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Anatomy of Cells
The Discovery of Cells
• DON’T WRITE THIS
• Robert Hooke discovered cells
when he looked under a
microscope at a think slice of
cork.
• In Holland, Anton van
Leeuwenhoek examined pond
water and a sample taken from
a human mouth.
• He drew the organisms he
saw—which today we call
bacteria. (Rotifers)
• Leeuwenhoek examined as
many types of cells as he could.
He even observed his own
semen!
Overview: The
Importance of Cells
• The early discoveries of cells are summarized in
the cell theory, a fundamental concept of biology.
• The cell theory states:
o All living things are made up of cells.
o Cells are the basic units of structure and function in living things.
o New cells are produced from existing cells.
Origin of Cellular Life
• DON’T WRITE THIS NOW
• The Earth formed about 4.6 billion years ago.
o For about 500 million years, the Earth was continually
bombarded by chunks of rock and ice in the solar system.
• The early atmosphere of Earth contained:
o
o
o
o
o
Water vapor H2O
Nitrogen N2
Carbon dioxide CO2
Methane CH4
Ammonia NH3
Two Types of Cells
1- Prokaryotes
First life forms
• Single celled
• No true nucleusDNA/RNA is just floating
around the cell
• No membrane bound
organelles
2- Eukaryotes
• Evolved from single
celled organisms
• True nucleus with
membrane bound
organelles
• Usually multi-cellular,
but not always.
Pili
Nucleoid
Ribosomes
Plasma
membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 µm
Flagella
A typical
rod-shaped
bacterium
A thin section through the
bacterium Bacillus
coagulans (TEM)
Parts of a Prokaryotic Cell
• Nucleoid – Area where DNA or RNA is located. Not
enclosed in a membrane like a nucleus.
• Ribosomes – Small structures that use DNA or RNA
instructions to produce proteins.
• Flagella – Spin to produce movement.
• Cell membrane – Controls what leaves or enters the
cell
• Do have cytoplasm – jelly like substance that is made
up of mostly water and dissolved substances.
Why are cells so small?
• To have a large surface area to volume area.
• Let me explain:
LE 6-7
• Volume represents the
size of the cell.
• Surface area represents
the amount of cell
membrane to transport
food, waste, water, and
oxygen.
1
Total surface area
Total volume
Surface-to-volume
ratio
Surface area increases while
Total volume remains constant
5
1
LE 6-7
Surface area increases while
Total volume remains constant
• A cell with a volume of
1mm3 will have a total
surface area of 6mm2.
• This provides plenty of
area for the cell to
absorb what it needs.
5
1
1
Total surface area
(height x width x
number of sides x
number of boxes)
6
Total volume
(height x width x length
X number of boxes)
1
Surface-to-volume
ratio
(surface area  volume)
6
LE 6-7
• A larger cell with a
volume of 125mm3 will
only have a surface area
of 150mm2.
• This cell will not be able to
transport wastes and
nutrients fast enough.
Surface area increases while
Total volume remains constant
5
1
1
Total surface area
(height x width x
number of sides x
number of boxes)
150
Total volume
(height x width x length
X number of boxes)
125
Surface-to-volume
ratio
(surface area  volume)
1.2
LE 6-7
• If the larger cell is instead
broken down into 125
smaller cells, it will once
again have enough
surface area.
• This is why multicellular
organisms exist!
Surface area increases while
Total volume remains constant
5
1
1
Total surface area
(height x width x
number of sides x
number of boxes)
6
150
750
Total volume
(height x width x length
X number of boxes)
1
125
125
Surface-to-volume
ratio
(surface area  volume)
6
1.2
6
Eukaryotic Cell
Organization
• The eukaryotic cell can be divided into two major parts: the
nucleus and the cytoplasm.
• The cytoplasm is the fluid portion of the cell outside the
nucleus.
o Organelles are small structures within cells that have
specific jobs.
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)
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
The Nucleus
• This is the Boss of the cell
• The nuclear envelope is a membrane
surrounding the nucleus.
• Contains the DNA
The Nucleus
• The nucleus also contains a small
dense region called the
nucleolus.
• The nucleolus produces
ribosomes, which are needed to
build proteins.
