Download Ribosomes translate the genetic message from mRNA that

The cell
Histology
Is the microanatomy of the cell and tissues, using different
histological methods of staining guided by LM and TEM
Cytology = is the study of the cell structure and function
Every cell consists of protoplasm surrounded by cell
membrane
The mass of the protoplasm is divided into two components:
o Cytoplasm which lies between the cell membrane and
nuclear membrane, it constitutes the main bulk of
protoplasm
o The nucleoplasm which fills the nucleus.
These plasms are colloid or (Semi fluid) and fluctuate between gel
and sol conditions.
Cytoplasm is not stationary. It is a state of flux i.e. organelles can
work quite and in autonomous manner as well as actual
movement of water and ions.
Cells divide into two major compartments
o Cytoplasm
o Nucleus
Suspended within the cytoplasm - organelles
- Inclusions
Organelles
They are specialized parts of living substance and probably
Always present
They are divided into membranous and non-membranous
Organelles
The cytoplasmic ground substance was called cytosol
now called cytoplasmic matrix.
Copyright@ 2003 pearson Education. Inc., publishing as Benjamin Cumming
Membranous organelles
That is surrounded by membrane:
 Plasma membrane.
 Mitochondria
 Endoplasmic reticulum
 sER
 Golgi apparatus
 Lysosomes
 Endosomes
 Peroxisomes
 rER
Non membranous organelles include:
 Microtubules
These form the cytoskeleton of the
Cell = (Cytoplasmic support)
NB
 Filaments
 Centrioles
 Ribosomes
Some references refer to ribosomes as membranous organelles
Inclusions: They are materials often of a temporary nature and
present under special conditions.
(1) Membranous organelles
Plasma membrane: Cell membrane = plasma lemma
It participates in many physiological and biochemical
activities essential to cell survival and function.
LM: It is not visible
EM: It displays a characteristic trilaminar appearance that
has been described as a unit membrane. Trilaminar i.e.
two electron dense lines (inner & outer) and a clear or
lucent single line in between (intermediate)
Diameter: 7 – 8 nm
Molecular composition: It mainly consists of lipid and
protein.
Lipid: Consists of a bimolecular leaflet of phospholipids
which is the back bone of the cell membrane
The fatty acid chains in the phospholipids facing each
other with their hydrophilic heads directed to the exterior
and their hydrophobic tails directed to interior surface.
The Cell Membrane
The Cell Membrane
(Schematic view of the neuronal cell membrane)
(The Eaton T. Fores Research Center)
Protein molecules
Fluid mosaic model like iceberg float in a sea of phospholipids, it
constitute about 60 – 70% of membrane mass. It is described
within lipid by two ways:
(1) Integral protein = contain hydrophobic + hydrophilic
regions are inscribed into the lipid bilayer and extend
completely or partially.
They attach firmly to the phospholipids only drastic measure
as using of detergent can release them.
(2) Peripheral protein = are external to lipid bilayer.
They are attached to the head by week bonds which easily
break by changing PH
Function:
 Participate in enzymatic activities.
 Maintain ionic conc. across to the opposite sides of
the membrane.
 Receptor protein recognizes the binding of substances
(important in hormones, antibody reaction).
For reading only
According to their function, there are six categories of
Proteins (e.g. pumps channels, Receptor, transducer carrier,
structural)
Read about: cell signaling.
Cholesterol:
Intracellular membrane
less cholesterol
It is associated with fatty acid tails and changes
their molecular nature i.e. fatty + cholesterol
acid determines whether the lipid tail is
crystalline or loose (fluid).
more cholesterol present, the more fluid (loose)
the membrane will be.
Carbohydrate: (glycocalyx = cell coat)
It is linked either to protein or lipid and present
in the extra cellular surface.
Link to protein
glycoprotein
Link to lipid
glycolipid
These surface molecules constitute a layer at the surface of the
cell called cell coat or glycocalyx.
Function
 Act as cell recognition and cell adhesion.
 Protect the cell against chemical injury.
 Act as specific receptor sites for incoming stimuli such as
hormones.
Reading sector
- (Read about theory of cancer and graft rejection)
Homework: Function of cell membrane (read it !)
1- Selective barrier
2- Exchange of materials between in + outside the
cells.
3- Conduct impulse such as nerve cells.
4- Cell recognition + adhesion.
5- Receptor sites are selective to stimuli.
Endocytosis, phagocytosis, pinocytosis, receptor mediated
Endocytosis, exocytose.
(2) Mitochondria
It is a membrane limited organelle.
They act as the chief source of energy in the cell.
Structure
They differ in their numbers and shapes.
Under phase contrast microscope: they appear like
threads that are about 0.2M and several micrometers in
length.
