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Eukaryotes
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Prokaryotes and Eukaryotes
prokaryotes: pro: before
karyon: kernel/seed (nucleus)
eukaryote:
eu: true
karyon: kernel/seed (nucleus)
So prokaryote = "before a nucleus"
And eukaryote = "true nucleus"
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Eukaryotes
Organelles
A eukaryotic cell contains a true nucleus,
as well as other
membrane bound "organelles"
(parts of a cell).
But what is a nucleus?
Where did these "organelles" come from?
Nucleus
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The Biological Nucleus
The nucleus from chemistry with protons and neutrons is not the
same nucleus involved with cells.
Biological
Nucleus
The biological nucleus is usually, but not always, in the center of a
cell and it is sometimes referred to as the "control center" of the cell.
We will come back to this in a little bit when we start looking at all of
these cell parts to see what they do. For now, just know that in a
eukaryotic cell, most of the cell's DNA is found in the nucleus.
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1 Cells that contain a "true nucleus" and other membrane bound
organelles are _______________.
A archaea.
B
bacteria.
C eukaryotes.
D prokaryotes.
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All Cells
One key difference between prokaryotic and eukaryotic
cells is that eukaryotic cells are partitioned into functional
compartments called organelles.
All eukaryotic cells, whether they belong to animals,
plants, fungi, or protists are fundamentally similar to one
another and very different from prokaryotic cells.
At the end of this chapter we will discuss how eukaryotes
are thought to have evolved from prokaryotes!
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All Cells
Are surrounded by a plasma membrane (or cell membrane).
Contain a semifluid substance called the cytosol/cytoplasm.
Contain structures called chromosomes, which carry the cell's
genes.
Have ribosomes, which assemble amino acids into proteins.
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Review of Prokaryotic Structure
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Eukaryotes are different because...
Eukaryotic cells have their chromosomes (structures in
which their DNA is configured) in a nucleus that is bound by
a membranous nuclear envelope.
Eukaryotic cells have many membrane-bound organelles.
Eukaryotic cells are generally much larger than prokaryotic
cells. Even still, the logistics of carrying out cellular
metabolism sets limits on the size of cells.
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2 Which of the following are prokaryotic cells?
A Plants
B
Fungi
C Bacteria
D Animals
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3 Which is NOT a basic feature of all cells?
A All cells are surrounded by a plasma membrane.
B
Al cells contain a semifluid substance called the cytoplasm.
C
All cells contain structures called chromosomes, which are contained in
the nucleus.
D All cells have ribosomes.
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4 Where is the DNA of a prokaryote found?
A
Nucleus
B
Nucleolus
C
Nucleoid region
D
Mitochondria
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Diversity of eukaryotes
Eukaryotes range from single-celled
Protists to 100-meter tall redwood
trees.
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Diversity of Eukaryotes
Protists: The first eukaryotic cells. Protists are single-celled
eukaryotes. They range from protozoans to algae.
Fungi: These organisms evolved second in time along with
plants. Examples include mushrooms, molds, and mildews.
Plants: Plants vary in type from the first plants called mosses to
the modern flowering plants.
Animals: Animals were the last eukaryotes to evolve. Animals
range from ancient sponges and hydra to primates.
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Surface Area to Volume Ratio
At the time when prokaryotic cells were evolving, there were most likely
different sizes of cells. The smaller cells were more efficient than larger
ones. They had an increased surface area to volume ratio.
This meant that the small cell had lots of cell membrane (therefore lots
of surface area) to service the smaller volume inside the cell.
The smaller cell could get substances it needed in faster and get waste
out faster because the substances only needed to travel a short distance
from anywhere inside the cell to the cell membrane and vice versa.
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Smaller Cell = More efficient metabolism?
Smaller cells are able to have a more efficient metabolism compared
to the larger cells. These smaller cells out-competed the larger ones
and were able to pass this small size to their offspring.
