitochondria → ATP

Chloroplast → Photosynthesis

Peroxisome → H₂O₂ metabolism

Cytoskeleton → Shape/movement/transport

Centriole → Spindle/basal body organisation

↓

Biomolecules

Carbohydrate → Energy/structure

Protein → Amino acids

Lipid → Energy/membrane

Nucleic acid → Genetic information

↓

Enzymes

Enzyme → Biological catalyst

Active site → Substrate binding

Cofactor → Helper

Holoenzyme → Apoenzyme + Cofactor

↓

Cell Cycle

G₁ → S → G₂ → M

↓

Mitosis

PMAT → 2 similar daughter cells

↓

Meiosis

Meiosis I + Meiosis II → 4 haploid cells

Prophase I → Leptotene → Zygotene → Pachytene → Diplotene → Diakinesis