Download Plasma Membrane

Cells
Plasma Membrane
Basic Parts of a Cell
• The three basic parts of a cell are the
plasma membrane, the cytoplasm, and
the nucleus.
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All living cells must maintain a
balance regardless of internal
and external conditions. Survival
depends on the cell’s ability to
maintain the proper conditions
within itself.
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Cells
Plasma Membrane
Internal Organization of a Cell
Click below to watch the Visual Concept.
Visual Concept
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Cells
Plasma Membrane
• Plasma Membrane
–The cell’s outer boundary,
called the plasma membrane
(or the cell membrane),
covers a cell’s surface and
acts as a barrier between the
inside and the outside of a
cell.
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It is the plasma membrane’s job to:
• allow a steady supply of glucose, amino
acids, and lipids to come into the cell no matter
what the external conditions are.
• remove excess amounts of these nutrients
when levels get so high that they are harmful.
• allow waste and other products to leave the
cell.
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Plasma
Membrane
Water
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Plasma Membrane &
Homeostasis
This process of maintaining the cell’s
environment is called homeostasis.
Selective permeability is a process used to
maintain homeostasis in which the plasma
membrane allows some molecules into the
cell while keeping others out.
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Cells
Plasma Membrane
Plasma Membrane
• Membrane Lipids
– Cell membranes consist of a phospholipid
bilayer.
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Cells
Plasma Membrane
Structure of
Lipid Bilayer
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Structure of the Plasma Membrane
The phospholipid
bilayer is
composed of two
layers of
phospholipids
back-to-back.
Phospholipids are lipids with a
phosphate attached to them.
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Cells
Plasma Membrane
Cell Membrane
Plasma Membrane Movie
QuickTime™ and a
Sorenson Video 3 decompressor
are needed to see this pictur e.
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Cells
Plasma Membrane
• Fluid Mosaic Model
–The fluid mosaic model states
that the phospholipid bilayer
behaves like a fluid more than
it behaves like a solid.
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The fluid mosaic model describes the plasma membrane as a
flexible boundary of a cell. The phospholipids move within the
membrane.
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Cells
Plasma Membrane
Plasma Membrane
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Other components of the plasma membrane:
Cholesterol plays the important role of
preventing the fatty acid chains of the
phospholipids from sticking together.
Cholesterol
Molecule
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Cells
Plasma Membrane
• Membrane Proteins
– Cell membranes often contain
proteins embedded within the
phospholipid bilayer.
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Transport
proteins allow
needed
substances or
waste materials to
move through the
plasma
membrane.
Click image to view movie.
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Which of the following best describes the plasma
membrane's mechanism in maintaining
homeostasis?
A. protein synthesis
B. selective permeability
C. fluid composition
D. structural protein attachment
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The answer is B. Selective permeability is the
process in which the membrane allows some
molecules to pass through, while keeping
others out.
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Describe the
structure of the
plasma membrane.
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The plasma membrane is composed of a
phospholipid bilayer, which has two layers of
phospholipids back-to-back. The polar heads
of phospholipid molecules contain phosphate
groups and face outward.
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Why is the
phosphate
group of a
phospholipid
important to
the plasma
membrane?
Phospholipid molecule
Polar head
(includes
phosphate
group)
Nonpolar
tails (fatty
acids)
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When phospholipid
Phospholipid molecule
molecules form a
bilayer, the phosphate
Polar head
groups lie to the
(includes
outside. Because
phosphate
Nonpolar
phosphate groups are
group)
tails
(fatty
polar, they allow the
acids)
cell membrane to
interact with its watery
(polar) environments
inside and outside the
cell.
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Explain why the model of the plasma
membrane is called the fluid mosaic model.
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It is fluid because the phospholipid molecules
move within the membrane. Proteins in the
membrane that move among the phospholipids
create the mosaic pattern.
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