UNIT 1: Biochemistry
Chapter 2: Cell Structure and Function
pg. 70 - 107
2.2: Membrane Structure and Functions
pg. 81 – 86
The Fluid Mosaic Model
Fluid mosaic model – is the idea that a biological membrane consists of a
fluid phospholipids bi-layer, in which proteins are embedded and float freely.
This model proposes that the membrane is not rigid with molecules locked
in place, but phospholipid and protein molecules are free floating, fluid like,
able to move laterally within the two layers.
The phospholipid bi-layer in all biological membranes is fluid and is very
important to the membrane function. The membrane is 10 nm thick.
The mosaic portion is the wide array of protein molecules found with the
phospholipid bi-layer. These proteins are for cell to cell interaction,
recognition, transport, and attachment. Some proteins have carbohydrates
linked to them.
The cell membrane is responsible for regulating the movement of molecules
into and out of the cell. The protein distribution is asymmetrical, that it is
different on either side of the membrane
Glycolipid – is any membrane lipid that is bound to a carbohydrate.
Glycoprotein – is a membrane component that contains a sugar, or
carbohydrate, bound to an amino acid.
The Role of Phospholipids
The structure of the phospholipid molecule makes it ideal to create a bi-layer
membrane. The phospholipid mole is made up of one phosphate group, one
glycerol group, and two fatty acid tails.
b) Individual molecules are free to flex, rotate, and exchange places in a
phospholipid bilayer in the fluid state.
The phosphate group is hydrophilic, attracted to water (polar), while the
fatty acid tails are hydrophobic, or afraid of water (non-polar).
Figure 3: Phospholipid Molecule, pg. 83
In a phospholipid molecule (phosphatidyl choline), the head has a polar
alcohol, a phosphate group (orange), and the glycerol unit (red).
The Role of Membrane Proteins
Integral membrane protein – is a protein that is embedded in the liquid bilayer.
Peripheral membrane protein – is a protein on the surface of the membrane.
The array of proteins found in the plasma membrane, determines its function
and its uniqueness. There are four functional categories of proteins;
a) Transport: certain substances are unable to diffuse through
the membrane, therefore they must pass through hydrophilic
protein channels.
b) Enzymatic Signals: proteins associated with respiration and
photosynthesis, are enzymes.
c) Triggering Signals: Proteins can bind to hormone signals,
which can cause changing events in the cell.
d) Attachment and Recognition: These proteins are found on
both the internal and external surfaces. One example would be
the recognition of invading microbes and stimulation an
immune response.