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Basic features of all cells
• All cells have the following features in
common:
– Plasma membrane
– Cytosol
– Chromosomes (carry genes in the form
of DNA)
– Ribosomes (make proteins according to
instructions from the genes)
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• Prokaryotic cells are characterized by having
– No nucleus
– DNA in an unbound region called the nucleoid
– No membrane-bound organelles
– Cytoplasm bound by the plasma membrane
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Fig. 6-6
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 µm
(a) A typical
rod-shaped
bacterium
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Flagella
(b) A thin section
through the
bacterium
Bacillus
coagulans (TEM)
Figure 4.5 A Prokaryotic Cell
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Figure 4.6 Prokaryotic Flagella (Part 1)
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Eukaryotic cells
• Eukaryotic cells are
characterized by having
– DNA in a nucleus that is
bounded by a nuclear envelope
– Membrane-bound organelles
– Cytoplasm in the region
between the plasma membrane
and nucleus
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Cytoplasm’s Components of
Eukaryotic Cells
The cytoplasm consists of:
– Organelles
– Cytosol
Organelles:
• Specific entities, each carries out a specific function
for the cell.
Cytosol:
• The viscous, semitransparent fluid in which other
cytoplasmic elements are suspended.
• Largely water with dissolved protein, salts, sugars,
and other solutes.
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A Panoramic View of the Eukaryotic Cell
• Every cell is surrounded by a plasma
membrane.
• The plasma membrane is a selective barrier that
allows sufficient passage of oxygen, nutrients,
and waste to service the volume of the cell
• Eukaryotic cells have internal membranes that
partition the cell into organelles
• Plant and animal cells have most of the same
organelles
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Fig. 6-7
Outside of cell
Inside of
cell
(a) TEM of a plasma
membrane
0.1 µm
Carbohydrate side chain
Hydrophilic
region
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
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LE 6-9a
ENDOPLASMIC RETICULUM (ER
Nuclear envelope
Flagellum
Rough ER
Smooth ER
NUCLEUS
Nucleolus
Chromatin
Centrosome
Plasma membrane
CYTOSKELETON
Microfilaments
Intermediate filaments
Microtubules
Ribosomes:
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
In animal cells but not plant cells:
Lysosomes
Centrioles
Flagella (in some plant sperm)
Figure 4.7 Eukaryotic Cells (Part 1)
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Figure 4.7 Eukaryotic Cells (Part 2)
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LE 6-9b
Nuclear
envelope
NUCLEUS
Nucleolus
Chromatin
Centrosome
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
Ribosomes
(small brown dots)
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
CYTOSKELETON
Mitochondrion
Peroxisome
Chloroplast
Plasma
membrane
Cell wall
Plasmodesmata
Wall of adjacent cell
In plant cells but not animal cells:
Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata
Figure 4.7 Eukaryotic Cells (Part 3)
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Figure 4.7 Eukaryotic Cells (Part 4)
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The Nucleus: Genetic Library of the Cell
•
The nucleus contains most of the genes (DNA) in a
eukaryotic cell.
Functions of the nucleus:
1. The nucleus controls cellular activities by sending
orders to the ribosomes to make proteins.
2. In the nucleus, DNA replication takes
place to transmit information from
parents to offspring.
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The Nucleus: Genetic Library of the Cell
The nucleus is made of the
following parts:
1. The nuclear envelope: a double
membrane with pores enclosing the
nucleus,.
2. The nucleolus: Where rRNA is
synthesized and assembled with
proteins to form small and large
ribosomal subunits.
3. The chromatin: the fibrous material in
the nucleus of a nondividing cell, made
of the complex of DNA and proteins
making up the chromosomes.
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Chromatin
• Form
condensed,
bar-like bodies
of
chromosomes
when the
nucleus starts
to divide
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Ribosomes: Protein Factories in the Cell
•
Ribosomes are particles made of ribosomal RNA and protein
•
Ribosomes carry out protein synthesis in two locations:
–
In the cytosol. Free ribosomes synthesize proteins that
function within the cytosol.
–
On the outside of the endoplasmic reticulum (ER) or the
nuclear envelope. Bound ribosomes synthesize
proteins that are destined for:
a. Insertion into membranes
b. Packing witin certain organelles such as lysosomes.
c. Export from the cell, a process called secretion.
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LE 6-11
Ribosomes
ER
Cytosol
Endoplasmic
reticulum (ER)
Free ribosomes
Bound ribosomes
Large
subunit
Small
subunit
0.5 µm
TEM showing ER
and ribosomes
Diagram of
a ribosome
Concept 6.4: The endomembrane system regulates protein
traffic and performs metabolic functions in the cell
• In the cell, the endomembrane system is the
membranous components that are either in direct
contact or connected via transfer by vesicles.
• These components make up the endomembrane
system that includes the:
– Nuclear envelope
– Endoplasmic reticulum
– Golgi apparatus
– Lysosomes
– Vacuoles
– Plasma membrane
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The Endomembrane System
Nucleus
Rough ER
Smooth ER
Nuclear envelope
cis Golgi
Transport vesicle
Plasma
membrane
trans Golgi
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Figure 4.8 The Endomembrane System
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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, with ribosomes studding
its surface
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Functions of Smooth ER
• The smooth ER
– Synthesizes lipids
– Stores calcium ions necessary for
muscle contraction.
