Cell Structure and Function
Chapter 4
4.1 What is a Cell?
 Each cell has a plasma membrane, cytoplasm,
and a nucleus (in eukaryotic cells) or a nucleoid (in
prokaryotic cells)
cytoplasm
DNA
plasma
membrane
a Bacterial cell (prokaryotic)
Fig. 4.3, p. 52
cytoplasm
DNA in
nucleus
plasma
membrane
b Plant cell (eukaryotic)
Fig. 4.3, p. 52
cytoplasm
DNA in
nucleus
plasma
membrane
c Animal cell (eukaryotic)
Fig. 4.3, p. 52
Animation: Overview of cells
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Components of Cell Membranes
 Lipid bilayer
“head”
two “tails”
Fig. 4.4, p. 53
fluid
lipid
bilayer
fluid
Fig. 4.4, p. 53
extracellular
environment
one layer
of lipids
one layer
of lipids
cytoplasm
membrane
protein
Fig. 4.4, p. 53
Cell Size and Shape
 Surface-to-volume ratio limits cell size
Key Concepts:
WHAT ALL CELLS HAVE IN COMMON
 Each cell has a plasma membrane, a boundary
between its interior and the outside environment
 The interior consists of cytoplasm and an
innermost region of DNA
Animation: Surface-to-volume ratio
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4.2 How Do We See Cells?
 Three key points of the cell theory:
• All organisms consist of one or more cells
• The cell is the smallest unit that retains the
capacity for life
• A cell arises from the growth and division of
another cell
Relative Sizes
Fig. 4.6, p. 54
Microscopes
 Different microscopes use light or electrons to
reveal details of cell shapes or structures
path of light rays (bottom to top) to eye
Ocular lens enlarges
primary image formed
by objective lenses.
prism that
directs rays to
ocular lens
Objective lenses (those closest
to specimen) form the primary
image. Most compound light
microscopes have several.
stage supports
microscope slide
Condenser lenses focus
light rays through specimen.
illuminator
light source (in base)
Fig. 4.7, p. 55
Animation: How a light microscope
works
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incoming electron beam
condenser lens (focuses a
beam of electrons onto
specimen)
specimen
objective lens
intermediate lens
projector lens
viewing screen (or
photographic film)
Fig. 4.7, p. 55
Animation: How an electron microscope
works
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Five Different Views
Key Concepts:
MICROSCOPES
 Microscopic analysis supports three
generalizations of the cell theory:
• Each organism consists of one or more cells and
their products
• A cell has a capacity for independent life
• Each new cell is descended from a living cell
4.3 Membrane Structure and Function
 Each cell membrane is a boundary (lipid bilayer)
that controls the flow of substances across it
 Fluid mosaic model
• Membrane is composed of phospholipids, sterols,
proteins, and other components
• Phospholipids drift within the bilayer
Membrane Proteins
 Many proteins are embedded in or attached to
cell membrane surfaces
• Receptors, transporters, communication proteins,
and adhesion proteins
 Plasma (outer) membrane also incorporates
recognition proteins
Common Membrane Proteins
EXTRACELLULAR FLUID
A glucose transporter
allows glucose to cross
the membrane through
a channel in its interior.
An ATP synthase,
which makes ATP when
H+ crosses a membrane
through its interior.
A calcium pump
moves calcium ions
across the membrane;
requires ATP energy.
LIPID
B cell receptor.
Recognition protein that
BILAYER It binds to bacteria, identifies a cell as belonging
other foreign agents. to one’s own body.
phospholipid
protein filaments of the cytoskeleton
CYTOPLASM
Fig. 4.9, p. 57
Membrane Structure Studies
human cell
mouse cell
fusion into
hybrid cell
proteins from
both cells
in fused
membrane
Fig. 4.10, p. 57
Key Concepts:
COMPONENTS OF CELL MEMBRANES
 All cell membranes are mostly a lipid bilayer (two
layers of lipids) and a variety of proteins
 The proteins have diverse tasks, including
control over which water-soluble substances
cross the membrane at any given time
Animation: Lipid bilayer organization
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Animation: Cell membranes
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4.4 Introducing Prokaryotic Cells
 Bacteria and archaeans
• The simplest cells
• The groups with greatest metabolic diversity
 Biofilms
• Shared living arrangements of prokaryotes
Prokaryote Structure
 Cell wall
• Surrounds plasma membrane
 Flagella
• Used for motion
 Pili
• Protein filaments used for attachment
• “Sex” pilus transfers genetic material
Prokaryote Structure
Prokaryote Structure
cytoplasm,
with ribosomes
bacterial flagellum
Most prokaryotic cells have a cell
wall outside the plasma membrane,
and many have a thick, jellylike
capsule around the wall.
