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Chapter 6 - The Cell
Outline
I. Cell Theory
II. Studying cells
III. Prokaryotic vs Eukaryotic
IV. Eukaryotic
A. Animal cells
B. Plant cells
Cells
Cell Theory
 Cells were discovered in 1665 by Robert
Hooke.
 Cells are the basic unit of life
 Cells maintain homeostasis
 They are enclosed in a phospholipid
membrane - the Plasma Membrane
 Cells vary in size but there is a limit on how
big a cell can be and survive
 There are different types of cells –
specialized cells
 Early studies of cells were conducted by
- Mathias Schleiden (1838)
- Theodor Schwann (1839)
 Schleiden and Schwann proposed the Cell
Theory.
4
Cell Theory
Cell Size
1. All organisms are composed of cells.
2. Cells are the smallest living things.
3. Cells arise only from pre-existing cells.
 Cell size is limited.
-As cell size increases, it takes longer for
material to diffuse from the cell membrane to
the interior of the cell.
All cells today represent a continuous line of
descent from the first living cells.
 Small cells have a greater surface area
relative to volume
 Surface area-to-volume ratio: as a cell
increases in size, the volume increases 10x
faster than the surface area
5
6
1
Figure 6.7
Surface area increases while
total volume remains constant
Some organisms are just one cell - yeast
5
1
1
Total surface area
[sum of the surface areas
(height  width) of all box
sides  number of boxes]
6
150
750
Total volume
[height  width  length
 number of boxes]
1
125
125
Surface-to-volume
(S-to-V) ratio
[surface area  volume]
6
1.2
6
Multi-celled organisms have specialized cells
Blood Cells
Nerve Cells
Figure 6.2a
10 m
10 m
Human height
Chicken egg
1 cm
Human height
1m
Frog egg
1 mm
0.1 m
Human egg
Most plant and
animal cells
10 m
1 m
100 nm
Nucleus
Most bacteria
Chicken egg
1 cm
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
10 nm
Superresolution
microscopy
Electron microscopy
100 m
Length of some
nerve and
muscle cells
Unaided eye
0.1 m
Length of some
nerve and
muscle cells
Unaided eye
1m
Light microscopy
Figure 6.2
Some cells are very small
Frog egg
1 mm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
100 m
Human egg
Atoms
2
Figure 6.2b
1 cm
As the size of a cell increase, the
surface:volume ratio
Frog egg
Human egg
Most plant and
animal cells
10 m
1 m
100 nm
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
10 nm
Superresolution
microscopy
Electron microscopy
100 m
Light microscopy
1 mm
1. Increase
2. Decrease
3. Stays the same
33%
33%
33%
Proteins
Lipids
1 nm
0.1 nm
Small molecules
Atoms
1
2
3
Copyright © 2009 Pearson Education, Inc.
Studying Cells
Microscopes
 Microscopes
1. Light microscopes
 Also called compound microscopes
because it uses multiple lens
2. Electron microscope
 Transmission electron microscope
 Scanning electron microscope
Microscopes
 Two features determine how clearly an object
is viewed:
1. Magnification = ocular lens x
magnifying lens
2. Resolution – quality of lens and type
of light
Electron Microscope
Light microscopes can resolve structures
that are 200nm apart.
 Transmission Electron Microscopes –
specimens are first embedded in plastic then
sliced thin
 Scanning Electron Microscope – specimen is
coated with film, scans surface only
Electron microscopes can resolve
structures that are 0.2nm apart.
17
3
Figure 6.3a
Figure 6.3b
Brightfield
(unstained specimen)
50 m
Brightfield
(stained specimen)
Figure 6.3c
Figure 6.3d
Phase-contrast
Differential-interferencecontrast (Nomarski)
Figure 6.3e
Figure 6.3i
Cilia
Fluorescence
10 m
2 m
Scanning electron
microscopy (SEM)
4
Figure 6.3j
Cell fractionation
Longitudinal section
of cilium
 Used to study organelles
 Homogenize the sample
 Lyse the cells (break open) and the resulting
cell extract spun in a centrifuge
Cross section
of cilium
 Centrifugal force separates extract
 Pellet – bottom of tube, contains large
components of cell, organelles like nucleus
 Supernatant – liquid on top of pellet, contains
lighter components
2 m
Transmission electron
microscopy (TEM)
Figure 6.4b
Figure 6.4a
TECHNIQUE (cont.)
TECHNIQUE
Centrifuged at
1,000 g
(1,000 times the
force of gravity)
for 10 min Supernatant
poured into
next tube
Differential
centrifugation
20,000 g
20 min
Homogenization
Pellet rich in
nuclei and
cellular debris
Tissue
cells
80,000 g
60 min
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a plant)
Pellet rich in
“microsomes”
Homogenate
Centrifugation
Cell Fractionation
 1000 g x 10 min = nuclei in pellet
 20,000 g x 30 min = mitochondria, chloroplast
 80,000 g x 60 min = microsomal fraction contains:
Pellet rich in
ribosomes
If you centrifuge cells at 80,000 g which fraction will contain
the endoplasmic reticulum?
