This presentation offers the bird's eye view of the cell as the basic structural and functional unit of life. It also addresses the origin of eukaryotic cells from the prokaryotic cell by the endosymbiotic theory.

1. CELL BIOLOGY
Welcome to the topic:
Cell as unit of Structure & Function
by
Dr. N.Sannigrahi, Associate Professor of Botany,
Nistarini College, Purulia(W.B) India

2. EUKARIOTES AND ENDOSYMBIOTIC THEORY
• COURSE CONTENTS
• The Cell: Cell as a unit of structure and function;
• Characteristics of prokaryotic and eukaryotic cells;
• Different Cell organelles,
• Comparative account between prokaryotic and eukaryotic cell
• Origin of eukaryotic cell (Endosymbiotic theory).
• Significance of this theory.

3. CELL- THE BASIC UNIT OF LIFE
• Cell is a unit of biological activity delimited by a semi permeable membrane and capable of self
reproduction in a medium free from other living system’- A.G. Loewy and P. Siekevitz (1963).
 The cell was first discovered by Robert Hooke in 1665.
 The Modern cell theory or cell doctrine advocates-
 All living organisms are composed of cell,
 Cell is the structural and functional unit of living organisms,
 All cells arise from the pre-existing cells of similar kind,
 The chemical composition and metabolism of all cells are basically similar,
 The function of an organism as a whole is the outcome of the activities and interactions of the
constituent cells,
 Each cell contains generally a centrally placed nucleus and many other organelles,
 Cell is the store house of genetic information and vehicle of expression,
 Energy flow occurs in cell.

4. PROKARIOTIC & EUKARIOTIC CELL

5. Cell-Structural & Functional unit of Life
• A cell is the smallest living thing in the human organism, and all living structures in the human
body are made of cells. There are hundreds of different types of cells in the human body, which
vary in shape (e.g. round, flat, long and thin, short and thick) and size (e.g. small granule cells of
the cerebellum in the brain (4 micrometers), up to the huge oocytes (eggs) produced in the female
reproductive organs (100 micrometers) and function. However, all cells have three main parts, the
plasma membrane, the cytoplasm and the nucleus. The plasma membrane (often called the cell
membrane) is a thin flexible barrier that separates the inside of the cell from the environment
outside the cell and regulates what can pass in and out of the cell. Internally, the cell is divided
into the cytoplasm and the nucleus. The cytoplasm (cyto- = cell; -plasm = “something molded”) is
where most functions of the cell are carried out. It looks a bit-like mixed fruit jelly, where the
watery jelly is called the cytosol; and the different fruits in it are called organelles. The cytosol
also contains many molecules and ions involved in cell functions. Different organelles also
perform different cell functions and many are also separated from the cytosol by membranes.

6. CONTINUATION------------
• The largest organelle, the nucleus is separated from the cytoplasm by a nuclear envelope
(membrane). It contains the DNA (genes) that code for proteins necessary for the cell to function.
• Generally speaking, the inside environment of a cell is called the intracellular fluid (ICF), (intra- =
within; referred to all fluid contained in cytosol, organelles and nucleus) while the environment
outside a cell is called the extracellular fluid (ECF) (extra- = outside of; referred to all fluid
outside cells). Plasma, the fluid part of blood, is the only ECF compartment that links all cells in
the body.
• The integration of the cell is maintained by the cytoskeleton and the cell wall coifers protection
and cell membrane maintain a selective permeability to design the cell as an osmotic system. In
addition to these, different membrane and non-membrane bound organelles along with other
substances make the cell as the structural & functional unit of life.

