Cell introduction

Definition
= Three part theory about cells
1. All living things are made of cells.

Part 2 of the Theory
2. The cell is the basic structural and functional
unit of life.

Part 3 of the Theory
3. All cells come from pre-existing cells.
yeast cells dividing

Cells are Us
A person contains about 100 trillion cells. That’s
100,000,000,000,000 or 1 x 1014 cells.
There are about 200 different cell types in
mammals (one of us).
Cells are teeny, tiny, measuring on average
about 0.002 cm (20 um) across. That’s about
1250 cells, “shoulder-to-shoulder” per inch.
nerve cell

Why Study Cell
Biology?
The key to every biological
problem must finally be
sought in the cell, for every
living organism is, or at some
time has been, a cell.

The Cell Theory (review)
The Cell Theory (proposed independently in 1838 and
1839) is a cornerstone of biology.
 Cells are the basic unit of life
 All Cells arise from previously existing cells

Two Types of Cells
Two Fundamentally Different Cell Architectures:
1) A prokaryotic cell
2) A eukaryotic cell

Prokaryotic cells
• have no nucleus or organelles
enclosed within membranes.
• All species in the domains Archaea and
Eubacteria have prokaryotic cells.

Eukaryotic cells
• have a nucleus and organelles that are
surrounded by membranes.
• Each organelle does a specific cell function.
• All species in the Eukaryota domain (protists,
fungi, plants, and animals) have eukaryotic cells.
Individual protists have only one cell, while plants
and animals can have trillions of cells.

• 1. A few types of cells
are large enough to be
seen by the unaided
eye.
• 2. Most cells are
visible only with a
microscope.
•The Female Egg is the largest cell in the body, and can be seen without the aid of a
microscope.

PROKARYOTES vs. EUKARYOTES: Differences
(Location)

Similarities: Common Features of
ALL CELLS!

The common features of prokaryotic
and eukaryotic cells are:
• 1. DNA
2. Plasma membrane (a.k.a. “cell membrane”)
• 3. Cytoplasm
• 4. Ribosomes

A rat liver cell (with color enhancement to show
organelles).

Relative sizes of cells and cell components

Prokaryotic and Eukaryotic Cellular Structure

Prokaryotic and Eukaryotic Cells
• Prokaryote comes from
the Greek words for
prenucleus.
• Eukaryote comes from
the Greek words for
true nucleus.

Prokaryotic Cells: Shapes
• Average size: 0.2 –1.0 μm ´ 2 – 8 μm
• Most bacteria are monomorphic
• A few are pleomorphic

Basic Shapes
• Bacillus (rod-shaped)
• Coccus (spherical)
• Spiral
– Spirillum
– Vibrio
– Spirochete

Prokaryotic & Eukaryotic Cells: An Overview
 Prokaryotes
 Do not have membrane surrounding their
DNA
 lack a nucleus
 Lack various internal structures bound
with phospholipid membranes
 Are small, ~1.0 μm in diameter
 Have a simple structure
 Composed of bacteria and archaea

 Eukaryotes
 Have membrane surrounding their
DNA
 Have a nucleus
 Have internal membrane-bound
organelles
 Are larger, 10-100 μm in diameter
 Have more complex structure
 Composed of algae, protozoa, fungi,
animals, and plants

[INSERT FIGURE 3.1]

Prokaryotic Cell Membrane
• Structure
– Referred to as phospholipid bilayer;
composed of lipids and associated
proteins
– Approximately half composed of
proteins that act as recognition
proteins, enzymes, receptors,
carriers, or channels
• Integral proteins
• Peripheral proteins
• Glycoproteins
– Fluid mosaic model describes current
understanding of membrane
structure

Cell Membrane
Membranes contain a
hydrophilic and
hydrophobic side
Composed of many
different types of
proteins
Proteins in the lipid
bilayer move freely
within the membrane

Cell Membrane
Thin pliable lipid and protein envelope
that defines a cell.
Phospholipid bilayer
Functions:
• Regulates nutrient and water intake
• Regulates waste removal
• Site of prokaryotic respiration
• Site of prokaryotic flagella
attachment
• Involved in the distribution of genetic
material during binary fission

Prokaryotic Cytoplasmic Membranes
• Function
– Energy storage
– Harvest light energy in
photosynthetic prokaryotes
– Selectively permeable
– Naturally impermeable to most
substances
– Proteins allow substances to cross
membrane
• Occurs by passive or active
processes
– Maintain concentration and electrical
gradient
• Chemicals concentrated on one
side of the membrane or the
other
• Voltage exists across the
membrane

Trilaminar appearance of membranes

Structure of the Plasma membrane

• Plasma Membrane
• A lipid/protein/carbohydrate complex, providing a
barrier and containing transport and signaling
systems.

