Transcript cell membrane

In or Out?
• 1. What are some things that can pass through a
window screen?
• 2. What are some things that cannot pass
through a window screen? Why is it important to
keep these things from moving through the
screen?
• 3. The cell is surrounded by a cell membrane,
which regulates what enters and leaves the cell.
Why is it important to regulate what moves into
and out of a cell?
8-1 Cell Membrane
Cell Membrane
• Every cell is surrounded by a cell membrane
Functions
• provides structural support and protects the
cell
• recognizes foreign material
• gatekeeper – allows only certain substances
in and out of the cell
• communicates with other cells
Homeostasis
• Maintenance of stable internal conditions
in a changing environment.
• Achieved by controlling the movement of
substances across the cell membrane
Lipid Bilayer
Phospholipid
• is a specialized lipid made of a phosphate
“head” and two fatty acid “tails.”
• Main component of the cell membrane
• Cells are suspended in a fluid environment.
– phosphate head = polar = attracted to water.
– fatty acid tails = nonpolar = repelled by water.
Lipid Bilayer
Lipid Bilayer
• the phospholipids form a double layer as a result of
water inside and outside the cell
• The nonpolar tails, repelled by water, make up the
interior of the lipid bilayer.
• The polar heads are attracted to the water, so they
point toward the surfaces of the lipid bilayer.
– One layer of polar heads faces the cytoplasm, while the
other layer is in contact with the cell’s immediate
surroundings.
Lipid Bilayer
• Only certain substances can pass through
the lipid bilayer.
– only small, nonpolar substances can pass.
• Ions and most polar molecules are
repelled by the nonpolar interior of the
lipid bilayer.
Checkpoint
• What are the functions of the cell
membrane?
• What is homeostasis?
• What is a lipid bilayer?
– What are the two parts of a phospholipid?
Membrane Proteins
Where are proteins found within the membrane
• face inside the cell
• face outside the cell
• stretch across the lipid bilayer and face both
inside and outside.
• Proteins are made of amino acids. Some amino
acids are polar, and others are nonpolar.
• The attraction and repulsion of polar and
nonpolar parts of the protein to water help hold the
protein in the membrane.
Membrane Proteins
Types of proteins
• Cell-surface markers
– act like a name tag
– unique chain of sugars acts as a marker to
identify each type of cell.
• Receptor proteins
– enable a cell to sense its surroundings
– binds to certain substances outside the cell
resulting in changes inside the cell.
Membrane Proteins
Types of proteins
• Enzymes
– specialized proteins in the cell membrane
– helps with important biochemical reactions inside
the cell.
• Transport proteins
– aid the movement of substances that the cell
needs but cannot pass through of the lipid
bilayer.
Key Ideas
• How does the cell membrane help a cell
maintain homeostasis?
• How does the cell membrane restrict the
exchange of substances?
• What are some functions of membrane
proteins?
Membrane Proteins
Summary
• One way that a cell maintains homeostasis is
by controlling the movement of substances
across the cell membrane.
• The lipid bilayer is selectively permeable to
small, nonpolar substances.
• Proteins in the cell membrane include cellsurface markers, receptor proteins, enzymes,
and transport proteins.