7. ULTRASTRUCTURE OF PROKARIOTIC CELL

8. ULTRASTRUCTURE OF EUKARIOTIC CELL

9. DIFFERENCE BETWEEN PROKARIOTES AND EUKARIOTES
FEATURES PROKARIOTIC CELL EUKARIOTIC CELL
Cellular organization Mostly unicellular with 1-10 nm. Mostly multicellular with 10-100 nm
Cell wall Present with mucopeptide or peptidoglycan Cell wall in plant without mucopepetide
Nucleus True nucleus absent, only nucleoid, All features of true nucleus present
Chromosome True chromosomes absent, DNA without histone Chromosome with DNA & histone
Organelles Membrane bound organelles absent Membrane bound organelles present
Ribosome Smaller of 70S with 50S & 30S Larger of 80S type-60S & 40S
Mitotic apparatus Absent Present
Cell Cycle Shorter; 20-30 minutes duration Longer with 12-24 hrs
Centioles Absent Present
Microtubules Absent Present
Plasmids Present of diverse types like Rec. Plasmids Absent
Sexual Process Parasexuality Typical sexuality
Endocytosis &
exocytosis
Absent Present

10. CELL MEMBRANE-PROTEIN ICEBERGS IN THE SEA OF
LIPID
• The plasma (cell) membrane separates the inner environment of a cell from the extracellular fluid.
It is composed of a fluid phospho-lipid bi-layer (two layers of phospholipids) as shown and other
molecules. Not many substances can cross the phospholipids bi-layer, so it serves to separate the
inside of the cell from the extracellular fluid. Other molecules found in the membrane include
cholesterol, proteins, glycolipids and glyco-proteins below. Cholesterol, a type of lipid, makes the
membrane a little stronger. Different proteins found either crossing the bilayer (integral proteins)
or on its surface (peripheral proteins) have many important functions. Channel and transporter
(carrier) proteins regulate the movement of specific molecules and ions in and out of cells.
Receptor proteins in the membrane initiate changes in cell activity by binding and responding to
chemical signals, such as hormones (like a lock and key). Other proteins include those that act as
structural anchors to bind neighboring cells and enzymes. Glycoprotein and glycolipids in the
membrane act as identification markers or labels on the extracellular surface of the membrane.
Thus, the plasma membrane has many functions and works as both a gateway and a selective
barrier.

11. CELL MEMBRANE

12. CELL ORGANELLES
 An organelle is any structure inside a cell that carries out a metabolic function. The cytoplasm
contains many different organelles, each with a specialized function. (The nucleus discussed
above is the largest cellular organelle but is not considered part of the cytoplasm). Many
organelles are cellular compartments separated from the cytosol by one or more membranes very
similar in structure to the cell membrane, while others such as centrioles and free ribosome do not
have a membrane.
 Let us learn the structure and functions of different organelles such as mitochondria (which are
specialized to produce cellular energy in the form of ATP) and ribosome (which synthesize the
proteins necessary for the cell to function). Membranes of the rough and smooth endoplasmic
reticulum form a network of interconnected tubes inside of cells that are continuous with the
nuclear envelope. These organelles are also connected to the Golgi apparatus and the plasma
membrane by means of vesicles. Different cells contain different amounts of different organelles
depending on their function. For example, muscle cells contain many mitochondria while cells in
the pancreas that make digestive enzymes contain many ribosome and secretary vesicles.

13. CELL ORGANELLES IMAGES

14. CELL ORGANELLES-FUNCTION

15. PLANT CELL STRUCTURE

16. MITOCHONDRIA
 Mitoochondria’ derived from Mitos: thread. Chondrion: grain, popularly called power house of cell
and the store house of energy,
 First discovered by Kolliker in 1850 but Benda coined the term ,
 Variable in shape but cylindrical or tubular (yeast) to spherical, filamentous, club-shaped,
 Width 0.05 µm-1.0µm in width and 1.5-10µm in length,, with 5-10 days life span, animal cells contain
higher mitochondria than plant cells; kidney cell with 300-400, hepatic cells 2with 1000, muscle cells
5,00,000,
 Chemically contains proteins 60-70%, lipids 25-35%, RNA 5-10%, DNA in small amount with little
mineral traces and more than 60 diverse enzymes,
 Outer membrane with mitochondrial envelope , integral proteins, porins that form channels for
permeability of solute and metabolites, outer and inner membrane ,
 Inner semi-permeable membranes with different carrier proteins, electron carrier, coupling factors and
enzymes with two surfaces-C-face & M-face,
 Finger like folding towards inner side known as cristae or mitochondrial crests, numerous stalked
tennis like particles known as oxysomes as F0-F1 particles with 10000-100000 per mitochondria.
Three parts- a base, a stalk and a head functioning as ATPase for phosphorylation.

