CELLS
Structure
Cell Membrane
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Surrounds the cell to separate it from its external
environment
Composed of a phospholipid bilayer that has proteins
embedded in it
Cholesterol is also an important component of cell
membranes since it keeps the membrane intact yet fluid
The membrane acts as a selective barrier by controlling
what substances enter and leave the cell
Membrane Structures
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Microvilli (microvillus):
extensions of the cell membrane
used to increase the surface
area of the cell
Cilia (cillium): short, hair-like
extensions on the cell membrane
used for movement
Flagella (Flagellum): long, whiplike structures used for
movement
Cell Interior
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Cytoplasm:
 A semi-fluid
substance in which all of
the cell’s organelles are suspended
 Located between the nucleus and the
cell membrane
 Contains the cytoskeleton
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Cytoskeleton: a network of
microtubules that support the cell
and give it shape
Nucleus
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Nucleus: the control center of the cell
and where the cell’s DNA is located
Nuclear Membrane:
 Separates the nucleus from the cytoplasm
 Contains pores so that substances may enter
or leave the nucleus
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Nucleolus: structure within the nucleus
that is responsible for making rRNA
Nucleoplasm: similar to the cytoplasm, it
is a semifluid substance in which the
DNA and nucleolus are suspended
Organelles
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Endoplasmic reticulum (ER):
 Extensive
 There are
network of membranes
2 types:
 Rough ER: contains ribosomes that
make proteins destined to leave the
cell
 Smooth ER: makes lipids, steroids,
and is involved in detoxification;
important in cells that are
responsible for ridding the body of
toxic substances (i.e. liver)
Organelles (cont.)
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Ribosomes:
 Structures
involved in protein
synthesis
 Found attached to the RER or
suspended in the cytoplasm
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Mitochondria: structures used to
make ATP (energy compound)
Golgi complex (apparatus):
 Series of flat membrane-bound sacs
 Packages proteins made from the
RER and sends them in membranebound vesicles to their destination
Organelles (cont.)
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Vacuole:
 Membrane-bound
compartment that
serves many functions (i.e. absorbs
water, stores proteins, stores wastes,
etc.)
 Plant cells have one large central
vacuole whereas animal cells contain
several small vacuoles
Organelles (cont.)
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Lysosome:
 Membrane-bound
organelles filled with
hydrolytic enzymes
 These enzymes are used to break down
substances (i.e. carbohydrates,
proteins, lipids, old organelles, etc.)
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Pinocytotic Vesicles:
 Membrane-bound
compartments used
to bring substances across the cell
membrane
 The membrane of these vesicles is
actually part of the cell membrane that
has “pinched” off
Cell Division Structures
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Centrosome:
 Structure
used during cell division
 Spindle apparatus attaches here
 Made up of a pair of centrioles
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Centrioles:
 Made
up of 9 sets of triplet
microtubules