So, if it is good for a cell to be small, why didn't cells evolve to be even
smaller than they are?
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Limits of Cell Size
We know that cells need to be small enough so that they have
an increased surface area to volume ratio, but be large enough to
fit the parts of the cell inside.
most efficient
The smaller the cell, the larger
its surface area and the smaller
its volume.
least efficient
The bigger the cell, the smaller
the surface area is compared
to its large volume inside.
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Eukaryotic vs. Prokaryotic Cells
Eukaryotic cells are, on average, much larger than prokaryotic
cells. The average diameter of most prokaryotic cells is between
1 and 10μ. By contrast, most eukaryotic cells are between 5 to
100μ in diameter.
Animal Cell (Eukaryote)
Bacterium (Prokaryote)
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Eukaryotic vs. Prokaryotic Cells
What could have been a potential problem as these first cells
began to grow in diameter?
Hint: think of the cell's energy and nutritional requirements
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Eukaryotic vs. Prokaryotic Cells
Diffusion allows nutrients and other molecules, such as ATP, to
get to where they are needed in a prokaryote.
Prokaryotes are small enough for diffusion to be an effective
transport mechanism. In fact, the size of these cells is probably
limited by the distance that molecules need to travel inside the
cell.
Eukaryotes are much larger.
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Eukaryotic vs. Prokaryotic Cells
The problem for larger cells is that ions and small molecules
(ATP, amino acids, nucleotides, etc.) cannot diffuse quickly
across a large volume.
If they are needed to go the other side of a cell, it could take a
long time to get there. This would be detrimental to the cell.
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Eukaryotic Problem of Diffusion
Eukaryotic cells are
comprised of many
bacterium-sized parts
known as organelles.
Organelles subdivide the
cell into specialized
compartments.
The advantage of this is the molecules required for specific
chemical reactions are often located within a certain compartment
and do not need to diffuse long distances to be useful.
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Main Advantage for Compartmentalization
Separating incompatible chemical reactions increases their
efficiency by keeping substrates and their enzymes in close
proximity.
Each compartment or organelle can specialize at what it does.
Diffusion of nutrients and substances is easier in a larger cell
because substances needed to perform reactions (like reactants
and enzymes) within the organelle either travel a short distance
from another organelle or are stored in the organelle itself.
This is why compartmentalization in the eukaryote makes this
type of cell very efficient, despite its larger size.
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5 How did eukaryotes solve the problem of diffusion?
A By remaining the same size as prokaryotes.
B
By using a nucleus.
C Compartmentalization.
D They haven't solved the problem.
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6
Which is NOT an advantage of compartmentalization?
A It allows incomaptible chemical reactions to be separated.
B
It increases the efficiency of chemical reactions.
C
It decreases the speed of reactions since reactants have to
travel farther.
D
Substrates required for particular reactions can be localized
and maintained at high concentrations within organelles.
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Organelles
Organelles making up Eukaryotic cells include:
Nucleus
Lysosomes
Ribosomes
Peroxisomes
Rough ER
Vacuoles
Smooth ER
Chloroplasts
Golgi Apparatus
Mitochondria
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Cell Fractionation
Using a technique known as cell fractionation, the cell components
can be separated and each organelle can be studied individually.
Cell Fractionation involves splitting cells
open in a test tube and getting the
organelles to spill out.
When put in a centrifuge, the different
organelles will then settle out and
make layers according to their size
and weight. The heaviest settle to the
bottom of the test tube.
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Nucleus
The nucleus contains a blueprint for
all of the functions necessary
for that cell's survival.
The nucleus contains DNA,
the genetic material of the cell.
The "directions" are in the DNA's genes. Genes are configured
into structures called chromosomes.
The nucleus controls the cell's activities by directing protein
synthesis from DNA.
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Inside the Nucleus
The nucleus is enclosed by a double cell
membrane structure called the nuclear
envelope.
