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CHAPTER 4
CELLS
LIVING ORGANISMS are HIGHLY ORGANIZED
• Cells, the simplest collection of matter that
can live, were first observed by Robert Hooke
in 1665
• Antoni van Leeuwenhoek later described
cells that could move
– He viewed bacteria with his own hand-crafted
microscopes
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The CELL THEORY:
• The early microscopes provided data to
establish the cell theory
– All living things are composed of cells
– All cells come from other cells (NO
Spontaneous Generation)
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INTRODUCTION TO THE CELL
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Microscopes reveal the world of the cell
• A variety of microscopes have been developed for
a clearer view of cells and cellular structure
• The most frequently used microscope is the light
microscope (LM)—like the one used in biology
laboratories
• We will use a COMPOUND LIGHT MICROSCOPE
– Light passes through a specimen then through 2 glass
lenses into the viewer’s eye
– Specimens can be magnified up to 400 times the
actual size of the specimen
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Enlarges image
formed by objective
lens
Eyepiece
Magnifies specimen,
forming primary
image
Objective lens
Focuses light
through specimen
Ocular
lens
Specimen
Condenser
lens
Light
source
Microscopes reveal the world of the cell
• Microscopes have limitations
– Both the human eye and the microscope have
limits of RESOLUTION—the ability to
distinguish between small structures
– Therefore, the light microscope cannot
provide the details of a small cell’s structure
– SO…we can stain the specimen
– Can you think of a problem with this???
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10 m
Length of some
nerve and
muscle cells
Chicken egg
10 mm
(1 cm)
100 µm
10 µm
1 µm
100 nm
10 nm
1 nm
0.1 nm
Frog egg
Most plant
and animal
cells
Nucleus
Most bacteria
Mitochondrion
Mycoplasmas
(smallest bacteria)
Viruses
Ribosome
Proteins
Lipids
Small molecules
Atoms
Electron microscope
1 mm
Light microscope
100 mm
(10 cm)
Human height
Unaided eye
1m
Prokaryotic cells are structurally simpler than
eukaryotic cells
• Bacteria and archaea are prokaryotic
cells
• All other forms of life are eukaryotic cells
– Both prokaryotic and eukaryotic cells have a
plasma membrane and one or more
chromosomes (DNA) and ribosomes
– Eukaryotic cells have a membrane-bound
nucleus and a number of other organelles,
whereas prokaryotes have no nucleus and no
true organelles
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Prokaryotic Cells
• Prokaryotic cells are like a studio (oneroom) apartment
– All functions take place within the plasma
membrane of the cell
Pili
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
A typical rod-shaped
bacterium
Flagella
A thin section through the
bacterium Bacillus coagulans
(TEM)
Eukaryotic cells are partitioned into functional
compartments
• Eukaryotic cells are like a multiple room
apartment
– Different functions take place in different
organelles
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Eukaryotic cells are partitioned into functional
compartments
• Manufacturing of protein
molecules involves the nucleus,
ribosomes, endoplasmic
reticulum, and Golgi apparatus
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The nucleus is the cell’s genetic control center
• It contains the information (DNA) to make
protein molecules
• The nuclear envelope is a double
membrane with pores that allow material
(messenger RNA) to flow out of the nucleus
– It is attached to a network of cellular
membranes called the endoplasmic reticulum
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Two membranes of
nuclear envelope
Nucleus
Nucleolus
Chromatin
Pore
Endoplasmic
reticulum
Ribosomes
Ribosomes make proteins for use in the cell and
outside of the cell
• Ribosomes are involved in the
cell’s protein synthesis
–Ribosomes are synthesized in
the nucleolus, which is found
in the nucleus
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Ribosomes
ER
Cytoplasm
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large
subunit
TEM showing ER
and ribosomes
Diagram of
a ribosome
Small
subunit
The endoplasmic reticulum is a biosynthetic
factory
• There are two kinds of endoplasmic
reticulum—smooth and rough
• Smooth ER lacks attached ribosomes
• Rough ER lines the outer surface of
membranes
– They differ in structure and function
– However, they are connected
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Nuclear
envelope
Ribosomes
Smooth ER
Rough ER
The endoplasmic reticulum is a biosynthetic
factory
• Smooth ER is involved in a variety of
diverse metabolic processes
– For example, enzymes produced by the
