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The Eukaryotic Cell
Organelles
Basic Parts of a Eukaryotic Cell

Plasma Membrane
• a.k.a. Cell Membrane

Nucleus
• DNA
• RNA

Cytoplasm
• Cytosol
• Organelles
Plasma Membrane



a.k.a. Cell membrane
Provides a barrier between the cell and the rest of
the world!
Regulates the passage of materials into and out of
the cell.
• Selectively permeable
• Thin barrier = 8 nm thick

Made of phospholipids, proteins, & other
macromolecules
Plasma Membrane
Nucleus
Control center of
the cell
 Contains chromatin
– DNA that is
“spread out”
 Contains the
nucleolus – made of
RNA
 Surrounded by a
double membrane
 Nuclear pores
allow materials to
enter and leave
the nucleus.

Anatomy of the Nucleus
Nucleus

Nucleus with
Nuclear Pores
(TEM
x73,200).

The
cytoplasm
also contains
numerous
ribosomes.

Copyright
Dennis Kunkel
Cytoplasm
Everything inside a cell between the plasma
membrane and the nucleus.
 Consists of a semi-fluid medium (colloid) and
organelles.
 Cytoplasm was formerly referred to as
protoplasm.
 The portion of the cytoplasm that lies outside
organelles and includes other insoluble cellular
components is called cytosol.
 The cytoplasm contains dissolved nutrients and
salts, helps dissolve waste products, and is an
excellent conductor of electricity.
 It facilitates the movement of materials around
the cell by moving and churning through a process
called cytoplasmic streaming.

Endomembrane System

A system of interrelated membranes, many
physically connected (and connected to the
outer nuclear membrane!).
• Nuclear envelope
• ER
• Golgi body (a.k.a. Golgi apparatus)
• Vesicle
– Lysosome (specialized vesicle)
• Vacuole
Function together in the synthesis, storage
and export of important molecules.
 Creates compartments restricting
enzymatic reactions to specific regions.

Endoplasmic Reticulum

Endoplasmic
reticulum is a
mesh of
interconnected
membranes that
serve a function
involving protein
synthesis and
transport.

Often called the
highway system
of the cell.
Endoplasmic Reticulum

Two types:
• Rough ER
• Smooth ER
Rough ER


Rough endoplasmic reticulum (Rough
ER) is so-named because of its rough
appearance due to the numerous
ribosomes that occur along the ER.
Rough ER connects to the nuclear
envelope through which the
messenger RNA (mRNA) that is the
blueprint for proteins travels to the
ribosomes.
Rough ER: Makes proteins!



Makes more membrane!
• Membrane proteins
• Can add a sugar chain: glycoproteins
Makes proteins secreted by the cell
• In special WBC’s the RER makes antibodies
• In the pancreas, the RER makes insulin
Helps protein folding: tertiary and quaternary
structure.
Same cells: fluorescent stain vs. phase contrast
RER with ribosome making a protein…
2
1
3
4
Smooth ER

Smooth ER; lacks
the ribosomes
characteristic of
Rough ER.

Continuous with
Rough ER.

The smooth ER has a wide range of functions
including carbohydrate and lipid synthesis.
• Fatty acids
• Phospholipids
• Steroids

In brain cells, ovaries
and testes it
synthesizes male
and female hormones.
Smooth ER
It serves as a transitional
area for vesicles that
transport ER products to
various destinations.
 In liver cells the smooth
ER produces enzymes that
help to detoxify certain
compounds (ex.
barbituates, alcohol)
 In muscles the smooth ER
assists in the contraction
of muscle cells by storing
calcium ions which trigger
the contractions.

Golgi Apparatus
Golgi Apparatus (a.k.a.
Complexes
Golgi Body)  Golgi
are flattened
stacks of
membrane-bound
sacs (saccules).
 They function as a
packaging plant,
modifying proteins
and lipids
transported in
vesicles from the
Rough ER.