The nuclear envelope has many
openings called nuclear pores. Nuclear
pores help the nucleus "communicate"
with other parts of the cell.
Inside the nucleus is a dense region known as the nucleolus.
The nucleolus is where rRNA is made and ribosomes are
assembled. They then exit through the nuclear pores.
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Prokaryotic Nucleoid
Unlike the eukaryotic cell,
the prokaryotic cell has a
nucleoid where the
genetic material is found
that is without a nuclear
membrane.
Recall that the prokaryote genetic material is double-stranded and
circular. Eukaryotic genetic material is usually found in the form of
chromatin, a tightly coiled mass of DNA and associated proteins.
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3 Main Functions of the Nucleus
1. To keep and contain a safe copy of all chromosomes (DNA)
and pass them on to daughter cells in cell division.
2. To assemble ribosomes (specifically in the nucleolus).
3. To copy DNA instructions into RNA (via transcription).
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7
How does the nucleus control the activities of the cell?
A By making DNA.
B
By directing protein synthesis.
C By allowing DNA to leave the nucleus to make proteins.
D By sending instructions to the mitochondria.
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8
What is the importance of nuclear pores?
A
They allow the nucleus to communicate with other parts of
the cell.
B
They allow DNA to leave the nucleus in order to direct
protein synthesis.
C
They allow RNA to leave the nucleus and become functional
in the cytoplasm.
D
They allow single stranded DNA molecules to enter the
nucleus and assemble into the double helix.
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Ribosomes
Recall that the ribosome is
made of rRNA and proteins.
This is where translation
occurs.
Ribosomes consist of two
subunits, a small and a
large. Each subunit consists
of proteins and rRNA. The
two subunits come together
when proteins are needed
to be made.
Large
subunit
Small
subunit
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Ribosomes
Recall ribosomes make peptide bonds between amino acids in
translation.
The instructions for making ribosomes are in the DNA. From
DNA, rRNA is made. Some of the rRNA is structural and other
rRNA holds the code from the DNA to make the ribosomal
proteins from mRNA.
transcription
DNA
mRNA
translation
Protein
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9
Where are ribosomal subunits made in the cell?
A Cytoplasm
B
Nucleus
C Nucleolus
D On the Plasma membrane
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10
What do ribosomes consist of?
A proteins and DNA
B
proteins and rRNA
C proteins only
D
DNA only
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The Endomembrane System
The endomembrane system is exclusive to eukaryotic cells only.
Several organelles, some made up mainly of membranes, form a
type of assembly line in the cell. They make a product, then
process and ship it to its final destination whether that be inside or
outside the cell. Organelles included in this system include the
nucleus, rough and smooth ER, golgi, and lysosomes.
Collectively, we refer to them as the endomembrane system.
Note: The nuclear envelope and plasma membrane
also are considered part of this system
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The Endomembrane System
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11
Which of following are parts of the endomembrane system?
(more than one answer)
A smooth ER
B
rough ER
C nucleus
D lysosome
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12
The endomembrane system serves to
A ship cell products to places in and out of the cell
B
assemble DNA
C give directions to other organelles
D create pathways for organelles to travel
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Endoplasmic Reticulum
The Endoplasmic reticulum is a network within the cytoplasm
(reticulum comes from the latin word for little net).
This organelle is a series of membrane-bound sacs and
tubules. It is continuous with the outer membrane of the
nuclear envelope.
There are two types of Endoplasmic Reticulum: Rough and
Smooth
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Rough and Smooth
Endoplasmic Reticulum
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Rough and Smooth
Endoplasmic Reticulum
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Smooth Endoplasmic Reticulum
This type of E.R. is called Smooth because it lacks ribosomes on
its surface. (it looks smooth compared to rough ER)
There are a variety of functions of this organelle, which include:
· making lipids.
· processing certain drugs and poisons absorbed by the cell.
· storing calcium ions (for example, in muscle cells).