– Detoxifies poisons and drugs
– Metabolism of carbohydrates.
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Functions of Rough ER
• The rough ER
– Has bound ribosomes
– Functions:
• Make secretory
proteins
• Acts as a membrane
factory for the cell.
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The Golgi Apparatus: Shipping and Receiving Center
• The Golgi apparatus consists of flattened
membranous sacs called cisternae
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The Golgi Apparatus: Shipping and Receiving Center
1
Proteincontaining
vesicles pinch
off rough ER
and migrate to
fuse with
membranes of
Golgi
apparatus.
Rough ER
ER Phagosome
membrane
Proteins in
cisterna
Pathway C:
Lysosome containing
acid hydrolase
enzymes
Vesicle becomes
lysosome
2 Proteins are
modified within
the Golgi
compartments.
3 Proteins are
then packaged
within different
vesicle types,
depending on
their ultimate
destination.
Plasma
membrane
Golgi
apparatus
Pathway A:
Vesicle contents
destined for exocytosis
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Secretory
vesicle
Secretion by
exocytosis
Pathway B:
Vesicle membrane
to be incorporated
into plasma
membrane
Extracellular fluid
Figure 3.20
The Golgi Apparatus: Shipping and Receiving Center
• Functions of the Golgi apparatus:
– Modifies products of the ER
– Sorts and packages materials into
transport vesicles and targets them for
various parts of the cell
– Manufactures certain macromolecules,
including some polysaccharides.
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LE 6-14a
1 µm
Nucleus
Lysosome
Lysosomes
can fuse with
food vacuoles
containing
food items
brought into
the cell by
phagocytosis.
Lysosome contains Food vacuole Hydrolytic
active hydrolytic
enzymes digest
fuses with
enzymes
food particles
lysosome
Digestive
enzymes
Plasma
membrane
Lysosome
Digestion
Food vacuole
Phagocytosis: lysosome digesting food
Figure 4.9 Lysosomes Isolate Digestive
Enzymes from the Cytoplasm
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LE 6-14b
Lysosome containing
two damaged organelles
1 µm
Mitochondrion
fragment
Peroxisome
fragment
Lysosome fuses with
vesicle containing
damaged organelle
Hydrolytic enzymes
digest organelle
components
Lysosome
Digestion
Vesicle containing
damaged mitochondrion
Autophagy: lysosome breaking down
damaged organelle
Lysosomes
use
enzymes to
recycle
organelles
and macromolecules,
a process
called
autophagy.
Vacuoles: Diverse Maintenance Compartments
• Vesicles and vacuoles (larger
versions of vesicles) are membranebound sacs with varied functions
• A plant cell or fungal cell may have one
or several vacuoles
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Types of vacuoles in various cells:
• 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. The membrane surrounding the central
vacuole is called the tonoplast.
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Functions of the Central Vacuole:
Storing:
-
Central vacuole
Cytosol
proteins
inorganic ions.
pigments.
defensive
compounds
against
herbivores.
Tonoplast
Nucleus
Central
vacuole
Cell wall
Chloroplast
5 µm
The Endomembrane System (EMS): A Review
Nucleus
Rough ER
Smooth ER
Nuclear envelope
-
-
EMS
regulates
protein traffic
within the cell
performs
metabolic
functions in the
cell (e.g. makes
proteins)
cis Golgi
Transport vesicle
Plasma
membrane
trans Golgi
Concept 6.5: Mitochondria and chloroplasts
change energy from one form to another
• Mitochondria and chloroplasts are not parts
of the endomembrane system.
• Both organelles have:
1- Small quantities of DNA
2- Their own ribosomes
3- Double membranes.
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Mitochondria: Structure
• Mitochondria are in nearly all
eukaryotic cells
• They have a smooth outer membrane
and an inner membrane folded into
cristae
• The inner membrane creates two
compartments: intermembrane space
and mitochondrial matrix
• Mitochondria are the sites of cellular
respiration, generating energy for the
cell in the form of ATP.
• Cristae present a large surface area for
enzymes that synthesize ATP
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LE 6-17
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Mitochondrial
DNA
100 nm
Chloroplasts: Capture of Light Energy
• Chloroplasts contain the green pigment
chlorophyll, as well as enzymes and other
molecules that function in photosynthesis.
• In photosynthesis, the plants make sugar by
using light energy, carbon dioxide and
water.
• Chloroplasts are found in the leaves and
other green organs of plants and in algae
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 6-18
Chloroplast structure includes:
-Thylakoid membranes:
membranous sacs that are stacked
in some regions like poker chips into
grana (singular is granum)
Chloroplast
- Stroma, the internal fluid
surrounding the thylakoid
membanes.
Ribosomes
Stroma
Chloroplast
DNA
Inner and outer
membranes
Granum
1 µm
Thylakoid
The Cell: A Living Unit Greater Than the Sum of Its Parts
• Cells rely on the integration of structures and
organelles in order to function
• For example, a macrophage’s ability to destroy
bacteria involves the whole cell, coordinating
components such as the cytoskeleton, lysosomes,
and plasma membrane
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