Upload
taw-alzu
View
280
Download
6
Tags:
Embed Size (px)
DESCRIPTION
Â
Citation preview
CYTOLOGYBY
Dr. TAREK ATIA
Histology and Cell Biology
Course of Histology
- Cytology: Cell, Nucleus, DNA, and
Chromosomes.
- Tissues: 4 basic tissues including;
Epithelium, Connective (Cartilage, Bone,
Blood), Muscular, and Nervous tissues.
- Body systems and different Organs.
Cytology
- Any cell consists of two main compartments:
- The Nucleus and the Cytoplasm.
- The cytoplasm; includes membranous and
non-membranous organelles.
- Membranous organelles such as; Cell
membrane, RER, SER, Golgi, Lysosomes,
Endosomes, Mitochondria,…….
- Non-membranous organelles such as,
Ribosomes, Centrioles, Microtubules,
Glycogen inclusions,,…..
Cell membrane
- Maintain the structural integrity of the cell.
- Control movement of substances in and out
the cell.
- Regulate cell – cell interaction.
- Act as interface between the cytoplasm and
the external environment.
Recognition via receptors, antigens,…. -
Cell membrane
- Cell membrane is not visible by the light
microscope, seen only by E/M.
- It is 7.5nm thick, and appears as a
trilaminar structure of two thin, dense
lines, and a light line in between.
-The entire structure is called a
unit membrane.
Cell membrane
- The inner cytoplasmic dense line is its
inner leaflet, and its outer dense line
is the outer leaflet.
- Each leaflet is composed of a single
layer of phospholipids and associated
proteins.
- Each phospholipid molecule is composed
of a polar hydrophilic head (at the
surface) and two long non-polar
hydrophobic fatty acyl tail (toward the
center).
- The polar head is composed of glycerol,
to which other molecules are attached.
- The protein components of the cell
membrane either span the entire lipid
bilayer (integral proteins) or attached to
the cytoplasmic aspect of the lipid bilayer
(peripheral proteins).
- The integral or trans-membrane
proteins form channels proteins (ion
channels) and carrier proteins that
facilitate passage of specific ions and
molecules across the cell membrane.
P-Face
E-Face
Membrane transport protein
- The hydrophobic components of the
plasma membrane limit or prevent
movement of polar molecules across it.
- The presence and activity of trans
membrane proteins will facilitate the
transfer of these hydrophilic molecules
across this barrier.
-These transmembrane proteins form :
- Channel proteins:
- Carrier proteins:
Membrane transport protein
Function of cell membrane
1- It maintains and preserves the integrity of the
cell.
2- It permits the movement of substances in and
out the cell by:-
A- Passive diffusion of simple substances as
water and some ions.
B- Facilitated diffusion: some substances as
glucose and amino acids can pass through it
with the help of carrier, but not need energy.
C- Active transport: some substances can pass
through it against diffusion gradient, and
required energy.
D- Selective transport: depends on the presence
of receptors on the surface of cell
membrane to select and determine the
substances to enter the cell.
3- Phagocytosis
4- Pinocytosis
5- Exocytosis
6- Regulate the cell to cell interaction by special
type of cell junctions.
Endocytosis
The process by which a cell ingests
macromolecule, particulate matter,
and other substances from the
extra-cellular space is referred as:
ENDOCYTOSIS.
- Then, endocytosed material is engulfed in a
vesicle.
- If the vesicle is large (>250 nm in diameter): the
method is called phagocytosis (cell eating), and
a vesicle is called a phagosome.
- If the vesicle is small (<150 nm in diameter): the
method is called pinocytosis (cell drinking),
and a vesicle is called a pinocytotic vesicle.
- Phagocytosis; the process of engulfing large
particles, or even cells by phagocytic cells
such as monocytes, neutrophils,
macrophages.
- Membrane trafficking; the cycle of
membrane shuffling during exocytosis
and endocytosis (membrane recycling).
Receptors mediated endocytosis
- Many cells specialize in pinocytosis of
specific macro- or micro-molecules.
- The most efficient form of capturing these
substances depends on the presence of
receptors proteins (cargo protein) in the
cell membrane.
Cargo proteins are
trans-membrane
proteins associated
with a particular
macro-molecules
(ligand) extracellulary,
and with a clathrin
coat intracellular.
Mitochondria
- They are flexible, rod-shape organelles;
with diameter of 0.5 girth and ~7.0μ
length.
- Their number are variable in human cells;
e.g. they are abundant in hepatocytes
(~2000) and muscles.