Note: The liver is an organ that detoxifies substances that are
brought into the body. Therefore, liver cells have huge amounts
of Smooth E.R.
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Rough Endoplasmic Reticulum
Rough E.R. has ribosomes attached to its membrane (thus a
rough appearance).
These ribosomes synthesize proteins that will be used in the
plasma membrane, secreted outside the cell or shipped to
another organelle called a lysosome.
As proteins are made by the ribosomes, they enter the lumen
(opening) of the E.R. where they are folded and processed.
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Rough Endoplasmic Reticulum
Once the proteins are processed, short chains of sugars
are sometimes linked to these proteins, which are then
known as glycoproteins. These glycoproteins serve as
"zip codes" that will tell the protein where it will go. Most
secretory proteins have glycoproteins.
When the molecule is ready to be exported out of the E.R.,
it gets packaged into a transport vesicle. This vesicle is
made of membranes from the E.R. itself. The transport
vesicle travels to another organelle known as the Golgi
apparatus.
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Insulin - a product of the Rough
Endoplasmic Reticulum
Insulin is a protein hormone made by certain cells of the
pancreas that enable cells to take glucose (sugar) in from the
blood.
Insulin is made in the rough E.R. because it is a secretory
protein. Specifically, it is secreted out of the pancreas cells
into the blood stream.
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13
Which organelle is involved in making proteins?
A Smooth E.R.
B
Ribosomes
C
DNA
D
Nuclear membrane
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14
What determines if we classify endoplasmic reticulum as
smooth or rough?
A presence or absence of nuclear pores
B
presence or absence of genetic material
C presence or absence of ribosomes
D presence of absence of DNA
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15
Where in the cell are lipids made?
A Nucleus
B
Ribosomes
C Rough endoplasmic reticulum
D Smooth endoplasmic reticulum
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Golgi Apparatus
The main function of this
organelle is to finish, sort, and
ship cell products. It works like
the postal department of the
cell.
Structurally, the golgi consists
of stacked flattened sacs (sort
of looks like a stack of pita
bread).
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Golgi Apparatus
The Golgi is located near the cell membrane. The Golgi works
closely with the E.R. of a cell.
It receives and modifies substances manufactured by the E.R.
Once the substances are modified, they are shipped out to other
areas of the cell.
One key difference between the Golgi apparatus and endoplasmic
reticulum is that the sacs comprising the Golgi are not
interconnected.
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The Golgi Apparatus & the E.R.
The Golgi receives transport vesicles that bud off from the E.R. and
contain proteins. It takes the substances contained in these
vesicles and modifies them chemically in order to mark them and
sort them into different batches depending on their destination.
The finished products are then packaged into new transport
vesicles which will then move to lysosomes, or will be inserted into
the plasma membrane or dumped out of the cell if the protein is a
secretory protein.
Video on
Protein Trafficking
through the Golgi
http://www.youtube.com/watch?v=rvfvRgk0MfA
click
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16
A difference between the Golgi Apparatus and the E.R. is that
A The ER takes the vesicles from the Golgi to transport
B
The sacs making the Golgi are not interconnected
C The Golgi has ribosomes, the ER does not
D There is no difference, they are part of the same organelle
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17
Which organelle receives and modifies substances from the
endoplasmic reticulum?
A Nucleus
B
Ribosomes
C Lysosomes
D Golgi Bodies
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Lysosomes
As the name
suggests, lysosome
is an organelle that
breaks down other
substances.
(lyse: to cause destruction)
They consist of hydrolytic
enzymes enclosed within
a membrane. Hydrolytic
enzymes break polymers
into monomers
(hydrolysis).
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Lysosomes
Lysosomes may fuse with vacuoles containing food
particles and then the enzymes digest the food, releasing
nutrients into the cell. Protists do this.
Damaged organelles may become enclosed within a
membranous vesicle which then fuses with a lysosome.
The organic molecules from the breakdown process are
recycled and reused by the cell.