1. Pellet
2. Supernate
50%
50%
 ER, Golgi, plasma membrane
pe
rn
at
e
Su
Pe
 To separate the ER, Golgi and plasma
membrane you can use a density gradient
centrifuge
ll e
t
 150,000 g x 3 hr = ribosomes
5
Inner Life of a Cell - Harvard
Cell Structures
All cells have certain structures in common.
 Inner life of a cell - short version, music
only
1. genetic material – in a nucleoid or nucleus
2. cytoplasm – a semifluid matrix (fluid portion is
the cytosol)
3. plasma membrane – a phospholipid bilayer
4. Ribosomes (make proteins)
32
Figure 6.6
Plasma Membrane
Outside of cell
 The plasma membrane is a selective barrier
that allows sufficient passage of oxygen,
nutrients, and waste to service the volume of
every cell
Inside of cell
 The general structure of a biological membrane
is a double layer of phospholipids
0.1 m
(a) TEM of a plasma
membrane
Carbohydrate side chains
Hydrophilic
region
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
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The main component of the plasma
membrane is:
1.
2.
3.
4.
Trigylcerides
Cholesterol
Protein
Phospholipids
25%
25%
Prokaryotic vs Eukaryotic
25%
25%
 Prokaryotic – Pro (before) karyotic (nucleus)
 Eukaryotic – Eu (true) karyotic (nucleus)
 The presence or absence of a nucleus is the
most obvious difference between these types of
cells.
1
2
3
4
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6
Eukaryotic cells have internal membranes
that compartmentalize their functions
 The basic structural and functional unit of every
organism is one of two types of cells: prokaryotic
or eukaryotic
Figure 6.5
Fimbriae
Nucleoid
Ribosomes
Plasma
membrane
Bacterial
chromosome
 Only organisms of the domains Bacteria and
Archaea consist of prokaryotic cells
 Protists, fungi, animals, and plants all consist of
eukaryotic cells
Cell wall
Capsule
0.5 m
(a) A typical
rod-shaped
bacterium
Flagella
(b) A thin section
through the
bacterium Bacillus
coagulans (TEM)
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Figure 6.5a
Prokaryotic Cells – Characteristics and Features
1. Include bacteria and archaea
2. Has no nucleus, have nucleoid region
3. Also lack membrane bound compartments
(organelles)
4. Many use folds in the plasma membrane to
accomplish the tasks of organelles
0.5 m
(b) A thin section through the
bacterium Bacillus coagulans
(TEM)
Prokaryotic Cells – Characteristics and Features
5. Many prokaryotic cells have cell walls
6. Some have a capsule
Prokaryotic Cells
6. Have a plasma membrane
7. Have cytoplasm
8. Many have flagella for locomotion
9. Contain ribosomes for protein production
10. Have storage granules – contain glycogen,
lipids, and phosphate compounds
11. Some can perform photosynthesis
42
7
Do prokaryotic cells contain ribosomes?
Prokaryotic cells have a nucleus
50%
1. Yes
2. No
3. Some do
33%
Fa
ls
e
50%
Tr
ue
1. True
2. False
1
33%
33%
2
3
Copyright © 2009 Pearson Education, Inc.
Eukaryotic cells
 Highly organized, have organelles including
a nucleus. Eukaryotic cells are generally
much larger than prokaryotic cells




Animal cells
Plant cells
Protists
Fungi
Major Features of Animal Cells (page 79)
 Membrane bound Organelles
1. Nucleus – contains the DNA
2. Mitochondria – energy production
3. Endoplasmic reticulum – modifies new polypeptide
chains (rough) and synthesizes lipids (smooth)
4. Golgi body – modifies, sorts, ships new proteins
and lipids
5. Vesicles – storage, transport, digestion
6. Lysosomes – digestion
7. Peroxisomes – lipid metabolism, detoxification
Major Features of Animal Cells
 Structures:
1. Plasma membrane – controls entry in/out of cell
2. Cytoplasm – semi-fluid matrix outside the
nucleus, liquid portion is the cytosol
3. Ribosomes - assembling polypeptide chains
4. Chromosomes - DNA
5. Cytoskeleton - gives shape, structure, transport
6. Flagella - movement
Figure 6.8a
ENDOPLASMIC RETICULUM (ER)
Flagellum
Rough
ER
Nuclear
envelope
Smooth
ER
Nucleolus
Chromatin
NUCLEUS
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate filaments
Microtubules
Ribosomes
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
8
Figure 6.8c
Nuclear
envelope
NUCLEUS
Nucleolus
Chromatin
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
CYTOSKELETON
Mitochondrion
Peroxisome
Chloroplast
Plasma membrane
Cell wall
Plasmodesmata
Wall of adjacent cell
BioFlix: Tour of an Animal Cell
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Cell Membranes
1. Plasma membrane: Divides outside from
inside of cell
2. Organelles: specialized membrane bound
compartments
BioFlix: Tour of a Plant Cell
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Organelles
Protein Production/Synthesis
 Compartments allow the cells to keep reactive
compounds from causing injury
Organelle/feature
Function
Nucleus
Contains DNA
DNA is copied to make RNA
 Some membranes form vesicles that are used
for transporting things
Ribosomes
“reads” mRNA to assemble amino acids
into a polypeptide chain
 Some membranes are attached to other
membranes
Rough Endo Ret
Polypeptide chain that are to be exported
or membrane bound are processed here
Golgi complex
Further processes and sorts proteins to be
exported or membrane bound
Vesicles
Transports proteins
9
The eukaryotic cell’s genetic instructions are housed in
the nucleus and carried out by the ribosomes
