Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 4
Cell Structure
(Sections 4.1 - 4.7)
Albia Dugger • Miami Dade College
4.1 Food for Thought
• Helpful intestinal bacteria make vitamins that mammals can’t,
and they crowd out more dangerous germs
• Escherichia coli is one of the most common intestinal bacteria
of warm-blooded animals – only a few of the hundreds of
types (strains) are harmful
E. coli O157:H7
• E. coli O157:H7 makes
a potent toxin that can
severely damage the
lining of the human
intestine
• Causes serious illness
in people who eat
contaminated foods
4.2 What, Exactly, Is a Cell?
• cell
• The smallest unit that
has the properties of life
• Cells pictured are
individual organisms
(protists)
Traits Common to All Cells
• Although cells differ in size, shape, and function, each starts
out with a plasma membrane, cytoplasm, and a region of
DNA (in eukaryotic cells, a nucleus)
• plasma membrane
• A cell’s outermost membrane
• A lipid bilayer is the structural foundation of cell
membranes, including organelle membranes
Key Terms
• organelle
• Structure that carries out a specialized metabolic function
inside a cell
• cytoplasm
• Semifluid substance enclosed by a cell’s plasma
membrane
• nucleus
• Organelle with two membranes that holds a eukaryotic
cell’s DNA
Single Cells
Bacterial Cell
• Bacteria are singlecelled organisms
• Archaeans are similar to
bacteria in overall
structure
cytoplasm
DNA
plasma
membrane
A Bacterial cell
Fig. 4.3a, p. 52
Plant Cell
cytoplasm
DNA in
nucleus
plasma
membrane
B Plant cell
Fig. 4.3b, p. 52
Animal Cell
cytoplasm
DNA in
nucleus
plasma
membrane
C Animal cell
Fig. 4.3c, p. 52
ANIMATION: Overview of cells
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Constraints on Cell Size
• Surface-to-volume ratio limits cell size
• If the cell gets too big, inward flow of nutrients and outward
flow of wastes across the membrane will not be fast enough
• surface-to-volume ratio
• A relationship in which the volume of an object increases
with the cube of the diameter, but surface area increases
with the square of the diameter
Surface-to-Volume Ratio
• The physical relationship between increases in volume and
surface area constrains cell size and shape
ANIMATION: Surface-to-volume
ratio
Cell Theory
• The cell is the structural and functional unit of all organisms
• cell theory
• Theory that all organisms consist of one or more cells,
which are the basic unit of life
History of Cell Discovery
• 1665: Antoni van Leeuwenhoek first observed “many very
small animalcules”
• Robert Hooke magnified a piece of thinly sliced cork and
named the tiny compartments he observed “cellae”
• 1820s: Robert Brown was first to identify a cell nucleus
• Matthias Schleiden, hypothesized that a plant cell is an
independent living unit even when it is part of a plant
• Schleiden and Theodor Schwann concluded that the tissues
of animals as well as plants are composed of cells
Cell Theory
• Four generalizations constitute the cell theory:
1. Every living organism consists of one or more cells
2. A cell is the smallest unit of life, individually alive even as
part of a multicelled organism
3. All living cells come from division of preexisting cells
4. Cells contain hereditary material, which they pass to their
offspring during division
Key Concepts
• What Is a Cell?
• A cell is the smallest unit of life
• Each has a plasma membrane that separates its interior
from the exterior environment
• A cell’s interior contains cytoplasm and DNA
4.3 Spying on Cells
• Most cells are far too
small to see with the
naked eye
• We use different types
of microscopes and
techniques to reveal
cells and their internal
and external details
Types of Microscopes
• Light microscopes
• Electron microscopes
• Phase-contrast
microscopes
• Transmission electron
Microscopes
• Fluorescence
microscope
• Scanning electron
microscopes
Examples of Microscopes
• Compound light
microscope
• Transmission electron
microscope (TEM)
path of light rays (bottom to top) to eye
prism that
directs rays
to ocular lens
ocular lens
objective lenses
focusing
knob
specimen
stage
condenser lens
illuminator
light source
(in base)
Fig. 4.5a, p. 54
incoming electron beam
condenser
lens
specimen
on grid
objective
lens
projective
lens
phosphor
screen
Fig. 4.5b, p. 54
ANIMATION: How a light microscope works
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Different Views, Same Organism
A Light micrograph.
A phase-contrast
microscope yields
high-contrast images
of trans- parent
specimens. Dark
areas have taken up
dye.
B Light micrograph.
A reflected light
microscope
captures light
reflected from
specimens.
C Fluorescence
micrograph.
This image
shows
fluorescent
light emitted by
chlorophyll
molecules in
the cells.
D A transmission
electron micrograph
reveals fantastically
detailed images of
internal structures.
E A scanning
electron micrograph shows
surface details.
SEMs may be
artificially colored
to highlight
specific details.
