Ch 6.3 & 6.4: The Organelles
of Eukaryotic Cells
In eukaryotic cells genetic instructions
(DNA) are housed in the nucleus and the
instructions are carried out at the
ribosomes
The Nucleus
FUNCTION: Contains most of the DNA in eukaryotic
cells.
Some DNA can
be found in the
mitochondria and/or
chloroplasts
The Nucleus
STRUCTURE: Nucleur Envelope
It’s surrounded by a nuclear envelope (AKA nuclear membrane)
The nuclear envelope is made of a phospholipid bilayer with
embedded proteins.
What other structure does this remind you of???
The Nucleus
The nuclear envelope
has nuclear pores.
Proteins around the pores
regulate the entry/exit of
molecules into the nucleus
The shape of the
nucleus is maintained by a
net of filaments called the
nuclear lamina
The Nucleus
STRUCTURE: Nucleolus
When it’s not dividing, a nucleus contains a nucleolus
The nucleolus is a dense region where rRNA is made
In the nucleolus, rRNA combines with proteins to form
ribosomes
The Nucleus
STRUCTURE: Chromosomes
Inside the nucleus is the cell’s DNA. The DNA is organized and
packaged into chromosomes
Chromosomes are made of chromatin = a combination of DNA
& protein
Quick Think
The nuclear pores of the nuclear
envelope allow molecules into and out
of the nucleus. Think of specific
molecules that would need to get into
and out of the nucleus
Ribosomes
*Found in both prokaryotes & eukaryotes
FUNCTION: The site of protein synthesis
Two types:
Free
Found floating
in cytosol
Bound
Found bound
to the ER
Cells will have more of 1 kind of
Typically make Make proteins ribosome than the other
proteins that’ll that will usually depending on the function of the
cell
be used inside be exported
the cell
from the cell
Ribosomes
Each ribosome, whether bound or
free, is made of a large and
small subunit.
each subunit is composed of
RNA and proteins
unlike other organelles,
ribosomes are NOT membrane
bound
Quick Think
Suppose you observe a cell with a
BUNCH of bound ribosomes. What
could you deduce from this
observation?
6.4: The Endomembrane System
 The endomembrane system
(EMS) as a whole regulates
protein traffic and performs
metabolic functions in eukaryotic
cells
 Components of the EMS: nuclear
envelope, ER, Golgi apparatus,
lysosomes, vacuoles, and the
cell membrane (even though the
cell membrane is not an
endomembrane)
6.4: The Endomembrane System
 The EMS consists of internal
membranes in the cell that
interact with each other either by
direct physical contact, or
indirectly by transferring vesicles
between them
Parts of the
endomembrane
system…
1. Endoplasmic Reticulum (ER)
Biosynthetic Factory
• Overall basic structure: a
network of membranous
tubes & sacs = cisternae
– The inside of the ER
tubes is called the
lumen
– The ER is continuous
with the nuclear
envelope
Two distinct kinds of ER:
• Smooth ER
Structure: lacks bound ribosomes
Function:
*Enzymes of the smooth ER help synthesize lipids like
oils, phospholipids, & steroids (ex: sex hormones)
*Other enzymes detoxify drugs/poisons by adding –
OH groups to drugs which makes them more soluble
in water and easier to flush out
*Stores Ca 2+ = part of the mechanism that causes cell
contraction
Two distinct kinds of ER:
• Rough ER
Structure: has ribosomes
bound to the outer side of
the membrane
Two distinct kinds of ER:
• Rough ER
Function: protein secretion
*Excretory proteins are
made on the bound
ribosomes. As the protein
is being built, it enters the
ER lumen through a pore.
The proteins then become
enveloped in part of the
ER membrane which buds
off, becoming a transport
vesicle:
Two distinct kinds of ER:
• Rough ER
Function: the rough ER is
also a membrane factory
for the cell. It can make its
own phospholipids and the
bound ribosomes make
the membrane proteins
Parts of the
endomembrane
system…
2. The Golgi Apparatus
The Shipping and Receiving
Center
Function: Modifies,
stores, & ships the
products of the ER.
The Golgi also
makes certain
macromolecules
itself. (pectins and
polysaccharides)
Structure: Stacks of
flat membranous
sacs= cisternae.
Each golgi has two
distinct ends:
a) the cis face receives
transport vesicles from the
rough ER. Cis face AKA
“receiving side”
b) The trans face
produces different
vesicles that bud off and
transport their contents to
other parts of the cell.
AKA “shipping side”.
i. Before molecules
are shipped, they’re
tagged with a molecular
ID
Describe the flow of
molecules through the
endomembrane system
3. Lysosomes
Digestive Compartments
Structure: membranous sac of hydrolytic (think
hydrolysis) enzymes digest macromolecules.
Mini quick think: why is it important to have these
hydrolytic enzymes compartmentalized?
3. Lysosomes: Digestive Compartments
• Under what circumstances might lysosomes be
utilized?
Recycle the cells own organic material= autophagy
When a cell engulfs or “eats” outside particles =
phagocytosis. Ex: an amoeba eating food particles, white
blood cells destroying pathogens
Parts of the
endomembrane system…
4. Vacuoles
Diverse Maintenance Compartments
Structure: Membranous sac
Function:
1. May act as a lysosome at times
2. Food vacuoles can carry food from outside the cell to
a lysosome to be digested
3. Contractile vacuoles pump excess water out of the
cell in many protists
Contractile Vacuole
4. Vacuoles Diverse Maintenance Compartments
Function: Plant cells usually have a big central vacuole, the
membrane of which is called the tonoplast.
a. Central vacuoles can
act as storage. They
store extra organic &
inorganic molecules as
well as excess metabolic
waste produced by the
cell.
b. Central vacuoles may
also contain a plant cells
pigments, or poisons that
deter herbivores
The spectacular symphony that is
the Endomembrane System