CELL
2010
What is a cell?
• “ Life is a dynamic equilibrium of hundreds and
thousands and millions of chemical and biochemical
reactions going on between non-living substances at
ionic and molecular level”.
-Panday S.N & Sinha B.K,Plant Physiology
Is the structural and functional unit of a living body.
History
• Term “Cell”- coined by Robert Hooke (1665).
• Nucleus – Robert Brown (1831).
• Mirbel (1819)-” plants are formed by a membranous cellular
tissue”.
• White Lamarck (1819)- “nobody can have life, if its
constituent parts are not cellular tissue or not formed by cell”.
• M.J Scheleiden and Theodore Schwann 91839)- propounded
cell theory- “ The cells are organisms; animals as well as
plants are aggregates of these organisms arranged in
accordance with definite laws”.
• Virchow (1855)- Omnis cellula-e-cellula, i.e., new
living cells arise only by reproduction of pre-existing
living cells.
• Von Mohl (1846)- protoplasm is the physical basis of
life.
• Purkinje (1840) introduced the term Protoplasm.
Cell Theory
1. All living things are composed of cells and their
products.
2. All cells arise from pre-existing cells.
3. All cells are basically alike in chemical composition
and metabolic activities.
4. The function of an organization as a whole is the
outcome of the activities and interactions of the
constituents cells.
Criticisms of cell theory
• Viruses do not fit in the definition of a cell and these are
therefore often described as living chemicals.
• Among other examples, coenocytic forms such as vaucheria
(alga) and Rhizopus (fungus) may also be found placed
outside the definition limit.
•
Their living substances are enclosed in a wall and there is
hardly any organization like that of a cell.
• It is therefore difficult to accommodate these kinds of units in
the context of cell theory.
Differences
Prokaryote
1. Cell is covered with
gelatinous sheath or
capsule
2. Lacks chloroplasts.
3. Lacks mitochondria.
4. Mesosome present.
5. Golgi bodies, ER,
lysosomes, vacuoles are
absent.
6. Cytoplasmic streaming is
absent
Eukaryote
1. Cell is not covered with a
sheath or capsule.
2. Chloroplast are present as
double membrane strs.
3. Present as double membrane
str.
4. Mesosome absent.
5. Present.
6. Cytoplasmic streaming is
often found.
• Nucleus, nuclear membrane
and nucleolus are absent
• Chromosomes of
prokaryotes are referred to a
genophores. DNA not
associated with protein.
• Present
• Ribosomes are of 70S type
• Ribosomes are of 80S type
• DNA is circular and double
stranded
• Muramic acid is present in
almost all prokaryotic cell
walls
• Chromosomes are made of
DNA and histone proteins
• DNA is spirally coiled,
helical and double stranded.
• Muramic acid is absent
PLANT CELL
Cell wall
Cell wall
• Is the non-living component of a cell and is secreted and
maintained by the living portion of the cell, called
protoplasm.
• Synthesis- controlled by golgi bodies.
•
1.
2.
3.
Typical cell wall is composed of three different regions:
Middle lamella
Primary cell wall
Secondary cell wall
1. Middle lamella:
• works as a cementing layer between the two daughter cells.
•
Consist of Ca and Mg pectate.
2. Primary wall:
• is the first layer of individual cell, synthesized by
protoplasm.
• Composed of hemcellulose 50%, cellulose- 25%, and smaller
amount of pectic substances, non-cellulosic polysaccharides,
fats and proteins.
3.
Secondary cell wall:
• formed next to primary wall towards the protoplasm.
• Mainly consist of cellulosic or varying mixture of
cellulose and non-cellulosic material.
• Gives structural independence to the cell and
provides rigidity to the wall.
Function:
1. Mechanical support, definite shape, protection to
cell & cellular content.
2. Being hydrophilic in nature- imbibing water & helps
in movement of water & solutes towards
protoplasm.