They can divide by binary division i.e. self replicated;
because they contain DNA loops, particles resemble
ribosomes and RNA molecules; therefore, they can also
synthesis their own protein.
EM: Mitochondria consist of a smooth outer membrane and
highly folded inner membrane convolutes into cristae that
project into the matrix.
The space between the two membranes is called outer
compartment.
Matrix is the inner compartment.
Mitochondria
The inner surface of the cristae that faces the inner
compartment possesses elementary particles. Each
consists of a head projects into the matrix and a stalk that
attaches to the inner membrane.
Matrix contains mitochondrial granules, DNA loops and
RNA particles.
Function
 It is the energy source of the cell utilizing pyruvate
and generates ATP by the process of oxidative
phosphorylation.
They are found in large amount in muscle
 Matrix granules
contain enzymes of kreb's
cycle
 Respiratory chain enzymes are in the inner
mitochondrial membrane
 Elementary particles contain the enzyme of the
electron transport system and AT pase
enzyme.
 They control the conc. of certain ions especially
ca++ and release it into the cytoplasm when
needed.
(3) Endoplasmic reticulum
 They are branching network of tubules
 There are two types: rough (rER) and smooth
(sER).
Smooth endoplasmic reticulum (sER)
Structure:
They consist of a complex system of anastomosing
short tubules that are associated with ribosome's.
LM: cells, which are rich in sER, have a distinct acidophilia
Function: It has a despair function in different cells.
FOR EXAMPLE
o SER is very well developed in cells that synthesize and
secrete steroid hormone, a precursor of steriodogenesis
(cholesterol) is stored in SER.
Site: sex organs (testicular interstitial cells) and adrenal
cortical cell.
o Striated muscle (skeletal + cardiac muscle) possesses
highly developed system of SER called sarcoplasmic
reticulum.
Ribosomes and rough endoplasmic reticulum
It helps in uptake and releasing of ca++ ions
which are essential in contractile process of the
muscle.
o sER of the liver hepatocyte contain enzymes that are
responsible for detoxification of lipid soluble chemicals
e.g hydroxylated enzymes.
sER may involve in lipid absorption.
Ribosomes and rough endoplasmic reticulum
They are abundant in the cells that produce protein for
secretion.
LM: the cells rich in rER and ribosomes stain intensely with
basic dye (basophilic cells)
TEM: rER appears as a serious of branching and interconnecting
Membrane limited flattened sacs or saccules that called
cisternae.
- Cisternae are closely packed in parallel rays.
- The outer membranes of these cisternae facing
cytoplasm are studded with granules called
ribosomes.
- Saccule of rER usually continues with the outer
nuclear membrane.
(4) Ribosomes
 They are granules that consist of two subunits
which are large and small subunits with different
sedimentation coefficient.
 They attach to the rER by their large subunit and contain
RNA and protein.
 They present in either free or attached form.
 The free ribosomes circulate in the cytoplasm.
 There are two types of the attached ribosomes:
1- Ribosomes attached to his side of rER that face
the cytoplasm.
2- Polysomes or polyribosomes: Several
ribosomes attached to a thread of RNA.
Function
 RER responsible for protein for destination (secreted
outside the cells) and cell membrane integrity.
 Free ribosomes are responsible for protein synthesis that
is used inside the cell.
TEM: Transmission electron microscope
Ribosomes translate the genetic message from mRNA that
Determine the sequence of amino acids for particular
protein.
These proteins will be elaborated immediately to the 14 men
of rER.
RER give off buds of ribosome free vesicle (transfer vesicle),
so the protein has been segrated by those vesicles more to
ward the immature surface of golgi saccule.
Golgi apparatus
It is discovered by Golgi in 1898.
It is usually located between rER and plasma lemma.
LM: - The position f golgi complex appears (using H&E)
unstained area near the nucleus while the whole
cytoplasm is stained (Basophilic).
This is called negative golgi image.
- By silver or lead or osmium staining, golgi complex
appears as fibril or granular network. These network
appear as brownish or black network supranuclear in
position.
Site: Highly present in cell secret protein e.g. acinar cells of
Pancreas and epidemics.
EM: Golgi is membrane bounded organelles formed of a stack
of:
-Parallel flattened cisternae with smooth surface membrane.
They associated with vesicles. Each cisternae has two
sides or faces. They are composed of:
a- Cisternae or saccules:
A, 1- Cis – Golgi or forming face (convex side) facing rER
A, 2- Trans – Golgi or maturing face ( concave side) that
face the plasmalemma.
b- Transport vesile: carry newly formed protein from rER.
c- Condensing vacuoles: that pinch out from the trans-face
containing protein ready for secretion.