17. MITOCHODRIA-STRUCTURE & FUNCTION

18. MITOCHONDRIA
 Inter-membrane space- normal space between the outer and inner membrane of mitochondrion known
as perichondrial space whose width is 60-100Ȧ, extended into intracristal space, this chamber is filled
with a fluid containing enzymes and store ATP molecules after synthesis,
 Matrix- Central space enclosed by the inner membrane known as mitochondrial matrix, dense semi
fluid containing proteins, lipids, enzymes of Krebs Cycle, amino acid synthesis, fatty acid synthesis;
double stranded DNA molecules, RNA molecules, 70S ribosome, granules of inorganic salt, mtDNA
codes for 2 rRNAs , 19tRNAs and mRNAs code for protein synthesis.
 FUNCTION
 Site for cellular respiration in general and TCA cycle in particular,
 Acts as ATP mill of the cell to produce ATP currency,
 Different types of substrates like carbohydrates, proteins ad fats are mainly oxidized and degraded
through mitochondria it acts as the centre of metabolic pool,
 Site of the synthesis of Biomolecules like Chlorophyll, cytochrome, steroids, alkaloids , amino acids
etc,
 It is the mitochondrial inheritance that pass from mother to offspring via cytoplasm of egg responsible
for different genetic traits-either good or bad.

19. CHLOROPLASTS
 Chloroplasts derived from chloros : green , plastos: moulded, green plastids containing chlorophyll
pigments that perform photosynthesis by the anabolic processes,
 A . Schimper (1883) divided plastids into three categories- Leucoplasts i.e. colorless plastids,
Chromoplasts i.e. colored and Chloroplasts i.e. green plastids,
 Derived from common precursor called proplasts; Chloroplasts first observed by N. Grew (1862),
 Number of chloroplasts varies per cell, 1 in Chlorella, Ulothrix and Chlamydomonas, 16 in Spirogyra,
20-40 in mesophyll cells of leaf and several hundred in Chara and 40000 in 1 mm of Ricinus leaf.
 Variable in shape; cup-shaped in Chlamaydomonas, ribbon shaped in Spirogyra, collar like in Ulothrix
, discoid in Voucheria etc.
 Biochemically in contains 50-60% proteins, 20-30% lipid, 5-10% chlorophyll, 1-2% Carotenoids, 1-
2% RNA, 0.5% DNA and other mineral elements, Quinone, Vitamin-E & K etc.
 4-10µm in diameter and 2-4 µm in thickness,
 Bounded by two lipoproteins membranes –outer and inner membrane with peri-plastidial space ; inner
membrane encloses with a matrix called stroma having small cylindrical structures known as granum;
inner membrane develop infoldings lamellar structures called thylakoids,

20. PLASTIDS-STRUCTURE & FUNCTION

21. CHLOROPLASTS
 Thylakoid membrane possess chlorophyll molecules, Carotenoids, cytochrome, quinones, ATP
synthetase, etc
 Photosystem I (PS I) and Photosystem II (PS II) and their photochemical reaction centers (PRC) are
present in the thylakoid,
 PSI is more abundant in stroma lamellae and PSII more in granum lamellae; PRC is a special
chlorophyll molecule present both in PSI & PSII,
 The stroma contains osmophilic droplets, proteins, lipids, starch grains, DNA, RNA , 70S ribosome,
enzymes, metal ions etc.,
 It is semiautonomous as it synthesizes its own proteins and enzymes by following central dogma,
 Stigma or eye spot present in chloroplast in some motile algae , contains photoreceptor being
photosensitive ; photosynthetic bacteria contains bacterio-chlorophyll and bacterioviridin.
 FUNCTION: Photosynthesis as the kitchen house of cell, Carbon assimilation, storage of starch,
evolution of oxygen, Formation of ATP by photosynthetic phosphorylation by non-cyclic method
mostly, formation of reducing powers in the form of reduced NADP, photosensitivity by the
possession of stigma or eye spot along with fatty acids and amino acid synthesis are some of the
function extended by the chloroplasts.

