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THE DISCOVERY OF THE CELL
• It was not until the mid-1600’s
that scientists began to use
microscopes to observe cells.
• In 1665, Englishman Robert
Hooke used an early compound
microscope to look at a slice of
cork, plant material.
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CORK CELLS
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• Hooke saw thousands of empty
chambers in which he called cells.
• They reminded him of a
monastery’s tiny rooms, which
were called cells.
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• In Holland around the same time,
Anton van Leeuwenhoek used a
single-lens microscope to observe
pond water and other things.
• He discovered that living things
seemed to be everywhere, even in
the water he was drinking.
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DUST MITE
EUGLENA
FLAGELLA
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THE CELL THEORY
• In 1838, German botanist
Matthias Schleiden concluded
that all plants were made of cells.
• In 1839, German biologist
Theodor Schwann stated that all
animals were made of cells.
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• In 1855, German physician
Rudolf Virchow concluded that
new cells could be produced only
from the division of existing cells.
• These discoveries, confirmed by
other biologist, are summarized
in the cell theory.
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• CELL THEORY STATES…
1. All living things are composed of
cells.
2. Cells are the basic units of
structure and function in living
things.
3. New cells are produced from
existing cells.
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THE CHANGE OF THE
MICROSCOPE
• Hooke, Virchow, and others
used crude microscopes to study
the cells.
• Today scientist can use…
1. Fluorescent Labels (to mark
moving cell parts)
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2. Confocal light ( scans cells with
a laser beam to build threedimensional images )
3. High resolution video to make
movies of cells as they grow.
4. Transmission electron
microscope ( electrons pass
through thin slices of cell parts)
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5. Scanning electron microscope
( produces three-dimensional
images of cells without having to
cut cell parts into small slices)
6. In the 1990’s, researchers
developed the scanning probe
microscope ( produce images
that trace objects with a
probe…DNA )
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STEM
CELLS
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CONFOCAL
LIGHT
TEM
TEM
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CHLOROPLAST
MARINE DIATOM
SEM
SCANNIING
ELECTRON
MICROSCOPE
pea weevil egg
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White pine sheath mite
on eastern white pine
Scanning electron microscope
image of white pine sheath mite
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SCANNING PROBE
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PROKARYOTES and
EUKARYOTES
• Cells fall into two categories,
depending on whether they contain
a nucleus.
1. Eukaryotes (YOUkaryotes)- have a
nucleus. (means “true nut”)
2. Prokaryotes (Pro=Before)- no
nucleus. (means “before nut”)
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PROKARYOTIC CHACTERISTICS
• Smaller than eukaryotic cells
• Genetic information is not
contained by a nucleus.
• Some have a few internal
membranes
• Less complicated compared to
eukaryotic cells
• They grow, reproduce, and
respond to their environment.
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• Some glide and swim through
liquids.
• Forms of locomotion are:
1. Cilia – hair like structures
2. Flagella – whip like structure.
(sperm)
• Examples: Bacteria
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EUKARYOTIC CHARACTERISTICS
• Larger than prokaryotes
• They usually contain dozens of
structures and internal membranes.
• Genetic information is carried by a
nucleus.
• Some live solitary lives while others form
large multicellular organisms.
• Examples: plants, animals, fungi, and
protists.
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A typical animal cell
ENDOPLASMIC RETICULUM (ER)
Rough ER
Smooth ER
Nuclear envelope
Nucleolus
NUCLEUS
Chromatin
Flagelium
Plasma membrane
Centrosome
CYTOSKELETON
Microfilaments
Intermediate filaments
Ribosomes
Microtubules
Microvilli
Golgi apparatus
Peroxisome
Figure 6.9
Mitochondrion
Lysosome
In animal cells but not plant cells:
Lysosomes
Centrioles
Flagella (in some plant sperm)
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PARTS OF THE CELL
• Cell biologists divide eukaryotic cell
into two parts: the nucleus and the
cytoplasm.
• The cytoplasm is the portion of the
cell that is outside the nucleus.
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NUCLEUS
Nucleus
1 µm
Nucleus
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Rough ER
Surface of nuclear
envelope.
Ribosome
1 µm
0.25 µm
Close-up of
nuclear
envelope
Pore complexes (TEM).
Nuclear lamina (TEM).
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THE NUCLEUS
• The nucleus is the control center
of the cell.
• It contains the cell’s DNA and the
code for making proteins (mRNA)
and other important molecules
(rRNA and tRNA).
• The nucleus is surrounded by a
nuclear envelope composed of two
membranes.
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• The envelope is dotted with
thousands of pores, which allows
materials to leave the nucleus to
other parts of the cell.
• Inside of the nucleus is a granular
material called chromatin.
• Chromatin consists of DNA bound
to protein.
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• When a cell divides, the chromatin
condenses to form chromosomes.
• These are the distinct structures that
are passed from cell to
cell…generation to generation.
• Deep inside the nucleus is the
nucleolus which is where assembly
of ribosomes begins.
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? QUESTION ?
