Download 3.3 Cell Membrane - Deer Creek Schools

3.3 Cell Membrane
KEY CONCEPT The cell membrane is a barrier that
separates a cell from the external environment.
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
The fluid mosaic model is used
to describe the structure of the
cell membrane.
Video:
3.3 Cell Membrane
The cell membrane has two major functions.
1. forms a boundary between inside and outside of the
cell
2. controls passage of materials into and out of the cell
cell membrane
inside cell
outside cell
3.3 Cell Membrane
The cell membrane is made of a phospholipid bilayer.
• The phosphate
“head” is polar.
Water is polar.
Therefore, they form
hydrogen bonds
with each other.
• The fatty acid “tails”
are non-polar and
therefore repelled by
water
(hydrophobic).
3.3 Cell Membrane
The cell membrane is made of a phospholipid bilayer.
• There are other molecules embedded in the membrane.
– Protein, cholesterol, carbohydrates
cell membrane
carbohydrate
chain
cholesterol
protein
protein channel
protein
3.3 Cell Membrane
Cholesterol’s role in the cell membrane
Cholesterol is found in every cell of your body. It helps
maintain the integrity of these membranes, and plays a
role in facilitating cell signaling-- meaning the ability of
your cells to communicate with each other. Cholesterol
helps prevent extremes-- whether too fluid, or too firm-in the consistency of the cell membrane.
Infer: Note that cholesterol is
located between the fatty acid
chains. Do you think cholesterol is
polar or nonpolar? Explain your
answer.
3.3 Cell Membrane
The cell membrane is selectively permeable.
- Some molecules can cross the membrane while others cannot.
Connect:
Describe a
semipermeable
membrane
with which
you are already
familiar.
3.3 Cell Membrane
Chemical signals are transmitted across the cell membrane.
• Receptors bind with ligands and change shape.
– Receptor is a protein that detects a signal molecule and performs
and action in response. A ligand is the molecule the receptor binds
to. Specific receptors bind to specific ligands.
• There are two types of receptors.
1. intracellular receptor
– “within, or inside, a cell”
– are generally nonpolar
– small in size
-- Example: hormones can
interact with the nucleus to turn
on genes to make needed
proteins.
3.3 Cell Membrane
Chemical signals are transmitted across the cell membrane.
• Receptors bind with ligands and change shape.
• There are two types of receptors.
2. membrane receptor
•Cannot cross the membrane
•The receptor sends the
message to the cells interior
by changing its shape
•Example: receptors in red
blood cells trigger processes
to CO2 from the body tissues
to the lungs
Contrast: How do
intracellular receptors differ
from membrane receptors?