Cell Structure and Function
Impacts, Issues:
Food For Thought
 A strain of E. coli bacteria that causes severe
illness or death occasionally contaminates foods
such as ground beef and fresh vegetables
4.1 The Cell Theory
 The cell theory, a foundation of modern biology,
states that cells are the fundamental units of life
Measuring Cells
 One micrometer (μm) is one-thousandth of a
millimeter
Animalcules and Beasties
 Van Leeuwenhoek was the first to describe
small organisms seen through a microscope,
which he called animalcules and beasties
 Hooke was the first to sketch and name cells
Development of the Microscope
The Cell Theory Emerges
 In 1839, Schleiden and Schwann proposed the
basic concepts of the modern cell theory
• All organisms consists of one or more cells
• A cell is the smallest unit with the properties of life
• Each new cell arises from division of another,
preexisting cell
• Each cell passes its hereditary material to its
offspring
4.2 What Is a Cell?
 Cell
• The smallest unit that shows the properties of life
 All cells have a plasma membrane and
cytoplasm, and all start out life with DNA
The Basics of Cell Structure
 Eukaryotic cell
• Cell interior is divided into functional
compartments, including a nucleus
 Prokaryotic cell
• Small, simple cells without a nucleus
All Cells Have Three Things In Common
 Plasma membrane
• Controls substances passing in and out of the cell
 DNA containing region
• Nucleus in eukaryotic cells
• Nucleoid region in prokaryotic cells
 Cytoplasm
• A semifluid mixture containing cell components
Prokaryotic and Eukaryotic Cells
Fig. 4-4a, p. 56
Fig. 4-4b, p. 56
Cells Have Large Surface
Area-to-Volume Ratio
Cell Size
 Surface-to-volume ratio restricts cell size by
limiting transport of nutrients and wastes
Preview of Cell Membranes
 Lipid bilayer
• A double layer of phospholipids organized with
their hydrophilic heads outwards and their
hydrophobic tails inwards
• Many types of proteins embedded or attached to
the bilayer carry out membrane functions
Basic Structure of Cell Membranes
hydrophilic
head
two
hydrophobic
tails
A A phospholipid,
the main type of lipid
in cell membranes.
Fig. 4-6a, p. 57
Fig. 4-6b, p. 57
Fig. 4-6c, p. 57
4.1-4.2 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 consist of cytoplasm and an
innermost region of DNA
4.3 How Do We See Cells?
 We use different types of microscopes to study
different aspects of organisms, from the smallest
to the largest
Modern Microscopes
 Light microscopes
• Phase-contrast microscopes
• Reflected light microscopes
• Fluorescence microscopes
 Electron microscopes
• Transmission electron microscopes
• Scanning electron microscopes
Light and Electron Microscopes
Fig. 4-7a, p. 58
Fig. 4-7b, p. 58
Different Microscopes,
Different Characteristics
a) Light
micrograph. A
phase-contrast
micro-scope yields
high-contrast
images of
transparent
specimens, such
as cells.
b) Light
micrograph. A
reflected light
micro-scope
captures light
reflected from
opaque
specimens.
c) Fluorescence
micro-graph. The
chlorophyll
molecules in these
cells emitted red
light (they
fluoresced)
naturally.
d) A transmission
electron
micrograph
reveals
fantastically
detailed images
of internal
structures.
e) A scanning
electron micrograph shows
surface details of
cells and
structures. Often,
SEMs are
artificially colored
to highlight certain
details.