3. Molecular mechanism of auxins action through
proton extrusions
4. has adsorption sites for cation
5. Cutin and suberin deposition on the wall reduce the
rate of water loss through transpiration
Cell Membrane
Cell Membrane
• Outer most covering of the protoplast
• Living and differentially permeable membrane.
Chemical composition:
1. Proteins- 42%
2. Lipids – 32%
3. Carbohydrate – 6%
4. Water – 20%
Structure of cell membrane
Fluid Mosaic Model:
• Proposed by Singer & Nicholson (1972).
• Central bilipid layer is composed of phosplolipids, with their
spherical polar head group on the outer surface, form the basic
str. of a membrane.
• The two non-polar trails of each molecule point inwards.
• This arrangements forms a water resistant barrier through
which lipid soluble substance can pass through.
• They described the model as protein ice berg in a sea
of lipids.
• In fact, proteins are found in the form of discrete
particles which may either be embedded in the lipid
layer – integral protein or intrinsic protein .
• Superficially attached – peripheral or extrinsic
proteins.
Functions
1. Permeability barrier
2. Cytoskeleton- provide mechanical frame on which
enzymes can be superficially oriented.
3. Participate in biogenesis of cell wall
Chloroplasts
Plastids
• Schimper (1885)- derived from Greek word Plastikas.
• Discoid organelles about 5µm in diameter and 3 µm
in thickness
• Free cytoplasm in plant cell.
Three types:
1. Chromoplast- red, yellow and orange
2. Leucoplast
3. Chloroplast
Chloroplasts
• Chloroplast are plastids that contain the green pigment
chlorophyll
• along with other photosynthetic pigments.
• Chloroplasts perform photosynthesis.
• Chloroplasts are double membrane-bounded organelles
present in plant cells.
• In the stroma chloroplast DNA and ribosomes can be
found
Functions
1. Main site of photosynthesis in which both light and
dark reactions are found
2. Participates in photorespiration and a site of glycolic
acid production which functions as the substrate of
photorespiration.
3. Some amt. of protein synthesis takes place.
4. Carries out lipid metabolism to synthesis pigment
molecules
5. Has its own genetic system and self replicating
Peroxysomes
•
•
•
•
Isolated by Tolbert et al in 1968 from broken choloroplast.
Are microbodies and range from 0.5- 1µm in diameter.
Transitory Lifespan of 4-5 days.
Oval, single membraned str. enclosing dense homogenous
stroma.
• Associated with chloroplast or ER.
• Found in C3 and CAM plants.
• Peroxysomes originates from ER.
1. Site for photorespiration.
2. Contain enzymes catalase, urate oxidase etc.
3. Protective function – oxidises accumulated substance
hydrogen peroxide.
Central Vacuole
Vacuole
• Non-living reservoir and are enveloped by unit membrane str.
• The envelop of a vacuole- tonoplast
• Vacuole contains cell sap contains mineral salts, sugars,
organic acids and at times anthocyanin pigment.
• The various colour of petals are due to the presence of various
dissolved anthocyanin pigments present in vacuoles.
Function:
1. Cell metabolism
2. Storage compartment
3. Turgor pressure
4. Detoxification
5. Movement of gametes in spirogyra
Ribosomes
Ribosomes
• First observed by Robinson and Brown (1953) in plant cell &
Palade in animal cell.
• about 150-200 Å
• two types are recognized
1. 70 S in Prokaryotes
2. 70 S and 80 S in Eukaryote
• 70 S has (i) smaller unit 30S and (ii) larger unit 40 S
• 80S has ( i) smaller unit 40S and (ii) larger unit 60 S
Function:
• Protein synthesis
Nucleus
Nucleus
• First discovered by Robert brown in 1931 in orchid
cell
• More or less spherical embedded in cytoplasm.
• 5-10µm in diameter.
Consists of four different components:
1. Nuclear membrane/ nuclear envelop
2. Karyolymph / nucleoplasm
3. Chromatin
4. Nucleolus
Functions
1. It contains the genetic information in its chromatin
for reproduction, development, metabolism as well
as behavior of organisms.