Cell membrane - Function
• The cell membrane's function, in general, revolves
around is membrane proteins. General functions
include:
• Receptor proteins which allow cells to
communicate,
• transport proteins regulate what enters or leaves
the cell,
• and marker proteins which identify the cell

Cell membrane - Function - Regulation of
transport
• Transport Proteins come in two forms:
Carrier proteins are peripheral proteins which
do not extend all the way through the
membrane. They move specific molecules
through the membrane one at a time.

Channel proteins extend through the
bilipid layer. They form a pore through
the membrane that can move
molecules in several ways.

• The cell membrane can also engulf structures
that are much too large to fit through the
pores in the membrane proteins.
• This process is known as endocytosis.
• In this process the membrane itself wraps
around the particle and pinches off a vesicle
inside the cell.

Structure of Cholestrol molecule

External Structures of Prokaryotic Cells
• Types of Glycocalyces
– Capsule
• Composed of organized
repeating units of organic
chemicals
• Firmly attached to cell surface
• Protects cells from drying out
• May prevent bacteria from
being recognized and destroyed
by host

• Glycocalyces
– Gelatinous, sticky substance
surrounding the outside of
the cell
– Composed of
polysaccharides,
polypeptides, or both

Capsule
Polysaccharides or
polypeptides in composition.
Surround the cell wall in some
bacteria.
Function:
•Protection from phagocytosis
•Osmotic barrier
•Reservoir for nutrients
•Virulence factor

Slime Layer
Consist of polysaccharide
fibers that extend form the
bacterial surface
Functions:
•Protection
•Attachment
•Associated with biofilms

• Types of Glycocalyces
– Slime layer
• Loosely attached to cell surface
• Water soluble
• Protects cells from drying out
• Sticky layer that allows
prokaryotes to attach to
surfaces

Bacterial
Appendages
Flagella
Axial Filaments
Pili (Fimbriae)

Bacterial Appendages Flagella
Structures of locomotion
Originate in the plasma
membrane
In bacteria rotate like a
propellar
Many different
arrangements

• Flagella
– Are responsible for
movement
– Have long structures that
extend beyond cell surface
– Are not present on all
prokaryotes

 Flagella
 Structure
 Composed of filament, hook, and
basal body
 Flagellin protein (filament)
deposited in a helix at the
lengthening tip
 Base of filament inserts into hook
 Basal body anchors filament and
hook to cell wall by a rod and a
series of either two or four rings
of integral proteins
 Filament capable of rotating 360º

Bacterial Appendages Arrangements of Flagella
A.Monotrichous
B.Lophotrichous
C.Amphitrichous
D.Peritrichous

Bacterial Appendages
Axial filament (endoflagella)
Originates in the cell membrane and
transverses the length of the cell in the
periplasmic space.
As the endoflagella rotate to move the cell the
characteristic shape is formed .
Endoflagella are associated with spirochetes.

Endoflagellum is also know as an
axial filament.
Attached to the plasma embrane
and transverses the entire cell.
Responsible for the spirochete
morphology.

• Flagella
– Function
• Rotation propels bacterium
through environment
• Rotation reversible, can be
clockwise or counterclockwise
• Bacteria move in response to
stimuli (taxis)
– Runs
– Tumbles

Bacterial Appendages
• Fimbriae and Pili
– Rod-like proteinaceous
extensions

Bacterial
Appendages Fimbriae
Hollow tubes that
protrude from some
bacteria
Compose of protein

• Fimbriae
• Sticky, bristlelike projections
• Used by bacteria to adhere
to one another, to hosts, and
to substances in
environment
• Shorter than flagella
• May be hundreds per cell
• Serve an important function
in biofilms
• Virulence factor

• Pili
– Tubules composed of pilin
– Also known as conjugation pili
– Longer than fimbriae but shorter
than flagella
– Bacteria typically only have one or
two per cell
– Mediate the transfer of DNA from
one cell to another (conjugation)

Bacterial Conjugation
Transfer of plasmid DNA
from a donor to a
recipient.
Process strengthens the
bacterial cell and alows for
survival in a competitive
environment.