 The nucleus contains most of the DNA in a
eukaryotic cell
 Ribosomes use the information from the DNA to
make proteins
Nucleus
 Nucleus protects DNA
 Separates DNA from rest of cell
 Place where DNA replicates itself
 Place where DNA is copied to make RNA
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The Nucleus: Information Central
 The nucleus contains most of the cell’s genes and
is usually the most conspicuous organelle
 The nuclear envelope encloses the nucleus,
separating it from the cytoplasm
Figure 6.9a
Nucleus
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Rough ER
 The nuclear membrane is a double membrane;
each membrane consists of a lipid bilayer
Pore
complex
Ribosome
Close-up
of nuclear
envelope
Chromatin
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Figure 6.9b
Figure 6.9c
Nuclear envelope:
0.25 m
1 m
Inner membrane
Outer membrane
Nuclear pore
Pore complexes (TEM)
Surface of nuclear
envelope
10
 In the nucleus, DNA is organized into discrete
units called chromosomes
 Pores regulate the entry and exit of molecules
from the nucleus
 The shape of the nucleus is maintained by the
nuclear lamina, which is composed of protein
 Each chromosome is composed of a single DNA
molecule associated with proteins
 The DNA and proteins = histones are together
called chromatin
 Chromatin condenses to form discrete
chromosomes as a cell prepares to divide
 The nucleolus is located within the nucleus and is
the site of ribosomal RNA (rRNA) synthesis
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Parts of the Nucleus
2. Nucleolus – dense area in the nucleus is
where rRNA are produced and ribosomes
are assembled
3. Nucleoplasm – area within nucleus
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Ribosomes: Protein Factories
 Ribosomes are particles made of ribosomal RNA
and protein
 Ribosomes carry out protein synthesis in two
locations
 In the cytosol (free ribosomes)
 On the outside of the endoplasmic reticulum or the
nuclear envelope (bound ribosomes)
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Ribosomes
 Has two components: a small subunit and a
large subunit
Figure 6.10
0.25 m
Free ribosomes in cytosol
Endoplasmic reticulum (ER)
 Each subunit is made up of strands of rRNA
and many proteins
 The ribosome is like the workbench for
assembling polypeptide chains. It is here that
amino acids are bound together with a peptide
bond.
Ribosomes bound to ER
Large
subunit
TEM showing ER and
ribosomes
Small
subunit
Diagram of a ribosome
11
The endomembrane system regulates protein
traffic and performs metabolic functions in the cell
 Components of the endomembrane system






Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vacuoles
Plasma membrane
 These components are either continuous or
connected via transfer by vesicles
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Endoplasmic reticulum
The Endoplasmic Reticulum: Biosynthetic Factory
 The endoplasmic reticulum (ER) accounts for
more than half of the total membrane in many
eukaryotic cells
 The ER membrane is continuous with the nuclear
envelope
 There are two distinct regions of ER
 Smooth ER, which lacks ribosomes
 Rough ER, surface is studded with ribosomes
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Figure 6.11
Smooth ER
Nuclear
envelope
Rough ER
 Network of folded internal membranes
located in the cytoplasm
ER lumen
 Attached to nucleus
Cisternae
Transitional ER
Ribosomes
Transport vesicle
Smooth ER
Rough ER
200 nm
 Lumen = space inside endoplasmic reticulum
Functions of Smooth ER
 The smooth ER




Synthesizes lipids
Metabolizes carbohydrates
Detoxifies drugs and poisons
Stores calcium ions
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Functions of Rough ER
 The rough ER
 Has bound ribosomes
 Creates transport vesicles
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12
Rough Endoplasmic Reticulum (RER)
 Ribosomes that are producing polypeptide
chains for export or to be embedded in
membranes dock with the surface of the
RER
 The growing polypeptide chain enters the
lumen of the RER
Functions of Rough Endoplasmic Reticulum (RER)
 In the RER the polypetide chain is folded
 Enzymes called molecular chaperones aid in the
folding of the polypeptide chains into proteins
 Some of the polypeptide chains may get modified
here “tagged” with carbohydrate chain =
glycoproteins
 The polypeptide chains/proteins are put into
transport vesicles
The Golgi Apparatus: Shipping and Receiving Center
 The Golgi apparatus consists of flattened
membranous sacs called cisternae
Figure 6.12
cis face
(“receiving” side of
Golgi apparatus)
0.1 m
Cisternae
 Functions of the Golgi apparatus
 Modifies products of the ER
 Manufactures certain macromolecules
 Sorts and packages materials into transport
vesicles
 Produces lysosomes
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
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V Cell Movie
 Golgi – Protein Trafficking
All polypeptide chains go to the RER
1. True
2. False
50%
1
50%
2
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13
Protein Production - Overview
1. DNA in the nucleus are the instructions for making
protein
2. A copy of the DNA is made = mRNA
3. mRNA leaves the nucleus
4. mRNA docks with a ribosome to assemble a chain
of amino acids.