Golgi Apparatus in a plant
parenchyma cell from Sauromatum
guttatum (TEM x145,700). Note
the numerous vesicles near the
Golgi. This image is copyright
Dennis Kunkel
Golgi body
Molecular
warehouse
and finishing
factory
 Has both a
receiving
side or cis
face (from
ER) and a
shipping side
or trans
face (to
plasma
membrane)


Notice the
cis and
trans face
of the Golgi
apparatus…
why cis and
trans? (It
has nothing
to do with
lipids!)
Golgi Apparatus: Summary

Consists of 3-20 flattened, curved
saccules

Resembles stack of hollow pancakes

Modifies proteins and lipids
• Packages them in vesicles
• Receives vesicles from ER on cis face
• Prepares for “shipment” in vesicles from
trans face
• Within cell
• Export from cell (secretion, exocytosis)
Vesicles


Vesicles are small
membraneenclosed
transport units
that can transfer
molecules
between
different
compartments.
Some vesicles
develop into
lysosomes and
vacuoles.
Vesicles transport
neurotransmitters (chemical nerve
cell messengers).
Lysosome
•**Found only in
animal cells!

Lysosomes are
relatively large vesicles
formed by the Golgi.

They contain hydrolytic
enzymes that could
destroy the cell.

Lysosome contents
function in the
extracellular breakdown
of materials.

Often called the
“suicide sac” of the cell
because damaged or
“old” cells often
autolyse. (apoptosis)
Hummmm…

When a tadpole
undergoes
metamorphosis,
how does it lose
its tail?
Lysosomal Storage Diseases



Missing one of the hydrolytic enzymes of the
lysosome.
The abnormal lysosome becomes engorged with
indigestible substances which interfere with
other cellular functions.
Usually fatal in
early childhood.
• Pompe’s disease:
glycogen builds up in liver
• Tay-Sachs disease: lipid
digesting enzyme and
nerve cells accumulate
excess lipids
Endomembrane
System: A Visual
Summary
Now do you see it?
Peroxisomes


Similar to lysosomes
• Membrane-bounded vesicles
• Enclose enzymes
However
• Enzymes synthesized by free ribosomes in
cytoplasm (instead of ER)
• Active in lipid metabolism (Have you seen the
movie Lorenzo’s Oil?)
• Catalyze reactions that produce hydrogen
peroxide H2O2
• Toxic
• Broken down to water & O2 by catalase
• Plants have peroxisomes (but not lysosomes)
Vacuole




a single layer of
unit membrane
enclosing fluid in
sack
In plants, a large
central vacuole
produces turgor
pressure against
cell wall for support
stores water and
various chemicals
may store insoluble
wastes
In plants the vacuole…
Is filled with cell sap!
 The large central vacuole can

•
•
•
•
•
•
•
Help the plant grow by absorbing water
Store food
Store vital chemicals
Store waste
Can act like a lysosome does in animal cells
Contain pigments to attract pollinators
Contain poisons to protect plants against plant
eating animals.
Vacuoles
Membranous sacs that are larger than
vesicles
• Store materials that occur in excess
• Others very specialized (contractile
vacuole)
 Plants cells typically have a central vacuole
• Up to 90% volume of some cells
• Functions in:
• Storage of water, nutrients, pigments,
poisons, and waste products
• Development of turgor pressure
• Some functions performed by
lysosomes in other eukaryotes

Plant Vacuoles
Contain pigments
to attract
pollinators
 Contain poisons to
protect plants
against plant
eating animals.

Plant Vacuole
One large Plasma Cell with pale, frayed
cytoplasm that contains several vacuoles and
three large Vacuoles Overlying its Nucleus.
Marrow - 100X
Mitochondria




Sites of energy
release and ATP
formation: cellular
respiration
Termed the
powerhouse of the
cell.
Have their own DNA!
Bounded by two
membranes. The inner
membrane folds into a
series of cristae, which
are the surfaces on
which ATP is generated
from glucose.
Mitochondria
Mitochondria
The
matrix is
the fluidfilled
space
between
cristae.
 Cristae
increase
surface
area

Ribosomes

Composed of 2 subunits

Manufacture proteins
(assemble amino acids)

All cells have ribosomes,
the difference between
the eukaryotic
ribosomes and the
prokaryotic ribosomes
is the size of the
subunits.

liver cell (TEM
x173,400).

Copyright Dennis Kunkel
Centrioles

Involved in cell
division
• Produces the
spindle fibers which
separate copied
pairs of
chromosomes for
each of the new
cells forming during
division.
Composed of
microtubules
 Found only in animal
cells

Cytoskeleton

Fibrous proteins
in the cytoplasm
that maintain
the shape of the
cell as well as
anchoring
organelles,
moving the cell
and controlling
internal
movement of
structures.
Cytoskeleton

Three types of
macromolecular
fibers
• Actin Filaments
• Intermediate
Filaments
• Microtubules

Assemble and
disassemble as
needed
Lily (Plant) Parenchyma Cell

(cross-section)
(TEM x7,210).