Bacterial Inclusion Bodies
1. poly-Beta-hydroxybutyric acid - stores lipids for use in plasma membrane
2. glycogen - stores starch like polymer of sugar for energy production
3. Polyphosphate granules (metachromatic granules) - storage for
phosphates for plasma membrane and the formation of ATP from ADP.
4. Sulfur granules - stores sulfur which is necessary for the metabolic
reactions in biosynthesis.

5. Mesosome
Mesosomes - invagination of the
plasma membrane that increases the
surfaces area of the plasma membrane
during binary fission.
The mesosome also serves as a site
for the attachment and distribution of
genetic material during binary fission.

Mesosome
In prokaryotic cell division, called
binary fission.
A diagram of the attachment of
bacterial chromosomes, indicating the
possible role of the mesosome (an
inward fold of the cell membrane) in
ensuring the distribution of the
"chromosomes" in a dividing cell.
Upon attachment to the plasma
membrane, the DNA replicates and
reattaches at separate points.
Continued growth of the cell gradually
separates the chromosomes and
allocates chromosome copies to the
two daughter cells.

Inclusion Bodies
6. gas vacuoles - storage of metabolic gases such as methane or hydrogen gas. The
gas vacuoles help in the buoyancy of the cell and aids in it motility.
7. ribosomes - responsible for the synthesis of proteins.
8. nucleoid material - the genetic material of bacteria, which usually is balled up in
the cell. During binary fission the nucleoid material unravels within the cell in
order to be copied and distributed to the daughter cells.
9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for
the resistance to antibiotics or for the productions of a specific metabolite, i.e.
toxins, pigments. These plasmids may be transferred from one bacterial cell to
another by the F-pili.

Inclusion Bodies
9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes
for the resistance to antibiotics or for the productions of a specific metabolite, i.e.
toxins, pigments. These plasmids may be transferred from one bacterial cell to
another by the F-pili.

Inclusion Bodies
These plasmids may be transferred from one bacterial cell to another by the
F-pili.

Inclusion Bodies
10. Endospores - a survival mechanism of certain genera of bacteria such as
Clostridium and Bacillus.
The endospores are composed of a complex of dipicolinc acid and
calcium and the function of the endospore is to protect the bacterial
chromosome.
The endospores are very resistant to heat, desiccation, freezing, and
other physical properties such as pesticides, antibiotics, dyes, and acids.

Inclusion Bodies
The endospores may remain dormant for many years until the
environment becomes suitable to sustain the life of the bacteria.
The endospore will then germinate to form an exact copy of the parent
cell that produced it.

Eukaryotic Cell Walls & Cytoplasmic Membranes
• Fungi, algae, plants, and some protozoa
have cell walls but no glycocalyx
• Composed of various polysaccharides
– Cellulose found in plant cell walls
– Fungal cell walls composed of
cellulose, chitin, and/or
glucomannan
– Algal cell walls composed of
cellulose, proteins, agar,
carrageenan, silicates, algin,
calcium carbonate, or a
combination of these

Cell Walls
Three different types of cell walls and
their compositions:
Fungal cell walls are composed of
cellulose and/or chitin.
Plant cell walls are composed of
cellulose.
Algal cell walls are composed of
cellulose, silicon, and calcium
carbonate.

Plasma Membrane
Consist of a lipid bilayer and
associated proteins. The Plasma
Membrane of Eukaryotic cells
resembles and functions in the same
manner as the prokaryotic plasma
membrane with the following
exceptions;
Contains high levels of sterols such as
cholesterol.
No respiratory enzymes are located in
the eukaryotic plasma membrane.
Respiration occurs in the
mitochondria.