5. tRNA brings amino acids to ribosomes
6. At the ribosome the amino acids are linked together
with a peptide bond to form a polypeptide chain
Protein Production Cont
10. The golgi processes, sorts, packages
proteins and lipids from the RER and SER
11. Proteins that are exported are shipped in
transport vesicles to the plasma membrane
Protein Production Cont
7. Ribosome with the growing polypeptide
chain docks with the rough endoplasmic
reticulum if the protein is to be exported or
embedded in a membrane
8. The polypeptide chain enters the lumen of
the RER where they are folded and may get
a carbohydrate “tag” attached to it
9. The RER buds off a transport vesicles that
can carry the newly formed proteins to the
golgi
Cytosolic proteins
 Proteins that are not shipped out of cell
are made on free floating ribosomes
 Chaperone proteins fold the proteins in the
cytosol
12. Proteins may be put into lysosomes
13. Proteins that are membrane bound are
embedded in the transport vesicles
membrane
Lysosomes
 Produced by the Golgi
Lysosomes
1. Contain strong acids and enzymes
2. Engulf molecules and digest them or
 Lysosomes are small membrane bound sacs that
contain digestive enzymes. The pH is relatively
acidic (pH 5) in the lysosomes.
 Because the lysosomes are acidic and contain
digestive enzymes, their contents must be kept
separate from the rest of the cell
3. Fuse with other organelles and vesicles to
destroy them
4. Can fuse with plasma membrane to expel
waste
5. Destroy bacteria
14
Fig. 4.14
 Some types of cell can engulf another cell by
phagocytosis; this forms a food vacuole
 A lysosome fuses with the food vacuole and
digests the molecules
 Lysosomes also use enzymes to recycle the cell’s
own organelles and macromolecules, a process
called autophagy
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Figure 6.13
Vesicle containing
two damaged
organelles
1 m
Nucleus
1 m
Mitochondrion
fragment
Peroxisome
fragment
Lysosome
Digestive
enzymes
Lysosome
Lysosome
Plasma membrane
Peroxisome
Digestion
Food vacuole
Mitochondrion
Digestion
Vesicle
(a) Phagocytosis
(b) Autophagy
Animation: Lysosome Formation
Right-click slide / select “Play”
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Scavenger cells
Tay-Sachs Disease
Throughout the
body there are
scavenger cells
that engulf
bacteria, foreign
material or old
cellular material
 Tay-Sachs is a hereditary disease –
 people with this disease don’t have an
enzyme normally found in lysosomes that
breaks down lipids in nerve cells.
15
Vacuoles: Diverse Maintenance Compartments
 Plant cell, protists, and fungal cells may have
one or several vacuoles, derived from
endoplasmic reticulum and Golgi apparatus
Vacuoles: Diverse Maintenance Compartments
 Food vacuoles are formed by phagocytosis
 Contractile vacuoles, found in many freshwater
protists, pump excess water out of cells
 Central vacuoles, found in many mature plant
cells, hold organic compounds and water
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Figure 6.14
Central vacuole
Cytosol
Nucleus
Central
vacuole
Cell wall
Chloroplast
5 m
Video: Paramecium Vacuole
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Central Vacuole in Plants
 Plant central vacuoles
 Large area of cell space – up to 90%
 Fluid filled with water, amino acids, sugars,
H+ ions, and wastes.
 Stores nutrients
 Digests wastes – similar to lysosomes in
animal cells
The Endomembrane System: A Review
 The endomembrane system is a complex and
dynamic player in the cell’s compartmental
organization
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16
Figure 6.15-1
Figure 6.15-2
Nucleus
Nucleus
Rough ER
Smooth ER
Rough ER
Smooth ER
cis Golgi
Plasma
membrane
Figure 6.15-3
Nucleus
Rough ER
Smooth ER
trans Golgi
Plasma
membrane
Mitochondria and chloroplasts change energy from
one form to another
• Mitochondria are the sites of cellular respiration,
a metabolic process that uses oxygen to generate
ATP
cis Golgi
 Chloroplasts, found in plants and algae, are the
sites of photosynthesis
trans Golgi
Plasma
membrane
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The Evolutionary Origins of Mitochondria and
Chloroplasts
 Mitochondria and chloroplasts have similarities with
bacteria
 Enveloped by a double membrane
 Contain free ribosomes and circular DNA
molecules
 Grow and reproduce somewhat independently in
cells
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The Evolutionary Origins of Mitochondria and
Chloroplasts
 The Endosymbiont theory
 An early ancestor of eukaryotic cells engulfed a
nonphotosynthetic prokaryotic cell, which formed
an endosymbiont relationship with its host
 The host cell and endosymbiont merged into a
single organism, a eukaryotic cell with a
mitochondrion
 At least one of these cells may have taken up a
photosynthetic prokaryote, becoming the
ancestor of cells that contain chloroplasts
© 2011 Pearson Education, Inc.
