Standing on the shoulders of giants
Or having a really
good telescope
Early
microscope ca. 1673
Robert Hooke (1635-1703) in
wrote Micrographia in 1667
coined the
term cell
Anton van
Leeuwenhoek (1632-1723) in
improved
quality
Cell Theory
Schleiden & Schwann (1839) postulated theory
The cell
is the fundamental unit of structure and function in living things
All living
things are composed of cells
The third
basic tenet comes from Virchow claimed (1855)
powerful dictum, Omnis cellula e cellula
All cells
arise from pre-existing cells
Light microscopes (LM)
magnify up to 1500X but cannot resolve objects that are smaller than 200nm (about
0.2 microns).
See handout
Into the subcellular
1950s
brought electron microscopy (EM)
Resolution
improved hundredfold (up to 2 nm the diameter of DNA double helix)
New
advances could bring resolution to 0.002nm the diameter of an atom!
Researchers
viewed cell ultrastructure for the first time
Scanning
EM and Transmission EM most useful to biologists
Types of Cells
Two basic
types
Eukaryote
(true nucleus)
Prokaryote
(before nucleus)
Cell type
determines domain of life
Prokaryotes
are found in Archaea and Bacteria
Eukarya
include animals, plants, fungi, and protists
Whats common to all cells?
Plasma
membrane maintains cell integrity, regulates traffic, serves as
protection
Cytosol semi-fluid
substance that allows chemical reactions to occur
Nucleic
material DNA and ribosomes
Cytosol
cytoplasm
includes everything in the cell except the nucleus
cytosol is the
soluble portion of the cytoplasm
Contains
about 80% water, nucleic acids, proteins, lipids, carbohydrates, pigments, etc
Variable
viscosity
How to ID a prokaryote
Cell has
no nucleus (no membrane surrounding DNA)
DNA is
naked and circular
May have
cell wall, pili, flagella, mesosomes,
capsule, and photosynthetic membranes (in addition to basic cellular features)
Unicellular,
but may form colonies
Eukaryotic cells
Have a
well-defined nucleus
Complex
organelles contained in cytosol
May be
single- or multi-cellular
Exist in four
kingdoms
Animalia (see handouts for typical animal and plant
cells)
Planta
Protista
Fungi
Contains
most of the genetic material (linear chromosomes)
Average
diameter 5 μm
Separated
from cytoplasm by a double membrane (20-40 nm apart)
Nuclear pores
allow traffic flow
Fluid
interior termed nucleoplasm
Nuclear
lamina maintain the shape of the nucleus
Is a region,
not a structure!
Site of
ribosome construction (rRNA and
proteins assembled into ribosomal subunits)
Subunits
flow out into cytoplasm and combine the
two (large and small) subunits to form functional ribosomes
Cells that
synthesize large quantities of protein have prominent nuclei and thousands of
ribosomes
Ribosomes
are the workbenches upon which proteins are synthesized
Ribosomes
may be free in the cytosol, or bound to the
ERlocation dictated by type of polypeptide
Many
membrane-bound organelles make up the endomembrane
system
Vesicles
contact organelles directly, or indirectly through transfer of materials
Includes
the nuclear envelope, ER, Golgi apparatus, lysosomes, vacuoles, and the plasma membrane
Why all these organelles?
Compartmentalization
Organelles
help to increase internal surface area
Organelles
maintain duties and functions that would otherwise fall upon the plasma membrane
Comprises
50% of internal membrane
Rough ER:
appearance due to bound ribosomes
Functions
in protein modification and export, some membrane synthesis
Smooth
ER-appears smooth
Functions
in metabolism, and synthesis of lipids, and energy mobilization; plays key role
in alcohol and drug detoxification in liver
In muscle
cells, the sarcoplasmic ER holds Ca++ to be mobilized
when the muscle contracts
The smooth
ER includes transitional ER: sites of
vesicle formation
The rough
ER is connected to the nuclear envelope
Centre of
manufacturing, warehousing, packaging, and shipping
Transport
vesicles from ER will travel to Golgi for further
modifications and packaging
Cells that
specialize in secretion of products have extensive Golgi
apparatus
One side (cis side) receives material; the other (trans
side) releases end-products
During the
transit from cis to trans side,
products are modified. Modifications include adding sugars onto proteins
(glycoproteins) destined
for the plasma membrane.