- Mitochondria are self replicating and
possess their own DNA, and perform
oxidative phosphorylation and lipid
synthesis. -
Mitochondria considered as
the power house of the
cell.
They also control calcium level within the
cytoplasm.
- Each mitochondrion possesses an smooth
outer membrane and folded inner
membrane (Cristae) with a narrow
space (10 – 20nm) between them is called
inter-membrane space.
-The space enclosing cristae is called inter-
crystals space or matrix space.
- Cristae increase the surface area of the
inner membrane for ATP synthase
and the respiratory chain; and also
their number are related directly to
the energy requirement of the cell.
- The outer mitochondrial membrane
possesses a large number of porins
(Multipass trans-membrane proteins).
- Porins form large aqueous channels
through which water soluble
molecules can pass.
- The outer membrane is relatively
permeable to small molecules, so the
contents of the inter-membrane space
resemble the cytosol.
- Other proteins located on the outer
membrane are responsible for the
formation of mitochondrial lipids.
- The inner mitochondrial membrane is
richly endowed with phospholipids
(Cardiolipin) that makes it permeable
to ions, electrons and protons.
- In certain regions, the outer and the inner
membranes contact each other; the contact
site (composed of carrier protein) acts as
channels for proteins and small molecules
to enter or leave the matrix space.
- The inner and outer membranes possess
receptor molecules that recognize the
transported macromolecules and the
cytosolic carrier molecules and
chaperones responsible for their delivery.
- The inner membrane display a large
number of protein complexes such as ATP
synthase and Respiratory chains, so
mitochondria can be regarded as the
power house of the cell .
- Each respiratory chain composed of three
respiratory enzymes : NADH
dehydrogenase, Cytochrome b-c1 and
Cytochrome oxidase complexes.
- These enzyme complexes form electron
transport chains that are responsible for
passage of electrons along this chain and act
as proton pumps that transport H+ from
the matrix into the inter-membrane space
that provide energy for ATP-generating
action of ATP synthase.
- The matrix space is filled with dense
composed of 50% protein, mainly
enzymes responsible for degradation of
fatty acids and pyruvate to the
metabolic intermediate acetyl CoA and
the subsequent oxidation of this
intermediate in the tricarboxylic acid
(Krebs) cycle.
- The matrix space contain also
mitochondrial ribosomes, mRNA,
tRNA, and dense spherical matrix
granules.
- Moreover, matrix contain the double-
stranded circular DNA (cDNA) and
enzymes necessary for expression of
the mitochondrial genome.
- The mitochondrial cDNA contains
information for the formation of only
13 mitochondrial proteins, 16S and
12S rRNA, genes for 22 tRNAs.
- Therefore, most encodes necessary for
the formation and functioning of
mitochondria are located in the
nuclear genome.
Protein Synthetic and Packaging
Machinery of the Cell
The protein synthetic machinery of the
cell composed of:-
Ribosomes, and polyribosomes
Endoplasmic reticulum
Golgi apparatus
Ribosomes
- They are small (12nm wide and 25nm
long), non-membranous particles
composed of protein and ribosomal
RNA.
- Each ribosome is composed of large
subunit and small subunit.
- They are assembled in the nucleolus
and released in the cytoplasm as
separate entities.
- Small subunit is composed of 33
proteins and 18S rRNA, but the large
subunit is composed of 49 proteins
and 3 rRNA.
- The small subunit has a site for binding
mRNA, a P-site to bind to peptidyl
tRNA, and an A-site for binding
aminoacyl tRNAs.
- The small and large subunits are present
in the cytoplasm individually, and do not
form ribosomes until protein synthesis
begins.
Rough endoplasmic reticulum and Polyribosomes
Endoplasmic Reticulum (ER)
- It is the largest membranous system in the
cell.
- It is a system of interconnection tubules
and vesicles whose lumen is referred as
cistern.
- ER has 2 types; smooth and rough ER.
- Their Functions are:-
- Manufacture of all membranes of the
cell.
- Protein synthesis and modification.
- Lipid and steroid synthesis.
- Detoxification of certain toxic
compounds.
Smooth Endoplasmic Reticulum (SER)
- SER is a system of anatomising tubules
and flattened membrane-bound
vesicles.
- The lumen of SER is assumed to be
continuous with that of RER.
- They are abundant in cells that active
in synthesis of steroids, cholesterol,
triglycerides, and also in cells that
are functioning in detoxification.
- Their surface is not attached to
ribosomes, and so, it is called smooth.
