Lecture 2
Cell size comparison
2 TYPES OF CELLS
Prokaryotic cells
Eukaryotic cell
Prokaryotic Cells
• All bacteria and Blue-green
Algae are included in
prokaryotic cell
• Archaea and eubacteria
• DNA is not enclosed in nucleus
• Generally the smallest, simplest
cells
• No organelles
Prokaryotic Structure
bacterial flagellum
plasma membrane
pilus
bacterial flagellum
Most prokaryotic cells have a
cell wall outside the plasma
membrane, and many have
a thick, jellylike capsule around
the wall.
cytoplasm, with
ribosomes
DNA in
nucleoid
region
Basic Aspect of Cell Structure and Function
 In multi-celled organisms, cell is the smallest
entity that retains the properties of life, while
in single cell organisms, cell is the organisms.
 Structural Organization of Cell:
1. Plasma Membrane
2. DNA containing region
3. Cytoplasm
 Two fundamental different kinds of cell are
Prokaryotic and Eukaryotic
DEFINING FEATURES OF EUKARYOTIC CELLS
 An organelle is an internal, membrane-
bound sac or compartment that serves one
or more specialized function inside these
cells.
 Compartmentalization allows a large
number of activities to proceed
simultaneously in very limited space.
 Organelles physically separate chemical
reactions, many of which are incompatible.
1. PLASMA MEMBRANE
 Cell membranes are mostly phospholipids and
proteins. The phospholipids form a double layer.
This “bi-layer” gives membranes their structure
and serves as a barrier to water soluble
substances.
 Proteins carry out most of membrane function, as
when they actively or passively transport
substances into and out of cell.
 The hydrophobic parts of its lipid molecules are
sandwiched between the hydrophilic part.
Overview of Membrane Protein
 Proteins embedded in the bilayer or associated with
one of its surfaces carry out most of its membrane
functions. The plasma membrane also has proteins
that serve in signal reception, cell recognition, and
adhesion
 Differences in numbers and types of protein among
cell affect metabolism, cell volume, pH and
responsiveness to substances that make contact with
the membrane
PROTEINS IN MEMBRANE SYSTEM
Many of the proteins are enzymes, others are:
1.
Transport Proteins, which allow water soluble
substances to pass through their interior, which opens
to both sides of the membrane
2.
Receptor Proteins, which bind extracellular substances
that trigger alterations in metabolic activities
3.
Recognition Proteins, molecular fingerprints at the
surface of each cell type. Infection fighting white blood
cells chemically recognize self proteins and non self
proteins of foreign cells
4.
Adhesion Protein (in multicell organism), help cell
adhere to one another and form cell junction
VARIOUS PROTEINS IN CELL MEMBRANE
2. The Nucleus (DNA containing region)
• The nucleus is one of many organelles, which eukaryotic
DNA resides.
• Two Functions of nucleus:
1.
Tuck away all the DNA molecules
2. Membranous boundary of the nucleus help control the
exchange of substances and signals between the
nucleus and cytoplasm
• Nuclear envelope
functionally separate the DNA from the metabolic machinery
of the cytoplasm. The nuclear pores allow molecules to
move across the nuclear envelope
The Nucleus
 Control center
- Contains (DNA)
 3 regions
- Nuclear membrane
- Nucleolus
- Chromatin
 Nucleolus
Dense cluster of RNA and proteins that will
assembled into subunits of ribosome
 Chromosome
One DNA molecule and many proteins that
are intimately associated with it
 Chromatin
Total collection of all DNA molecules and
their associated proteins in the nucleus
 Nucleoplasms
Fluid interior portion of the nucleus
Nucleolus
 Nucleus contains
1 or more nucleoli
 Make ribosomes
 Ribosomes migrate
to cytoplasm through
nuclear pores
DNA – Chromatin & Chromosome Forms
 Composed of
DNA and protein
 Chromatin throughout
nucleus in thread
form
 Chromosomes condensed DNA
forms before cell
divides
 Major Organelles are:
No
Organelle
3. CYTOPLASM
Main Function
1
Nucleus
Localizing the cells’ DNA
2
Ribosome
Assembling protein (polypeptide chain)
3
Endoplasmic
reticulum
Route and modify new polypeptide chain as well as
synthesize lipids
4
Golgi Body
Modify polypeptide chain into mature protein,
sorting and shipping proteins and lipids
5
Vesicles
Transport, store and digest varies of substances and
structure within the cell
6
Mitochondria
Producing ATP in highly efficient fashion
7
Cytoskeleton
Imparting shape and internal organization; help
move the cell and its internal structure
Cytoplasm
Material outside nucleus and inside
plasma membrane
1. Cytosol
 Fluid that suspends
other elements
2. Organelles
 Machinery of cell
3. Inclusions
 Non-functioning units
1. Ribosomes
 Made of protein and RNA (made in nucleolus)
 Sites of protein synthesis
 Found at two locations
1. Free in the cytoplasm and
2. Attached to rough endoplasmic reticulum
2. Endoplasmic reticulum (ER)
 Fluid-filled tubules for carrying
substances
 Two types
- Rough ER
- Studded with ribosomes
- Makes parts for membranes
- Smooth ER
- Makes & breaks cholesterol
- Fat metabolism
- Detoxifies drugs
3. Golgi apparatus
 Modifies and packages proteins (3 types)
- Secretory vesicles
- Cell membrane components
- Lysosomes
4. Lysosomes
- Sacs of enzymes
- digest nonusable
materials
5. Peroxisomes
- Sacs of oxidase enzymes
- Detoxify harmful substances
- Break down free radicals
(highly reactive chemicals)
- Replicate by pinching in half
- Remember bubbling liver?
