THE CELL

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The Cell Structure and FunctionBy Dr Muhammad
Muqeem Mangi MBBS, MPhil.
Physiology Associate Professor Suleman
Roshan Medical College Tando Adam
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OBECTIVES

• STUDENTS SHOULD LEARNT THE BASIC STRUCTURE AND
  FUCTIONS OF CELL BY OBSERVING THESE SLIDES
• AND ALSO UNDERSTAND THE BASIC FUNCTIONS OF CELL
  ORGANELLS
• STUDENTS CAN DISTINGUESH DIFFERENT STRUCTURE
  EASILY OF CELL
• THEY MAY UNDERSTAND THE BASIC CELL THEORY.
• AND LEARN THE DISEASES OF ORGANELLS

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Organization of the Cell

• The cells are basic building blocks of the body,
  forms tissues , organs , converting nutrients
  into energy and perform its functions , having
  hereditary code that controls coping of
  themselves and processes required substances by
  cell.
• There are 100 trillion cells in human being.
• That can survive for months or years.
• Provide appropriate nutrition's to its
  surrounding fluid.

The different substances that makes the cell are
collectively called Protoplasm

• Water 70 to 85
• Ions Na(ecf) 142 (icf) 10, Cl103-04,
  K04-140, Ca2.4-0.0001
• Proteins 10 to 20
• Lipids 02
• Carbohydrates 01
• icf extra cullular fluid icf
  intracellular fluid

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• The CELL THEORY All organisms are composed of one
  or more cells.
• Cells are the basic unit of structure and
  function in organisms.
• All cells come from other cells.

Robert Hooke -An English Mathematician
Physicist. Robert Hooke, in 1665 took a piece of
cork of Spanish Oak and prepared thin slices
which was then observed under a microscope. Honey
Comb structure was observed with a number of
box-live compartments, each having a pore
separated from others by diaphragms. He called
these compartments Cellulae (singular- cellula),
now known as Cells (Latin cella, meaning hollow
space or compartments). This is mentioned in his
book Micrographia, Chapter Observe XVII
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Cell Organells
Eukaryotic cells contain well cellular
organelles such as Nucleus Mitochondria Endoplasm
ic reticulum Golgi apparatus Peroxisomes lysosomes
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Plasma Membrane

• Also called cell membrane / plasma lemma / bio
  membrane.
• Quasifluid (acts partially like fluid and
  partially like solid), elastic, pliable
  film-like thin partitions over and inside
  cytoplasm.
• Average is 75 A (50-100A).
• Selectively permeable for solutes but semi
  permeable for water.
• Dynamic in nature. Any injured part of Membrane
  is repaired within no time.
• Appear trilaminar or tripartite under electron
  microscope.
• Composition-
• Lipids (20-79)
• Proteins (20-70)
• Carbohydrates (1-5)
• Water (20)

• Also called cell membrane / plasma lemma / bio
  membrane.
• Quasifluid (acts partially like fluid and
  partially like solid), elastic, pliable
  film-like thin partitions over and inside
  cytoplasm.
• Average is 75 A (50-100A).
• Selectively permeable for solutes but semi
  permeable for water.
• Dynamic in nature. Any injured part of Membrane
  is repaired within no time.
• Appear trilaminar or tripartite under electron
  microscope.
• Composition-
• Lipids (20-79)
• Proteins (20-70)
• Carbohydrates (1-5)
• Water (20)

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. Lipids

• Phosphoglycerides or phospholipids.
• Lipid molecules are amphiatic or amphipathic i.e
  they posses both hydrophilic non polar
  hydrophobic ends.
• Hydrophilic region is the head hydrophobic
  part contains 2 tails of fatty acids.
• Hydrophobic tail usually occur towards the
  centre of members resulting in formation of a
  lipid bilayer

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Proteins

• They can be fibrous or globular, structural,
  carrier, receptor or enzymatic.
• These also posses both polar non polar side
  chains.
• Polar hydrophilic linkages are towards outer
  side.
• Non polar hydrophobic linkages are either kept
  folded inside or used to established connections
  with hydrophobic part of lipids.

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Carbohydrates

• These are branched or unbranched
  oligosaccharides
• e.g.-hexose,fucose, hexoamine, sialic acid etc.