Hydrolyze
proteins, fats, polysaccharides, and nucleic acids
Sometimes
called a suicide bag involved in self-destruction of cell
Interior
is more acidic (pH 5) than cytosol
Lysosome enzymes and
membrane are made in the ER, sent to the Golgi, and
bud from both the cis and trans
side of the Golgi
Frogs and
fingers? Lysosomes recyle!
fuse with
food vacuoles to digest incoming food particles
destroy
or recycle damaged organelles
Participate
in programmed destruction of cells
Vacuoles
Vesicles
and vacuoles (larger version) are membrane-bound sacs with various functions
Food
vacuoles: from phagocytosis, fuse with lysosomes
Central
vacuoles: found in mature plant cells
Contractile
vacuoles: found in freshwater protists to pump out excess
water
Surrounded
by single membrane, the tonoplast
Tonoplast regulates
traffic of solutes and pigments, stores ions and proteins
Stores
destructive metabolic by-products and defensive compounds against herbivores
Mitochondria and chloroplasts
Are not
part of the endomembrane system
Both
contain a naked circular DNA molecule of their very own
Both grow
and reproduce as autonomous organelles
Both have
more in common with bacteria than with the cell in which they reside
Both can
move around inside the cell along cytoskeleton tracks
Mitochondrion
(sing) mitochondria (plural)
Double-membrane
Own ribosomes
(and genetic code!)
Some
proteins coded for in nuclear DNA, proteins made on free ribosomes, imported
into mitochondrion
Number per
cell depends on cells function
Found in
animals AND plants (as well as fungi and protists)
A plastid found only in
plants and protists
Other
plastids include amyoplasts (starch storage) and chromoplasts (pigment storage)
Chloroplasts
develop when plastids are stimulated by sunlight (stems and leaves)
Contain
the green pigment, chlorophyll
May be visible under LM
Double-membrane
Inner
membrane system of chlorophyll-containing thylakoids
(stacked into grana)
Own
ribosomes (and genetic code!)
Fluid
interior termed stroma
Number per
cell depends on cells function
In animal
and plant cells
Single
membrane
Contains
enzymes that transfer H+ to oxygen
Produces
hydrogen peroxide which must be converted to water, this enzyme is often called
catalase
Essential
for support, motility and regulation
Dynamic
structure responds to pressure and inner tension
Provides
anchorage and movement for organelles
Motility
achieved through motor proteins interacting with cytoskeleton
Three types of fibres: microtubules, microfilaments and intermediate filaments
Plants and
animal cells contain centrosomes (a region from which
microtubules grow to form spindles during cell division)
Animal
cells contain a pair of centrioles within their centrosomes
Centrioles contain 9
triplets of microtubules arranged in a ring
Centrioles replicate
during cell division
Cilia and Flagella
(cilium
and flagellum singular)
Similar
diameter and structure- anchored in the cell by basal body (centrioles)
Very
important for motility in protists (unicellular
eukaryotes) and sperm
Cilia are
shorter, more numerous, and have an oar-like pattern of motion
Flagella
are longer, only one or two per cell, and beat in an undulating motion
Rarely
absent from plant cells
Never
found in animal cells
Much
thicker and stronger than plasma membrane
Composition
is mainly cellulose, but may also contain other polysaccharides (including
pectin)
Aids in
protection, support, transport, and water regulation
Communicating
junctions are called plasmodesmata
Cells may
organize into tissues and organs
Communication
and physical interactions require special structures
Communicating
junctions: Plasmodesmata (plants) and gap junctions
(animals)
Adhering junctions: desmosomes (animals only)
Tight junctions (animals
only)