2. Controls all cellular activities in the cell.
3. Nucleolus takes part in the production of ribosome.
Endoplasmic Reticulum (ER)
Endoplasmic Reticulum (ER)
• The ER is a membrane bounded organelle.
• The smooth and rough regions of the ER are
interconnected.
Smooth ER.
• lacks ribosomes.
• It is a network of pipe-like interconnected tubes.
Functions of the SER
• include synthesis of lipids, processing of sugars, and
detoxification of drugs and poisons.
Rough ER
• has bound ribosomes attached to the outside.
• The RERis in fact an extension of the outer
nuclear membrane.
Functions:
• RER include anchorage of newly synthesize
proteins, and the finishing of proteins
Golgi Apparatus
Golgi Apparatus
• The Golgi Apparatus is a single membrane-bounded organelle
constituted of piled sac-like cisternae.
• Both animal and plant cells have Golgi Apparatus
Functions:
1. To finally process the immature enzymes into functional
forms and to secrete them in a closed vesicle. Thus , secretion
is the main functions of the golgi complex.
1. Participates in the transfer of glyco proteins.
3. Participates in cell plate formations by releasing
vesicles which actively organize cell plate
orientation with the help of phragmoplasts (
microtubules).
4. Plays roles in giving rise to the primary
lysosomes.
5. Suppose play role in regulation of fluid balance.
6. Believe to play role in phospholipids synthesis
and lipid absorption
Lysosomes
lysosomes
• Named in 1955 by Christain de Duve on the basis of composition.
• Contain about 50 hydrolytic enzymes & as a matter of fact these are
the lytic bodies functioning as suicidal bags.
• Structurally, polymorphic, sub-microscopic bodies ranging in size
from 0.4 – 0.8 microns.
• Has a single limiting membrane composed of lipoprotein, densely
granulated stroma and a large vacuole.
• Chemically a lysosome is a bag filled with acid hydrolases
functioning at acid pH.
Functions:
Intracellular digestion:
• digestion of particles that are taken into the cell by
phagocytosis.
Autophagy:
• begin to digest the other cell inclusions such as
mitochondria and ER.
• A process of obtaining the needful energy by making
use of these constituents as a source.
Ageing:
1. produce autolytic enzymes, that slowly disrupt the delicate
intracellular machines.
2. Produce some biproduct that clog the gears of metabolic
machinery.
3. They may digest some functional elements and then produce
insoluble residues.
Autolysis:
1. removing of dead or degenerating cells.
2. During the process, the lysosomes membrane ruptures and
3. enzymes are set free to digest the dead cells and to get rid of the
cell debris- Autolysis.
Seedlings:
1. in seedling, they are involved in the hydrolysis and removal of
protein and starch during germination.
Mitochondria
Mitochondria
• Named by C. Benda in 1897.
• Derived from Greek word Mitos- filaments and
chondros – granules.
• Shape variable.
• Occasionally influenced by environment and
physiological conditions.
• However, they may be granular, club-shaped, tennisracket shaped, vesicular or rod-shaped.
• Size also varies.
• Rod shaped are 0.5µ to 2µ but may attain a maximum
length of 7µ.
Outer membrane:
• smooth and contains about 40% lipid content with lipid/protein
ratio of 0.8
• proteins are of intrinsic type which appears to have channels
for passage of solutes. Such proteins are called porins.
Inner membrane:
• Show complex infoldings called mitochondrial crest or cristae.
• On its inner surface towards matrix are found F1 particles (
oxysomes)
Matrix:
• Contains RNA, DNA, ribosomes and enzymes involved in
nucleic acid metabolism and protein synthesis.
Functions of mitochondria
• Major part of ATP is synthesized in mitochondria by
oxidation of food stuffs.
• Provide raw materials for synthesis of chlorophyll.
Cytochrome, pyrimidine, alkaloid and steroids.
• Site for amino acid and fatty acid synthesis.
Task
Differentiate between the following:
1. 70S and 80S ribosome.
2. Mitochondrial DNA and nuclear DNA.
3. Plant cell and animal cell