Cell biology is the study of cell structure and function. Key developments include Hooke observing cork cell structure in the 1600s, van Leeuwenhoek observing bacteria in the 1670s, and the cell theory proposed by Schleiden and Schwann in the 1830s stating that all organisms are composed of cells. Eukaryotic cells contain membrane-bound organelles like the nucleus, mitochondria and chloroplasts, while prokaryotic cells like bacteria lack membrane-bound organelles. Organelles perform specialized functions like ATP production in mitochondria and photosynthesis in chloroplasts. The cytoplasm and cytoskeleton provide structure and transport within the cell.

1. Cell Biology
Presented by
Rajwanti Saran
Ph. D. (Ag.) PBG
RARI, Durgapura, Jaipur

2. Matter of Concern………..
1. Introduction
2. History of cell
3. Cell theory
4. Cell organelles

3. Introduction
Cell biology: Branch of biological science
which deals with the study of structure,
function, molecular organization, growth,
reproduction and genetics of the cells.
 Cell biology mainly concern with study of
structure of cell and function of specialized
cells.

4. History
The term cell - Robert Hooke (1635-1703) in
the mid seventeenth century to describe the
structure of cork.
Anton van Leeuwenhoek (1632-1723) - first
recorded observations of bacterial cells (termed
"animalcules") from pond water & tooth
scrapings.
1830s –importance of cells realized
1838 - German botanist Matthias Schleiden
(1804-1881) observed that despite differences in
tissue structure, all plants tissues were made of
cells.

5. CONT….
1839 - German zoologist Theodor Schwann (1810-1882)
realized animals were also composed of fundamental
cellular units or cells.
Schwann proposed first 2 principles of Cell Theory:
a) All organisms consist of 1 or more cells
b) The cell is the structural unit of life
 Schleiden-Schwann view of cell origin was less
insightful – i.e. cells could arise from non-cellular
materials
German physician Rudolf Virchow (1821-1902)
demonstrated that living cells could arise only from other
living cells (biogenesis), and not from inanimate matter
(abiogenesis).

6. CELL
Cell is the basic structural and functional unit
of cellular organisms, except viruses.
Cell is a Latin word, that means “small room”
A.G. Loewy and P. Siekevitz (1963) have
defined a cell as “a unit of biological activity
delimited by a semi-permeable membrane and
capable of self-reproduction in a medium free
of other living systems”.

7. Properties of a Cell
Cells are -
Highly complex and organized
Possess a genetic program and the means to use it
Capable of producing more of themselves
 Acquire and utilize energy
Carry out a variety of chemical reactions
Engage in mechanical activities
 Able to respond to stimuli
Capable of self-regulation

8. TYPES OF CELL
Cell
Eukaryotic
cell
Plant cell Animal cell
Prokaryotic
cell
Eg.
Bacteria

9. Differences b/w prokaryotic cell and
eukaryotic cell
Prokaryote Cell Eukaryote Cell
1. Size – small 1- 10 μm
2. Unicellular
3. Has single membrane and cell wall
4. No nucleus.
5. Circular DNA
6. No Histones.
7. No cell organelles
8. Ribosomes – free in cytoplasm. 50S
+30S {70S}
9. Cell division – by fission
10. Cytoskeleton – absent has flagella
Ex- bacteria,rickettsia
1.Large - 10 - 100 μm
2. Multicellular
3. Membrane bilayer.
4. Nucleus –well defined.
5. Linear DNA.
6. Histones
7. Membrane bound Organelles.
8. Ribosomes – on surface of E.R. 60S
+40S {80S}
9. By mitosis.
10. Present.
Ex- fungi,plants,animals

10. Prokaryotic cell

11. Eukaryotic cell
ANIMAL CELL PLANT CELL

12. Animal cell v/s plant cell

13. Components of a cell
A cell is composed of hyloplasm and
various structures or cell organelles like
cell wall, cell membrane / plasma lemma,
endoplasmic reticulum, ribosomes, golgi
bodies, lysosomes, spherosomes,
chloroplasts, mitochondria, centriole and
nucleus.