• WHAT KIND OF INFORMATION IS
CONTAINED IN CHROMOSOMES ?
• ANSWER: GENETIC INFORMATION
KNOWN AS DNA
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RIBOSOMES
• One of the most important jobs
carried out in the cell is
ribosomes making proteins.
• Proteins are assembled on
ribosomes.
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• Ribosomes are small particles of
RNA and protein and are found
throughout the cytoplasm.
• Ribosomes produce proteins by
following coded instructions that
come from the nucleus.
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? QUESTION ?
• WHAT DO RIBOSOMES
PRODUCE ?
• ANSWER: PROTIENS
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PARTS OF THE CELL
• Cell biologists divide eukaryotic cell
into two parts: the nucleus and the
cytoplasm.
• The cytoplasm is the portion of the
cell that is outside the nucleus.
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Cell basics . . .
Plasma membrane
Nucleus
Cytosol
Organelles
Cytoplasm
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Cytoskeleton fibers
adsorb water and
crosslink to each other,
giving the cytoplasm the
consistency of gelatin
(without the strawberry flavor)
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ENDOPLASMIC RETICULUM
• The ER membrane
– Is continuous with the nuclear envelope
Smooth ER
Rough ER
ER lumen
Cisternae
Ribosomes
Transport vesicle
Smooth ER
Nuclear
envelope
Transitional ER
Rough ER
200 µm
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ENDOPLASMIC RETICULUM
• The endoplasmic reticulum is also
known as ER.
• It is the site where lipid components
of the cell membrane are assembled
along with proteins and other
materials.
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• The portion of the ER involved in
synthesis of plasma membrane,
lysosomal, and secretory proteins
is called Rough ER.
• Rough ER = ribosomes found on the
surface of endoplasmic reticulum.
• Newly made proteins leave
ribosomes and are inserted into the
Rough ER, where they can be
chemically modified.
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• There are other portions of the ER
called Smooth ER because no
ribosomes are embedded.
• Smooth ER contains enzymes that
synthesize lipids and are involved in
the detoxification of drugs. (liver
cells contain Smooth ER)
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? QUESTION ?
• WHAT IS THE ROLE OF THE
ROUGH ER ?
• ANSWER: TO SYNTHESIZE
PLASMA MEMBRANE,
LYSOSOMAL AND SECRETORY
PROTEINS
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GOLGI APPARATUS
• The Golgi Apparatus receives
proteins from the Rough ER.
• The job of the Golgi Apparatus is to
modify, sort, and package
proteins for storage or secretion
outside the cell.
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• Functions of the Golgi apparatus
Golgi
apparatus
cis face
(“receiving” side of
Golgi apparatus)
1 Vesicles move
2 Vesicles coalesce to
6 Vesicles also
form new cis Golgi cisternae
from ER to Golgi
transport certain
Cisternae
proteins back to ER
3 Cisternal
maturation:
Golgi cisternae
move in a cisto-trans
direction
5 Vesicles transport specific
proteins backward to newer
Golgi cisternae
0.1 0 µm
4 Vesicles form and
leave Golgi, carrying
specific proteins to
other locations or to
the plasma membrane for secretion
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
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• The Golgi Apparatus is like a
customizing shop that puts on the
final touches before proteins are
shipped out.
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? QUESTION ?
• WHAT IS THE ROLE OF THE
GOLGI APPARATUS ?
• ANSWER: IT MODIFIES, SORTS,
AND PACKAGES PROTEINS.
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LYSOSOMES
• Lysosomes are the clean up crew
of the cell.
• They are small organelles filled with
enzymes that break down and
digest lipids, carbohydrates, and
proteins.
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Lysosomes carry out intracellular digestion by
Phagocytosis
Nucleus
- Autophagy
1 µm
Lysosome containing
two damaged
organelles
1µm
Mitochondrio
n
fragment
Peroxisome
fragment
Lysosome
Lysosome contains
active hydrolytic
enzymes
Food vacuole
fuses with
lysosome
Hydrolytic
enzymes digest
food particles
Lysosome fuses with
vesicle containing
damaged organelle
Hydrolytic enzymes
digest organelle
components
Digestive
enzymes
Lysosome
Plasma membrane
Lysosome
Digestion
Food vacuole
Vesicle containing
damaged mitochondrion
(a) Phagocytosis: lysosome digesting food
Digestion
(b) Autophagy: lysosome breaking down damaged organelle
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? QUESTION ?
• WHAT IS THE ROLE OF THE
LYSOSOME ?
• ANSWER: CLEAN UP THE
CELL AND GET RID OF WASTE
MATERIALS.
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VACUOLES
• Vacuoles are saclike structures that
store materials such as water, salts,
proteins, and carbohydrates.
• Plant cells have vacuoles. They help
each cell maintain water pressure to
hold up heavy structures such as
leaves and flowers.
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• Some single-celled organisms
have contractile vacuoles which
regulates the water inside the cell.