17
Figure 6.16
Endoplasmic
reticulum
Engulfing of oxygenusing nonphotosynthetic
prokaryote, which
becomes a mitochondrion
Nucleus
Nuclear
envelope
 Most all Eukaryotic cells (plants, animals, fungi
and protists) contain mitochondria
Ancestor of
eukaryotic cells
(host cell)
Mitochondrion
Nonphotosynthetic
eukaryote
Mitochondria
At least
one cell
Engulfing of
photosynthetic
prokaryote
Chloroplast
 Produces energy for the cell (ATP)
 Cells that require lots of energy have lots of
mitochondria (liver cells can have over 1000
mitochondria
 Requires oxygen = site of aerobic respiration
Mitochondrion
 Important in apoptosis (programmed cell death)
Photosynthetic eukaryote
Mitochondria - Structure
 Bound by a double membrane
 Forms two compartments
 Outer membrane faces cytoplasm
 Inner membrane folded forming cristae which
increases surface area
 The cristae contain many enzymes and other proteins
important for cellular respiration
 Intermembrane space is between outer and inner
membrane
Mitochondria
 The double membrane structure is important in
its function (cellular respiration) and to keep
dangerous oxygen species and free radicals
from damaging the cells.
 Mitochondria contain its own DNA
Apoptosis
 Apoptosis is planned cell death
 In contrast, necrosis is uncontrolled cell death
 When a cell is no longer needed or is not
functioning properly, the cell will undergo
apoptosis.
Apoptosis
 Mitochondria can initiate apoptosis in several
ways – one way is through a cascade of
enzymatic reactions.
 When the mitochondria gets the signal to
begin apoptosis it releases cytochrome c,
which activates a group of enzymes called
caspases
18
Figure 6.17
Apoptosis Video
10 m
 Apoptosis
Intermembrane space
Mitochondria
Outer
membrane
DNA
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Mitochondrial
DNA
Cristae
Nuclear DNA
Matrix
(a) Diagram and TEM of mitochondrion
0.1 m
(b) Network of mitochondria in a protist
cell (LM)
Chloroplasts: Capture of Light Energy
 Chloroplasts contain the green pigment
chlorophyll, as well as enzymes and other
molecules that function in photosynthesis
Chloroplasts: Capture of Light Energy
 Chloroplast structure includes
 Thylakoids, membranous sacs, stacked to form a
granum
 Stroma, the internal fluid
 Chloroplasts are found in leaves and other green
organs of plants and in algae
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 The chloroplast is one of a group of plant organelles,
called plastids
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19
Figure 6.18
Chloroplasts
50 m
Ribosomes
Stroma
Inner and outer
membranes
Granum
Chloroplasts
(red)
DNA
Thylakoid
Intermembrane space
(a) Diagram and TEM of chloroplast
1 m
(b) Chloroplasts in an algal cell
115
Peroxisomes
 Peroxisomes are membrane bound vesicles that
contain oxidative enzymes
 These enzymes function by oxidizing their
substrates (many of their substrates are fatty
acids)
Peroxisomes
 Oxidation is when a substance loses an electron
 RH2 + O2 → RH + H2O2
 This produces H2O2 which is dangerous
therefore another enzyme, catalase, removes
the H2O2
 2 H2O2 → O2 + 2H2O
Functions of Peroxisomes
Fig. 4.15
 Involved in lipid metabolism and detoxification
 Contain enzymes that produce and degrade
hydrogen peroxide
20
What organelle produces energy (ATP)?
1.
2.
3.
4.
5.
Ribosomes
Golgi complex
Mitochondria
SER
Lysosomes
20%
1
20%
2
20%
20%
3
4
Where are polypeptide chains assembled?
20%
Ribosomes
Golgi complex
Peroxisomes
SER
Lysosomes
20%
1
20%
2
Ribosomes
Golgi complex
SER
RER
25%
5
1
25%
25%
2
3
25%
4
These are membrane bound sacs with digestive enzymes
Where are lipids synthesized?
1.
2.
3.
4.
5.
1.
2.
3.
4.
20%
20%
3
4
Inner Life of a Cell - Harvard
 Inner Life of a Cell Narrated, long version
20%
1.
