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CELL ORGANELLES
 Cell organelles are membrane-bound structures that each has
a specific function for cellular survival.
 Separation of chemical reactions into distinct compartments
in the cell allows multiple cellular reactions to occur at the
same time.
Nucleus - The nucleus is the control center of the cell and the
most obvious organelle in any eukaryotic cell. It is a membranebound organelle and is surrounded by a double membrane. It
communicates with the surrounding cytoplasm via numerous
nuclear pores. The nucleus contains DNA, which provides the
instructions to direct all cell activities and to build another “you”.
Chromatin - Chromatin are strands of DNA before they condense
to form the structures known as chromosomes.
Nucleolus - The nucleolus is inside the nucleus and it produces
ribosomes, which move out of the nucleus to position themselves
on the endoplasmic reticulum where they are critical in the
assembly of proteins.
Ribosomes - The ribosomes are the site of the assembly of all
proteins. They use the information in the mRNA to string together
the correct amino acids to create the correct protein. There are only
20 amino acids found in living things and thousands of proteins
can be made by combining them.
Endoplasmic Reticulum - The ER is a vast membrane that is a
continuation of the outer nuclear membrane. It is highly corrugated
as it is responsible for many chemical reactions and needs a large
surface area in which to conduct them.
Smooth Endoplasmic Reticulum - The smooth ER is important in
the synthesis and storage of lipids.
Rough Endoplasmic Reticulum - The rough ER is important in
transporting proteins from the ribosomes on its surface around the
cell (especially to the Golgi Complex).
Golgi Complex - The Golgi complex/bodies is a membranebound structure with a single membrane. It is actually a stack of
membrane-bound vesicles that are important for modifying and
packaging macromolecules (proteins) for transport elsewhere in
the cell or to the cell membrane where they may be secreted
outside the cell.
Mitochondria - The Mitochondria provide the energy a cell needs
to move, divide, produce products, contact etc. – they are the
power centers of the cell. They are about the size of bacteria.
Mitochondria are membrane-bound organelles that have a double
membrane. The outer membrane is fairly smooth but the inner
membrane is highly convoluted, forming folds called cristae. The
cristae greatly increase the inner membrane’s surface area where
sugar is combined with oxygen to produce ATP for energy.
Chloroplasts - The chloroplasts are specialized organelles that are
found only in plant cells. These organelles contain the plant cell’s
green pigment called chlorophyll. Chlorophyll traps sunlight
energy to make glucose or food for the plant – photosynthesis.
They are made of a double outer membrane and inner small
membrane-bound discs (thylakoids) where photosynthesis takes
place.
Vacuole - A vacuole is a membrane-bound sac that is a temporary
storage area for food, enzymes, other materials needed by the cell
and waste products. In plant cells there is a large vacuole that plays
a part in the rigidity of the plant and in animal cells the vacuoles
are small.
Lysosomes - Lysosomes are small membrane-bound organelles
that contain hydrolytic enzymes that help in cell digestion. The
lysosome digests food, worn out organelles, bacteria, viruses and
anything that the cell needs to get rid of.
Cytoskeleton - The cytoskeleton helps maintain the shape of the
cell. It is made of rods and fibers that form a framework for the
cell. It helps the internal movement of cell organelles in the
cytoplasm and is a constantly changing structure.
Cell Wall - The cell wall (made of a polysaccharide called
cellulose) forms an inflexible barrier that protects the cell and
gives it support. Cell wall is present in prokaryotes and plant cells
but not animal cells.
Cell membrane - Every cell is enclosed in a membrane. The
membrane is a double layer of lipids, which is studded with
proteins that are important for cell activity.
Cytoplasm - The cytoplasm is the “soup” within which all other
cell organelles reside and where most of the cellular metabolism
occurs. It is mostly water and is full of proteins that control cell
metabolism.
Cilia - These are short hair-like projections that move in a wavelike motion. eg. Paramecium
Flagella - Flagella are longer projections that move in a whip-like
motion. In unicellular organisms, cilia and flagella are the major
means of locomotion. eg. Sperm
Centrioles - The centrioles are in pairs. One is perpendicular to
the others. They are made of filaments called microtubules. These
structures are used for cell division, they move to opposite ends of
the cell so that the chromosomes in the nucleus separate. They are
found only in animal cells.