CYTOLOGY & HISTOLOGY
Lecture one
DR. ASHRAF SAID
The aim of the present course
 is to present histology and cytology in
relation to the principles of physiology,
biochemistry and molecular biology.
 Duration: 80hours
 (Practical 4/week/16week)
 (Lecures 1/week/16week)
Course Objectives
 Reviews basic cell structure and discuss the scope and nature of cell biology.
 Describes the chemical components and processes of cells.
 Describes the storage of genetic information within cells and how this information is passed
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on to the next generation.
Describes key concepts in molecular biology.
Discusses membrane structure and transport across cell membranes.
Describe the significant processes involved in transfer and storage of energy in a cell.
Describes the significant processes that occur in cell communication and intracellular
transport.
Describes the life cycle of cells and how they combine to create different types of tissues
Develops both a range of transferable skills as well as to allow you to acquire a
comprehensive understanding of the processes involved in health and disease.
Provides a broad scientific training in biological science and is particularly appropriate for
those who wish to work in research, toxicological, forensic and diagnostic laboratories in
hospitals and other medical research institutions.
Develops both general skills and subject-specific knowledge and understanding by using a
variety of teaching methods, including lectures, study skills exercises, problem solving,
teamwork, project-type practical, independent study with discussions and oral presentations,
data interpretation, videos and case studies.
Gives a good grounding for students wishing to pursue careers in research (higher degrees),
teaching and marketing or management within biological-related industries.
Overall Objective
An understanding of cell biology
is important in many areas of
study, for the cell is the building
block of all living forms. This
course complements studies in
any area of applied biology
including human health and
fitness, horticulture, agriculture
and wildlife management.
Lectures main outlines
No.
Lecture
1
Introduction in cytology and histology
Use of different types of microscopes in cytology and histology
Isolating Organelles by Cell Fractionation
2
A Panoramic View of the Pro/Eu-karyotic Cells
The Nucleus: Genetic Library of the Cell
Ribosomes: Protein Factories in the Cell
3
The Endoplasmic Reticulum: Biosynthetic Factory
Lysosomes: Digestive Compartments
4
Vacuoles: Diverse Maintenance Compartments
The Endomembrane System
5
Mitochondria: Chemical Energy Conversion
Components and roles of the Cytoskeleton: Support, Motility, and
Regulation
6
Centrosomes and Centrioles
Cilia and Flagella
7
The Extracellular Matrix (ECM) of Animal Cells
Intercellular Junctions
date
Overview:
The Importance of Cells
 All organisms are made of cells
 The cell is the simplest collection of
matter
that can live
Cell structure is correlated to
cellular function
Figure 1.1
10 µm
Concept 1
To study cells, biologists
use microscopes and the
tools of biochemistry
Microscopy
 Scientists use microscopes to visualize
cells that are too small with the naked eye
 Light microscopes (LM.s)
– Pass visible light through a specimen
– Magnify cellular structures with lenses
 Electron microscopes (EM.s)
– Focus a beam of electrons through a
specimen (TEM) or onto its surface (SEM)
Different types of microscopes
 Can be used to visualize different sized cellular structures
1m
0.1 m
Human height
Length of some
nerve and
muscle cells
Chicken egg
1 cm
Light microscope
Unaided eye
10 m
10 µ m
1µm
100 nm
Most plant
and Animal
cells
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
10 nm
Ribosomes
Proteins
1 nm
Lipids
Small molecules
Figure 1.2
0.1 nm
Atoms
Electron microscope
100 µm
Electron microscope
Frog egg
1 mm
Measurements
1 centimeter (cm) = 102 meter (m) = 0.4 inch
1 millimeter (mm) = 10–3 m
1 micrometer (µm) = 10–3 mm = 10–6 m
1 nanometer (nm) = 10–3 mm = 10–9 m
Use different methods for enhancing
visualization of cellular structures
TECHNIQUE
RESULT
(a) Brightfield (unstained specimen).
Passes light directly through specimen.
Unless cell is naturally pigmented or
artificially stained, image has little
contrast. [Parts (a)–(d) show a
human cheek epithelial cell.]
50 µm
(b) Brightfield (stained specimen).
Staining with various dyes enhances
contrast, but most staining procedures
require that cells be fixed (preserved).
(c) Phase-contrast. Enhances contrast
in unstained cells by amplifying
variations in density within specimen;
especially useful for examining living,
unpigmented cells.
Figure 1.3
Use different methods for enhancing
visualization of cellular structures
(d)
Differential-interference-contrast (Nomarski).