2.
3.
4.
5.
Ribosomes
Golgi complex
Mitochondria
SER
Lysosomes
5
20%
1
20%
2
20%
20%
3
4
20%
5
Cytoskeleton
 Interconnected system of fibers and lattices
 Gives cells their organization, shape, ability to
move, transport things in cell, important in cell
division
 Some permanent others only present when
needed
 Microtubules
 Microfilaments
 Intermediate filaments
21
Fig. 4.20
Components of the Cytoskeleton
 Three main types of fibers make up the
cytoskeleton
 Microtubules are the thickest of the three
components of the cytoskeleton
 Microfilaments, also called actin filaments, are the
thinnest components
 Intermediate filaments are fibers with diameters in
a middle range
© 2011 Pearson Education, Inc.
Table 6.1a
Microtubules
10 m
 Thickest type of cytoskeleton
 Important in




The structure of cell
Cell division – separates the chromosomes
Transport of organelles in the cell
Movement of cells (cilia and flagella)
Column of tubulin dimers
25 nm


Tubulin dimer
Microtubules
 Composed of two proteins that form a dimer:
α-tubulin and β-tubulin.
Dimer
 -Tubulin
Plus end
 -Tubulin
 These assemble by adding dimers and
disassemble by removing them
 Structural microtubule-associated proteins
(MAPs) regulate microtubule assembly
Dimer on
(a)
Minus end
Dimers off
22
Microtubule Anchoring
10 m
 Microtubules may be anchored in the
microtubule-organizing centers (MTOCs)
 In animal cells the main MTOC is the
centrosome – this is important in cell division
Column of tubulin dimers
25 nm


Tubulin dimer
 The centrosome is composed of two
centrioles
 The centrioles have nine sets of three
microtubules
Fig. 4.21
Figure 6.22
Centrosome
Microtubule
Centrioles
0.25 m
Longitudinal
section of
one centriole
Microtubules
Cross section
of the other centriole
Microtubules – cell division
 During cell division much of the cytoskeleton
breaks down and microtubule form that will
help in cell division = spindles
 Spindles move the chromosomes so when the
cell divides the chromosomes are evenly
divided
23
Microtubule – transport of organelles
Fig. 4.22
 Microtubule can be used to transport vesicles
and other structures.
 The microtubule is stationary, transport proteins
(kinesin and dynein) move the item.
 Kinesin moves items in one direction (+) and
Dynein moves items in the opposite direction (-)
Cilia and flagella
Cilia and Flagella
 Microtubules important in movement of the cell
 Project from cell surface
 Flagella are long microtubules
 Cilia are short microtubules
 Flagella are found on sperm and many one
celled organisms
 Cilia found on many one celled organisms and
on cells that line passageways in multi-celled
organisms
142
Flagella and Cilia
 Both flagella and cilia have nine pairs of
microtubules in an outer ring and a pair in the
center (9 + 2).
 Anchored by a basal body
 A motor protein called dynein, which drives
the bending movements of a cilium or
flagellum
Animation: Cilia and Flagella
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
24
Figure 6.24
0.1 m
Outer microtubule
doublet
Dynein proteins
Central
microtubule
Radial
spoke
Microtubules
Plasma
membrane
Plasma membrane
Flagella and Cilia
 How dynein “walking” moves flagella and cilia
Cross-linking
proteins between
outer doublets
(b) Cross section of
motile cilium
 Dynein arms alternately grab, move, and release
the outer microtubules
 Protein cross-links limit sliding
 Forces exerted by dynein arms cause doublets to
curve, bending the cilium or flagellum
Basal body
0.1 m
0.5 m
(a) Longitudinal section
of motile cilium
Triplet
(c) Cross section of
basal body
© 2011 Pearson Education, Inc.
Figure 6.25
Microtubule
doublets
ATP
Dynein protein
(a) Effect of unrestrained dynein movement
Cross-linking proteins
between outer doublets
ATP
Anchorage
in cell
(b) Effect of cross-linking proteins
1
3
2
(c) Wavelike motion
Fig. 4.24b
25
Figure 6.23
Cilia
Direction of swimming
(a) Motion of flagella
5 m
Direction of organism’s movement
Power stroke Recovery stroke
(b) Motion of cilia
15 m
Microfilaments
 Microfilaments are made two chains of actin
protein molecules
Important in:
1. providing support for cell structures
2. movement of cells (ameoba-like movement)
3. dividing cells in two
Microfilaments (Actin Filaments)
 Microfilaments are solid rods about 7 nm in
diameter, built as a twisted double chain of actin
subunits
 The structural role of microfilaments is to bear
tension, resisting pulling forces within the cell
 They form a 3-D network called the cortex just
inside the plasma membrane to help support the
cell’s shape
 Bundles of microfilaments make up the core of
microvilli of intestinal cells
© 2011 Pearson Education, Inc.