DNA in
cell plasma
pilus capsule wall membrane nucleoid
Fig. 4.11, p. 58
Animation: Typical prokaryotic cell
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4.5 Microbial Mobs
 Biofilm formation
Key Concepts:
PROKARYOTIC CELLS
 Archaeans and bacteria are prokaryotic cells
which have few, if any, internal membraneenclosed compartments
 In general, they are the smallest and structurally
the simplest cells
4.6 Introducing Eukaryotic Cells
 Start with a nucleus and other organelles
• Carry out specialized functions inside a cell
plasma
membrane
nucleus
mitochondria
Fig. 4.14, p. 60
cell wall
plasma
membrane
central
vacuole
nucleus
chloroplast
Fig. 4.14, p. 60
Components of Eukaryotic Cells
4.7 Components of The Nucleus
 Nucleus separates DNA from cytoplasm
• Chromatin (all chromosomal DNA with proteins)
• Chromosomes (condensed)
 Nucleolus assembles ribosome subunits
 Nuclear envelope encloses nucleoplasm
• Pores, receptors, transport proteins
Nucleus and Nuclear Envelope
Nucleus and Nuclear Envelope
Nucleus and Nuclear Envelope
Animation: Nuclear envelope
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nuclear envelope
chromatin
nucleolus
cytoplasm
Fig. 4.15, p. 61
nucleus
pore across the
nuclear envelope
nucleoplasm
nucleolus
chromatin
nuclear envelope’s
outer lipid bilayer
merging with an
ER membrane
Fig. 4.15, p. 61
nuclear pore
nuclear envelope
(two lipid bilayers)
cytoplasm
Fig. 4.15, p. 61
4.8 The Endomembrane System
 Endoplasmic reticulum (ER)
• An extension of the nuclear envelope
• RER modifies new polypeptide chains
• SER makes lipids; other metabolic functions
 Golgi bodies
• Further modify polypeptides
• Assemble lipids
The Endomembrane System
 Vesicles
• Endocytic and exocytic: Transport or store
polypeptides and lipids
• Peroxisomes: Digest fatty acids and amino acids;
break down toxins and metabolic by-products
• Lysosomes: Intracellular digestion (animals)
• Central vacuole: Storage; fluid pressure (plants)
Endomembrane System
Endomembrane System
Endomembrane System
nucleus
rough ER
smooth ER
Golgi body
vesicles
Fig. 4.16, p. 62
Animation: The endomembrane system
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chromatin
pore
cytoplasm
nucleolus nuclear envelope
(two lipid bilayers)
the cell nucleus
ribosome
vesicle
rough ER
Fig. 4.16, p. 62
smooth ER channel, cross-section
budding vesicle
plasma membrane
smooth ER
Golgi body
Fig. 4.16, p. 62
4.9 Mitochondria and Chloroplasts
 Mitochondria
• Break down organic compounds by aerobic
respiration (oxygen-requiring)
• Produce ATP
 Chloroplasts
• Produce sugars by photosynthesis
Mitochondria and Chloroplasts
two outer
membranes
stroma
thylakoids
(inner membrane
system folded into
flattened disks)
Fig. 4.18, p. 63
Animation: Structure of a chloroplast
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Animation: Structure of a mitochondrion
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4.10 Visual Summary: Plant Cells
Visual Summary: Animal Cells
CELL WALL
CHLOROPLAST
CENTRAL
VACUOLE
NUCLEUS
nuclear envelope
nucleolus
DNA in
nucleoplasm
CYTOSKELETON
microtubules
microfilaments
intermediate
filaments
(not shown)
RIBOSOMES
ROUGH ER
MITOCHONDRION
SMOOTH ER
PLASMODESMA
GOLGI BODY
PLASMA
MEMBRANE
a Typical plant cell components.
