Eukaryotic cells and their organelles

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Eukaryotic cells and their organelles Plant
cells and animal cells have many common
organelles- and a few unique ones What are the
major differences between prokaryotic and
eukaryotic cells?
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Presence of a nucleus Internal membrane system
produces special compartments for cell
functions Tubules and filaments involved in
motility Exocytosis and endocytosis Chromosome
formation Mitosis vs. cell fission RNA
processing
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Model animal and plant cells

• Animal cell

• Plant cell

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The nucleus

• double membrane fused by nuclear pores
• pores are lined by pore complexes
• regulate movement of mRNA, ribosomes, enzymes,
  etc.

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Ribosomes

• Free or attached to endoplasmic reticulum
• Found in all cells
• Products may be retained in the cell or secreted

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Endoplasmic reticulum is rough or smooth Rough
ER is covered with ribosomes Ribosomes
synthesize polypeptide chains processed and
formed in RER Proteins are modified in the
ER glycosylation enzymes Secreted and plasma
membrane proteins are made in the RER
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Smooth ER Synthesis of lipids and
steroids Glycogen synthesis in liver Drug
detoxification , esp. in liver SER synthesis is
inducible (so is RER) Muscle cells-
sarcoplasmic reticulum sequesters and releases
calcium
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The Golgi apparatus receives proteins from the
ER Golgi is oriented cis-trans Vesicles
transport proteins from RER and fuse Vesicles
bud off from Golgi to transport proteins to
their destination Processing continues in Golgi
glycosylation, phosphate groups, etc. Can
synthesize (and process) saccharides
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The Golgi
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The endomembrane system

• Protein synthesis
• Transport
• Lipid metabolism
• Detoxification
• Why compartments?

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Lysosomes contain hydrolytic enzymes that digest
large biomolecules Enzymes are synthesized
similarly to secreted proteins tagged as
lysosomal with mannose-6-phosphate Packaged
into vesicles and transported to endosomes (or
bud off from Golgi) Discovered by Christian de
Duve, 1950s
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Findings with acid phosphatase Activity
increased after a few days Acid phosphatase
seemed to pellet with mito- chondrial portion.
Activity increased upon exposure to
detergents (i.e., enzyme was within a
membrane-bound particle) Slower centrifugation
showed that activity was NOT associated with
mitochondrion Acid phosphatase was associated
with other hydrolytic enzymes
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Hypothesis enzymes were packaged together in
membrane-bound organelle Presence of lysosomes
later confirmed by electron microscopy
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Peroxisomes Animal cells Detoxification, esp.
in liver and kidney Breakdown of fatty acids
(small ones can be handled in mitochondria, but
slowly) adrenoleukodystrophy- sex-linked enzyme
deficiency fatal Plant cells Glyoxysomes
(seeds) store fat and contain enzymes that
convert it to sugar
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A plant peroxisome
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Vacuoles especially important in
aquatic organisms Contractile Food (in variety
of cells) Central vacuole (tonoplast
membrane) may be most conspicuous part of plant
cell
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Mitochondria and chloroplasts convert energy to
forms that cells can use Have their own
ribosomes and DNA inherited from maternal
parent in sexual reproduction Have double
membranes Mitochondria are found in most
eukaryotic cells (not RBCs) Chloroplasts are
found in photosynthetic tissues- plants and
algae
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Mitochondria the powerhouses of the cell

• Two inner compartments are essential for function
• Most ATP is generated here
• Mitochondria have their own DNA and ribosomes,
  but cant replicate independently

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Photosynthesis is performed in chloroplasts
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Chloroplasts are a type of plastid Amyloplasts
store starch Chromoplasts store
pigment Chloroplasts generate ATP and sugar from
light
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Cytoskeleton Organization and motility of
cell cilia and flagella movement of organelles
within cells cytoplasmic streaming
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Functions of microtubules
centrioles
Flagella and cilia
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Microfilaments
Actin predominates
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Intermediate filaments harder to classify May be
different subsets with specialized
function Important for stability rather than
movement
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Cell wall Plants, bacteria, fungi, some
protists Bacteria- peptidoglycan Fungi-
chitin Plants- complex cellulose, pectins,
proteins
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Plant cell walls
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Extracellular matrix

• Support
• Adhesion
• Movement
• Regulation
• Communication

fibronectin
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Intercellular junctions Organize cells into
tissues Enable these cells to communicate
with each other Movement of water and
nutrients Electrical/chemical signals Plasmodesm
ata in plants In animals
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Summary

• Eukaryotic cells have specialized compartments
• All activities of living organisms are conducted
  within the cell
• Different cells have different number and
  distribution of organelles
• Organ systems do the same thing, on a larger scale