14. Cell organelles
Cell
organelles
Membrane
bound
Membrane
non bound
Organelle (“little organ”)= a small structure in the cell
that performs a specific function.
 Membrane-bound organelles are found only in
eukaryotic cells.

15. Cytoplasm
Everything in a cell except the
nucleus is cytoplasm.
 Clear, gelatin-like, watery
substance surrounding the
organelles.
 Composition:
1) Water = 90%
2)Organic and inorganic compounds
= 10%

16. Functions of cytoplasm
Maintains the shape and consistency of
the cell.
 Allows for chemical reactions necessary
in metabolism.
Site for many metabolic pathways. Ex-
Glycolysis, Protein synthesis , fatty acid
synthesis, purine synthesis.

17. Cell wall
Plant cells are surrounded by a nonliving and
rigid coat called cell wall.

18. The cell wall of a differentiated cell has the
following 3 parts:
a) Middle lamella: The walls of contiguous cells are
joined by middle lamella.
 It is composed of calcium and magnesium pectate.
b) Primary cell wall: It is lies b/w ML and secondary
cell wall/plasma lemma.
 It is composed of hemicellulose (53%), cellulose
(30%), pectin (5%), protein (5%) and lipid (7%).
c) Secondary cell wall: Inner most layer of wall.
 It is composed mainly of cellulose but it also
contains lignin, suberin and cutin.

19. Functions of cell wall
Provide plants to a definite shape, mechanical
support and strength to tissues and organs.

20. Plasma lemma
Boundary of the cell.
Made of a phospholipid bilayer, with protein
molecules scattered all over.
Composition: Protein = 40% and lipid = 60%
Functions:
1. Regulate the movement of various molecules
into and out of the cytoplasm.
2. It forms a protective barrier b/w the
intracellular and extracellular environments.

21. Structure of plasma lemma

22. Mitochondria
Mitochondria was first seen by kollicker
in 1850 in muscles and called them
‘sarcosomes’
Altmann (1890) observed these
structures and named them ‘bioblasts’.
Benda (1898)stained these organelles
with crystal violet and renamed them
‘mitochondria’

23. Structure
Mitochondria have a double membrane
structure.
1) Outer membrane: Contain large number of
integral protein called porins (Allow material
in and out of the mitochondria).
Enclosed the entire organelle.
2) Inter membrane space/Peri-mitochondrial
space: ions and sugars in the intermembrane
space is the same as the cytosol.

24. Cont…
3)Inner Membrane: It is folded double
phospholipid layer .
Site for the production of ATP.
Specific transport of protein that regulate
metabolite passage in and out of the matrix.
4) Cristae and Matrix: Cristae is the folding of the
inner membrane that allows more surface area,
enhancing its ability to produce ATP.
The matrix is the space enclosed by the inner
membrane.

25. Chemical Composition
Protein = 70%
Lipid = 25-30%
RNA = 1%
DNA < 1%

26. Function
Important and main function is to produce
ATP. Therefore it is called the power house of
the cell (ETS).
Krebs cycle of cellular respiration is takes
place in mitochondrial matrix.
Regulate cellular metabolism.
Play important role in cytoplasmic
inheritance. Eg. CMS
Site of metabolic pathways.- TCA cycle,
Urea Cycle, F.A Oxidation etc.