LYSOSOMELIKE VESICLE
Fig. 4.19, p.65
NUCLEUS
nuclear envelope
nucleolus
DNA in
nucleoplasm
CYTOSKELETON
microtubules
microfilaments
intermediate
filaments
RIBOSOMES
ROUGH ER
MITOCHONDRION
SMOOTH ER
CENTRIOLES
GOLGI BODY
PLASMA
MEMBRANE
b Typical animal cell components.
LYSOSOME
Fig. 4.19, p. 64
NUCLEUS
nuclear envelope
nucleolus
DNA in
nucleoplasm
CYTOSKELETON
microtubules
microfilaments
intermediate
filaments
RIBOSOMES
ROUGH ER
MITOCHONDRION
SMOOTH ER
CENTRIOLES
GOLGI BODY
PLASMA
MEMBRANE
b Typical animal cell components.
LYSOSOME
Stepped Art
Fig. 4-19, p. 64
Animation: Common eukaryotic
organelles
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4.11 Cell Surface Specializations
 Most prokaryotes, protists, fungi, all plant cells
have a cell wall around their plasma membrane
• Protects, supports, maintains cell shape
• Primary and secondary cell walls
 Plasmodesmata across cell walls connect plant
cells
Plant Cell Walls
plasma membrane
middle
lamella
cytoplasm
primary
cell wall
secondary
cell wall
(added in
layers)
primary
cell wall
pipeline
made of
abutting
cell walls
Fig. 4.20, p. 66
Plant Cell Walls
middle lamella
Plasmodesmata
plasmodesma
middle lamella
Fig. 4.20, p. 66
Animation: Plant cell walls
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Plant Cuticle
 Protective surface secretion, limits water loss
thick, waxy
cuticle at
leaf surface
cell of leaf
epidermis
photosynthetic
cell inside leaf
Fig. 4.21, p. 67
Extracellular Matrixes
 Surrounds cells of specific tissues
Animal Cell Junctions
 Connect cells of animals
• Adhering junctions, tight junctions, gap junctions
free surface of
epithelial tissue
different kinds of
tight junctions
gap junction
basement membrane
(extracellular matrix)
adhering junction
Fig. 4.23, p. 67
Animation: Animal cell junctions
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Key Concepts:
EUKARYOTIC CELLS
 Cells of protists, plants, fungi, and animals are
eukaryotic; they have a nucleus and other
membrane-enclosed compartments
 They differ in internal parts and surface
specializations
4.12 The Dynamic Cytoskeleton
 Components of the cytoskeleton
• Microtubules
• Microfilaments
• Intermediate filaments (in most)
Fig. 4.12, p. 59
Fig. 4.12, p. 59
Fig. 4.12, p. 59
Components of the Cytoskeleton
tubulin
subunit
25 nm
Fig. 4.24, p. 68
actin
subunit
5–7 nm
Fig. 4.24, p. 68
one
polypeptide
chain
8–12 nm
Fig. 4.24, p. 68
Cytoskeleton Function
 Organizes and moves cell parts
 Reinforces cell shape
 Interactions between motor proteins and
microtubules in cilia, flagella, and pseudopods
can move the whole cell
Animation: Cytoskeletal components
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Motor Protein: Kinesin
 Moves vesicles along microtubules
Animation: Motor proteins
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Flagellum and Pseudopods
Eukaryotic Flagella and Cilia: Dynein
Eukaryotic Flagella and Cilia: Dynein
pair of microtubules in a central sheath
protein
spokes
plasma
membrane
pair of
microtubules
dynein arms
dynein arms
basal body
Fig. 4.27, p. 69
Animation: Flagella structure
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Key Concepts:
A LOOK AT THE CYTOSKELETON
 Diverse protein filaments reinforce a cell’s shape
and keep its parts organized
 As some filaments lengthen and shorten, they
move chromosomes or other structures to new
locations