Organelles of
Eukaryotic Cells
AHMP 5406
Objectives
List the principle functions and describe the
structure of the nucleus, mitochondrion,
endoplasmic reticulum, Golgi, lysosomes and
peroxisomes in higher eukaryotes
Describe the modification and transport of
proteins from the ER through the Golgi
Describe the intracellular transport of proteins
from the trans Golgi network to lysosomes
Describe the structure of the mitochondrion
and the process of ATP synthesis
Describe the contribution of organellar
dysfunction to the development of disease
Basic eukaryotic organelles
Nucleus
Endoplasmic reticulum (ER)
Golgi
Peroxisomes
Lysosomes
Mitochondria
General eukaryotic cell
How molecules are transported
around the cell…
The Nucleus
Nucleus
The largest organelle in eukaryotes
Surrounded by 2 phospholipid bilayers
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Inner nuclear membrane defines the nucleus
itself
Outer nuclear membrane is continuous with
the rough ER
Space between the inner and outer
membranes is continuous with the lumen of
the rough ER
Nucleus
The two nuclear membranes fuse at the
nuclear pores which regulate movement of
molecules between nucleus and cytosol
Contains the DNA of eukaryotic cells
DNA is packaged into chromosomes in
metabolically active nuclei (growing or
differentiating cells)
The cell’s rRNA is synthesized in the
nucleolus (a suborganelle)
Nucleus
How molecules are transported
around the cell…
The nucleus
The nucleus
The nucleus
Ran GTPases drive directional transport
through nuclear pore complexes
• Ran is a molecular switch
• Two conformations
• dependent on what is
bound to it
• Ran-GEF is in the nucleus
• GDP to GTP
• “Cocks the hammer”
•Creates a gradient
• Ran-GAP is in the cytosol
• GTP to GDP
• Uses energy to import
• “pulls the trigger”
The Endoplasmic
Reticulum
Endoplasmic reticulum
Second largest cellular organelle
Has many functions, but primarily
important in the synthesis of membrane
lipids and proteins
Two types: rough and smooth
Smooth Endoplasmic reticulum
Functions in synthesis of fatty acids and
phospholipids
Abundant in hepatocytes
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enzymes in SER detoxify hydrophobic
chemicals such as pesticides and
carcinogens to water soluble compounds that
can be excreted
High doses of these compounds result in
LOTS of SER proliferation
Rough Endoplasmic reticulum
Ribosomes bound to the surface make it “rough”
Responsible for synthesis membrane and organellar
proteins and virtually all proteins that are to be secreted
from the cell
Ribosomes that make these proteins are bound to the
ER by the newly growing peptide chain
The newly made protein passes through the RER with
the help of specific proteins
These new proteins accumulate in the lumen of the RER
and await transport
Very abundant in cells that produce secreted proteins:
plasma cells (antibodies), pancreatic acinar cells
(digestive enzymes)
Endoplasmic reticulum
Endoplasmic reticulum
Endoplasmic reticulum
How the endoplasmic reticulum
probably came to be…
The Golgi
Complex
Golgi
Responsible for protein modification and
transport
Divided into the cis-, medial and transGolgi
Transfer vesicles from the ER fuse with
the cis- region and deposit proteins
After movement through the Golgi, they
bud off through the trans- side
Golgi
Golgi
Transport of proteins from transGolgi to lysosomes
Lysosomal hydrolases carry a maker
 Mannose 6-phosphate (M6P)
M6P groups are recognized by M6P receptor proteins in
trans-Golgi
Bind to lumenal side by way of adaptins
Adaptins interact with clathrin molecules on the cytosolic
side
Shuttled to late endosome where pH change releases
hydrolase
Peroxisomes
Peroxisomes
Contain oxidases – enzymes that generate
hydrogen peroxide
Large amounts of catalase – degrades hydrogen
peroxide to water and oxygen
Oxidation is NOT linked to ATP generation
Produce acetyl groups that are used in the
production of cholesterol and biosynthetic
molecules in animal cells
Also degrade toxins produced by liver, kidney
cells, etc.