27. Structure

28. Chloroplast
Found only in plant cells and plant-like
protists
 It contains Chlorophyll, hence it imparts
the characteristic green colour to plants
and carry out photosynthesis, the ultimate
source of all organic compounds.
Average cell may have 20-40 chloroplast.
Chlamydomonas have 1chloroplast cell

29. Chemical Composition
Protein = 50-59%
Lipid = 21-34%
Chlorophyll = 5-8%
Carotenoids = 0.7-1.1%
RNA = 1-7.5%
DNA = 0.2-1%

30. Origin And Evolution

31. Structure
 Planoconvex lens- like
structures (5μm x 2-3
μm)
Double layered envelope
Granular stroma or
matrix
Lamellar system
Osmophilic globules
(Plastoglobuli)
Chloroplast DNA

32. Function
Main function is photosynthesis.
Contribute to heredity in the form of
cytoplasmic inheritance.

33. Energy Transduction

34. Photosynthetic complexes distributed in
thylakoid membrane

35. Maternal inheritance of chloroplast
genome
Nuclear genomes higher eukaryotic organisms are
diploid and shows sexual reproduction.
Gametes result from meiosis are haploid
Fertilized zygote inherits one nuclear allele of
each gene from each parent
But cytoplasmic organelles contain multiple,
homogeneous genomes inherited from female
parent (cytoplasmic inheritance).
In tobacco and many other plants, mitochondrial
and chloroplast genomes are specifically
degraded (in male gamete) before fertilization.
There are many exceptions

36. Alleles A, B and C from the female parent and
a, b and c from the male parent

37. Chloroplast DNA based cytoplasmic inheritance
of leaf color in Four O’clock (Mirabilis ) plant

38. Endoplasmic reticulum
A web-like series of membranes within the
cytoplasm in the form of flattened sheets, sacs,
tubes, creates many membrane enclosed
spaces - spreads throughout the cytoplasm -
has connections with the outer membrane of
the nucleus and the plasma membrane.
“E.R.” (endo means inside + cytoplasmic +
reticulum means network = network of
membranes inside the cytoplasm)
Interconnected network of tubules and vesicles
– cisternae.

39. Structure

40. Two types of ER
Rough ER - studded with ribosomes
Site of synthesis of many proteins
 All ribosomes on rER are actively involved in
protein synthesis -
Smooth ER - site for synthesis of steroids and
other lipids, Ca++ storage in muscles
Detoxification of drugs, toxins, alcohol
(especially in liver)

41. Function
RER- synthesizes proteins.
 SER- synthesizes phospholipids, cholesterol (in
many tissue) & steroid hormones (adrenals, gonads).
 SER - site of Glycogen metabolism.
Removes the phosphate group from G-6-P; and
release free glucose in blood.
In liver & Kidney - Detoxifies drugs, toxins &
Carcinogens.
Circulation and transport
Storage of proteins and minerals
A large surface area for enzyme action.

42. Golgi complex
 Consists of 3 to 20 cisternae, small, flattened
membranous sacs.
 Prominent in cells that secrete proteins
 Accept vesicles on one side and produce
vesicles on the other

43. Structure

44. Function
Modification of proteins and lipids
Storage and packaging of molecules
POST OFFICE OF CELL

45. Ribosome
Protein synthetic machinery
 Two subunits - large and small - each made of
protein and ribosomal RNA (rRNA)
 Granular structures present on surface
of ER & also as free
 1st observed by George Palade (1953)
 Non membrane bound organelle
Measure ~ 22 x 32 nm.
Contain 85% RNA of cell

46. Functions
Subunits associate when they are synthesizing
proteins
 Protein synthesis occurs on ribosomes that are
free-floating in the cytoplasm and on
ribosomes attached to ER
rRNA is synthesized in the nucleolus

47. Structure

48. Lysosome
Vesicles filled with digestive enzymes - used
for intracellular digestion.
Particles can be taken into cell by
phagocytosis and vesicle fused with lysosome.
The components of organelles can be recycled
after digestion by lysosomes.
Functions:
a) Garbage disposal.
b) Breakdown bacteria entering cell, worn out
organelles, intracellular digestion.