External Structure of Eukaryotic Cells
• Glycocalyces
– Never as organized as prokaryotic
capsules
– Help anchor animal cells to each
other
– Strengthen cell surface
– Provide protection against
dehydration
– Function in cell-to-cell recognition
and communication

Eukaryotic Appendages
Flagella
There are several different
arrangements of flagella in eucaryotes.
This diagram represents a
biflagellated eukaryotic cell.
One of the flagella aids in movement
laterally and the other aids in up and
down movement.
The eukaryotic flagella move like a
whip.
See Flagellar handout.

• Flagella
– Function
• Do not rotate, but undulate
rhythmically

Cilia
Similar to flagella both structurally and
functionally but are much shorter and
more numerous.
Cilia are found peritrichously to the cell.
Move in an undulating manner and
motility by those organisms with cilia is
much more rapid than those with flagella.

Intracellular Structures of Eukaryotic Organisms (organelles)
 Membranous Organelles
 Nucleus
 Often largest organelle in cell
 Contains most of the cell’s DNA
 Semi-liquid portion called
nucleoplasm
 One or more nucleoli present in
nucleoplasm; RNA synthesized in
nucleoli
 Nucleoplasm contains chromatin –
masses of DNA associated with
histones
 Surrounded by nuclear envelope –
double membrane composed of two
phospholipid bilayers
 Nuclear envelope contains nuclear
pores

Nucleus - double membraned
organelle that houses the genetic
material of cell.
Nuclear membrane contains numerous
pores through which proteins and RNA
can move.

 Endoplasmic reticulum
 Netlike arrangement of flattened, hollow
tubules continuous with nuclear
envelope
 Functions as transport system
 Two forms
 Smooth endoplasmic reticulum
(SER) – plays role in lipid
synthesis
 Rough endoplasmic reticulum
(RER) – ribosomes attached to
its outer surface; transports
proteins produced by
ribosomes

Endoplasmic reticulum - network of
cytoplasmic membranes where lipids
and proteins are produced.
Smooth ER - synthesis of lipids
Rough ER - associated with ribosomes
and is responsible for the synthesis of
proteins.
.

 Golgi body
 Receives, processes, and
packages large molecules for
export from cell
 Packages molecules in secretory
vesicles that fuse with
cytoplasmic membrane
 Composed of flattened hollow
sacs surrounded by
phospholipid bilayer
 Not in all eukaryotic cells

Golgi apparatus (dictyosome) is
associated with the ER.
It modifies and packages the lipids and
proteins manufactured by the ER and
places them in vesicles for cellular use.

• Membranous Organelles
– Lysosomes, peroxisomes,vacuoles, and
vesicles
• Store and transfer chemicals within
cells
• May store nutrients in cell
• Lysosomes contain catabolic
enzymes
• Peroxisomes contain enzymes that
degrade poisonous wastes

– Mitochondria
• Have two membranes
composed of phospholipid
bilayer
• Produce most of cell’s ATP
• Interior matrix contains 70S
ribosomes and circular
molecule of DNA

mitochondria - involved in the
production of chemical energy in the
form of ATP.
Consist of convoluted inner membrane
and outer membrane. Invaginations
are called cristae and contain enzymes
used to synthesis ATP.
All respiratory enzymes are located in
the inner membrane of the
mitochondria.

Cytoplasm of Eukaryotes
– Chloroplasts
• Light-harvesting structures
found in photosynthetic
eukaryotes
• Have two phospholipid
bilayer membranes and DNA
• Have 70S ribosomes

• Endosymbiotic Theory
– Eukaryotes formed from union of small aerobic
prokaryotes with larger anaerobic prokaryotes
– smaller prokaryotes became internal parasites
• Parasites lost ability to exist independently; retained
portion of DNA, ribosomes, and cytoplasmic
membranes
• Larger cell became dependent on parasites for aerobic
ATP production
• Aerobic prokaryotes evolved into mitochondria
• Similar scenario for origin of chloroplasts
– Not universally accepted

[INSERT TABLE 3.5]

[INSERT TABLE 3.4]

Eukaryotic Cell Walls & Cytoplasmic
Membranes
[INSERT TABLE 3.3]

Cell introduction

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