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18
Which is not a function of lysosomes?
A aiding the cell in creating ribosomes
B
fusing with vacuoles to digest food
C breaking polymers into monomers
D recycling worn out cell parts
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19
Which organelle contains hydrolytic enzymes that break down
other substances?
A Endoplasmic Reticulum
B
Golgi Bodies
C Lysosomes
D Vacuoles
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Peroxisomes
A peroxisome is a specific lysosome that forms and breaks down
hydrogen peroxide (H2O2) which is toxic to cells.
In all cells, hydrogen peroxide forms constantly (from the
combining of hydrogen and oxygen as bi-products of metabolism)
and needs to be broken down quickly.
Important note:
Peroxisomes are not part of the endomembrane system.
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Vacuoles
Vacuoles are also membranous sacs and they come in
different shapes and sizes and have a variety of functions.
PLANT
CELL
Central
Vacuole
PROTIST
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Types of Vacuoles
Central Vacuole
Contractile vacuoles
Food Vacuoles
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Central Vacuoles
Central Vacuole in plants stores water. Absorbing water makes
a plant cell more turgid, or having more pressure inside - leading
to strength and rigidity.
Central vacuoles that are full
will take over most of the
cytoplasm and literally push
the organelles to the sides
of the cell. It can also store
vital chemicals, pigments
and waste products.
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Increased Turgor Pressure
Increased turgor pressure results from the central vacuole
being full with water. It presses out on the cell membrane which
then presses out on the cell wall.
"Turgid" cells are
synonomous with fresh
fruits and veggies.
The plant cell will not explode or lose its shape
like an animal cell would in a hypotonic
environment.
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Decreased Turgor Pressure
Decreased turgor pressure results when the central vacuole is
not full with water. The central vacuole pulls away from the cell
membrane which pulls away from the cell wall.
When this happens the
cell is limp and droopy.
This is associated with
wilted, limp lettuce, as
well as droopy flowers.
However, the plant cell will not lose its shape.
Only the central vacuole shrinks.
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Contractile Vacuoles
Contractile vacuoles
can be found in certain
single-celled organisms.
These act as a pump to
expel excess water
from the cell. This is
especially helpful to
those organisms living
in a freshwater
environment to keep the
cell from exploding.
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Food Vacuoles
Food Vacuoles are
mainly found in
protists.
The protist ingests
food particles. The
particles then fuse
with a lysosome.
The lysosome
contains hydrolytic
enzymes that break
the food down.
Paramecium fed dyed food showing vacuoles.
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20
An organelle found in plant cells that stores water as well as
other important substances is called the ___________.
A Lysosome
B
Contractile Vacuole
C Central Vacuole
D Golgi bodies
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21
Food vacuoles are primarily found in which organisms?
A Plants
B
Animals
C Protists
D Bacteria
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Energy-Converting Organelles
Chloroplasts reside in plant cells only and convert solar
radiation into energy stored in the cell for later use.
Mitochondria reside in plant and animal cells and convert
chemical energy from glucose into ATP.
Interestingly, both chloroplasts and mitochondria have their own
DNA, separate from that found in the nucleus of the cell. They
also have a double cell membrane.
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Chloroplasts
These organelles convert solar
energy to chemical energy through
photosynthesis. Chloroplasts are
partitioned into three major
compartments by internal
membranes.
eukaryotic chloroplast
Remember that during photosynthesis it is on the
thylakoid that the Light Dependant Reactions take place.
In prokaryotes, thylakoids are areas of highly folded
membranes.In eukaryotes, they are stacked in the
chloroplasts.
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Mitochondria
Mitochondria are sometimes
referred to as the "powerhouses"
of the cell. They convert chemical
energy(glucose) into a more
usable and regenerative form of
chemical energy(ATP).
The mitochondrion is also
partitioned like the
chloroplast.
The mitochondrion only has two
compartments as opposed to three
in the chloroplast.