Microfilaments are in green
Microfilaments
 Actin molecules will assemble to form
microfilaments
 Microfilaments are important in formation of
microvilli
26
Figure 6.26
Microfilaments Role in Movement - Muscle
Microvillus
 Microfilaments that function in cellular motility
contain the protein myosin in addition to actin
Plasma membrane
 In muscle cells, thousands of actin filaments are
arranged parallel to one another
Microfilaments (actin
filaments)
 Thicker filaments composed of myosin interdigitate
with the thinner actin fibers
Intermediate filaments
0.25 m
© 2011 Pearson Education, Inc.
Microfilaments Role in Movement - Pseudopodia
Figure 6.27a Muscle Cells
 Localized contraction brought about by actin and
myosin also drives amoeboid movement
Muscle cell
0.5 m
Actin
filament
Myosin
filament
Myosin
head
 Pseudopodia (cellular extensions) extend and
contract through the reversible assembly and
contraction of actin subunits into microfilaments
(a) Myosin motors in muscle cell contraction
© 2011 Pearson Education, Inc.
Figure 6.27b
Cortex (outer cytoplasm):
gel with actin network
100 m
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
(b) Amoeboid movement
27
Microfilaments Role in Movement – Cytoplasmic streaming
Figure 6.27c
 Cytoplasmic streaming is a circular flow of
cytoplasm within cells
 This streaming speeds distribution of materials
within the cell
 In plant cells, actin-myosin interactions drive
cytoplasmic streaming
Chloroplast
30 m
(c) Cytoplasmic streaming in plant cells
© 2011 Pearson Education, Inc.
Intermediate filaments
 Do not self assemble/disassemble –
permanent
 Important in cell shape
 Tough but flexible fibers
 Found in high amounts in cells that are
subjected to mechanical stress (in skin)
Video: Cytoplasmic Streaming
© 2011 Pearson Education, Inc.
Intermediate filaments
Fig. 4.20.c
 Amyotrophic lateral sclerosis (ALS) is
caused by abnormal intermediate filaments
in nerve cells
28
Cilia and flagella are composed of this type of cytoskeleton
1. Microtubules
2. Microfilaments
3. Intermediate
filaments
Kinesin
Actin
Tubulin
Dynein
33%
25%
25%
2
3
25%
fil
a
te
rm
ed
ia
te
In
1
This type of cytoskeleton is more permanent
1. Microtubules
2. Microfilaments
3. Intermediate
Fibers
25%
m
en
t
ts
s
ic
ro
f il
am
en
ub
ul
e
M
ic
ro
t
M
1.
2.
3.
4.
s
33% 33% 33%
Microfilaments are composed of:
33%
33%
4
Extracellular components and connections
between cells help coordinate cellular activities
 Most cells synthesize and secrete materials that are
external to the plasma membrane
 These extracellular structures include
 Cell walls of plants
 The extracellular matrix (ECM) of animal cells
 Intercellular junctions
1
2
3
Copyright © 2009 Pearson Education, Inc.
Cell Walls of Plants
 The cell wall is an extracellular structure that
distinguishes plant cells from animal cells
 Prokaryotes, fungi, and some protists also have cell
walls
 The cell wall protects the plant cell, maintains its
shape, and prevents excessive uptake of water
© 2011 Pearson Education, Inc.
Cell Wall
 Composed of :
1.
2.
3.
4.
Cellulose
Lignins
Sticky polysaccharides
Glycoproteins
 Plant cell walls are made of cellulose fibers
embedded in other polysaccharides and protein
© 2011 Pearson Education, Inc.
29
Figure 6.28
Cell Wall - Layers
Secondary
cell wall
Primary
cell wall
Middle
lamella
 Plant cell walls may have multiple layers
 Primary cell wall: relatively thin and flexible
 Middle lamella: thin layer between primary walls of
adjacent cells
 Secondary cell wall (in some cells): added
between the plasma membrane and the primary
cell wall
1 m
Central vacuole
Cytosol
 Plasmodesmata are channels between adjacent
plant cells
Plasma membrane
Plant cell walls
Plasmodesmata
© 2011 Pearson Education, Inc.
Figure 6.28a
The Extracellular Matrix (ECM) of Animal Cells
Plasma membrane
 Animal cells lack cell walls but are covered by an
elaborate extracellular matrix (ECM)
Secondary
cell wall
Primary
cell wall
 The ECM is made up of glycoproteins such as
collagen, proteoglycans, and fibronectin
Middle
lamella
 ECM proteins bind to receptor proteins in the
plasma membrane called integrins
1 m
© 2011 Pearson Education, Inc.
Figure 6.30a
Collagen
Functions of the Extracellular Matrix (ECM) of
Animal Cells
EXTRACELLULAR FLUID
Proteoglycan
complex
Fibronectin
Integrins
 Functions of the ECM




Support
Adhesion
Movement
Regulation
Plasma
membrane
CYTOPLASM
Microfilaments
© 2011 Pearson Education, Inc.