Like phase-contrast microscopy, it uses optical
modifications to exaggerate differences in
density, making the image appear almost 3D.
(e) Fluorescence. Shows the locations of specific
molecules in the cell by tagging the molecules
with fluorescent dyes or antibodies. These
fluorescent substances absorb ultraviolet
radiation and emit visible light, as shown
here in a cell from an artery.
(f) Confocal. Uses lasers and special optics for
“optical sectioning” of fluorescently-stained
specimens. Only a single plane of focus is
illuminated; out-of-focus fluorescence above
and below the plane is subtracted by a computer.
A sharp image results, as seen in stained nervous
tissue (top), where nerve cells are green, support
cells are red, and regions of overlap are yellow. A
standard fluorescence micrograph (bottom) of this
relatively thick tissue is blurry.
50 µm
50 µm
The scanning electron
microscope (SEM)
 Provides for detailed study of the surface of a
specimen
TECHNIQUE
RESULTS
1 µm
Cilia
(a) Scanning electron microscopy (SEM). Micrographs taken
with a scanning electron microscope show a 3D image of the
surface of a specimen. This SEM
shows the surface of a cell from a
rabbit trachea (windpipe) covered
with motile organelles called cilia.
Beating of the cilia helps move
inhaled debris upward toward
the throat.
Figure 1.4 (a)
The transmission electron
microscope (TEM)
 Provides for detailed study of the internal
ultrastructure of cells
TECHNIQUE
RESULTS
Longitudinal
section of
cilium
(b) Transmission electron microscopy (TEM). A transmission electron
microscope profiles a thin section of a
specimen. Here we see a section through
a tracheal cell, revealing its ultrastructure.
In preparing the TEM, some cilia were cut
along their lengths, creating longitudinal
sections, while other cilia were cut straight
across, creating cross sections.
Figure 1.4 (b)
Cross section
of cilium
1 µm
Isolating Organelles by Cell Fractionation
 Cell fractionation
– Takes cells apart and separates the major
organelles from one another
 The centrifuge
– Is used to fractionate cells into their
component parts
The process of cell fractionation
Cell fractionation is used to
isolate (fractionate) cell components, based on
size and density.
APPLICATION
Homogenization
Tissue
cells
First, cells are homogenized in a
blender to break them up. The resulting mixture (cell
homogenate) is then centrifuged at various speeds
and durations to fractionate the cell components,
forming a series of pellets.
TECHNIQUE
1000 g
Homogenate
(1000 times the
force of gravity)
Differential centrifugation
10 min
Supernatant poured
into next tube
20,000 g
20 min
RESULTS
In the original experiments, the
researchers used microscopy to identify the
organelles in each pellet, establishing a baseline for
further experiments. In the next series of
experiments, researchers used biochemical methods
to determine the metabolic functions associated with
each type of organelle. Researchers currently use cell
fractionation to isolate particular organelles in order to
study further details of their function.
Pellet rich in
nuclei and
cellular debris
80,000 g
60 min
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a Pellet rich in
plant)
“microsomes”
(pieces of
plasma membranes and
Pellet rich in
Figure 1.5
cells’ internal ribosomes
membranes)
Concept 2
Eukaryotic cells have internal
membranes that compartmentalize
their functions
 Two types of cells make up
every organism
– Prokaryotic
– Eukaryotic
Comparing Prokaryotic and Eukaryotic Cells
 All cells have several basic features in
common
– They are bounded by a plasma membrane
They contain a semi-fluid substance called
the cytosol
– They contain chromosomes
– They all have ribosomes
 Eukaryotic cells
– Contain a true nucleus,
bounded by a membranous
nuclear envelope
– Are generally quite a bit bigger
than prokaryotic cells
– The logistics of carrying out
cellular metabolism sets limits
on the size of cells
– Have extensive and elaborately
arranged internal membranes,
which form organelles
 Prokaryotic cells
– Do not contain a nucleus
– Have their DNA located
in a region called the
nucleoid
A smaller cell
 Has a higher surface to volume ratio, which
facilitates the exchange of materials into and
out of the cell
Surface area increases while
total volume remains constant
Figure 1.7
5
1
1
Total surface area
(height  width 
number of sides 
number of boxes)
6
150
750
Total volume
(height  width  length
 number of boxes)
1
125
125
Surface-to-volume
ratio
(surface area  volume)
6
12
6
The plasma membrane
 Functions as a selective barrier
 Allows sufficient passage of nutrients
and waste
Outside of cell
Figure 1.8 A, B
Carbohydrate side chain
Hydrophilic
region
Inside of cell
0.1 µm
Hydrophobic
region
(a)
TEM of a plasma
membrane. The
plasma membrane,
here in a red blood
cell, appears as a
pair of dark bands
separated by a
light band.