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FLUID MOSAIC MODEL

• The plasma membrane has 2 layers (a bilayer) of
  phospholipids (fats with phosphorus attached)
  which at body temperature is like vegetable oil.
• Membrane is not solid but Quasifluid.
• Protein molecules occur at places both inside (
  intrinsic, integral proteins) and on outer side
  of lipid bilayer (extrinsic, peripheral protein )
• Protein icebergs in a sea of lipids.
• Integral proteins pass into lipid bilayer
  establish hydrophobic bonds with lipid
  molecules. Some run through out the lipid bilayer
  called tunnel protein or transmembrane proteins.
• These tunnels from channels for passage of water
  and water soluble substance which passes
  selective properties for passage of different
  ions.
• Proteins are held by both polar and non-polar
  side chains

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FLUID MOSAIC MODEL

• The extrinsic proteins are located more so on
  cytosolic face than on external face ( e.g.
  spectrin)
• Extrinsic proteins are attached covalently to
  phospholipid head or non-covalently to
  transmembrane protein.
• Proteins provide structural functional specifici
  ty to
• membranes
• Proteins may shift laterally hence providing flexi
  bility dynamism to membrane.
• Proteins may function as enzymes, permeases,
  carriers.
• Some lipids extrinsic proteins present on outer
  side possess small carbohydrate molecule to form
  glycolipids glycoproteins. They constitute
  glycocalyx or cell coat.
• Conjugated oligosaccharides function as -
• Recognition centres.
• Sites of attachments.
• Antigens.
• Provide negative charge to outer surface.

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FLUID MOSAIC MODEL
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FUNCTIONS OF CELL MEMBRANE

• Compartmentalisation.
• Protection from injury
• Providing organic connections between adjacent
  cells (plasmodesmata gap junctions)
• Providing selective permeability barrier.
• Transporting solutes.
• Responding to external stimuli.
• Energy transduction.
• Secretory, excretory waste products thrown out
  by exocytosis.

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MITOCHONDRIA

• In electron micrographs of cells, mitochondria
  appears as rods, spheres or filamentous bodies.
• Size 0.5µm -1µm in diameter up to 7µm in
  length.

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Cont Mitochondria

• Mitochondria has got an inner membrane and an
  outer membrane. The space between these two is
  called intermembranous space.
• Inner membrane convolutes into cristae and this
  increases its surface area.
• Both the membranes have different appearance and
  biochemical functions

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Cont Mitochondria

• Inner membrane
• It surrounds the matrix.
• It contains components of electron transport
  system.
• It is impermeable to most ions including H, Na,
  ATP, GTP, CTP etc and to large molecules.
• For the transport special carriers are present
  e.g. adenine nucleotide carrier(ATP ADP
  transport).
• Complex II i.e. Succinate dehydrogenase .
• Complex V i.e. ATP synthase complex.

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Cont Mitochondria

• Outer membrane
• It is permeable to most ions and molecules which
  can move from the cytosol to intermembranous
  space.
• Matrix
• It is enclosed by the inner mitochondrial
  membrane.
• Contains enzymes of citric acid cycle.

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Cont Mitochondria

• Enzymes of ß-oxidation of fatty acids.
• Enzymes of amino acids oxidation.
• Some enzymes of urea and heme synthesis.
• NAD
• FAD
• ADP,Pi.
• Mitochondrial DNA.
• Mitochondrial cytochrome P450 system- it causes

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Cont Mitochondria

• Hydroxylation of cholesterol to steroid hormones
  (placenta, adrenal cortex, ovaries and testes)
• Bile acid synthesis (liver)
• Vitamin D formation( kidney).

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Cont Mitochondria

• Mitochondria plays a key role in aging-
• Cytochrome c component of ETC plays a main role
  in cell death and apoptosis.
• have a role in its own replication- they
  contain copies of circular DNA called
  mitochondrial DNA, this DNA have information for
  13 mitochondrial proteins and some RNAs.
• This is DNA inherited from mothers.

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Cont Mitochondria

• Most mitochondrial proteins are derived from
  genes in nuclear DNA.
• Mutation rate in mt DNA is 10 times more.
• Mitochondrial Diseases
• Fatal infantile mitochondrial myopathy and renal
  dysfunction
• MELAS(mitochondrial encephalopathy, lactic
  acidosis and stroke).
• Lebers hereditary optic neuropathy
• Alzheimers disease, Parkinsons ,
  Cardiomyopathies and diabetes.

