Cell Membrane & Transport Notes (Compact)
Big Idea: The cell (plasma) membrane is a selectively permeable, flexible barrier that controls movement
in and out of the cell, supports cell communication, and helps maintain homeostasis. This barrier is found
in every type of cell and is essential for survival.
1. Structure of the Cell Membrane:
The plasma membrane contains four major components:
● Phospholipids - form the selective bilayer
● Cholesterol - Buffers membrane fluidity in animal cells
● Carbohydrates - Cell recognition/signilaing; found on the outer surface as glycoproteins or
glycolipids
● Proteins - Transport, enzymes, receptors, joining, recognition, and attachment
Phospholipid bilayer: a layer created by phospholipids; these structures have a polar, hydrophilic
(water-loving) head that faces the water environments and a non-polar, hydrophobic (water-fearing) tail
facing inwards.
What blocks most of the unwanted molecules? The hydrophobic core of the phospholipid bilayer
blocks most ions and large/polar molecules.
Fluid-mosaic model & Fluidity:
● Fluid mosaic: lipids and many different proteins move laterally within the membrane.
- Fry-Edidin experiment: Found that differently labeled human and mouse membrane
proteins mixed after cell fusion, which supported lateral movement.
● Temperature: Higher temperatures and shorter tails will usually increase the cell's fluidity, while
longer tails will decrease the cell's fluidity.
● Cholesterol: Limits the excessive fluidity at high temperatures and helps prevent tight packing at
low temperatures. Its -OH group sits near the phospholipid heads.
● Unsaturated v.s. Saturated tails: If a phospholipid has unsaturated tails, they will be kinked and
result in the membrane being loosely packed, resulting in increased fluidity. On the other hand,
saturated tails will be straight and result in a tightly packed membrane, resulting in less fluidity.
Membrane proteins:
● Integral proteins- Embedded in the membrane, may span throughout the plasma membrane as
channels, carriers, pumps, or receptors.
● Peripheral proteins- Loosely attached to the membrane surface, is there for support, signaling,
and enzymes.
● Lipid-anchored proteins- Covalently bonded to the lipid group embedded in the bilayer.
Big Idea: The cell (plasma) membrane is a selectively permeable, flexible barrier that controls movement
in and out of the cell, supports cell communication, and helps maintain homeostasis. This barrier is found
in every type of cell and is essential for survival.
1. Structure of the Cell Membrane:
The plasma membrane contains four major components:
● Phospholipids - form the selective bilayer
● Cholesterol - Buffers membrane fluidity in animal cells
● Carbohydrates - Cell recognition/signilaing; found on the outer surface as glycoproteins or
glycolipids
● Proteins - Transport, enzymes, receptors, joining, recognition, and attachment
Phospholipid bilayer: a layer created by phospholipids; these structures have a polar, hydrophilic
(water-loving) head that faces the water environments and a non-polar, hydrophobic (water-fearing) tail
facing inwards.
What blocks most of the unwanted molecules? The hydrophobic core of the phospholipid bilayer
blocks most ions and large/polar molecules.
Fluid-mosaic model & Fluidity:
● Fluid mosaic: lipids and many different proteins move laterally within the membrane.
- Fry-Edidin experiment: Found that differently labeled human and mouse membrane
proteins mixed after cell fusion, which supported lateral movement.
● Temperature: Higher temperatures and shorter tails will usually increase the cell's fluidity, while
longer tails will decrease the cell's fluidity.
● Cholesterol: Limits the excessive fluidity at high temperatures and helps prevent tight packing at
low temperatures. Its -OH group sits near the phospholipid heads.
● Unsaturated v.s. Saturated tails: If a phospholipid has unsaturated tails, they will be kinked and
result in the membrane being loosely packed, resulting in increased fluidity. On the other hand,
saturated tails will be straight and result in a tightly packed membrane, resulting in less fluidity.
Membrane proteins:
● Integral proteins- Embedded in the membrane, may span throughout the plasma membrane as
channels, carriers, pumps, or receptors.
● Peripheral proteins- Loosely attached to the membrane surface, is there for support, signaling,
and enzymes.
● Lipid-anchored proteins- Covalently bonded to the lipid group embedded in the bilayer.