Rough Endoplasmic Reticulum (RER)
- Their membranes possess integral proteins
that function in recognizing and binding
ribosomes to their surfaces and maintain
their flattened shape.
- RER participates in the synthesis of all
proteins that are packaged and delivered
to the plasma membrane.
- RER performs post-translational
modification of these proteins.
- RER also manufactures lipid and
integral proteins of the cell membrane.
The cisterna of
RER are
continuous with
the peri-nuclear
cisterna (the
space between
the inner and the
outer nuclear
membrane).
Golgi complex
- Proteins manufactured in the RER go to Goli
apparatus for post-translational modification
and packaging.
- Golgi is composed of one or more series of
flattened, slightly curved membrane-bound
cisternae.
- Each Golgi stack has three levels of
cisternae:- the cis-face, the medial-face,
and the trans-face, and then smooth or
coated vesicles.
- The cis-face is convex in shape and present
closes to the RER.
- The newly formed proteins from RER inter
first to the cis-face.
- The trans-face is concave in shape and
is located at the distal part of the
Golgi apparatus, where the modified
proteins is ready to be packaged and
transport.
There are another two compartments, one
associated with the cis-face and the other with
trans-face:
- The endoplasmic reticulum/Golgi intermediate
compartment (ERGIC), which is known as
tubulo-vesicular complex: located between
RER and cis-face Golgi.
- The trans-Golgi network (TGN): located at the
distal side of Golgi apparatus.
Lysosomes
- Lysosomes are small rounded or
polymorphic in shape, with a diameter of
0.3 – 0.8μ.
- Lysosomes have an acidic pH, and contain
hydrolytic enzymes (~ 40 different types
of acid hydrolases).
- Lysosomal membranes contain proton
pumps that transport H+ ions into the
lysosomes to maintain its luminal pH at
5.0.
- Lysosomes help in digesting
macromolecules, phagocytosed micro-
organisms, cellular debris, cells, and
senescent organelles such as
mitochondria & RER.
- Lysosomes receive their hydrolytic
enzymes and membranes from the
Trans-Golgi Network that arrive in
different clathrin coated vesicles.
- The vesicles loss their clathrin coat shortly
after formation, and fused with late
endosomes.
Substances subjected for degradation within
lysosomes pass through 3 ways:-
1 - Phagosomes either join lysosomes or late
endosomes. The hydrolytic enzymes digest
most the contents of phagosomes except
lipid which resist complete digestion and
changed into residual body.
2 - Pinocytotic vesicles.
3 - Autophagosomes: Organelles that no
longer required by the cell become
surrounded by elements of SER, and
then enclosed in vesicles called
autophagosomes.
Endosomes
- Endosomes are divided into early and late
compartments:
- Early endosomes are situated near the
periphery of the cell.
- Late endosomes are situated deeper in the
cytoplasm.
Peroxisomes
- They are small (0.2 – 1.0 μ) spherical or ovoid
membranous organelles that present in almost
all animal cells and function in catabolism long
chain fatty acids (Beta oxidation) forming acyle
coenzyme A (CoA) and H2O2.
- Peroxisomes (microbodies) are self replicating
organelles (can divide) that contain more than
40 oxidative enzymes (urate oxidase; catalase;D-
amino acid oxidase).
Proteasomes
- Proteasomes are small organelles composed
of protein complex that are responsible for
proteolysis of mal-formed and ubiquitin
tagged protein.
- The process of cytosolic proteolysis is
controlled by the cell, and it requires that
the protein be recognized as a potential
candidate for degradation.
Cell Inclusions
- Thy are non-living components of the cell that do
not possess metabolic activity and are not
bounded by membranes.
- The most common inclusions are:-
1- Stored food:
: abundant in liver and muscle cellsGlycogen-a
; stored mainly in adipocytes, Lipid droplets-b
and present also in other cells.
: could be endogenous or exogenous.Pigments-3
a- Exogenous pigments as carotene, carbon,
and dust.
b- Endogenous pigments such as; Hemoglobin,
Melanin, lipofuscin or lipochrom.
: are not commonly seen. Present in Crystals-4
Sertoli cells as (Crystals of Charcot-Bottcher)
and in interstitial cells as (Crystals of Reinke).
-
Cytoskeleton
- They are meshwork of protein filaments
responsible for maintenance of cellular
morphology, and participate in cellular
motion.
- The cytoskeleton has three major components;
1- Thin filaments
2- Intermediate filaments
3- Microtubules
1- Thin Filaments (Actin)
- The actin filaments are composed of 2 chains
of G-actin (globular actin) subunits coiled
around each other to form F-actin (filamentous
proteins).