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
Concept 3
Cellular membranes are fluid
mosaics of lipids and proteins
Phospholipids
– Are the most abundant lipid in
the plasma membrane
– Are amphipathic, containing
both hydrophobic and
hydrophilic regions
The fluid mosaic model
of membrane structure
– States that a membrane
is a fluid structure with a
“mosaic” of various
proteins embedded in it
Membrane Models: Scientific
Inquiry
Membranes have
been chemically
analyzed
– And found to be
composed of proteins
and lipids
Scientists studying the plasma membrane
Reasoned that it must be a phospholipid
bilayer
WATER
Hydrophilic
head
Hydrophobic
tail
Figure 7.2
WATER
The Davson-Danielli sandwich
model of membrane structure
– Stated that the membrane was
made up of a phospho-lipid bilayer sandwiched between two
protein layers
– Was supported by electron
microscope pictures of
membranes
In 1972, Singer and Nicolson
– Proposed that membrane proteins
are dispersed and individually
inserted into the phospho-lipid bilayer
Hydrophobic region
of protein
Phospholipid
bilayer
Figure 7.3
Hydrophobic region of protein
Freeze-fracture studies of the
plasma membrane
– Supported the fluid mosaic
model of membrane structure
APPLICATION
TECHNIQUE
A cell membrane can be split into its two layers, revealing the ultrastructure of the membrane’s interior.
A cell is frozen and fractured with a knife. The fracture plane often follows the hydrophobic interior of a membrane,
splitting the phospholipid bilayer into two separated layers. The membrane proteins go wholly with one of the layers.
Extracellular
layer
Proteins
Knife
RESULTS
Figure 7.4
Plasma
Cytoplasmic layer
membrane
These SEMs show membrane proteins (the “bumps”) in the two layers,
demonstrating that proteins are embedded in the phospholipid bilayer.
Extracellular layer
Cytoplasmic layer
The Fluidity of Membranes
 Phospholipids in the plasma membrane
– Can move within the bi-layer
Lateral movement
(~107 times per second)
(a) Movement of phospholipids
Figure 7.5 A
Flip-flop
(~ once per month)
Proteins in the plasma membrane
– Can drift within the bi-layer
EXPERIMENT
Researchers labeled the plasma mambrane proteins of a mouse cell and a human cell with two
different markers and fused the cells. Using a microscope, they observed the markers on the hybrid cell.
RESULTS
Membrane proteins
+
Mouse cell
Human cell
CONCLUSION
Hybrid cell
Mixed
proteins
after
1 hour
The mixing of the mouse and human membrane proteins indicates that at least some membran proteins
move sideways within the plane of the plasma membrane.
The type of hydrocarbon tails in
phospholipids
– Affects the fluidity of the plasma
membrane
(b) Membrane fluidity
Fluid
Unsaturated hydrocarbon
tails with kinks
Viscous
Saturated hydroCarbon tails
The steroid cholesterol
– Has different effects on
membrane fluidity at different
temperatures
(c) Cholesterol within the animal cell membrane
Cholesterol
Membrane Proteins and Their
Functions
 A membrane
– Is a collage of different proteins embedded in
the fluid matrix of the lipid bilayer
Fibers of
extracellular
matrix (ECM)
Glycoprotein
Carbohydrate
Glycolipid
Microfilaments
of cytoskeleton
Cholesterol
Peripheral
protein
Figure 7.7
EXTRACELLULAR
SIDE OF
MEMBRANE
Integral CYTOPLASMIC SIDE
protein OF MEMBRANE
 Integral proteins
– Penetrate the hydrophobic core of the lipid
bilayer
– Are often transmembrane proteins,
completely spanning the membrane
EXTRACELLULAR
SIDE
N-terminus
EXTRACELLULAR
SIDE
C-terminus
a Helix
CYTOPLASMIC
SIDE
Peripheral
proteins
–Are appendages
loosely bound to
the surface of the
membrane
An overview of six major functions of
membrane proteins
(left) A protein that spans the membrane
(a) Transport.
may provide a hydrophilic channel across the
membrane that is selective for a particular solute.