22. RIBOSOMES-SUB UNITS & FUNCTION

23. RIBOSOMES-SUB UNITS & FUNCTION
 A complex amembranous organelle that serves as the site for biological protein synthesis due to the
presence of translational apparatus,
 Made from the complex of RNA and proteins called ribo-nucleoproteins and also called ribozymes
because of catalytic peptidyl- transferase activity that links amino acids together ,
 Ribosome from bacteria, archaea and eukaryotes resemble each other and it indicates common origin
in the three domain of life,
 The ribosome in mitochondria called mito-ribosomes produced from mitochondrial genes that reflect
the origin from prokaryotes aerobic bacteria by endosymbiotic theory,
 A. Claude (1943) observed the basophilic granules rich in nucleic acids Palade in 1955 first isolated it
and Richard B Roberts in 1956 proposed the term ‘ribosome’,
 Ribosomal proteins and rRNAs arranged in two sub-units-large and small sub unit of the ribosome;
differences are there between prokaryotic and eukaryotic ribosome,
 Prokaryotes have 70S with 50S and 30S ; small sub unit has 16S RNA with 1540 nucleotides bound to
21 proteins and the large sub unit composed of 5S RNA sub unit with 120 nucleotides and 23S RNA
sub unit with 2900 nucleotides and 31 proteins.

24. RIBOSOMES-ROLE IN PROTEIN SYNTHESIS

25. RIBOSOMES-SUB UNITS & FUNCTION
 Eukaryotic have 80S ribosome with 40S and 60S sub unit ; the 40S sub unit has an 18S RNA of 1900
nucleotides and 33 proteins and the 60S sub unit is composed of 5S RNA of 120 nucleotides , 28S
RNA of 4700 nucleotides and 5.8S RNA of 160 nucleotides and 46 proteins,
 Ribosome of mitochondria and chloroplast contains 70S type , believed to be descendents of
prokaryotic origin,
 The catalytic activity of ribosome is carried out by RN and the protein residue responsible for
stabilizing the structure,
 The association of ribosomal sub unit is dependent upon the concentration of Mg+2 ions , the lesser
the concentration of the ions, more the chance of dissociation or vice versa,
 Ribosome in protein synthesis appear in chain called polysomes,
 Ribosome are of diverse types- Free ribosome present anywhere in the cytosol, membrane bound
ribosome associated with endoplasmic reticulum in eukaryotic cell called rEr ; bound ribosome
usually produce proteins that are used within plasma membrane or are expelled from the cell via
exocytosis,
 FUNCTION: Acts as site for protein synthesis and it is the translational site where the mRNA
comprises a series of codon that dictate to the ribosome the sequence of amino acids needed to make
protein.

26. ENDOSYMBIOTIC THEORY
 More than 100 theories have figured out in thoughts between prokaryotic and eukaryotes,
 More than 20 endosymbiotic theories like Independent hypothesis, Endogenous theory, Chimera
hypothesis, Endosymbiotic theories etc have been presented to explain the origins of eukaryotes and
their mitochondria,
 Endosymbiotic theory was first articulated by Russian botanist, Konstantin Marsh Kowski in 1910 and
it was first explain by Boris Kozo-Polyansky in 1924.
 The role of energy and the energy constraints that prokaryotic cell organization placed on evolutionary
innovation in cell history has come to bear on endosymbiotiic theory.
 Only cells that possess mitochondria had the bioenergetics means to attain eukaryotic cell complexity,
 It indicates the transition between prokaryote to eukaryotes,
 The evolutionary history and biology of archaea increasingly comes to bear on eukaryotic origins.
 Molecular data have played an important role in supporting exogenous origin (from outside of cell)
rather than autogenously origin (from within the cell) of organelles. Recent phylogenetic analyses
reveal that many eukaryotic organelle and nuclear genes whose prokaryotic ancestry can be pinned
down are of bacterial origin.
 Phylogenetic analyses reveal that many eukaryotic orgnallear and nuclear genes whose prokaryotic
ancestry can be pinned down are of bacterial origin. In the case of endosymbiosis one type of cell
(symbionts) entered into another type of cell (host) through phagocytosis.

