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Cell Structure and Function
Chapter 4
Early Discoveries
• Mid 1600s - Robert Hooke observed
and described cells in cork
• Late 1600s - Antony van Leeuwenhoek
observed sperm, microorganisms
• 1820s - Robert Brown observed and
named nucleus in plant cells
Hooke’s compound microscope & his drawings
Antony van Leeuwenhoek
Credit: © Science VU
Robert Hooke's sketches of cork cells.
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Credit: © David Phillips
Microscopic technique series - Cheek cells. Phase view. LM X75.
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Credit: © David Phillips
Microscopic technique series - Cheek cells. Nomarski view. LM X75.
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Credit: © George Wilder
Parenchyma cells of the potato, showing the central cell with obvious nucleus and purple-stained
starch. LM X83.
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Credit: © Michael Abbey
This living protozoan is the common Paramecium multimicronucleatum that moves by means of its numerous cilia.
Paramecia feed on smaller organisms which are swept into the oral groove by beating cilia. Food and water are stored in
vacuoles and this species may have as many as seven nuclei. LM X100.
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Credit: © Manfred Schliwa
Cytoskeleton, immunofluorescent double labeled, showing microtubules in green and actin
microfilaments in red. LM X700.
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Credit: © Dr. Dennis Kunkel
Paramecium, a ciliated protozoan. SEM X130.
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Credit: © Dr. David Phillips
Ciliated protozoan Tetrahymena with buccal cavity visible. SEM X3500.
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Credit: © Dr. David Phillips
Root cells of an onion showing the cell wall. TEM X47,000.
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Credit: © RMF
Thin cross-section cut through the isolated axoneme. Chlamydomonas algae flagella have the 9+2 structure
characteristic of all eukaryotic cells. The axoneme has a central unit containing two single microtubules and nine
peripheral doublet microtubules. Dynein sidearms project from the A tubule of each doublet. Also visible are the
radial spokes and the inner sheath. TEM.
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Credit: © Dr. Richard Kessel & Dr. Gene Shih
Freeze-fracture technique used to show nuclear pores. Nuclear pores are structures in the nuclear envelope that
allow passage of certain materials between the cell nucleus and the cytoplasm. TEM X100,000.
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Credit: © Dr. Donald Fawcett
Mitochondrion showing foliate cristae and matrix granules. Mitochondria are the main energy
source of the cell. TEM.
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Developing Cell Theory
• Matthias Schleiden
• Theodor Schwann
• Rudolf Virchow
Matthias Jakob Schleiden
Theodor Schwann
Rudolf Virchow
Cell Theory
1) Every organism is composed of one or
more cells
2) Cell is smallest unit having properties
of life
3) Continuity of life arises from growth
and division of single cells
Cell
• Smallest unit of life
• Can survive on its own or has potential
to do so
• Is highly organized for metabolism
• Senses and responds to environment
• Has potential to reproduce
Structure of Cells
All start out life with:
Two types:
– Plasma membrane
– Prokaryotic
– Region where DNA
is stored
– Eukaryotic
– Cytoplasm
Lipid Bilayer
• Main component of cell membranes
• Gives the membrane its fluid properties
• Two layers of phospholipids
one layer
of lipids
one layer
of lipids
Figure 4.3
Page 56
Membrane Proteins
Recognition
protein
Receptor
protein
extracellular
environment
lipid bilayer
cytoplasm
Protein
pump across
bilayer
Protein
channel
across bilayer
Protein pump
Figure 4.4
Page 57
Why Are Cells So Small?
