Cell Structure and Function
Chapter 4
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
4.1 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
4.3 Eukaryotic Cells
• Have a nucleus and other
organelles
• Eukaryotic organisms
– Plants
– Animals
– Protistans
– Fungi
•
•
•
•
•
•
•
•
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
4.4 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
4.5 Endomembrane 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
Endomembrane 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
4.6 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
4.7 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
4.9 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
4.10 Flagella and Cilia
microtubule
• Structures for
cell motility
• 9 + 2 internal
structure
Figure 4.25
Page 73
dynein
4.11 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
4.12 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