27. ENDOSYMBIOTIC THEORY

28. ENDOSYMBIOTIC THEORY
• It is thought that life arose on earth around four billion years ago. The endosymbiotic theory states that
some of the organelles in today's eukaryotic cells were once prokaryotic microbes. In this theory, the
first eukaryotic cell was probably an amoeba-like cell that got nutrients by phagocytosis and contained
a nucleus that formed when a piece of the cytoplasmic membrane pinched off around the
chromosomes. Some of these amoeba-like organisms ingested prokaryotic cells that then survived
within the organism and developed a symbiotic relationship. Mitochondria formed when bacteria
capable of aerobic respiration were ingested; chloroplasts formed when photosynthetic bacteria were
ingested. They eventually lost their cell wall and much of their DNA because they were not of benefit
within the host cell. Mitochondria and chloroplasts cannot grow outside their host cell.
• Evidence for this is based on the following:
 Chloroplasts are the same size as prokaryotic cells, divide by binary fission, and, like bacteria, have
Fts proteins at their division plane. The mitochondria are the same size as prokaryotic cells, divide by
binary fission, and the mitochondria of some protists have Fts proteins at their division plane.
 Mitochondria and chloroplasts have their own DNA that is circular, not linear.
 Mitochondria and chloroplasts have their own ribosome that have 30S and 50S subunits, not 40S
and60S.

29. EVIDENCE IN SUPPORT OF ENDOSYMBIOTIC THEORY
 Genome comparison indicate the aerobic bacteria contributed to the genetic origin of mitochondria,
 The origin of plastid has been strengthened by the genomic comparison of cyanobacteria being
autotrophic in nature,
 Several enzymes and transport systems of mitochondria are similar to those of bacteria,
 Most of the internal structure and biochemistry of plastids for example the presence of thylakoids and
chlorophyll molecules , are very similar to that of cyanobacteria. Phylogenetic estimates constructed
with bacteria , plastids and eukaryotic genomes suggest that plastids are most closely related to
cyanobacteria.
 A membrane lipid , cardiolipin is exclusively found in the inner membrane of mitochondria and
bacterial cell membrane.
 Several more primitive eukaryotic microbes, such as Giardia and Trichomonas have a nuclear
membrane but no mitochondria.

30. ENDOSYMBIOTIC THEORY

31. ENDOSYMBIOSIS
 Thus, the endosymbiosis theory of Symbiogenesis theory explains-
 An evolutionary idea to explain the origin of eukaryotes from prokaryotes,
 Several key organelles of eukaryotes originates as symbiosis between separate single celled organism,
 It also explains the development of gradual complexity of the structural and functional unit in this
context through the passage of evolution,
 Mitochondria and chloroplasts have been derived from the ancient prokaryotes to address the need of
evolution through the changing environmental consequences

32. THANKS TO VISIT THE CONTENT
• References:
1. Google for images,
2. Different open sources of information of WebPages
3. Biochemistry- Lehninger
4. Biomolecules & Cell Biology- Arun chandra Sahu,
5. A textbook of Botany (Vol. II) Ghosh, Bhattacharya, Hait
6. Fundamentals of Biochemistry- Jain, Jain, & Jain,
7. A Textbook of Genetics- Ajoy Paul
• DISCLAIMER:
• This presentation has been made to enrich open source of learning without any financial interest. The
presenter acknowledges Google for images and other open sources of information to develop this
PPT.