Function
 Golgi apparatus concern with secretory activity of the
cell and processing the secretory product in one or
more of the following ways:
1- Glycosylation and sulfation of glycoproteins
and glycolipid.
2- Proteolytic processing of presecretory protein.
3- Concentration, packaging and sorting of the
secretory product into membrane secretory
vesicles.
4- Membrane biogenesis though the process of
fading of secretory vesicles.
Protein synthesis
The formed protein polypeptide chain in rER will be segregated
and transfer toward the Golgi complex through transfer vesicle
then fuse with membrane, subsequently release to the lumen and
pass through cisternae toward the mature face (trans – Golgi).
Within Golgi carbohydrate is added
(glycosylation)
glycoprotein or sulpha group is added
protoglycan is formed.
- The enzymes responsible for these processes are
found in the membrane of Golgi saccule.
- Then the protein will be secreted by condensing
vacuole which a bud from the dilated rim by transface vacuole.
- In the vacuole will be concentrated and vacuoles
become smaller and called secretory vesicles.
- It will pass to toward the plasmalema, fuse within it
and release its content to outside.
Two types of protein could be release for golgi:
1- Lysosomal enzyme
2- Protein for secretion
Perixosomes: Microbodies
They are small membrane limited spherical (0.5Mn)
bodies that contain oxidative enzymes involve in
hydrogen peroxidase metabolism.
They contain catalase and other peroxidase that break
down hydrogen peroxide. (H2O2), (toxic substance).
They are present almost in most of the cells but they are
numerous in liver and kidney cells.
The number of peroxisomes present in the cells
increases in response to diet, drugs and hormonal
stimulation.
Endosomes = They are product of phagocytosis.
Lysosomes
LM: They are of visible membrane bounded
vacuoles 0.2 – 0.5Mn
EM:
They have heterogeneous morphology
They contain hydrolytic enzymes responsible for
digestion of intra or extra cellular substance
They present in almost all cells except erythrocyte.
Types
a- Primary lysosomes: these are lysosomes that recently
formed from Golgi apparatus and doesn't contain digested
material
b- Secondary lysosome: when primary lysosome fuses with
membrane of structure that contains the material to be
digested and release their enzyme. They either called
phagosomes or digestive vacuoles or autophagic vacuoles
depending on (the intra- or extra-cellular) material to be
digested.
Example of phagosome = any bacteria e.g of autophagic
vacuole = old mitochondria.
If secondary lysosome (phagosome)
digests its content
residual body will be formed
exocytosis to expel the digested
material.
Pinocytotic vesicle when fuse with lysosome, it is called
multivesicular body.
In nerve and cardiac cells there are accumulation of residunal
body (can’t be expelled outside the cell) to form lipofucsin
granules or age pigment a golden brown pigment. It is a normal
feature of aging.
Diagram of the basic architecture of a cell. Note the location of the
Rough Endoplasmic Reticulum and the Golgi apparatus within the cell.
Taken from: Junqueira and Carneiro, Basic Histology, Text and Atlas,
page 42, Figure 2-27.
Molecular Biology of the Cell (Hardcover)
Secondary lysosome (red arrow) and peroxisomes with lamellar nucleoids (blue
arrows) in the pyramidal cell. N - nucleus. Scale = 400 nm. (Rat, hippocampus.)
Atlas of Ultrastructural Neurocytology (Josef Spacek)
Reading section
Lysosomal storage disease = where accumulation of residual
bodies in the cells result in interference with normal function of the
cells, .g. Tay sachs disease (nervous tissue).
Mucopolysaccarydosis.
Cytoskeleton
They are interna cytoplasmic support system that maintains
control of the cell shape.
It is mainly include:
1- Microtubules.
2- Thick filaments.
3- Intermediate filaments.
4- Thin filament microfilaments.
Microtubules
They can’t be seen by LM unless if they are present in thick
bundles.
They are non-branching – hollow cylinders that measure
20 – 25nm in
Diameter they are composed of tubulin diamers.
They are labile structure that can change by polymerization
and depolymerization.
Microtubules found in most of the cells but particularly:
1- Axonema of cilia, flagella.
2- Basal bodies of cilia
3- Mitotic spindle.
4- Centrioles from which spindle fibers radiate.
5- Growing axons
6- Cytoplasm in general.
Microtubules involved in numerous essential cellular activity that
relate to cytoskeletal function including:
1. Cell elongation and movement (migration).
2. Intracellular transport of secretary granules.
3. Movement of chromosomes during mitosis and meiosis.
4. Maintenance of cell shape.
5. Beating of cilia and flagella.
Cytoskeleton
Microtubules
Microtubules with dark centers (arrow) in a small dendrite. Scale = 100 nm. (Mouse,
cerebellar cortex.) (Atlas of Ultrastructural Neurocytology - Josef Spacek)
Filaments
They are as following:
1- The microfilament
Actin = thin filaments – in all cell types on plasma membrane
Myosin = thick filaments in muscle cell
Tropomyosin these all responsible for muscle contraction,
spectrin (in RBC).