Fig. 4.6, p. 55
Relative Sizes
Measurements
• Units of length:
• 1 centimeter (cm) = 1/100 meter, or 0.4 inch
• 1 millimeter (mm) = 1/1000 meter, or 0.04 inch
• 1 micrometer (μm) = 1/1,000,000 meter, or 0.00004 inch
• 1 nanometer (nm) = 1/1,000,000,000 meter, or
0.00000004 inch
• 1 meter = 102 cm = 103 mm = 106 μm = 109 nm
Key Concepts
• Microscopes
• Most cells are too small to see with the naked eye
• We use different types of microscopes to reveal different
details of their structure
ANIMATION: How an electron microscope
works
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4.4 Membrane Structure
and Function
• A cell membrane functions as a selectively permeable barrier
that separates an internal environment from an external one
• Membranes of most cells can be described as a fluid mosaic
of lipids (mainly phospholipids) and proteins
• Lipids are organized as a lipid bilayer: a double layer of
lipids in which the nonpolar tails of both layers are
sandwiched between the polar heads
Key Terms
• lipid bilayer
• Structural foundation of cell membranes; double layer of
lipids arranged tail-to-tail
• fluid mosaic
• Model of a cell membrane as a two-dimensional fluid of
mixed composition
A Lipid Bilayer
Basic Cell
• At its most basic, a cell
is a lipid bilayer bubble
filled with fluid
Membrane Proteins
• Proteins associated with a membrane carry out most
membrane functions
• All membranes have transport proteins
• Plasma membranes also have receptor proteins, adhesion
proteins, enzymes, and recognition proteins
Key Terms
• transport protein
• Protein that passively or actively assists specific ions or
molecules across a membrane
• adhesion protein
• Membrane protein that helps cells stick together in tissues
• receptor protein
• Binds to a particular substance outside of the cell
• recognition protein
• Tags a cell as belonging to self (one’s own body)
Membrane Proteins
Recognition and Receptor Proteins
Transport Proteins
B Recognition
proteins such as this
MHC molecule tag a
cell as belonging to
one’s own body.
C Receptor proteins
such as this B cell
receptor bind
substances outside the
cell. B cell receptors
help the body eliminate
toxins and infectious
agents such as bacteria.
D Transport proteins
bind to molecules on
one side of the
membrane, and
release them on the
other side. This one
transports glucose.
E This transport
protein, an ATP
synthase, makes
ATP when
hydrogen ions flow
through its interior.
Extracellular Fluid
Lipid
Bilayer
Cytoplasm
Fig. 4.8b-e, p. 57
ANIMATION: Cell membranes
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Variations on the Model
• Archaeans do not build phospholipids with fatty acids –
instead, the tails of archaean phospholipids form covalent
bonds with one another
• Archaean membranes are far more rigid than those of
bacteria or eukaryotes
Key Concepts
• Cell Membranes
• All cell membranes consist mainly of a lipid bilayer and
different types of proteins
• The proteins carry out various tasks, including control over
which substances cross the membrane
ANIMATION: Lipid bilayer organization
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ANIMATION: Fluid mosaic model
4.5 Bacteria and Archaeans
• Single-celled bacteria and archaeans are the smallest and
most diverse forms of life:
• The cytoplasm contains ribosomes and plasmids
• A single, circular chromosome is located in a nucleoid
• Many have a cell wall, flagella or pili
Key Terms
• ribosome
• Organelle of protein synthesis
• plasmid
• Small circle of DNA in some bacteria and archaeans
• nucleoid
• Region of cytoplasm where the DNA is concentrated
inside a bacterium or archaean
Key Terms
• flagellum
• Long, slender cellular structure used for motility
• pilus
• A protein filament that projects from the surface of some
bacterial cells – sex pilus
• cell wall
• Semi-rigid but permeable structure that surrounds the
plasma membrane of some cells
Bacteria
Archaeans
Body Plan of Bacteria
and Archaeans
flagellum
cell plasma
DNA in cytoplasm,
pilus capsule wall membrane nucleoid with ribosomes
Fig. 4.11, p. 58
ANIMATION: Typical prokaryotic cell
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Cell Walls
• The cell wall of most archaeans consists of proteins
• The wall of most bacteria consists of a polymer of peptides
and polysaccharides
• Sticky polysaccharides form a slime layer, or capsule, around
the wall of many types of bacteria
Biofilms
• Biofilms are shared living arrangements among bacteria and
other microbial organisms
• biofilm
• Community of different types of microorganisms living
within a shared mass of slime
• May include bacteria, algae, fungi, protists, and archaeans
A Biofilm
• A biofilm organizes itself
into “neighborhoods,”
each with a distinct
microenvironment that
stems from its location
within the biofilm and
species that inhabit it
Key Concepts
• Bacteria and Archaea
• Archaeans and bacteria have few internal membraneenclosed compartments
• In general, they are the smallest and structurally the
simplest cells, but they are also the most numerous
4.6 Introducing Eukaryotic Cells
• All protists, fungi, plants, and animals are eukaryotes
• Eukaryotic cells start out life with membrane-enclosed
organelles, including a nucleus
• Most eukaryotic cells contain an endomembrane system (ER,
vesicles, and Golgi bodies), mitochondria, and a cytoskeleton
Components of Eukaryotic Cells
Animal and Plant Cells
cell wall
central
vacuole
vacuole
plasma
membrane
chloroplast
mitochondrion
nucleus
Fig. 4.13, p. 60
4.7 The Nucleus
• The nucleus contains the cell’s genetic material (DNA)
• In the nucleus, ribosome subunits are assembled in dense
regions called nucleoli
• The nucleus has a double-membraned nuclear envelope
surrounding nucleoplasm
Key Terms
• nucleolus
• In a cell nucleus, a dense, irregularly shaped region where
ribosomal subunits are assembled
• nuclear envelope
• A double membrane that constitutes the outer boundary of
the nucleus
• nucleoplasm
• Viscous fluid enclosed by the nuclear envelope
The Nuclear Envelope
• The nuclear membrane controls passage of certain molecules
between the nucleus and the cytoplasm
• Receptors and transporters stud both sides of the nuclear
envelope; other proteins form nuclear pores
• The outer bilayer of the double membrane is continuous with
the membrane of the ER
The Nucleus
nuclear
envelope
DNA
nucleoplasm
nuclear pore
nucleolus
cytoplasm
ER
Fig. 4.14, p. 61
Nuclear Pores
nuclear pore
nuclear envelope
(two lipid bilayers)
cytoplasm
Fig. 4.15, p. 61
ANIMATION: Nuclear envelope
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