(right) Other transport proteins shuttle a substance
from one side to the other by changing shape. Some
of these proteins hydrolyze ATP as an energy ssource
to actively pump substances across the membrane.
activity. A protein built into the membrane
(b) Enzymatic
may be an enzyme with its active site exposed to
ATP
Enzymes
substances in the adjacent solution. In some cases,
several enzymes in a membrane are organized as
a team that carries out sequential steps of a
metabolic pathway.
transduction. A membrane protein may have
(c) Signal
a binding site with a specific shape that fits the shape
Signal
of a chemical messenger, such as a hormone. The
external messenger (signal) may cause a
conformational change in the protein (receptor) that
relays the message to the inside of the cell.
Receptor
(d) Cell-cell recognition. Some glyco-proteins serve as
identification tags that are specifically recognized
by other cells.
(e) Intercellular joining. Membrane proteins of adjacent cells
may hook together in various kinds of junctions, such as
gap junctions or tight junctions
Attachment to the cytoskeleton and extracellular matrix
(f) (ECM). Microfilaments or other elements of the
cytoskeleton may be bonded to membrane proteins,
a function that helps maintain cell shape and stabilizes
the location of certain membrane proteins. Proteins that
adhere to the ECM can coordinate extracellular and
intracellular changes
Glycoprotein
The Role of Membrane
Carbohydrates in Cell-Cell
Recognition
 Cell-cell recognition
– Is a cell’s ability to distinguish one type of
neighboring cell from another
Membrane carbohydrates
– Interact with the surface
molecules of other cells,
facilitating cell-cell
recognition
Synthesis and Sidedness of
Membranes
 Membranes have distinct inside and outside
faces
 This affects the movement of proteins
synthesized in the endomembrane system
 Membrane proteins and lipids
– Are synthesized in the ER and Golgi apparatus
1
Transmembrane
glycoproteins
ER
Secretory
protein
Glycolipid
Golgi 2
apparatus
Vesicle
3
4
Secreted
protein
Figure 7.10
Plasma membrane:
Cytoplasmic face
Extracellular face
Transmembrane
glycoprotein
Membrane glycolipid
Concept 7.2: Membrane
structure results in selective
permeability
A cell must exchange
materials with its
surroundings, a process
controlled by the plasma
membrane
The Permeability of the Lipid
Bilayer
 Hydrophobic molecules
– Are lipid soluble and can pass through the
membrane rapidly
 Polar molecules
– Do not cross the membrane rapidly
Transport Proteins
 Transport proteins
– Allow passage of hydrophilic substances
across the membrane
 Concept 7.3: Passive transport is diffusion
of a substance across a membrane with no
energy investment
 Diffusion
– Is the tendency for molecules of any substance
to spread out evenly into the available space
(a) Diffusion of one solute. The membrane
has pores large enough for molecules
of dye to pass through. Random
movement of dye molecules will cause
some to pass through the pores; this
will happen more often on the side
with more molecules. The dye diffuses
from where it is more concentrated
to where it is less concentrated
(called diffusing down a concentration
gradient). This leads to a dynamic
equilibrium: The solute molecules
continue to cross the membrane,
but at equal rates in both directions.
Figure 7.11 A
Molecules of dye
Membrane (cross section)
Net diffusion
Net diffusion
Equilibrium
 Substances diffuse down their concentration
gradient, the difference in concentration of a
substance from one area to another
(b) Diffusion of two solutes. Solutions of
two different dyes are separated by a
membrane that is permeable to both.
Each dye diffuses down its own concentration gradient. There will be a net
diffusion of the purple dye toward the
left, even though the total solute
concentration was initially greater on
the left side.
Net diffusion
Net diffusion
Figure 7.11 B
Net diffusion
Net diffusion
Equilibrium
Equilibrium
Effects of Osmosis on Water
Balance
 Osmosis
– Is the movement of water across a
semipermeable membrane
– Is affected by the concentration gradient of
dissolved substances
Lower
concentration
of solute (sugar)
Higher
concentration
of sugar
Same concentration
of sugar
Selectively
permeable membrane: sugar molecules cannot pass
through pores, but
water molecules can
Water molecules
cluster around
sugar molecules
More free water
molecules (higher
concentration)
Fewer free water
molecules (lower
concentration)
Osmosis

Water moves from an area of higher
free water concentration to an area
of lower free water concentration
Water Balance of Cells
Without Walls
 Tonicity
– Is the ability of a solution to cause a cell to
gain or lose water
– Has a great impact on cells without walls
 If a solution is isotonic
– The concentration of solutes is the same as it
is inside the cell
– There will be no net movement of water
If a solution is
hypertonic
–The concentration of
solutes is greater than
it is inside the cell
–The cell will lose
water
If a solution is
hypotonic
– The concentration of
solutes is less than it is
inside the cell
– The cell will gain water
 Animals and other organisms without rigid
cell walls living in hypertonic or hypotonic
environments
– Must have special adaptations for
osmoregulation
Hypotonic solution
(a) Animal cell. An
animal cell fares best
in an isotonic environment unless it has
special adaptations to
offset the osmotic
uptake or loss of
water.
