THE CELL
Chapter 4
History Behind the Discovery of the Cell
• Cells, as well as microscopic life forms
– protists, bacteria, etc. were unknown
until the invention and refinement of
the light microscope.
• https://www.youtube.com/watch?v=Ue86MDmjns
• In the late 1600s Anton van
Leewenhoek used hand ground lenses
of high quality to study drops of water.
• He was able to see tiny living
microorganisms.
History Behind the Discovery of the Cell
• Also in the late 1600s
Robert Hooke
studied plant cork
under a light
microscope and
coined the term cell.
Light Microscopes
• Microscope technology
has advanced since the
single lens light
microscope.
• Compound light
microscope – uses light
and a series of lenses to
magnify an image up to
1,000X
• can be used to view
living cells
Watch the contractile vacuoles at work!
https://www.youtube.com/watch?v=VP2ckcFdm28
Light Microscopes
• Resolution is the
ability of an
instrument to show
two close objects as
separate.
• Light microscopes
have resolution up to
0.2µm
Light Microscopes
Electron Microscopes
Electron Microscopes
• Scanning electron
microscope (SEM)–
scans external
surfaces and creates
a 3D image
• Transmission
electron microscope
(TEM) – extremely
thin cross sections
are stained and
studied
Cell Size
Inside the cell intro:
https://www.youtube.com/watch?v=B_zD3NxSsD8
• Most
cells are
microscopic due to
certain limitations on size
–
• DNA
• Rate of diffusion
• Surface area to volume
ratio
Major Cell Types - Prokaryotic
• Prokaryotic – found in
archaea and bacteria
• Contain DNA, ribosomes,
plasma membrane
• Usually contain cell wall
• Can contain a capsule,
pili, flagella
• 1/10 the size of eukaryotic
cells
• Do NOT contain nucleus
or membrane bound
organelles
Major Cell Types - Eukaryotic
• Eukaryotic – found in all other organisms (protists,
fungi, plants, animals)
• Have a nucleus.
• Have membrane bound organelles where a majority
of cellular metabolism is accomplished
• The folded membranes of eukaryotic cells
dramatically increase workable surface area and
create compartments
• Representative eukaryotic cells = plant and animal
cells
• Have most organelles in common with a few key
differences
Eukaryotic Cells – Plant and Animal
FM Image
Eukaryotic Cell Organelles
• Nucleus – contains DNA.
• DNA usually exists as
chromatin.
• Prior to cell division it
shortens into discrete
chromosomes.
• Controls cellular activities
by directing protein
synthesis.
• Enclosed by the nuclear
envelope – membrane with
pores that highly regulate
traffic in and out
• Nucleolus – inside nucleus,
produces ribosome
precursors
Eukaryotic Cell Organelles
• Ribosome – also
found in prokaryotes.
• Site of protein
synthesis.
• Receives instructions
from genes in DNA to
build specific
polypeptides
(proteins)
• Free vs. bound
Organelles of the Endomembrane
System
• Many organelles are
connected either physically
or by the transfer of
materials in tiny membrane
fragments called vesicles.
• Collectively these make up
the endomembrane system.
• Organelles include –
nuclear envelope, Smooth
and Rough ER, Golgi
apparatus, lysosomes, and
vacuoles
Smooth Endoplasmic Reticulum
● Interconnected tubules
that lack ribosomes
● Synthesis of lipids (oils,
and steroids)
● Detoxify certain drugs
and alcohol
● Stores calcium ions
inside and releases
them into the cytosol
when a nerve signal
stimulates a muscle cell
to contract
Rough Endoplasmic Reticulum
• Membrane is continuous
with nuclear membrane
• Has ribosomes attached
• Modifies proteins and
transports them to the
Golgi apparatus
• Transport occurs in
vesicles that bud off of the
rough ER
• Proteins can be modified
in rough ER, ex. Attach
small sugars =
glycoprotein
Golgi Apparatus
• Series of flattened sacs
• Receives, modifies, and
ships molecules (usually
proteins from rough ER)
• Has receiving side and
shipping side
• Products usually shipped
to other organelles or to
the plasma membrane
and can be exported
from the cell entirely
Lysosomes
• Contain hydrolytic
enzymes enclosed in a
membrane
• The membrane
provides an acidic
environment
• Digest food, worn out
cell parts, pathogens
• Apoptosis
• Tay Sachs
Autophagy
Vacuoles
• Used for storage of a
variety of substances
• Plant cells usually
contain one large
vacuole = central vacuole
(water, pigments,
poisons)
• Paramecium contain
contractile vacuoles to
maintain water balance
• Now looking at
organelles that are not
part of endomembrane
system
Chloroplast
• Site of photosynthesis in
plants and algae
• Has two membranes that are
compartmentalized into
several areas
• Space between membranes
(inner and outer)
• Space inside inner
membrane filled with fluid
called stroma (site of sugar
production)
• Stacked disks = granum
• Individual disk = thylakoid
(contains pigments for
absorbing solar energy)
Mitochondria
• Site of cellular respiration
in eukaryotic cells
• Produce ATP
• Has two
compartmentalized
membranes
• Outer membrane = smooth
• Inner membrane = highly
folded (cristae)
• Inside the inner membrane
= mitochondrial matrix
• Between outer and inner
membranes =
intermembrane space
Cytoskeleton
• A network of protein fibers throughout the cytoplasm
• Provide structural support, organelle anchorage, helps
maintain cell shape
• Involved in cell movements
• Three main types of fibers –
• Microfilaments – thinnest, made of actin molecules (globular
proteins) that are arranged in a twisted double chain, support
shape, contractions
• Intermediate filaments – made of fibrous proteins that
supercoil into cables, reinforce cell shape, anchorage of nucleus
and other organelles, more permanent than microtubules
• Microtubules – thickest, made of tubulin (protein), hollow, tracks
for movement, guide movement of chromosomes during cell
division, main components of cilia and flagella, readily
disassembled for subunit use in other areas of the cell
Cytoskeleton
support shape, contractions
reinforce cell shape, anchorage of
nucleus and other organelles
tracks for movement,
anchorage, rigidity, guide
movement of chromosomes
during cell division
Cilia and Flagella
• Used for locomotion
• Cilia – short and numerous, oarlike
• Flagella – longer, fewer, whiplike
• Similar internal structure – 9+2
arrangement of microtubules, spokes,
anchored to basal body
• Protein dynein creates movement
• https://www.youtube.com/watch?v=SgR4ojtPw5Q
•
Kartagener's syndrome: the dynein
arms malfunction = the inability of
cilia in the respiratory tract to clear
away bacteria or other materials.
Cell Surfaces and Junctions
• Plant cell walls provide
the rigid support plants
need to remain upright
• Made of cellulose
embedded in a matrix of
other polysaccharides
• Pectin acts as glue to
hold adjoining cell walls
together
• Plasmodesmata act like
canals for transport and
communication
Cell Surfaces and Junctions
• Animal cells have a
collection of proteins
and glycoproteins
outside their PM
called the
extracellular matrix
• Function in
connection,
communication, and
recognition
Cell Surfaces and Junctions
• •https://www.youtube.com/watch?v=gJ9WTD
0XEnc
• Animal cells also connect
at junctions –
• Tight junctions – tight,
leakproof sheets
• Anchoring junctions –
riveted, strong sheets,
under mechanical stress
• Gap junctions – channels
for transport