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Chapter 4
Cell Structure and
Function
Sections 1-6
Albia Dugger • Miami Dade College
4.1 Food For Thought
• E. coli O157:H7A, strain of bacteria that causes severe illness
or death, occasionally contaminates foods such as ground
beef and fresh vegetables
• Outbreaks, which occur with disturbing regularity, also have
severe economic impacts
• Food growers and processors are now using procedures that
they hope will reduce E. coli O157:H7 outbreaks
E. coli O157:H7
4.2 Cell Structure
• The cell is the smallest unit that shows the properties of life
• All cells have a plasma membrane and cytoplasm, and all
start out life with DNA
Components of All Cells
• 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
Organelles
• Organelles are structures that carry out special metabolic
functions inside a cell
Prokaryotic and Eukaryotic Cells
• Eukaryotic cell
• Cell interior is divided into functional compartments,
including a nucleus
• Prokaryotic cell
• Small, simple cells without a nucleus
A A prokaryotic cell.
cytoplasm
DNA
plasma membrane
nucleus
B A eukaryotic
(plant) cell. Only
eukaryotic cells
have a nucleus.
Figure 4-2 p54
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
cell’s exterior
plasma membrane
cell’s interior
Figure 4-3 p54
Constraints on Cell Size
• Surface-to-volume ratio restricts cell size by limiting
transport of nutrients and wastes
The Cell Theory Emerges
• Van Leeuwenhoek was the first to describe small organisms
seen through a microscope
• Hooke was the first to sketch and name cells
• Brown was the first to identify a cell nucleus
Cell Theory
• The cell theory, a foundation of modern biology, states that
cells are the fundamental units of life
•
•
•
•
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 a preexisting cell
Each cell passes its hereditary material to its offspring
Take-Home Message:
How are all cells alike?
• All cells start life with a plasma membrane, cytoplasm, and a
region of DNA, which, in eukaryotic cells only, is enclosed by
a nucleus
• The surface-to-volume ratio limits cell size and influences cell
shape
• Observations of cells led to the cell theory: All organisms
consist of one or more cells; the cell is the smallest unit of life;
each new cell arises from another cell; and a cell passes
hereditary material to its offspring
4.3 How Do We See Cells?
Table 4-1 p56
Modern Microscopes
• Light microscopes
• Phase-contrast microscopes
• Reflected light microscopes
• Fluorescence microscopes
• Electron microscopes
• Transmission electron microscopes
• Scanning electron microscopes
path of light rays (bottom to top) to eye
prism that
directs rays to
ocular lens
ocular
lens
objective
lenses
specimen
stage
condenser
lens
illuminator
focusing
knob
light source
(in base)
Figure 4-5a p56
incoming electron beam
condenser
lens
specimen
on grid
objective
lens
projective
lens
phosphor
screen
Figure 4-5b p56
ANIMATED FIGURE: How a light
microscope works
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Different Microscopes,
Different Characteristics
Relative Sizes
human eye (no microscope)
largest organisms
100 m
10 m
small animals
1m
10 cm
1 cm
frog eggs
1 mm
100 µm
Relative Sizes
electron microscopes
light microscopes
most
eukaryotic
cells
most
bacteria
mitochondria,
chloroplasts
viruses
molecules of life
DNA
small molecules
carbohydrates
proteins
lipids
10 µm
1 µm
100 nm
10 nm
1 nm
0.1 nm
Relative Sizes
Learn.genetice.utah.edu
Take-Home Message:
How do we see cells?
• Most cells are visible only with the help of microscopes
• Different types of microscopes reveal different aspects of cell
structure
4.4 Introducing “Prokaryotes”
• 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
General Prokaryote Body Plan
• Ribosomes
• Organelles upon which polypeptides are assembled
• Nucleoid
• An irregularly shaped region of cytoplasm containing a
single, circular DNA molecule
• Plasmids
• Small circles of DNA carry a few genes that can provide
advantages, such as resistance to antibiotics
General Prokaryote Body Plan
7
1
cytoplasm,
with
ribosomes
plasma
membrane
3
2
DNA in
nucleoid
5
4
capsule
cell wall
6
pilus
flagellum
ANIMATED FIGURE: Typical prokaryotic
cell
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Bacteria
Archaeans
Biofilms
• 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
Dental Plaque: A Biofilm
Take-Home Message:
How are bacteria and archaea alike?
• Bacteria and archaea do not have a nucleus. Most kinds have
a cell wall around their plasma membrane; the permeable wall
reinforces and imparts shape to the cell body
• The structure of bacteria and archaea is relatively simple, but
as a group these organisms are the most diverse forms of life;
they inhabit nearly all regions of the biosphere
• Some metabolic processes occur at the plasma membrane of
bacteria and archaea; they are similar to complex processes
that occur at certain internal membranes of eukaryotic cells
4.5 Introducing Eukaryotic Cells
• All protists, fungi, plants, and animals are eukaryotes
• 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
Components of Eukaryotic Cells
Components of Eukaryotic Cells
Cell
Central
Wall Chloroplast Vacuole
Cytoskeleton
microtubules
microfilaments
intermediate
filaments
(not shown)
Mitochondrion
Plasmodesma
nuclear
envelope
nucleolus
DNA in
nucleoplasm
Nucleus
Ribosomes
Rough ER
Smooth ER
Golgi Body
Plasma Membrane
Lysosome-Like
Vesicle
Figure 4-12a p61
3D ANIMATION: Tour of an Animal Cell
Inner life of cell
vacuole
cell wall
central
vacuole
plasma
membrane
chloroplast
mitochondrion
nucleus
B Photosynthetic cell from a blade of timothy grass.
Figure 4-11b p60
Rough ER
Modifies proteins made by
ribosomes attached to it
Smooth ER
Makes lipids, breaks down
carbohydrates and fats,
inactivates toxins
Golgi Body
Finishes, sorts, ships lipids,
enzymes, and proteins
Lysosome
Digests, recycles materials
Stepped Art
p64
vacuole
plasma
membrane
mitochondrion
nucleus
A Human white blood cell.
Figure 4-11a p60
Take-Home Message:
What do eukaryotic cells have in common?
• All eukaryotic cells start life with a nucleus and other
membrane-enclosed organelles
ANIMATION: Common eukaryotic
organelles
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4.6 The Nucleus
• All of a eukaryotic cell’s DNA is in its nucleus
• The nucleus keeps eukaryotic DNA away from potentially
damaging reactions in the cytoplasm
• The nuclear envelope controls when DNA is accessed
Table 4-2 p60
nuclear envelope
DNA
nucleolus
nuclear pore
nucleoplasm
cytoplasm
ER
Figure 4-13a p62
nuclear envelope
DNA
nucleolus
nuclear pore
nucleoplasm
cytoplasm
ER
Figure 4-13b p62
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
Structure of the Nuclear Envelope
B Each nuclear pore is an organized
cluster of membrane proteins that
selectively allows certain substances
to cross it on their way into and out of
the nucleus.
nuclear pore
A The outer surface of this nuclear
envelope was split apart to reveal the
pores that span the two lipid bilayers.
Figure 4-14ab p63
nuclear pore
nuclear envelope
(two lipid bilayers)
cytoplasm
Figure 4-14b p63
ANIMATED FIGURE: Nuclear envelope
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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
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
A Condensed Chromosome
Take-Home Message:
What is the function of the cell nucleus?
• A nucleus protects and controls access to a eukaryotic cell’s
DNA
• The nuclear envelope is a double lipid bilayer. Proteins
embedded in it control the passage of molecules between the
nucleus and the cytoplasm