H2O
Isotonic solution
Hypertonic solution
H2O
H2O
H2O
H2O
Lysed
Normal
Shrinkage
Facilitated Diffusion: Passive
Transport Aided by Proteins
In facilitated diffusion
– Transport proteins speed the
movement of molecules
across the plasma membrane
Channel proteins
– Provide corridors that allow a
specific molecule or ion to cross the
membrane
EXTRACELLULAR
FLUID
Channel protein
Solute
CYTOPLASM
(a)
A channel protein (purple) has a channel through which
water molecules or a specific solute can pass.
 Carrier proteins
– Undergo a subtle (little) change in
shape that translocates the solutebinding site across the membrane
Carrier protein
Solute
(b)
A carrier protein alternates between two conformations, moving a solute across the membrane as
the shape of the protein changes. The protein can transport the solute in either direction, with the net
movement being down the concentration gradient of the solute.
Concept 7.4:
Active transport
uses energy to
move solutes
against their
gradients
The Need for Energy in
Active Transport
Active transport
– Moves substances against their
concentration gradient
– Requires energy, usually in the form
of ATP
The sodium-potassium pump
– Is one type of active transport system
1 Cytoplasmic Na+ binds to
the sodium-potassium pump.
[Na+] high
[K+] low
+
Na
Na+
EXTRACELLULAR
FLUID
[Na+] low
Na+ +
CYTOPLASM[K ] high
2 Na+ binding stimulates
phosphorylation by ATP.
Na+
Na+
Na+
P ATP
ADP
Na+
Na+
Na+
3 K+ is released and Na+
sites are receptive again;
the cycle repeats.
K+
K+
P
4 Phosphorylation causes the
protein to change its conformation,
expelling Na+ to the outside.
+
P P K
i
Figure 7.16
5 Loss of the phosphate
restores the protein’s
original conformation.
K+
K+
K+
6 Extracellular K+ binds to the
protein, triggering release of the
Phosphate group.
 Review: Passive and active transport compared
Passive transport. Substances diffuse spontaneously down
their concentration gradients, crossing a membrane with no use
of energy by the cell. The rate of diffusion can be greatly
increased by transport proteins in the membrane.
Active transport. Some transport proteins
act as pumps, moving substances across a
membrane against their concentration
gradients. Energy for this work is usually
supplied by ATP.
ATP
Diffusion. Hydrophobic molecules
and (at a slow rate) very small
uncharged polar molecules can diffuse
through the lipid bilayer.
Facilitated diffusion. Many hydrophilic
substances diffuse through membranes with
the assistance of transport proteins, either
channel or carrier proteins.
Maintenance of Membrane
Potential by Ion Pumps
Membrane potential
– Is the voltage difference across a
membrane
An electrochemical gradient
– Is caused by the difference in
concentration of
ions across a
membrane
 An electrogenic pump
– Is a transport protein that generates the voltage
across a membrane
–
–
ATP
EXTRACELLULAR
FLUID
+
+
H+
H+
Proton pump
H+
+
–
H+
H+
+
–
CYTOPLASM
–
+
+
H+
Cotransport: Coupled Transport
by a Membrane Protein
 Cotransport
– Occurs when active transport of a specific
solute indirectly drives the active transport of
another solute
 Cotransport: active transport driven by a
concentration gradient
–
+
H+
ATP
–
H+
+
H+
Proton pump
H+
–
+
H+
–
+
Sucrose-H+
cotransporter
H+ Diffusion
of H+
H+
–
–
+
+
Sucrose
Concept 7.5: Bulk
transport across the
plasma membrane
occurs by exocytosis
and endocytosis
Large proteins
– Cross the membrane by
different mechanisms
Exocytosis
 In exocytosis
– Transport vesicles migrate to the plasma
membrane, fuse with it, and release their
contents
Endocytosis
 In endocytosis
– The cell takes in macromolecules by forming
new vesicles from the plasma membrane
A Panoramic View of the Eukaryotic
Cell
 Eukaryotic cells
– Have extensive and elaborately arranged
internal membranes, which form organelles