Organelles that Build
Proteins
• Because proteins carry out so many of the essential
functions of living things, a big part of the cell is
devoted producing and transporting them.
• Proteins are synthesized(made) in ribosomes, which
can be found in two places:
o Freely floating in the cytoplasm
o Attached to the endoplasmic reticulum
Ribosomes: Protein
Factories
• Ribosomes are particles made of RNA and protein
o Ribosomes produce proteins by following coded instructions
that come from DNA.
o Each ribosome is like a small machine in a factory, turning out
proteins on orders that come from its DNA “boss.”
Endoplasmic Reticulum
• The endoplasmic reticulum (ER) is a huge membrane
that is connected to the nuclear membrane.
• There are two distinct regions of ER:
o Smooth ER, which lacks ribosomes
o Rough ER, with ribosomes studding its surface
Smooth Endoplasmic
Reticulum
• The smooth endoplasmic reticulum:
o
o
o
o
Synthesizes lipids
Metabolizes carbohydrates
Stores calcium
Detoxifies poison
• The smooth endoplasmic reticulum does not contain
any ribosomes, so it is unable to synthesize proteins.
Rough Endoplasmic
Reticulum
• The rough ER
o Holds ribosomes
o Produces any proteins needed by the cell.
The Golgi Apparatus
• The Golgi apparatus is a series of flattened membrane
sacs in the cytoplasm.
• Functions of the Golgi apparatus:
o Modifies, sorts, and packages materials into transport vesicles
for storage or transport out of the cell.
o A typical path for a protein produced by the cell:
o DNARNARibosomeRough ER → Golgi → Cell membrane
→ Released by cell
Cell/Plasma Membrane
• The plasma/Cell membrane is a selective
barrier.
o Allows passage of oxygen, nutrients into the cell,
and waste out of the cell.
• The general structure of a biological
membrane is a bilayer(double)of phospholipids
o This allows the cell to control what goes in and
out.
LE 6-16-1
Nucleus
Rough ER
Smooth ER
Nuclear envelope
LE 6-16-2
Nucleus
Rough ER
Smooth ER
Nuclear envelope
cis Golgi
Transport vesicle
trans Golgi
LE 6-16-3
Nucleus
Rough ER
Smooth ER
Nuclear envelope
cis Golgi
Transport vesicle
Plasma
membrane
trans Golgi
Organelles that Store,
Clean Up, and Support
• These are organelles that help the cell maintain its
shape, clean up wastes, and store material needed
later.
o Lysosomes
o Vacuoles
o Vesicles
Vacuoles
• vacuoles are membrane-bound sacs that store many
materials.
• Mostly found in plant cells
• Plant cells often have one large central vacuole. This
fills with water, making the cell rigid.
o When they are empty and dry, plants wilt!
o Hold cell sap ( full of sugars and water)
Lysosomes
• Lysosomes serve as the cell’s cleanup crew.
• A lysosome is full of enzymes that can digest proteins,
lipids, polysaccharides, and nucleic acids.
o Can also breakdown old organelles so they can be re-used.
Animation: Lysosome Formation
Vesicles
• Spherical Sacs that transport materials within a cell.
Cytoskeleton
• The cytoskeleton is a network of protein filaments that
give the cell shape.
o Can also help transport materials across the cell.
• Centrioles are part of the cytoskeleton that help move
chromosomes during cell division.
Organelles that Capture
and Release Energy
• All life requires energy.
• Organisms either can get their energy from sunlight
via photosynthesis, or by eating other organisms via
cell respiration.
• Photosynthesis occurs in chloroplasts.
• Cell respiration occurs in mitochondria.
Chloroplasts
• Chloroplasts contain the green pigment
chlorophyll, as well as enzymes and other
molecules that function in photosynthesis
• Chloroplasts are found in leaves and other
green organs of plants and in algae
Mitochondria
• Mitochondria are the power plants of the cell.
• They convert the chemical energy stored in food into
smaller molecules for the cell to use.
• Mitochondria have two membranes, outer and inner.
• The inner membrane is folded up to increase the
amount of surface area to do chemical reactions.
Cell Wall
• The cell wall is made of cellulose and serves as
support and protection for the cell.
• Animals do not have cell walls, but plants, fungi, and
algae do.
• The cell wall is outside of the cell membrane.
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