Cell Organelles
Section 3-3
Nucleus
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Large membrane-enclosed structure that
contains the cell’s genetic information.
Acts to control the metabolic activities of cell
Control center which monitors internal and
external conditions and turns on or off genetic
programs
Structure – surrounded by a membrane which
is similar to the cell membrane. Nuclear pores
or holes occur at intervals along the
membrane.
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Nuclear envelope – the membrane that surrounds the
nucleus
Chromatin – consists of DNA wrapped around
proteins
Chromosomes – condensed string-like structure that
forms from DNA just before the cell divides. Carries
the genetic code which determines organism’s
characteristics
Nucleolus – structure within nucleus that makes
ribosomes. Rich in RNA.
Nuclear pores – small channels that go through the
nuclear envelope. Substances made in the nucleus
pass through these pores to move into the cytoplasm.
Ribosomes
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Made of RNA and protein
Make proteins!
Endoplasmic Reticulum
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Internal membrane system of the cell.
Lipids, proteins, and other products are made
here.
Rough Endoplasmic Reticulum
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Has ribosomes
Helps transport proteins made by the attached
ribosomes
Series of interconnected membranes which spread
throughout the cytoplasm forming channels of flattened
sacs with ribosomes attached to them
The channels transport the proteins in vesicles
(portions of ER that “pinches” off)
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Smooth Endoplasmic Reticulum
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NO ribosomes
Synthesizes and transports lipids and steroids
Smooth appearance because there are no
ribosomes
Forms channels similar to those formed by rough
ER
Channels are tubular, NOT FLAT
Vesicle
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Small, membrane-bound sac that transports
substances in the cell
By enclosing certain proteins inside vesicles, the
eukaryotic cell keeps these proteins separate
from proteins produced by free ribosomes in
cytoplasm
Vesicles move from ER to Golgi apparatus (also
from Golgi apparatus)
Golgi Apparatus
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Modifies, sorts, and packages proteins
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Ribosomes make proteins on Rough ER. Proteins
are packaged into vesicles.
Vesicles then transport the newly made proteins from
the rough ER to the Golgi apparatus
In the Golgi, proteins are processed and then
packaged into new vesicles.
Many of these vesicles move to the cell membrane.
The vesicle fuses with the membrane and releases
their contents outside the cell. Other vesicles,
including lysosomes, remain within the cytoplasm.
Appears as flattened stacks of membranes
Lysosomes
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Small organelles filled with enzymes
Digest molecules to be used by the cell
Disposes of foreign particles, malfunctioning
structures, and worn out organelles
Contents of lysosomes are contained in vesicles
Contain 40 or more enzymes used to break large
biological molecules down.
Vacuoles
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Store materials such as ions, sugars, amino acids, and
toxic compounds
Main function – to increase cell size and surface area to
enhance ion absorption
Bound by a lipid bilayer
IN PLANTS ONLY – Central Vacuole
Takes up most of the cell’s volume
 Unique to plants
 Stores water
 May contain ions, nutrients, and waste
 When full – causes cell to be rigid because it presses against the
cell wall. This makes a plant stand upright
REMEMBER… BOTH PLANT AND ANIMAL cells have vacuoles,
but only plant cells have a central vacuole.
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Mitochondria
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Converts chemical energy stored in food into compounds
that are more convenient for the cell to use
“Powerhouse” of the cell – produces energy or ATP (main
energy currency of cells)
Mitochondria have their own DNA, but MOST
mitochondrial proteins are made by free ribosomes in the
cytoplasm
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Mitochondrial DNA is similar to circular prokaryotic DNA
Reflects theory that primitive prokaryotes are ancestors to
mitochondria
Has double membrane which creates two areas within organelle
(area between membrane – matrix; surface membranes – cristae)
Chloroplasts
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Organelles that capture energy from sunlight and
convert it into chemical energy – Photosynthesis
ONLY in plants
Like the mitochondria, supplies much of the energy
needed to power the activities of plant cells
Surrounded by two membranes and contains its
own DNA – thought to be descendents of ancient
prokaryotic cells
Cytoskeleton
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Helps cell to maintain shape, move, and to
move organelles
Composed of microfilaments and
microtubules
Centrioles
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Help organize cell division and mitosis
NOT found in plant cells
Cell Wall
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Rigid layer around membrane
Found only in bacteria, fungi, and plants
Support and protect cell
Does not prevent the movement of substances
across cell membrane
In bacteria – peptidoglycan; in eukaryotes –
protein and carbohydrates
Helps cells to connect with adjacent cells