Malaysia Chinese Independent School Senior 1 Biology (English)

1. 2.2.1.1 Fluid
mosaic model

2. Fluid mosaic model
• Lipid bilayer
• Flexible
• Hydrophobic tails
• Hydrophilic heads
• Carbohydrates
(saccharides)
• Cholesterol
• Proteins

3. Fluid mosaic model 流动镶嵌模型
• Proposed by SJ Singer and
GL Nicolson in 1972.
• Fluid – the phospholipid
bilayer is viscous and
individual phospholipids
can move position.
• Mosaic – the phospholipid
bilayer is embedded with
proteins, resulting in a
mosaic of components.

4. Evidence of
lateral
movement on
the cell
membrane
with
Fluorescence
recovery after
photobleaching
(FRAP)

5. Evidence of
lateral
movement on
the cell
membrane
Photobleaching. Cells expressing a GFP-labelled protein in the endoplasmic
reticulum were subjected to photobleaching.
(a) A cell before bleaching.
(b) The same cell immediately after bleaching of the square section shown.
(c) The same cell 5 min after photobleaching.
Adapted from Figure 1b from Lippincott-Schwartz, J., Snapp, E. and Kenworthy, A. (2001) Studying protein dynamics in living
cells. Nat. Rev. Mol. Cell. Biol. 2, 444–456.

6. Quiz
• Which of the following describes the fluid-mosaic model of the
plasma membrane structure?
a. phospholipid monolayer with embedded proteins
b. phospholipid bilayer with embedded proteins
c. phospholipid trilayer with embedded proteins
d. triglyceride bilayer with embedded proteins
e. triglyceride monolayer with embedded proteins

7. 2.2.1.2
Phospholipids of the
cell membrane

8. Structure of a phospholipid
• Two fatty acids tails
and one phosphate
groups attached to a
glycerol.
• The fatty acids are
hydrophobic.
• The phosphate group
is charged.
• The phosphate head
of phospholipid is
hydrophilic.

9. Arrangements of phospholipid
• Spontaneously forms a
bilayer sheet, called
phospholipid bilayer
• Sequestered the
hydrophobic tail from water
• Hydrophilic head facing the
inside of the cell or the
environment
• Phospholipid can move
freely within the structure

11. Quiz
• Which of the following statements is NOT correct about the
phospholipid molecules in the plasma membrane?
a. Each phospholipid molecule has four nonpolar tails.
b. Each phospholipid molecule has one polar head.
c. The phospholipid heads are attracted to water.
d. The phospholipid tails are not attracted to water.
e. The phospholipid heads face outward.

12. Yeast cell membrane visualized by some membrane proteins
fused with RFP and GFP fluorescent markers. Imposition of
light from both of markers results in yellow colour.
Microscopic image showing presence of major histocompatibility
complex (MHC) II molecules (green) and cell nuclei (blue) in
dendritic cells. MHC molecules presents antigen on the cell
surface for recognition by the T-cells.

13. 2.1.1.3
Protein of the
cell membrane

14. Protein on the cell membrane
• Peripheral membrane proteins attach
to the surface of the cell membrane.
• do not interact with the hydrophobic core
of the phospholipid bilayer.
• Integral membrane proteins embed in
the phospholipid bilayer.
• Includes transmembrane proteins and
lipid-anchoring proteins.
• Also able to move laterally within the
phospholipid bilayer

15. Main classes of membrane protein

16. How does the protein attaches to the
membrane
• The side chains of the
amino acids determine the
affinity of a protein to
water.
• Amino acids with polar or
charged side chain are
hydrophilic.
• Amino acids with non-
polar side chain are
hydrophobic.
Hydrophobic
Hydrophilic

17. Hydrophobic and/or hydrophilic
• Once folded neatly into its
quaternary structure, a protein will
have hydrophobic and/or hydrophilic
regions.
• The hydrophobic regions of a protein
will interact with the hydrophobic
tails of the lipid bilayer.
• The hydrophilic regions of a protein
will interact with the hydrophilic
head of the lipid bilayer.

18. Quiz
• Which of the following is a peripheral membrane protein?
a. 1
b. 2
c. 3
d. 4
e. 5

20. Quiz
• A hormone such as insulin acts by attaching to _____ proteins in the
plasma membrane and increasing the glucose carriers present.
a. receptor
b. enzymatic
c. carrier
d. channel
e. cell-recognition

21. 2.1.1.4
Saccharide on the
cell membrane

22. Saccharides on the cell membrane
• Saccharide on cell membrane exists as glycoprotein (and glycolipid).
• These are present as short oligosaccharides, either branched or
unbranched.
• Only present on the exterior surface of the membrane. The interior
surface is devoid of any carbohydrates.

23. Functions of saccharides on cell membrane
• Cell recognitions and interactions– only present in the outer surface
of the membrane.
• Adhesive – linking neighbouring cells together and hence maintain
the integrity of the tissue.
• Cell activities – transport proteins, hormones and enzymes.
• Protein orientation – sugars are hydrophilic
• Various human blood groups, e.g. ABO type etc. are due to the
carbohydrate chains of the erythrocyte membrane glycoproteins.

24. Quiz
• Figure shown a region of a cell
membrane. The hexagons
represented monosaccharides.
Which side represent
extracellular space?
a. 1
b. 2
c. 3

25. Quiz
• Which indicate
extracellular space?
• 1
• 2
• 3
1
2
3

26. Conclusion
• The fluid mosaic model describes the cell membrane as a fluid combination of
phospholipids, cholesterol, and proteins (and glycoproteins) which the
components of the cell membrane can move laterally freely.
• The cell membrane mainly consists of phospholipids that form a bilayer sheet.
The head of a phospholipid is hydrophilic while the tails of a phospholipid is
hydrophobic.
• Proteins on the cell membrane are either peripheral membrane proteins or
integral membrane proteins. Integral membrane proteins contain hydrophobic
regions which can interact with the hydrophobic fatty acid tails of the
phospholipids.
• Protein on the cell membrane can form channels, act as receptors or enzymes
etc.
• Saccharide on cell membrane exists as glycoprotein. They only presents in the
extracellular surface of the cell.
• Glycoproteins are important for cell recognition and interaction, and other
cellular activities as hormones, transport proteins and enzymes.