6. Mitochondria
 “Powerhouses” of the cell
 Change shape continuously
 Uses O2 to break down food
 Provides ATP for energy
7. Cytoskeleton
• Protein structures
throughout the cytoplasm
• Internal framework
Three different types
 Microfilaments
 Intermediate
filaments
 Microtubules
COMPONENTS OF CYTOSKELETON
 Every eukaryotic cell has cytoskeleton, the diverse
elements of which are the basic of its shape, its
internal structure, and its capacity for movement
 Microtubules
Key organizers of cytoskeleton and help move
certain cell structure
 Microfilaments
take part in diverse movements and in formation
and maintenance of cell shape
 Intermediate Filaments
Reinforce cell and internal cell structure
CELL SURFACE SPECIALIZATION
 A variety of organisms have porous but
protective wall that surrounds the plasma
membrane
 Cell to cell junction
in multi-celled organisms, coordinated cell
activities depend on cell to cell junctions, which
are protein complexes or cytoplasmic bridges
that serve as physical links and forms of
communication between cells
 Plasmodesma
a channel cross the adjacent primary wall of
living cells and connect their cytoplasms
TISSUE
In Animals
Example: Adipose tissue
In Plants
Body Tissues
 Cells are specialized for particular functions
 Tissues - Groups of cells with similar structure
and function
 Four primary types
-
Epithelium
Connective tissue
Nervous tissue
Muscle
Connective Tissue Types
Elastic cartilage
 Provides elasticity
 found in external ear,
epiglottis, & trachea
Connective Tissue Types
Adipose
 Similar to areolar with fat globules
 Many cells contain large lipid deposits
 Functions
- Insulates body
- Protects organs
- Fuel storage
Connective Tissue Types
Blood
 cells & fluid matrix
 Fibers visible
during clotting
 Transports
materials
Muscle Tissue
 Function = produce movement
 3 types
- Skeletal muscle
move muscles of skeleton
- Cardiac muscle
only found in heart
- Smooth muscle
found in organs & vessels
Nervous Tissue
 Neurons and nerve
support cells
 Function = send
impulses to other
areas of the body
- Irritability – able to
respond to stimuli
- Conductivity –
conducts messages
ORGAN
Organ Systems - ANIMAL
How Substance Cross Cell Membrane
Selective Permeability
Because of its molecular structure, it allows some
substances but not others to cross it in a certain times
 Concentration Gradients and Diffusion
A concentration gradients is a form of energy that can
drive the directional movement of a substance across
membrane. Molecules or ions tend to move from a
region of higher to lower concentration. Diffusion is
the net movement of molecules or ions down a
concentration gradient.
 Factors Influencing the Rate and Direction of Diffusion
Diffusion rates are influenced by the steepness of
concentration gradient, temperature, molecular size as
well as by gradient in electrical charge and pressure

 Mechanisms which Solutes Cross Cell
Membrane
- Cells have built-in mechanisms that
work with or against gradients of
adjoining region
- Non polar substances and water
can diffuse across the lipid bilayers of
cell membranes. Polar substances and
water cross by passive transport
(facilitated diffusion) and by active
transport.
 Passive Transport
By passive transport, the protein allows a
solute simply to diffuse through its interior, in
the direction of concentration gradient. The
proteins shape changes without an input of
energy
 Active Transport
By active transport, the protein pumps a
solute across the membrane against its
concentration gradient. The changes in protein
shape that trigger the process require an
energy boost from ATP
EXOCYTOSIS AND ENDOCYTOSIS
• Substances also move in bulk across the plasma
membrane by exocytosis and endocytosis
• Exocytosis
Involves fussion of a vesicle (that form earlier in
the cytoplasm) with the cell’s plasma membrane
• Endocytosis
• Involves an inward sinking of small patch of
plasma membrane, which then seals back on
itself to form cytoplasmic vesicle
 Osmosis
is a net diffusion of water between two
solution that differ in water concentration
and that are separated by a selectively
permeable membrane.
The greater the number of molecules and
ions dissolved in a solution, the lower its
water concentration will be
 Tonicity
is a measure of the solute concentration of
one solution relative to other solution
Water tends to move from hypotonic solution,
the lower solute concentration to hypertonic
solution, the higher solute concentration.
If the fluids are isotonic, equal solute
concentration, the water will show no net
movement in either direction
TONICITY