• Contractile vacuoles help cells
maintain Homeostasis (“internal
balance”)
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• Central vacuoles
– Are found in plant cells
– Hold reserves of important organic compounds
and water
Central vacuole
Cytosol
Tonoplast
Nucleus
Central
vacuole
Cell wall
Chloroplast
5 µm
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• Central vacuoles
– Are found in plant cells
– Hold reserves of important organic
compounds and water
Central vacuole
Cytosol
Tonoplast
Nucleus
Central
vacuole
Cell wall
Chloroplast
Figure 6.15
5 µm
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? QUESTION ?
• WHAT IS THE ROLE OF A
VACUOLE ?
• ANSWER: THEY STORE
MATERIALS AND HELP
PLANTS MAINTAIN THEIR
STRUCTURE.
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CELLS AND THEIR POWER
• Nearly all eukaryotic cells, including
plants contain Mitochondria.
• Mitochondria are organelles that
convert the chemical energy stored
in food into compounds that are
more convenient.
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• In humans, all or nearly all our
mitochondria come from the
cytoplasm of the ovum, or egg cell.
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• In plants chloroplasts are the
organelles that capture the energy
from the sunlight and convert it into
chemical energy in a process called
photosynthesis.
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• Both mitochondria and chloroplasts
are the only organelles that have
small DNA molecules.
• Scientists believe that these two
organelles may have been
descendants of ancient prokaryotes
at one time.
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CYTOSKELETON
• The cytoskeleton is a network of protein
filaments that help the cell maintain its
shape.
• Microfilaments and Microtubules
make up the cytoskeleton.
• Microfilaments are threadlike and
made of a protein called actin.
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• Microtubules are hollow structures
that are made up of proteins called
tubulins.
• In animal cells, tubulin helps in the
development of centrioles.
• Centrioles are located near the
nucleus and help in cell division.
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CELL MEMBRANE
• The cell membrane regulates what
enters and also leaves the cell and also
provides protection and support.
• The cell membrane is made up of two
layers called a phospholipid bilayer.
• Scientists refer to it as a “mosaic model”
that contains different molecules.
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CELL WALL
• Many cells also produce a strong
supporting layer around the membrane
known as the cell wall.
• Cell walls are present in plants, algae,
fungi, and many prokaryotes.
• The main function of the cell wall is to
provide support and protection for the cell.
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A typical plant cell
Nuclear envelope
Nucleolus
Chromatin
NUCLEUS
Centrosome
Rough
endoplasmic
reticulum Smooth
endoplasmic
reticulum
Ribosomes (small brwon dots)
Central vacuole
Tonoplast
Golgi apparatus
Microfilaments
Intermediate
filaments
CYTOSKELETON
Microtubules
Mitochondrion
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell
In plant cells but not animal cells:
Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata
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CELL WALL
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DIFFUSION THROUGH CELL
BOUNDARIES
• In a solution, particles move constantly. They will
collide into one another and tend to spread out
randomly.
• Diffusion is the process by which molecules of a
substance move from areas of higher
concentration to areas of lower concentration.
• This process will continue until equilibrium is
reached.
• No energy is required by the cell.
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•
•
Osmosis is the diffusion of water through
a selectively permeable membrane.
Selectively permeable membrane means
that some substances can pass and
some cannot.
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• There are 3 effects of Osmosis on the cell:
1.Isotonic: The concentration is the same on
both sides of the cell. (Normal Cell)
2.Hypertonic: The solution, in which the cell
is in, is of higher solute concentration than
the cell. (Skinny Cell)
3.Hypotonic: The solution, in which the cell
is in, is of lower solute concentration than
the cell. (Swollen Cell)
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FACILITATED DIFFUSION
• Sometimes in a cell there are certain molecules
that cross the selective permeable membrane
that are to large for it to happen by osmosis.
• The process that helps large molecules pass the
membrane in a cell is called facilitated diffusion.
• This happens when protein molecules act as
channels for large molecules to pass from one
side of the membrane to the other side.
• No energy is required by the cell.
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ACTIVE TRANSPORT
• This a process in which the cell does
require energy to transport materials
across the cell membrane.
• This is the movement of molecules against
the concentration differences.
• Types of active transport consist of:
• 1. Endocytosis= this occurs by infoldings,
or pockets, of the cell membrane.
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2. Phagocytosis= “cell eating” extensions of
the cytoplasm surround a particle and
package it within a cell a food vacuole.
3. Pinocytosis= tiny pockets form along the
cell membrane, fill with liquid and then
pinch off to form vacuoles within the cell.
4. Exocytosis= this is the removal of
contents from the cell. Contractile
vacuoles are examples of exocytosis.
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THE DIVERSITY OF CELLULAR
LIFE
• Single cell organisms are called
unicellular.
• Organisms made of many cells are called
multicellular organisms.
• Cells through out organisms can develop
in different ways to perform different tasks.
This process is called cell specialization.
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LEVELS OF ORGANIZATION
• In multicellular organisms, cells are the
first level of organization.
• Similar cells are grouped into units called
tissues.
• Many groups of tissues working together
form an organ.
• A group of organs that work together to
perform a particular function is called an
organ system.
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