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ENDOPLASMIC RETICULUM

• Discovered by Porter Thompson (1945).
• Its a 3-D, complicated inter connected
  system of membranelined channels running through
  cytoplasm, called Cisterns.(Flat interconnected
  sac-like).
• Smooth E.R. Ribosomes absent.
• Agranular E.R.

Ribosomes present. Granular E.R.

• Rough E.R.

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Rough Endoplasmic ReticulumRough Endoplasmic
Reticulum

• Rough Endoplasmic Reticulum
• These membranes enclose a lumen.
• In this lumen newly synthesized proteins are
  modified.
• Rough appearance is due to the presence of
  ribosomes attached on its cytosolic side(outer
  side).
• These ribosomes are involved in the biosynthesis
  of proteins.

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Rough and SmoothENDOPLASMIC RETICULUM
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CONTI(R) ENDOPLASMIC RETICULUM

• These proteins are either incorporated into the
  membranes or into the organelles.
• Special proteins are present that are called
  CHAPERONES. Theses proteins play a role in proper
  folding of proteins.
• Protein glycosylation also occurs in ER i.e. the
  carbohydrates are attached to the newly
  synthesized proteins.

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Smooth Endoplasmic Reticulum

• Smooth endoplasmic reticulum is involved in lipid
  synthesis.
• Cholesterol synthesis
• Steroid hormones synthesis.
• Detoxification of endogenous and exogenous
  substances.
• The enzyme system involved in detoxification is
  called Microsomal Cytochrome P450 monooxygenase
  system(xenobiotic metabolism).

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CONT (S) ENDOPLASMIC RETICULUM

• ER along with Golgi apparatus is involved in the
  synthesis of other organelles lysosomes
  Peroxisomes.

Elongation of fatty acids e.g. Palmitic acid 16
C- Stearic acid 18 C. Desaturation of fatty
acids. Omega oxidation of fatty acids.
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GOLGI COMPLEX (APPARATUS)

• Made up of smooth membrane saccules or cisternae,
  a
• network of tubules with vesicles and vacuoles.
• First seen by George in 1867 but named after
  Camillo Golgi who in 1898 recognized its
  reticular structure.
• Functions
• Secretion - All glandular cells depend upon Golgi
  complex for concentrating packaging their
  products inside a soluble protein coat.
• Formation of glycoproteins glycolipids.
• Formation of sialic acid and galactose.
• Fat transport.
• Mediation of hormones produced by endocrine
  glands.
• Formations of lysosomes secretory vesicles.

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LYSOSOMES

• Small vesicles bounded by a single membrane
  containing hydrolytic enzymes in form of minute
  crystalline or semi crystalline granules of 5-8
  nm.
• Are called suicide bags.
• Work in acidic pH (pH5)
• Formed by Golgi complex.

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CONT LYSOSOMES

• Intracellular Digestion - food obtained via
• phagocytosis is digested by Lysosomes.
• Extracellular digestion by release of enzymes via
  exocytosis.
• Defence- lysosomes of leucocytes devour foreign
  proteins, bacteria toxic substances.
• Autophagy- In metamorphosis of many animals,
  certain embryonic parts are digested for growth
  of other parts.
• Autolysis-
• Formation of Thyroxine- active hormone thyroxin
  in thyroid is formed through hydrolysis of
  thyroglobulin by lysosomes.

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CONT LYSOSOMES

• In some genetic disease individual lysosomal
  enzymes are missing and this lead to the
  accumulation of that particular substance.
• Such lysosomes gets enlarged and they interfere
  the normal function of the cell.
• Such diseases are called lysosomal storage
  diseases
• Most impt is I-cell disease.

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PEROXISOMES

• Called Peroxisomes because of their ability to
  produce or utilize H2O2.
• They are small, oval or spherical in shape.
• They have a fine network of tubules in their
  matrix.
• About 50 enzymes have been identified.
• number of enzymes fluctuates according to the
  function of the cells.

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CONT OF PEROXISOMES

• Xenobiotics leads to the proliferation of
  Peroxisomes in the liver.
• Have an important role in the breakdown of
  lipids, particularly long chain fatty acids.
• Synthesis of glycerolipids.
• Synthesis of glycerol ether lipids.
• Synthesis of isoprenoids.
• Synthesis of bile.