- There are 3 types of actin filaments:
α-actin of muscle cells reacting with myocin.
β-actin in non-muscle cells.
Ƴ-actin in non-muscle cells.
- In non-muscle cells actin filaments form 3
types of bundles of variable length and
function:
- Contractile bundles
- Gel-like networks
- Parallel bundles
2- Intermediate filaments
- The intermediate filaments and their associated proteins perform the following:
- Provide structure support of the cell
- Establish a 3-dimensional structural framework for the cell.
- Anchor the nucleus in place.
- Provide connection between the cell membrane and the cytoskeleton.
- Maintenance of the nuclear envelop and its subsequent changes that takes place in mitosis
3- Microtubules
- Microtubules are long, strait, rigid, hollow-
like cylindrical structures act as
intracellular pathways.
- The centrosome is consider to be the micro-
tubule-organizing center (MTOC) of the
cell from which most of the cell's
microtubules emanate.
- Their main functions of microtubules are:
- Provide rigidity and maintain cell shape.
- Regulate intracellular movement of vesicles
and organelles.
- Established intracellular compartments.
- Provide the capability of ciliary motion.
- Microtubule-associated proteins:
Motor proteins that assist in translocation of
organelles and vesicles inside the cell, such as
Dynein and Kinesin.
Centromere: Centrioles
- Centromere is present in all dividing cells near
the nucleus, and is composed of 2 perpendicular
centriols.
- Centriol is cylindrical in shape.
- The centriols duplicated during cell division
- Each centriol composed of nine sets of triplet
microtubules.
Structure of microtubules organizing center (MTOC).
Cilia and Flagella
- Cilia (cilium) are hair-like motile processes
extend from the free surface of ciliated cells.
- Flagellated cells (sperm) has only one flagellum.
- Both cilium and flagellum composed of the same
core organization, which is called axoneme.
- The axoneme is formed of nine pairs (doublets)
and 2 central (singlet) microtubules.
- At the base of cilia or flagella there is a basal
body, which is similar to centriol in structure.
Cilia
microvilli
Stereocillum
Cell activities
- Cell division.
- Endocytosis
- Exocytosis
- Cell death:
- Necrosis
- Apoptosis
Nucleus
- All human cells contain nucleus except the
mature red blood corpuscles.
Normally each cell contains a single :Number-
nucleus, but sometimes contains two as liver
cells, or more (multinucleated) as skeletal
muscle cells, and osteoclasts.
: Nucleus could be spherical, oval, Shape-
flattened, or lobulated.
: Nucleus could be central, basal or Position-
peripheral.
Structure of the nucleus
- Nucleus composed of:
- Nuclear membrane (Envelop)
- Chromatin
- Nucleolus
- Nucleoplasm
1- Nuclear Envelop
- Nuclear envelop is composed of two
parallel unit membranes; the outer and
the inner membranes separated from
each other by a 10-30 nm space called
perinuclear cisterna.
- The two membranes fuse with each
other at certain regions known as
nuclear pores that permit
communication between cytoplasm
and nucleus .
- The nuclear pores is surrounded by a
non-membranous structure called
pore complex.
2- Chromatin
- Chromatin is a complex structure
formed of DNA associated with
histone and non-histone proteins.
- Depending on its transcriptional
activity chromatin can be divided into:-
- Euchromatin; not condensed, stained
lightly basophilic, gene rich, and early
transcript.
- Heterochromatin; condensed, stained
deeply basophilic, gene poor, and late
transcript.
3- Nucleolus
- Nucleolus is a non-membranous deeply
stained structure located in the nucleus.
- It present during interphase and
disappear during cell division.
- It contain ribosomal RNA, some proteins
and small amount of DNA.
- Structure of the nucleolus: It is formed of four
areas
- Pale staining Fibrillar center containing
inactive DNA, and nucleolar organizing
regions (tips of acrocentric chromosomes).
- Pars Fibrosa containing nucleoluar RNAs
- Pars Granulosa in which mature ribosomal
subunits are assembled
- Nucleolar Matrix: a network of fibers active
in nuclear organization.
4- Nucleoplasm
• Nucleoplasm composed of the following
1- Interchromatin Granules: They are
located in clusters scattered throughout
the nucleus among the chromatin
material.
2- Perichromatin Granules: They are
located at margins of heterochromatin,
and are composed of:
- Heterogeneous nuclear ribonucleo-
proteins
- Small nuclear riboprotein particles
3- Nuclear Matrix: Contain DNA, RNA,
Proteins, and nuclear phosphate.