4
Cells: The Working
Units of Life
History of the Cell
Hooke – coined the term
“cell”
Leewenhoek – bacteria
are made of cells &
first good microscope!
Concept 4.1 Cells Provide Compartments for Biochemical
Reactions
Cell theory was the first unifying theory of
biology.
1. Cells are the basic units of life.
2. Cells are the basic units of structure and
function.
3. All cells come from preexisting cells.
Animal Cells
Concept 4.1 Cells Provide Compartments for Biochemical
Reactions
Most cells are tiny
• to maintain a good surface area-tovolume ratio.
Figure 4.2 Why Cells Are Small
Figure 4.1 The Scale of Life
Concept 4.1 Cells Provide Compartments for Biochemical
Reactions
To visualize small cells, there are two types
of microscopes:
Light microscopes—use glass lenses and
light
Resolution = 0.2 μm (OK)
Electron microscopes—electromagnets
focus an electron beam
Resolution = 2.0 nm (awesome)
Figure 4.3 Microscopy
Concept 4.1 Cells Provide Compartments for Biochemical
Reactions
The plasma membrane:
• Is a selectively permeable barrier that
allows cells to maintain a constant internal
environment
• Is important in communication and
receiving signals
• Often has proteins for binding and
adhering to adjacent cells
4.1 CelConcept 4. Provide Compartments for Biochemical
Reactions
Two types of cells: Prokaryotic and
eukaryotic
Prokaryotes are without membraneenclosed compartments. NO NUCLEUS!
Eukaryotes have membrane-enclosed
compartments called organelles, such as
the nucleus.
In-Text Art, Ch. 4, p. 59
Concept 4.2 Prokaryotic Cells Do Not Have a Nucleus
Prokaryotic cells:
• Are enclosed by a plasma membrane
• Have DNA located in the nucleoid
The rest of the cytoplasm consists of:
• Cytosol (water and dissolved material)
and suspended particles
• Ribosomes—sites of protein synthesis
Figure 4.5 A Prokaryotic Cell
Concept 4.2 Prokaryotic Cells Do Not Have a Nucleus
Other Characteristics of a prokaryote:
• rigid cell wall (containing peptidoglycan)
outside the plasma membrane.
• Some bacteria have an additional outer
membrane that is very permeable.
Other bacteria have a slimy capsule made
of polysaccharides.
Some prokaryotes swim by means of
flagella, made of the protein flagellin
Figure 4.6 Prokaryotic Flagella (Part 1)
Figure 4.7 Eukaryotic Cells (Part 1)
Figure 4.7 Eukaryotic Cells (Part 8)
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
Ribosomes—sites of protein synthesis:
both prokaryotic and eukaryotic cells
similar structure—one larger and one
smaller subunit.
Ribosomes are not membrane-bound
organelles—in eukaryotes, they are free in
the cytoplasm, attached to the
endoplasmic reticulum, or inside
mitochondria and chloroplasts.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
The nucleus is usually the largest
organelle.
It is the location of DNA and of DNA
replication.
It contains the nucleolus, where ribosomes
are made
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
The nucleus is surrounded by two
membranes that form the nuclear
envelope.
Nuclear pores in the envelope control
movement of molecules between nucleus
and cytoplasm.
In the nucleus, DNA combines with proteins
to form chromatin in long, thin threads
called chromosomes.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
The endomembrane system includes the
nuclear envelope, endoplasmic reticulum,
Golgi apparatus, and lysosomes.
Tiny, membrane-surrounded vesicles
shuttle substances between the various
components, as well as to the plasma
membrane.
Figure 4.8 The Endomembrane System
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
Endoplasmic reticulum (ER)—network of
interconnected membranes in the
cytoplasm, with a large surface area
Two types of ER:
• Rough endoplasmic reticulum (RER)
• Smooth endoplasmic reticulum (SER)
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
Rough endoplasmic reticulum (RER) has
ribosomes attached to begin protein
synthesis.
Newly made proteins enter the RER lumen.
Once inside, proteins are chemically
modified and tagged for delivery.
The RER participates in the transport.
All secreted proteins and most membrane
proteins, including glycoproteins, which is
important for recognition, pass through the
RER.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
Smooth endoplasmic reticulum (SER)—
more tubular, no ribosomes
It chemically modifies small molecules such
as drugs and pesticides.
It is the site of glycogen degradation in
animal cells.
It is the site of synthesis of lipids and
steroids.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
The Golgi apparatus is composed of
flattened sacs (cisternae) and small
membrane-enclosed vesicles.
Receives proteins from the RER—can
further modify them
Concentrates, packages, and sorts proteins
Adds carbohydrates to proteins
Site of polysaccharide synthesis in plant
cells
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
The Golgi apparatus has three regions:
The cis region receives vesicles containing
protein from the ER.
At the trans region, vesicles bud off from the
Golgi apparatus and travel to the plasma
membrane or to lysosomes.
The medial region lies in between the trans
and cis regions.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
Primary lysosomes originate from the
Golgi apparatus.
They contain digestive enzymes, and are
the site where macromolecules are
hydrolyzed into monomers.
Figure 4.9 Lysosomes Isolate Digestive Enzymes from the Cytoplasm (Part 1)
Figure 4.9 Lysosomes Isolate Digestive Enzymes from the Cytoplasm (Part 2)
Figure 4.7 Eukaryotic Cells
Cristae –
increases
Surface AreaOuter
Membrane
(very porous)
Matrix –
Enzymes, DNA,
Ribosomes
Figure 4.7 Eukaryotic Cells
Thylakoids –
chlorophyll
Grana – stack
of thylakoids
Stroma aqueous
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
Peroxisomes collect and
break down toxic byproducts of metabolism,
such as H2O2, using
specialized enzymes.
Glyoxysomes, found only
in plants, are where
lipids are converted to
carbohydrates for
growth.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other
Membrane-Bound Compartments
Vacuoles :
• Storage of waste products, food, enzymes,
water, and pigments
• creates turgor pressure in plant cells
Contractile vacuoles in freshwater
protists get rid of excess water