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Mitochondria and Respiration
Remember cell respiration must take place near a membrane so
that a proton gradient can be built in a "membrane space" that is
separate from the rest of the cell. Thus, the membrane would
separate the inner volume, with a deficit of protons, from the
outside, with an excess.
In prokaryotes, the "inter- membrane space" is between the cell
membrane and the cell wall.
In eukaryotes, that membrane is the Inter- Membrane Space of
the Mitochondria in between the inner membrane and outer
membrane.
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The Mitochondrial Eve
Since mitochondrial DNA is not in the cell nucleus, it is only
passed along from mother to child; animals, including you, inherit
your mitochondria from your mother only.
This is because the egg from our mothers contained her
organelles. (Dad's sperm only contains the chromosomes, none
of his organelles usually).
All of our organelles we inherited from our mothers.
Mitochondrial DNA is a way to trace maternal heritage through a
family or through a species. The "Mitochondrial Eve" is the first
human female that gave rise to all humans. In theory, we can
trace all humans back to her through our mitochondrial DNA.
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22
Which organelle converts solar energy into chemical energy in
plants and other photosynthetic organisms?
A Nucleus
B
Chloroplast
C Mitochondrion
D
Golgi
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23
Which organelle converts food energy into chemical energy
that the cell can use?
A Nucleus
B
Chloroplast
C Mitochondrion
D
Golgi
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Cytoskeleton
Cytoskeleton is a network of
fibers within the cytoplasm.
Three types of fibers
collectively make up the
cytoskeleton:
· Microfilaments
· Intermediate filaments
· Microtubules
These fibers provide structural
support and are also involved
in various types of cell
movement and motility.
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24
Cells can be described as having a cytoskeleton of internal
structures that contribute to the shape, organization, and
movement of the cell. All of the following are part of the
cytoskeleton except
A the nuclear envelope.
B
microtubules.
C microfilaments.
D intermediate filaments.
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25
Which of the following is not a known function of the
cytoskeleton?
A to maintain a critical limit on cell size
B
to provide mechanical support to the cell
C to maintain the characteristic shape of the cell
D
to hold mitochondria and other organelles in place within the
cytosol
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Plasma Membrane
Remember the plasma membrane is a phospholipid bilayer with
proteins and other molecules interspersed throughout.
The 3 main
functions of the
plasma membrane:
· Selective Permeability
· Protection
· Structural support
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26
Which of the following statements about the role of
phospholipids in forming membranes is correct?
A they are completely insoluble in water
B
they form a single sheet in water
C they form a structure in which the hydrophobic portion
faces outward
D they form a selectively permeable structure
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Large Molecules and
the Plasma Membrane
But what if the substance that needs to
pass through the cell membrane is too
big for a protein carrier or intregal
protein?
Then, the substance uses other
ways of getting into or out of a
cell by fusing with the cell
membrane.
There are several special functions of the membrane as larger
substances enter and exit the cell.
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Exocytosis
The proteins the cell makes are too large to diffuse through the
phospholipid bilayer.
Exocytosis
The vesicles that
enclose the proteins
fuse with the plasma
membrane and the
vesicles then open up
and spill their contents
outside of the cell.
This process is known
as exocytosis. The
vesicle will become
This is how secretory proteins from the Golgi exit the cell.
part of the cell
This is true for insulin in the pancreas.
membrane
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Endocytosis
The opposite of exocytosis is
endocytosis.
In this process, the cell takes in
macromolecules or other
particles by forming vesicles or
vacuoles from its plasma
membrane.
This is how many protists ingest food particles
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3 Types of Endocytosis
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3 Types of Endocytosis
Phagocytosis Is for taking in solid particles. ("phago" mean to
eat)
Pinocytosis Is for taking in liquids. However what the cell wants
is not the liquid itself, but the substances that are dissolved in
the liquid. ("pino" means to drink)
Receptor-mediated endocytosis requires the help of a protein
coat and receptor on the membrane to get through.