49. Function

50. Vacuole
Membrane bound sac
 Contains liquids or
solids
 Larger than vesicles

51. Function
• Storage container for water, food, enzymes,
wastes, pigments, etc.

52. Centriole
part of specialized region of the cell called the
centrosome (cell center)
found in animals and most protists the
centrioles are involved in the production of
microtubules
microtubules have many functions including
moving chromosomes during cell division
centriole structure - 9 triplets of microtubules
surrounding a hollow core .
similar to the basal body of flagella

53. Structure
Centrioles are short
cylinders, arranged at right
angles to each other.

54. Cytoskeleton
 A network of protein filaments that extends
throughout the cytoplasm.
Anchored to plasma membrane.
Dynamic structure.
Three types of filamentous proteins -
1. Microtubules
2. Intermediate filaments
3. Microfilaments

55. Microtubules
Long, Hollow, unbranched, polar cylinders, made
up of protein “tubulin”(α & β tubulin),
The largest of cytoskeletal components.
 Major components of axons and dendrites.
Functions:-
1. Microtubules help in structural support and
maintain the shape of the cell.
2. Helps in movement of organelles,secretory
vesicles and exocytosis.
3. Formation and function of mitotic spindle.
4. Movement of cilia and flagella.

56. Intermediate filaments
Polymers of long rod like proteins.
These filaments are thicker than microfilaments
but thinner than microtubules.
Made up of – Keratin,desmin,neurofilaments etc.
Functions :-
1. Provide mechanical support to the cell.
2. Helps in intercellular attachment.
3. Provide strength and rigidty to neurons.
4. Major structural role in skin and hair cells.

57. Microfilaments
Thinnest elements of the cytoskeleton.
Composed of the protein actin, (β , γ actin )
Form a meshwork under plasma membrane
Stress fibres.
Functions :-
1. Mechanical support for the basic strength &
shapes of cells. ex- Microvilli is rich in
microfilaments – Shape.
2. Involved in muscle contraction, cell division,
and cell locomotion.

58. Structure
.

59. Function
Provides shape to cell. Acts as internal
framework.
Helps in uptake of materials into cell.
Helps in internal movement of cell organelles ,
movement of cells and muscle contraction.
Helps in Cell division.

60. Peroxisome
Also known as microbodies
 “Subcellular respiratory organelles”
 0.5 μm in diameter
Predominantly present in Hepatocytes &
Tubular Epithelial cells.
 Surrounded by a membrane.
Contain several oxidases. – Peroxidase ,
Catalase .
Create H2O2 as a byproduct and degrade it
with the enzyme catalase.

61. Functions
1. Oxidation of amino acids.
2. Oxidation of long chain fatty acids.
3. Protects cell from the toxic effects of H2O2.
4. Used for removing reactive compounds from
the cytoplasm
5. Essentially contain two types of Enzymes
Oxidases : which are active in oxidation of lipid
Catalase : which act on Hydrogen Peroxide to
liberate Oxygen.

62. Spherosome
Vesicles of 0.5-1 micron diameter, surrounded by
a membrane.
Found only in plant cells.
Composition:
98% lipid + some acid phosphates
Function:
- Lipid storage

63. Nucleus
Control center of the cell – has the information
needed to oversee the chemical reactions in
cells.
Prominent & Characteristic features
‘Eukaryon’ means ‘true nucleus’
Very essence of eukaryote – membrane
bounded nucleus

64. Functions
Stores genetic information
Controls cell division
 Directs functioning of cell (provides template
for RNA -protein synthesis)
Physically separates DNA from the
cytoplasm’s complex metabolic machinery
Nuclear membrane serve as boundary

65. Components of Nucleus
1. Nuclear Envelope –
pore riddled
2. Nucleoplasm –
Fluid interior
portion
3. Nucleolus – Dense
cluster of RNA &
Proteins –ribosomes
4. Chromatin – all
DNA + Proteins

66. The Nuclear Envelope
Inner and outer nuclear membrane with
perinuclear space
7-8 nm thick and trilamellar appearance
Inner membrane lined with fiber network –
Nuclear lamina- 10 to 40 nm
Nuclear lamina – intermediate filament
(protein) called as Lamins
Nuclear lamina – support to NE & attachment
sites for chromatin.