30
Cell Junctions
Plasmodesmata in Plant Cells
 Neighboring cells in tissues, organs, or organ
systems often adhere, interact, and communicate
through direct physical contact
 Plasmodesmata are channels that perforate
plant cell walls
 Intercellular junctions facilitate this contact
 There are several types of intercellular junctions




Plasmodesmata
Tight junctions
Desmosomes
Gap junctions
© 2011 Pearson Education, Inc.
 Through plasmodesmata, water and small solutes
(and sometimes proteins and RNA) can pass from
cell to cell
© 2011 Pearson Education, Inc.
Figure 6.31
Cell Junctions in Animal Cells
Cell walls
Interior
of cell
 At tight junctions, membranes of neighboring cells
are pressed together, preventing leakage of
extracellular fluid
 Desmosomes (anchoring junctions) fasten cells
together into strong sheets
Interior
of cell
Plasmodesmata
0.5 m
Plasma membranes
 Gap junctions (communicating junctions) provide
cytoplasmic channels between adjacent cells
© 2011 Pearson Education, Inc.
Figure 6.32
Tight junctions prevent
fluid from moving
across a layer of cells
Tight junction
TEM
0.5 m
Tight junction
Intermediate
filaments
Desmosome
TEM
1 m
Gap
junction
Space
between cells
Plasma membranes
of adjacent cells
Extracellular
matrix
TEM
Ions or small
molecules
Animation: Tight Junctions
Right-click slide / select “Play”
0.1 m
© 2011 Pearson Education, Inc.
31
Tight junctions
 Tight junctions: prevent substances from
leaking across tissues
 Found in high concentration between
cells:
 Lining the intestine
 Lining capillaries in the brain
Animation: Desmosomes
Right-
click slide / select “Play”
© 2011 Pearson Education, Inc.
Desmosomes Anchoring junctions
 Desmosomes - Anchoring junctions:
hold adjacent cells together (like
glue) and allow tissues to be flexible
 Found in high concentration in skin
epithelial cells
 Integrin and Cadherin proteins
 Attach to cytoskeleton
Animation: Gap Junctions
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Communicating Junctions
 Gap junctions – open channels between
cells allowing rapid communication due to
quick transfer of ions and small molecules
between neighboring cells
 These junctions can be opened or closed
 High concentration of gap junctions are
found in heart tissue
Animal and Plant cells
 Both animal and plant cells have:










Plasma membrane
Nucleus
Smooth and rough endoplasmic reticulum
Ribosomes
Golgi complex
Vesicles
Peroxisomes
Mitochodria
Cytoskeleton
Lysosomes
32
Plant Cells
Found only in Animal Cells
 Main Plant cell components not present in
animal cells




 Animal cells have centrioles, plants have a
different type of MTOCs
Cell wall
Vacuoles (usually central)
Plastids including Chloroplast
Glyoxysomes
 Not present in plant cells: centrioles
Glyoxysomes
Plastids
 Plants also have a type of organelle called
glyoxysomes
 Chromoplasts – contain pigments, give plant
color, attract pollinators
 Glyoxysomes contain enzymes that convert
stored fatty acids to sugar that is used for
energy, this is especially important in
germinating seedlings.
 Amyloplasts – store starch
 Chlorplasts – contain a green pigment,
chlorophyll and carotenoids – yellow and
orange pigments. Site of photosynthesis.
 Animal cells do not have these type of
peroxisomes (we can’t convert fatty acids to
sugar)
Plant cells do not contain:
Important Concepts
 Know the vocabulary in the lecture
1.
2.
3.
4.
Mitochondria
Centrioles
Nucleus
Ribosomes
25%
25%
25%
25%
 Be able to describe cell theory and the properties
of cells and structures common to all cells.
 Know how cells are studied, the types of
microscopy, the centrifugation techniques. How
would you separate the organelles of the cell?
 What are the main difference between
prokaryotic cells and eukaryotic cells, and
examples of each type?
1
2
3
4
33
Important Concepts
 What are the features and characteristics of
prokaryotic cells?
 What is apoptosis and what organelle is an
important player in the process? What molecules
are released and activated during apoptosis?
 What are the major features of eukaryotic cells,
their location, features, structure, and their
function – both plants and animals?
Important Concepts
 Describe the steps needed to make a protein and
ship it out of the cells, or embed the protein in a
membrane, or have the protein stay in the
cytosol.
 What is the cause of Tay Sachs disease?
 What are the differences between plant and
animal cells?
 Be able to describe the endosymbiont theory
Important Concepts
 What are the types of cytoskeleton – what are
their functions, structure, what proteins are they
composed of, and how they are assembled?
 How are microtubules assembled, anchored,
how do they transport items and what proteins
are used by microtubles to transport items.
Important Concepts
 Know the types of cell junctions, their
functions and locations where there are
found in high concentration
 Know the role and components of
extracellular matrix
 What is the cause of ALS?
 What are cell walls composed of, what are the
layers?
34