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27
The process by which a cell ingests large solid particles,
therefore it is known as "cell eating".
A Pinocytosis
B
Phagocytosis
C
Exocytosis
D Osmoregulation
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28
Protein coated vesicles move through the plasma membrane via
this process:
A Phagocytosis
B
Active Transport
C Receptor-Mediated Endocytosis
D Pinocytosis
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29
After a vesicle empties its contents outside a cell, the vesicle
becomes part of:
A the Golgi
B
the plasma membrane
C another vesicle
D the extracellular fluid
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Membrane Transport - review
Passive transport is the
movement of substances
from an area of high
concentration to an area
of low concentration
without the requirement
an energy input. Types
include diffusion, osmosis,
and facilitated diffusion.
Passive
Transport
Active
Transport
(REQUIRES
ENERGY)
Active transport is the movement of substances from an area of
low concentration to an area of high concentration and requires an
input of energy.
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30
Active transport moves molecules
A with their concentration gradients without the use of energy
B
with their concentration gradients using energy
C against their concentration gradients without the use of energy
D against their concentration gradients using energy
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31
Which of the following processes includes all others?
A passive transport
B
facilitated diffusion
C diffusion of a solute across a membrane
D osmosis
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Cell wall
The cell wall is an outer layer in
addition to the plasma membrane,
found in fungi, algae, and plant cells.
The composition of the cell wall varies
among species and even between cells
in the same individual.All cell walls have
carbohydrate fibers embedded in a stiff
matrix of proteins and other carbohydrates.
Plant cell walls are made of the polysaccharide
cellulose. Fungal cell walls are made of the
polysaccharide chitin.
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Outside the Plasma Membrane Extracellular Matrix
The extracellular matrix (ECM)
found surrounding cells provides
structural support to eukaryotic cells
in addition to providing various
other functions such as anchorage,
cellular healing, separating tissues
from one another and regulating
cellular communication.
The ECM is primarily composed of
an interlocking mesh of proteins
and carbohydrates.
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Cell Surfaces and Junctions
Cell surfaces protect, support, and join cells.
Cells interact with their environments and each other via their surfaces.
Cells need to pass water, nutrients, hormones, and many, many more
substances to one another. The way that cells that are adjacent to one
another communicate and pass substances to one another are called
Cell Junctions.
Animal and plant cells have different types of cell junctions. This
is mainly because plants have cell walls and animal cells do not.
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Junctions specific to plant cells
Plant cells are supported
by rigid cell walls made
largely of cellulose.
They connect by
plasmodesmata which
are channels that allow
them to share water, food,
and chemical messages.
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Animal Cell Junctions
Tight junctions
Adhering junctions
Communicating (Gap) junctions
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Tight Junctions
Tight junctions can
bind cells together into
leakproof sheets
tight junction
Example: the cells of the
lining of the stomach
or any epithelial
lining where leaking
of substances is not
good.
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Adhering Junctions
Adhering junctions
fasten cells together into
strong sheets. They are
somewhat leakproof.
Example: actin is held
together in muscle.
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Communicating (Gap) Junctions
Gap junctions
allow substances to
flow from cell to
cell. They are totally
leaky. They are the
equivalent of
plasmadesmata
in plants.
Example: important in embryonic development.
Nutrients like sugars, amino acids, ions, and other
molecules pass through.
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Organelles in Animal and Plant Cells
Only
Plant
mitochondria
golgi
apparatus
smooth
ER
central vacuole
Only
Animal
Both
cell wall
rough ER
ribosomes
lysosomes
plasma nucleus
membrane
chloroplasts
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Endosymbiotic Theory
The endosymbiotic theory
states that eukaryotic cells arose
as a result of a symbiotic
relationship between different
prokaryotic cells.
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Endosymbiotic Theory
This idea has been best explained by the "Theory of
Endosymbiosis" by Lynn Margulis in 1970.