Stepped Art
Fig. 4-8, p. 59
4.3 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
4.4 Introducing Prokaryotic Cells
 Bacteria and archaea are the prokaryotes
(“before the nucleus”), the smallest and most
metabolically diverse forms of life
 Bacteria and archaea are similar in appearance
and size, but differ in structure and metabolism
General Prokaryote Body Plan
 Cell wall surrounds the plasma membrane
• Made of peptidoglycan (in bacteria) or proteins (in
archaea) and coated with a sticky capsule
 Flagellum for motion
 Pili help cells move across surfaces
• Sex pilus aids in sexual reproduction
flagellum
capsule
cell wall
plasma membrane
cytoplasm, with
ribosomes
DNA in nucleoid
pilus
Fig. 4-10, p. 60
Archaeans
Bacteria
4.5 Microbial Mobs
 Although prokaryotes are all single-celled, few
live alone
 Biofilm
• Single-celled organisms sharing a secreted layer
of polysaccharides and glycoproteins
• May include bacteria, algae, fungi, protists, and
archaeans
A Biofilm
4.4-4.5 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
 Eukaryotic (“true nucleus”) cells carry out much
of their metabolism inside membrane-enclosed
organelles
 Organelle
• A structure that carries out a specialized function
within a cell
Organelles of Eukaryotic Cells
Eukaryotes: Animal and Plant Cells
vacuole
plasma membrane
mitochondrion
nucleus
(a) Human white blood cell.
1 µm
Fig. 4-14a, p. 62
cell wall
central
vacuole
plasma
membrane
chloroplast
mitochondrion
nucleus
1 µm
(b) Photosynthetic cell from a blade of timothy grass.
Fig. 4-14b, p. 62
4.7 Visual Summary of Eukaryotic Cells
4.7 Visual Summary of Eukaryotic Cells
4.8 The Nucleus
• The nucleus keeps eukaryotic DNA away
from potentially damaging reactions in the
cytoplasm
• The nuclear envelope controls when DNA
is accessed
The Nuclear Envelope
• Nuclear envelope
– Two lipid bilayers pressed together as a
single membrane surrounding the nucleus
– Outer bilayer is continuous with the ER
– Nuclear pores allow certain substances to
pass through the membrane
The Nucleoplasm and
Nucleolus
• Nucleoplasm
– Viscous fluid inside the nuclear envelope,
similar to cytoplasm
• Nucleolus
– A dense region in the nucleus where subunits
of ribosomes are assembled from proteins
and RNA
The Chromosomes
• Chromatin
– All DNA and its associated proteins in the nucleus
• Chromosome
– A single DNA molecule with its attached proteins
– During cell division, chromosomes condense and
become visible in micrographs
– Human body cells have 46 chromosomes
Chromosome Condensation
4.9 The Endomembrane
System
• Endomembrane system
– A series of interacting organelles between the
nucleus and the plasma membrane
– Makes lipids, enzymes, and proteins for
secretion or insertion into cell membranes
– Other specialized cell functions
The Endoplasmic Reticulum
• Endoplasmic reticulum (ER)
– An extension of the nuclear envelope that forms a
continuous, folded compartment
• Two kinds of endoplasmic reticulum
– Rough ER (with ribosomes) folds polypeptides into
their tertiary form
– Smooth ER (no ribosomes) makes lipids, breaks
down carbohydrates and lipids, detoxifies poisons
Vesicles
• Vesicles
– Small, membrane-enclosed saclike organelles
that store or transport substances
• Peroxisomes
– Vesicles containing enzymes that break down
hydrogen peroxide, alcohol, and other toxins
• Vacuoles
– Vesicles for waste disposal
Golgi Bodies and Lysosomes
• Golgi body
– A folded membrane containing enzymes that finish
polypeptides and lipids delivered by the ER
– Packages finished products in vesicles that carry
them to the plasma membrane or to lysosomes
• Lysosomes
– Vesicles containing enzymes that fuse with vacuoles
and digest waste materials
The Endomembrane System
The Endomembrane System
The Endomembrane System
4.10 Lysosome Malfunction
• When lysosomes do not work properly,
some cellular materials are not properly
recycled, which can have devastating
results
• Different kinds of molecules are broken
down by different lysosomal enzymes
– One lysosomal enzyme breaks down
gangliosides, a kind of lipid