• Surface-to-volume ratio
• The bigger a cell is, the less surface
area there is per unit volume
• Above a certain size, material cannot be
moved in or out of cell fast enough
Microscopes
• Create detailed images of something
that is otherwise too small to see
• Light microscopes
– Simple or compound
• Electron microscopes
– Transmission EM or Scanning EM
Limitations of Light
Microscopy
• Wavelengths of light are 400-750 nm
• If a structure is less than one-half of a
wavelength long, it will not be visible
• Light microscopes can resolve objects
down to about 200 nm in size
Electron Microscopy
• Uses streams of accelerated electrons
rather than light
• Electrons are focused by magnets
rather than glass lenses
• Can resolve structures down to 0.5 nm
Eukaryotic Cells
• Have a nucleus and other
organelles
• Eukaryotic organisms
– Plants
– Animals
– Protistans
– Fungi
Animal Cell Features
•
•
•
•
•
•
•
•
Plasma membrane
Nucleus
Ribosomes
Endoplasmic
reticulum
Golgi body
Vesicles
Mitochondria
Cytoskeleton
Figure 4.10b
Page 61
Plant Cell Features
•
•
•
•
•
•
•
•
Plasma membrane
Nucleus
Ribosomes
Endoplasmic
reticulum
Golgi body
Vesicles
Mitochondria
Cytoskeleton
• Cell wall
• Central vacuole
• Chloroplast
Figure 4.10a
Page 61
Functions of Nucleus
• Keeps the DNA molecules of eukaryotic
cells separated from metabolic
machinery of cytoplasm
• Makes it easier to organize DNA and to
copy it before parent cells divide into
daughter cells
Components of Nucleus
nuclear envelope
nucleoplasm
nucleolus
chromatin
Figure 4.11b
Page 62
Nuclear Envelope
• Two outer membranes (lipid bilayers)
• Innermost surface has DNA attachment sites
Nuclear pore
bilayer facing cytoplasm
Nuclear envelope
bilayer facing
nucleoplasm
Figure 4.12b
Page 63
Cytomembrane System
• Group of related organelles in which
lipids are assembled and new
polypeptide chains are modified
• Products are sorted and shipped to
various destinations
Components of
Cytomembrane System
Endoplasmic reticulum
Golgi bodies
Vesicles
Endoplasmic Reticulum
• In animal cells, continuous with nuclear
membrane
• Extends throughout cytoplasm
• Two regions - rough and smooth
Golgi Body
• Puts finishing touches on proteins and
lipids that arrive from ER
• Packages finished material for shipment to
final destinations
• Material arrives and leaves in vesicles
budding
vesicle
Figure 4.15
Page 65
Vesicles
• Membranous sacs that
move through cytoplasm
• Lysosomes
• Peroxisomes
Mitochondria
• ATP-producing powerhouses
• Membranes form two distinct
compartments
• ATP-making machinery embedded
in inner mitochondrial membrane
Mitochondrial Origins
• Mitochondria resemble bacteria
– Have own DNA, ribosomes
– Divide on their own
• May have evolved from ancient bacteria
that were engulfed but not digested
Specialized Plant Organelles
• Plastids
• Central Vacuole
Chloroplasts
Convert sunlight energy to ATP through
photosynthesis
Other Plastids
• Chromoplasts
– No chlorophyll
– Abundance of carotenoids
– Color fruits and flowers red to yellow
• Amyloplasts
– No pigments
– Store starch
Cytoskeleton
• Present in all eukaryotic cells
• Basis for cell shape and internal
organization
• Allows organelle movement within cells
and, in some cases, cell motility
Cytoskeletal Elements
intermediate
filament
microtubule
microfilament
tubulin
subunit
Microtubules
• Largest elements
• Composed of tubulin
• Arise from microtubule
organizing centers (MTOCs)
• Involved in shape, motility,
cell division
Figure 4.21
Page 71
Microfilaments
• Thinnest elements
• Composed of actin
• Take part in movement,
formation, and
maintenance of cell
actin
subunit
shape
Figure 4.21
Page 71
Intermediate Filaments
• Only in animal
cells of certain
tissues
• Most stable
cytoskeletal
elements
one
polypeptide
chain
• Six known groups
Figure 4.21
Page 71
Motor Proteins
• Kinesins and dyneins move along
microtubules
• Myosins move along microfilaments
kinesin
microtubule
Figure 4.24b, Page 72
Flagella and Cilia
microtubule
• Structures for
cell motility
• 9 + 2 internal
structure
Figure 4.25
Page 73
dynein
Plant Cell Walls
Secondary cell wall
(3 layers)
Primary cell wall
Plant Cuticle
• Cell secretions and waxes accumulate
at plant cell surface
• Semitransparent
• Restricts water loss
Matrixes between Animal Cells
• Animal cells have no cell walls
• Some are surrounded by a matrix of
cell secretions and other material
Cell-to-Cell Junctions
• Plants
– Plasmodesmata
• Animals
– Tight junctions
– Adhering junctions
– Gap junctions
plasmodesma
Animal Cell Junctions
tight
junctions
adhering
junction
gap
junction
Prokaryotic Cells
• Archaebacteria and Eubacteria
• DNA is not enclosed in nucleus
• Generally the smallest, simplest cells
• No organelles
Prokaryotic Structure
pilus
cytoplasm
with ribosomes
DNA
flagellum
capsule
cell plasma
wall membrane