Peroxisomes
Peroxisome-assembly related
diseases
X-linked adrenoleukodystrophy (ADL)
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Defective oxidation of very long chain fatty
acids
ADL gene encodes the peroxisomal
membrane protein that transports an oxidative
enzyme into the peroxisomes
Effects are evident in mid-childhood: severe
neurological disorders followed by death
within a few years
Peroxisome-assembly and function
related diseases
Pseudo-Zellweger syndrome
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Beta-oxidation disorder (fatty acid
metabolism)
Other peroxisomal functions remain intact
Symptoms are present at birth
Major body systems are affected: vision,
kidneys, cartilage, heart, muscle and liver
Lysosomes
Lysosomes
Acidic organelles – pH4.8
Contain degradative enzymes (acid
hydrolases): nucleases, proteases,
phosphatases, etc.
Can degrade intracellular components,
phagocytized or endocytized items
May be several hundred in a typical animal
cell
Degrade themselves by autophagy
Lysosomes
Lysosomes
Lysosomal Storage Diseases
Caused by genetic defects
Result in accumulation of undigested substrates in
lysosomes
Usually act on nervous system
Hurler’s syndrome
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Caused by mutation on gene that codes for enzyme that breaks
down glycosaminoglycan
Results in deformation and retardation
I-cell disease
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Severe form of Hurler’s syndrome
Detected by inclusion bodies in tissue cells
Cell hydrolases are misdirected and secreted
Tay Sachs Disease
1 in 27 Jews in the U.S. are carriers of the
defective Hex-A gene
Frequency in the general population is 1 in
250
Over 50 DNA mutations have been
identified in the Hex-A gene
DNA testing is usually done in conjunction
with biochemical testing for Hex-A levels in
the blood
Tay Sachs Disease
Individuals are lacking the ability to break
down gangliosides (glycolipids)
Symptoms usually appear before age 1
Children become blind and demented by
age 2
Usually fatal by age 3
Nerve cells are greatly enlarged with
swollen, lipid-filled lysosomes
How molecules are transported
around the cell…
Mitochondria
Mitochondria
Up to 25% of cytoplasm volume
Main site of ATP production
Inner and outer membrane
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Outer membrane allows molecules up to
10,000 mw to pass through, much like gram
negative bacteria
Inner membrane is composed of cristae that
function to increase oxidative surface area
Mitochondria
Fuels for ATP synthesis are fatty acids and
glucose
Degradation of 1 glucose to CO2 and H2O
can yield up to 36 ATP molecules
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Initial stage producing 2 ATPs’ occurs in the
cytosol
Terminal stages producing up to 34 ATP’s are
carried out by mitochondrial enzymes in the
matrix and cristae
Mitochondria
How the mitochondrion probably
came to be…
Summary Points
All eukaryotic cells contain a membrane bound
nucleus and organelles in their cytosol
Lysosomes, which are found only in animal cells,
have an acidic interior and contain various
hydrolases used to break down cellular
components
Peroxisomes are small organelles containing
enzymes that oxidize various organic
compounds, generating hydrogen peroxide
Summary Points
Mitochondria are bound by two membranes, the
inner one extensively folded. Enzymes in the
inner mitochondrial membrane and central
matrix carry out the terminal stages of sugar and
lipid oxidation coupled to ATP synthesis
Secretory and membrane proteins are
synthesized on the RER (a network of
membrane vesicles studded with ribosomes).
These proteins move to the Golgi complex
where they are stored and processed
Summary Points
The nucleus is surrounded by an inner and an
outer membrane. Movement of molecules into
and out of the nucleus occurs through the
nuclear pores. The outer nuclear membrane is
continuous with the RER.
The cytosol is the portion of the cell’s interior
that remains after you take away all of the
organelles. There are a lot of proteins in it –
lots of soluble enzymes, actin microfilaments,
microtubules and intermediate filaments. These
help to give the cell some sort of structure.
General eukaryotic cell