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

http://www.microscopy.fsu.edu/cells/animals/animalmodel.html

- 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.