smooth ER are involved in the synthesis of
lipids, oils, phospholipids, and steroids
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The endoplasmic reticulum is a biosynthetic
factory
• Rough ER makes proteins
–Once proteins are synthesized,
they are transported in vesicles
to other parts of the
endomembrane system
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The Golgi apparatus finishes, sorts, and ships
cell products
• The Golgi apparatus functions in
conjunction with the ER by modifying
products of the ER
– Products travel in transport vesicles from the
ER to the Golgi apparatus
– One side of the Golgi apparatus functions as a
receiving dock for the product and the other
as a shipping dock
– Products are modified as they go from one side of
the Golgi apparatus to the other and travel in
vesicles to other sites
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Transport vesicle
buds off
4
Ribosome
Secretory
protein
inside transport vesicle
3
Sugar
chain
1
Polypeptide
2 Glycoprotein
Rough ER
“Receiving” side of
Golgi apparatus
Golgi
apparatus
Transport
vesicle
from ER
New vesicle
forming
“Shipping” side
of Golgi apparatus
Transport
vesicle from
the Golgi
Golgi apparatus
PROTEIN SYNTHESIS
• In the nucleus, DNA information for protein
synthesis is copied into messenger RNA (mRNA)
• mRNA leaves the nucleus; goes to the ribosomes
• Proteins are synthesized at the ribosomes
• Proteins leave the ribosomes in transport vesicles
headed for the Golgi apparatus
• Proteins are modified at the Golgi apparatus
• Modified proteins leave the Golgi apparatus in
transport vesicles headed for their destination
(inside or outside of the cell)
Nucleus
Nuclear
membrane
Rough ER
Smooth
ER
Transport
vesicle
Transport
vesicle
Golgi
apparatus
Lysosome
Vacuole
Plasma
membrane
Lysosomes are digestive compartments within a
cell
• A lysosome is a membranous sac
containing digestive enzymes
– The enzymes and membrane are produced by
the ER and transferred to the Golgi apparatus
for processing
– The membrane serves to safely isolate these
potent enzymes from the rest of the cell
– These enzymes can be used to:
– Digest dead cells
– Digest “food” for unicellular organisms
– Destroy pathogens (WHITE BLOOD CELLS)
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Vacuoles function in the general maintenance of
the cell
• Vacuoles are membranous sacs that are
found in a variety of cells and possess an
assortment of functions
– Examples are the central vacuole in
plants
– Water is stored here
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Chloroplast
Nucleus
Central
vacuole
Mitochondria harvest chemical energy from
food
• Cellular respiration is accomplished in the
mitochondria of eukaryotic cells
– Cellular respiration involves conversion of
chemical energy in foods (GLUCOSE) to
chemical energy in ATP (adenosine
triphosphate)
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Mitochondrion
Outer
membrane
Intermembrane
space
Inner
membrane
Cristae
Matrix
Chloroplasts convert solar (sunlight) energy to
chemical energy
• Chloroplasts are the
photosynthesizing organelles of
plants
–Photosynthesis is the
conversion of light energy to
chemical energy of sugar
molecules
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Chloroplast
Stroma
Inner and outer
membranes
Granum
Intermembrane
space
Cilia and flagella move when microtubules
bend
• While some protists have flagella and cilia
that are important in locomotion, some
cells of multicellular organisms have them
for different reasons
– Cells that sweep mucus out of our lungs have
cilia
– Animal sperm are flagellated
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Cilia
Flagellum
Eukaryotic cells are partitioned into functional
compartments
• Although there are many similarities
between animal and plant cells,
differences exist
– Lysosomes and centrioles are not found in
plant cells
– Plant cells have a rigid cell wall, chloroplasts,
and a central vacuole not found in animal cells
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NUCLEUS:
Nuclear envelope
Smooth endoplasmic
reticulum
Chromosomes
Nucleolus
Rough
endoplasmic
reticulum
Lysosome
Centriole
Peroxisome
CYTOSKELETON:
Microtubule
Intermediate
filament
Microfilament
Ribosomes
Golgi
apparatus
Plasma membrane
Mitochondrion
Review of Cell Types
Bacterial Cell
Plant Cell
Animal Cell
Ten times
smaller (1-10
micrometers)
10-100
micrometers
10-100
micrometers
One “Naked”
Chromosome
Multiple
Chromosomes
Multiple
Chromosomes
Cell Wall
Cell Wall
No Cell Wall
No Nucleus
Nucleus
Nucleus
No Organelles
Organelles
Organelles
No Organelles
Chloroplasts;
Central Vacuoles
No Chloroplasts
or Central
Vacuoles
No Organelles
No Centrioles or
Lysosomes
Centrioles and
Lysosomes