Myofilaments
microfilaments
have role in wound
healing.
2- Intermediate filaments
1. tono filaments in epithelial cells.
2. Neurofilaments in nerve cells.
3. Glial filaments in glial cells.
4. Desmin filaments in muscle cells.
5. Vementin filaments in mesenchymal cells
Cell membrane specialization
Apical
microvilli, cilia cell coat (gylocalyx)
Lateral
junctional complex gap junction (nexus)
Basal
basement membrane
Hemidesmosomes
Centrioles:
 Usually occur in pairs each called centrosomes
 In non-dividing cell are present near the nucleus.
 They consist of nine triplets microtubules.
 The centriole and unknown materials surrounding it could
be microtubules forming
microtubules organizing
center
 It has important role in cell division and microtubules
production.
Microvilli:
Are projections of plasmalemma.
 Present in certain epithelial calls for absorption
 They contain thin filament (actin) which are the
structure core of microvilli at the apex they attach to a
dense area dense lip at the base embedded the actin
filament in to terminal web which also contain myosin.
These microfilament responsible for the movement of microvilli
e.g. brush border of small intestine .
Cilia
 Are invagination or finger like projection of cell membrane
found only on free surface of cell that lining lumens or
cavities.
 They facilitate movements of fluid e.g. R.S
 Each cilium has basal body, shaft and rootless
Basal body is identical to structure of centriole and it is the
center of production of cilia.
 It is composed of two central (pair) microtubules
surrounded by nine microtubules doublets.
 A radial spoke radiates from each doublet to the central
pair of microtubules.
 Each doublet has two short arms attach to adjacent
doublet they are formed from dynein that possess ATpase
activity the hydrolysis of ATP give the energy to generate
the cilia beating movement of flagella similar the cilia and
present in the tails of the sperm.
The nucleus
 It is the storage of genetic information in DNA
 In non-dividing cell called interphase.
 It is composed of nuclear envelope nucleoplasm
chromatin and nucleolus.
 It has affinity to basic dyes to it its rich content of
DNA.
 Usually spherical or ovoid.
Nuclear membrane
 It separates the nucleus from the cytoplasm

It has 3 structure:
a- Inner nuclear – usually fibrous (adjacent
chromatin)
outer nuclear usually rough
b- Nuclear pore complexes.
c- Nuclear lamina.
Inner + outer membrane separated by a space called
perinuclear cisternae which is continuous with lumen of
rER.
Chromatin
 Consisting of strands of DNA and its associated
protein.
 It is responsible for characteristic basophilia of the
nucleus.
 They are not homogenous structure.
- Highly condensed chromatin =
Heterochromatin which are predominate in less
active cell deeply stained.
- Extended (highly stained) or dispersed euchromatin
in high active cell.
Heterochromatin present in the location of
 Marginal – re – inner nuclear membrane
 Karyosome irregular bodies
 Nucleolar associated chromatin in association with nucleus
dead cell = nucleus usually shrunked integral and densely
shrind all chromatin is heterochromatin pyknotic cell.
Nucleolus = is non membranous intra nuclear structure.
In LM: most cells have one or more nucleoli they are ovoid in
shape and stain with basic dye.
It is responsible for ribosomal RNA synthesis.
In EM = it consist of 2 pairs
1- Pars granulose = nucleolonema = transcribed ribosomes.
2- Pars fibrosa (fibrillar).
Inclusions
Pigment
 Melanin in melanocytes in the iris of the eyes
 Golden brown pigment = lipofuscin.
 Haemosidrin = hemoglobin of aged RBC has been with
age escaped to circulation + phagocytosed.
Lipid
Usually lipid droplets dissolve in preparation of tissue for LM
and appears as round holes under LM.
In EM = Appear black + spherical
Glycogen = it can be demonstrated by periodic acid Schiff
reaction appear as magentacolour.
In EM = 2 particles identified:
1- α free part
2- β rosette
Cell junction
That bind cell to one another to form tissues.
1- Tight junction = zona occludens = built desmosome
A minute or thread like constituent of plasmalemma crosses
around the contiguous layer.
EM: 2 membranes appear sealed
Gap junction = nexus: allow ions and very small molecular
Weight substances to pass 2nm space between
the adjacent plasmalemma in between them.
the nucleus takes up nearly 10% of the volume of the cell.
Microsoft Encarta Picture
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