Note the large
nucleus and
nucleolus in the
center of the cell,
mitochondria and
plastids in the
cytoplasm.

Copyright Dennis
Kunkel
Plant Cells
Cell Wall
 Large Central
Vacuole
 Plastids

• Chloroplasts
• Chromoplasts
• Leucoplasts
Plant Cell
Plant cells have
a cell wall made
of cellulose and
lignin.
 Plant cells have
chloroplasts
which contain
chlorophyll for
photosynthesis.
 Plant cells have
a large central
vacuole. Filled
with water, it
creates
pressure on the
walls.

Plastids



Chloroplasts: for
photosynthesis;
contains the pigment
chlorophyll
Chromoplasts: for
pigment (other than
chlorophyll)
synthesis and
storage
Leucoplasts:
synthesis and
storage
• Ex. starch storage
Chloroplast

Their function is
to produce
glucose from
carbon dioxide
and water.

To do this they
need light
energy.

They contain a
green pigment
called
chlorophyll.
Chloroplast
Chloroplast
Grana (granum,
singular) are made
up of stacks of
membranes called
thylakoids. This is
where the
chlorophyll is
found.
 The stroma is the
fluid space
between the
membranes.

have a double
membrane : inner
membrane & outer
membrane
 have their own
DNA - this carries
the information to
make enzymes
 have their own
ribosomes to make
their own enzymes
required for
photosynthesis

Chloroplasts
How are plant and animal cells
different?

Plant
• Cell wall
• Large, central
vacuole
• Plastids:
• Chloroplast
• Chromoplast
• Leucoplast

Animal
• Lysosomes
• Centrioles
• Flagella
• Note: there
are exceptions
to some of this,
but in general
it holds true!
Comparing Plant and Animal Cells
Endosymbiosis

During the 1980s, Lynn Margulis proposed the
theory of endosymbiosis to explain the origin
of mitochondria and chloroplasts from
permanent resident prokaryotes. According
to this idea, a larger prokaryote (or perhaps
early eukaryote) engulfed or surrounded a
smaller prokaryote some 1.5 billion to 700
million years ago.
Endosymbiosis con’t.

Instead of digesting the smaller
organisms the large one and the smaller
one entered into a type of symbiosis
known as mutualism, wherein both
organisms benefit and neither is harmed.

The larger organism gained excess
energy (ATP), while providing a stable
environment and the raw materials the
endosymbionts required.

This is so strong that now
eukaryotic cells cannot survive
without mitochondria (likewise
photosynthetic eukaryotes
cannot survive without
chloroplasts), and the
endosymbionts can not survive
outside their hosts.

Nearly all eukaryotes have
mitochondria
Cell Junctions: connect cells
together


structures that help cells coordinate
as part of a tissue
Plant cells:
• Plasmodesmata - channels between
adjacent plant cells that form a
circulatory and communication system
Cell junctions in animal cells



Tight junctions - bind cells forming
leakproof sheet. Ex. Lines digestive
tract
Anchoring junctions - attach
adjacent cells with cytoskeletal
fibers but still allow materials to pass
along the spaces between cells
Communicating junctions - allow
water and small molecules to flow
between cells
JUNCTIONS
3 Types:
Communicating Junction
Anchoring Junction
Tight Junction
Cell Wall
Maintains cell
shape and
skeletal support
 Surface
protection
 Binding of cells
in tissues
(plants have
tissues! Ex.
Roots, stems
and leaves!)

Formation of Cell Wall



Primary cell wall: Forms 1st. Made of
cellulose, stretchy so cell can grow.
Secondary cell wall: Rigid, made of
lignin, forms once cell is full grown.
Pectin is a sticky substance that
holds neighboring cell walls together.
(Pectin is used to make jelly!)
Flagella and Cilia
Appendages that protrude
from the cell used for
movement.
 Flagella are long and usually
less numerous than cilia, which
are short and usually
numerous.
 Composed of microtubules
wrapped in an entension of
the plasma membrane.
 Dynein arms, protein knobs,
move causing microtubules to
bend.