67. Cont…
Outer membrane - continuous
with ER
Outer membrane studded with
ribosomes – protein synthesis.
Perinuclear space – 20 to 40
nm continuous with cisternae
of ER
E/M - filaments of
cytoskeleton extend outward
cytoplasm – anchored to
organells/ plasma membrane –
known as Nuclear matrix
Matrix - shape of nucleus

68. The Nuclear Pore
Most distinctive feature of NE
Small cylindrical channels –direct contact
b/w cytosol & Nucleoplasm
Readily visible – freeze fracture microscopy
Density - cell type & activity

69. The Nucleolus
Ribosome factory
large, prominent structures
Doesn’t have membrane
E/M it consists;
1. Fibrillar component
- DNA (unraveled chromatin loops) + RNA
component of ribosome
- DNA carries genes for rRNA - NOR
- RNA is r RNA – synthesized & processed
- dense areas, transcription going on

70. Cont…
2. Granular component
- rRNA molecules + Proteins
- forms ribosomal subunits – exported to
cytoplasm
Size correlated with level of activity
Cells having high rate of protein synthesis –
many ribosomes –20 to 25% of nucleus
Main difference – granular component present

71. Cont…
During cell division – condensation of
chromatin into compact chromosomes
Shrinkage and disappearance of nuclei
rRNA & protein disperse/ degraded
After mitosis – chromatin uncoils, NOR loop
out, rRNA synthesis resumes
Many tiny nucleoli visible – fuse & become
large nucleolus

72. Chromatin/ Molecular structure of
chromosomes
• Eukaryotic chromosomes – two broad
components.
1.Nucleic acids:
- DNA (primary nucleic acid) + small amt of RNA
(transit to the cytoplasm)
2. Proteins:
i. Histones (basic pH) – core histones (H2A, H2B,
H3 & H4), Linker histone (H1)
ii. Non-histone proteins

73. Cont…
Histones bind to –vely charged DNA – stability
to the DNA
Mixture of DNA & proteins – basic structural
unit of chromosomes - chromatin fiber
E/M examination of intephase chromatin –
ellipsoidal beads joined by linker DNA known as
Nucleosomes.

74. Nucleosome
Simplest packing str of
DNA
146 bp DNA wrapped
around histone octamer
Octamer = 2 copies of 4
core histones
DNA length varies b/w
species
Core DNA – DNA
associated with histone
octamer
Linker DNA – DNA b/w
histone octamer – 8 to 114
bp

75. Cont..
Model of
packing of
chromatin
and the
chromosome
scaffold in
metaphase
chromosome

76. Chromatin
Chromatin can be
differentiated into
two regions (during
interphase & early
prophase)
1.Euchromatin –
lightly staining
2.Heterochromatin
– densely staining

77. Types of chromatin
EUCHROMATIN
1. Lightly staining regions
2. Less tightly packed chromatin
fibers therefore non condensed
3. Not visible – light microscope,
undergo regular changes in
morphology with cell division
4. Genetically active regions
5. Replicates earlier during S phase
6. GC rich
HETEROCHROMATIN
1. Darkly staining
2. Tightly packed chromatin fibers
therefore condensed
3. Visible, remain highly condensed
in all stages
4. Genetically inactive regions –
either they lack genes/ contain genes
that are not expressed
5. Replicates later during S phase
6. AT rich

78. Organelles – “factory components
with function”
Support - Cell wall , cell membrane cytoskeleton, microtubles
Controls material entering and leaving - Cell membrane, pores
Internal transport system – Endoplasmic reticulum
Powerhouse - mitochondria
Control center – nucleus, organelle DNA for mitochondria and chloroplast
Production of key products – ribosomes, endoplastic reticulum, chloroplasts
Packaging center for shipment of products – Golgi Apparatus, ER
Shipment of materials out of cell - Golgi Apparatus, vesicles
Storage of liquids and solids – Vacuole, vesicles, plastids,
Recycling center – Lysosomes and perixosomes
Convert light energy to chemical energy - chloroplasts
Allows new cell factories to be produced – nuclear DNA, centrioles, cell wall