She used 2 very special eukaryotic organelles to explain:
· the mitochondria
· the chloroplast
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The Evolution of Eukaryotes
Remember how we said the mitochondria and chloroplast are different
from other eukarytoic organelles because they have their own DNA,
their own ribosomes, and have a double cell membrane.
Using these facts, she explained that the mitochondria and chloroplast
were once free-living prokaryotes that got taken up (or "eaten") by
another prokaryote.
The mitochondria was a bacteria that could make its own ATP. The
chloroplast was a bacteria that could make its own food.
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The Evolution of Eukaryotes
When they got taken up by another prokaryote, they dragged the one
prokaryote's cell membrane around theirs, thus the double cell
membrane. This now allowed the "new" eukaryote to make its own
ATP or be able to do photosynthesis and make its own food. Thus
the evolution of eukaryotes.
The nucleus and flagella could also have the same possible roots
although they are not as heavily supported with evidence as the
mitochondria and chloroplast.
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Endosymbiosis
Slide 108 / 113
Evidence for Symbiosis
Both mitochondria and chloroplasts can arise only from
preexisting mitochondria and chloroplasts. They cannot be
formed in a cell that lacks them.
Both mitochondria and chloroplasts have their own DNA and
it resembles the DNA of bacteria not the DNA found in the
nucleus.
Both mitochondrial and chloroplast genomes consist of a
single circular molecule of DNA, just like in prokaryotes.
Both mitochondria and chloroplasts have their own proteinsynthesizing machinery, and it more closely resembles that of
bacteria than that found in the cytoplasm of eukaryotes.
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Evidence for Symbiosis
Both mitochondria and chloroplasts can arise only from
preexisting mitochondria and chloroplasts. They cannot be
formed in a cell that lacks them.
Both mitochondria and chloroplasts have their own DNA and
it resembles the DNA of bacteria not the DNA found in the
nucleus.
Both mitochondrial and chloroplast genomes consist of a
single circular molecule of DNA, just like in prokaryotes.
Both mitochondria and chloroplasts have their own proteinsynthesizing machinery, and it more closely resembles that of
bacteria than that found in the cytoplasm of eukaryotes.
Slide 110 / 113
Evidence for Symbiosis
Both mitochondria and chloroplasts can arise only from
preexisting mitochondria and chloroplasts. They cannot be
formed in a cell that lacks them.
Both mitochondria and chloroplasts have their own DNA and
it resembles the DNA of bacteria not the DNA found in the
nucleus.
Both mitochondrial and chloroplast genomes consist of a
single circular molecule of DNA, just like in prokaryotes.
Both mitochondria and chloroplasts have their own proteinsynthesizing machinery, and it more closely resembles that of
bacteria than that found in the cytoplasm of eukaryotes.
Slide 111 / 113
Evidence for Symbiosis
Both mitochondria and chloroplasts can arise only from
preexisting mitochondria and chloroplasts. They cannot be
formed in a cell that lacks them.
Both mitochondria and chloroplasts have their own DNA and
it resembles the DNA of bacteria not the DNA found in the
nucleus.
Both mitochondrial and chloroplast genomes consist of a
single circular molecule of DNA, just like in prokaryotes.
Both mitochondria and chloroplasts have their own proteinsynthesizing machinery, and it more closely resembles that of
bacteria than that found in the cytoplasm of eukaryotes.
Slide 112 / 113
32
Which of the following does NOT provide evidence for the
endosymbiotic theory?
A Mitochondria and chloroplasts both have their own DNA.
B
Mitochondria and chloroplasts both come from pre-existing
mitochondria and chloroplasts.
C
The DNA of mitochondria and chloroplasts resembles the
DNA found in nuclei.
D
The DNA of mitochondria and chloroplasts resembles that of
bacteria.
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Plant and Animal Cell Organelle
Review
http://www.cellsalive.com/cells/3dcell.htm