Tay Sachs Disease
• In Tay Sachs
disease, a genetic
mutation alters the
lysosomal enzyme
that breaks down
gangliosides, which
accumulate in nerve
cells
– Affected children
usually die by age five
4.11 Other Organelles
• Eukaryotic cells make most of their ATP in
mitochondria
• Plastids function in storage and
photosynthesis in plants and some types
of algae
Mitochondria
• Mitochondrion
– Eukaryotic organelle that makes the energy molecule
ATP through aerobic respiration
– Contains two membranes, forming inner and outer
compartments; buildup of hydrogen ions in the outer
compartment drives ATP synthesis
– Has its own DNA and ribosomes
– Resembles bacteria; may have evolved through
endosymbiosis
Mitochondrion
Plastids
• Plastids
– Organelles that function in photosynthesis or
storage in plants and algae; includes
chromoplasts, amyloplasts, and chloroplasts
• Chloroplasts
– Plastids specialized for photosynthesis
– Resemble photosynthetic bacteria; may have
evolved by endosymbiosis
The Chloroplast
The Central Vacuole
• Central vacuole
– A plant organelle that occupies 50 to 90
percent of a cell’s interior
– Stores amino acids, sugars, ions, wastes,
toxins
– Fluid pressure keeps plant cells firm
4.12 Cell Surface
Specializations
• A wall or other protective covering often
intervenes between a cell’s plasma
membrane and the surroundings
Eukaryotic Cell Walls
• Animal cells do not have walls, but plant cells
and many protist and fungal cells do
• Primary cell wall
– A thin, pliable wall formed by secretion of cellulose
into the coating around young plant cells
• Secondary cell wall
– A strong wall composed of lignin, formed in some
plant stems and roots after maturity
Plant Cell Walls
Fig. 4-22a, p. 70
Fig. 4-22b, p. 70
Fig. 4-22c, p. 70
Plant Cuticle
• Cuticle
– A waxy covering that protects exposed
surfaces and limits water loss
Matrixes Between Animal Cells
• Extracellular matrix (ECM)
– A nonliving, complex mixture of fibrous
proteins and polysaccharides secreted by and
surrounding cells; structure and function
varies with the type of tissue
– Example: Bone is mostly ECM, composed of
collagen (fibrous protein) and hardened by
mineral deposits
ECM
• A bone cell surrounded by extracellular
matrix
Cell Junctions
• Cell junctions allow cells to interact with each
other and the environment
• In plants, plasmodesmata extend through cell
walls to connect the cytoplasm of two cells
• Animals have three types of cell junctions: tight
junctions, adhering junctions, gap junctions
Cell Junctions in Animal Tissues
4.6-4.12 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
4.13 The Dynamic Cytoskeleton
• Eukaryotic cells have an extensive and dynamic
internal framework called a cytoskeleton
• Cytoskeleton
– An interconnected system of many protein filaments –
some permanent, some temporary
– Parts of the cytoskeleton reinforce, organize, and
move cell structures, or even a whole cell
Components of the
Cytoskeleton
• Microtubules
– Long, hollow cylinders made of tubulin
– Form dynamic scaffolding for cell processes
• Microfilaments
– Consist mainly of the globular protein actin
– Make up the cell cortex
• Intermediate filaments
– Maintain cell and tissue structures
Fig. 4-26 (a-c), p. 72
Fig. 4-26d, p. 72
Motor Proteins
• Motor proteins
– Accessory proteins that move molecules
through cells on tracks of microtubules and
microfilaments
– Energized by ATP
– Example: kinesins
Motor Proteins: Kinesin
Cilia, Flagella, and False Feet
• Eukaryotic flagella and cilia
– Whiplike structures formed from microtubules
organized into 9 + 2 arrays
– Grow from a centriole which remains in the
cytoplasm as a basal body
• Psueudopods
– “False feet” used by amoebas and other
eukaryotic cells to move or engulf prey
Moving Cells
• Flagellum of the human sperm, and pseudopods of a
predatory amoeba
Eukaryotic Flagella and
Cilia
Fig. 4-29a, p. 73
Fig. 4-29b, p. 73
Fig. 4-29c, p. 73
4.13 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 cell structures or the whole cell
Summary: Components of
Prokaryotic and Eukaryotic
Cells