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CONT OF PEROXISOMES

• Oxidation of D- amino acids.
• Oxidation of Uric acid to allantoin (animals)
• Oxidation of Hydroxy acids which leads to the
  formation of H2O2.
• Contain catalase enzyme, which causes the
  breakdown of H2O2 .

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CONT OF PEROXISOMES

• Diseases associated
• Most important disease is Zellweger Syndrome.
  There is absence of functional peroxisomes. This
  leads to the accumulation of long chain fatty
  acids in the brain, decreased formation of
  plasmalogens, and defects of bile acid
  formation.

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NUCLEUS

• A specialized double membrane bound protoplasmic
  body containing all the genetic information for
  controlling cellular metabolism transmission
  to the posterity.
• Its the largest cell organelle.
• Found in the region of maximum metabolic
• activity. Commonly situated in the geometric
  centre of cell .
• Spherical or oval in shape.

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• Nuclear Envelope
• a.Nuclear Envelope-
• separates nucleus from cytoplasm.
• Made up of lipoprotein trilaminar membrane.
• Has pores or perforations which control passage
  of substances to inside or outside of
  nucleus.
• b.Nucleoplasm
• its transparent semifluid colloidal
• substances filling the nucleus.
• Contains nucleosides enzymes.
• c. Nuclear matrix
• A network of fine fibrils of acid proteins
  functioning as scaffold for chromatin.

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• d. Chromatin
• Hereditary DNA - protein fibrillar complex.
• e. Nucleolus -
• Naked, round or slightly irregular structure
  attached to chromatin at the NOR (nuclear
  organiser region).
• Has 4 components -
• Amorphous matrix.
• Granular portion (proteins RNA,21)
• Fibrillar portion (nucleonema)
• Chromatin portion.
• Principal site for development of ribosomal RNA.
• Stores nucleoproteins.

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CONT OF NUCLEUS

• I. Chromatin-
• Hereditary material.
• Bear genes.
• Contains genetic information required for growth
  development.
• Nucleus controls cell metabolism.
• Formation of ribosomes in nucleolus.
• Directs cell differentiation.
• Replication of nucleus essential for cell
  replication.

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• Chromosomes Rod shaped or thread-like condensed
  chromatin fibres which are hereditary vehicles
  as they store transmit coded hereditary
  information.
• There are 2 chromosome halves or chromatids
  attached to each other by CENTROMERE.
• Chromosomes are of 4 types (based on position of
  centromere) -
• Telocentric (centromere terminal at area of
  telomere)
• Acrocentric Centromere inner to telomere.
• Submetacentric Centromere submedian
• Metacentric Centromere median.
• Chromosomes contain a coiled filament called
• Chromonema.

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CONT OF CHROMOSOMES

• Contains genes. All hereditary information
  located in genes.
• Control synthesis of structural proteins thus
  helping in cell division cell growth.
• Control cellular differentiation.
• Can replicate themselves or produce their carbon
  copies for passage to daughter cells next
  generation.
• Produce nucleoli for synthesis of ribosomes.

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CONT OF CHROMOSOMES

• Form a link between offspring parents.
• Determine the sex of individual.
• By process of crossing over, they introduce
  variations.
• Mutations are produced due to change in gene
  Chemistry.

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CYTOSKELETON

• Extremely minute, fibrous tubular structures
  which form the structural frame-work inside
  cell.
• 3 main types of protein filaments-
• Microfilament.
• Intermediate filaments.
• Microtubules.
• Function-
• Maintain the integrity of cells.
• Cause Cyclosis.
• Responsible for change in plasma membrane during
  endocytosis exocytosis.

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• Ameboid Movement
• Mechanism of ameboid locomotion
• Control of movement
• Types of cells involved
• Cilia and Ciliary Movements

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REFERENCES

• R Orbans histology and embryology,11th
  edition.
• GUYTON and HALL 13th Edition
• Robbins and Cotrans Pathologic Basis of
  Disease, 8th edition.
• Santos A. Susin Daugas, E Ravagnan, L
  Samejima, K Zamzami, N Loeffler, M
  Costantini, P Ferri, KF et al. (2000).
• Two Distinct Pathways Leading to Nuclear
  Apoptosis". Journal of Experimental Medicine 192
  (4) 57180. doi10.1084/jem.192.4.571. PMC
  2193229. PMID 10952727

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• Thank

you