The document discusses cell membranes, including their structure and functions. It describes the fluid mosaic model, which states that membranes are fluid structures composed of phospholipids and various embedded proteins. Phospholipids form a bilayer, with hydrophobic fatty acid tails facing inward and hydrophilic heads facing outward. Membrane proteins have various roles like transport, signaling, and attaching to other structures. The fluid mosaic model improved upon earlier models and best explains the observed properties of cell membranes.

1. CELL
MEMBRANES
CHAPTER 2A

4. LEARNING OBJECTIVES
 Know the structure and properties of cell membranes
 Understand how models such as the fluid mosaic model of
membrane structure are interpretations of data used to
develop scientific explanations of the structure and
properties of cell membranes.

5. MEMBRANES
 All membranes act as
barriers, controlling what
passes through them and
allowing the fluids either side
of them to have different
compositions.

6. FUNCTIONS OF MEMBRANES
 Some reactions of respiration occur in here (cristae)
 Contain enzymes for reactions
 Are flexible for shape change(WBC phagocytosis)
 Vesicles bind to membrane for releasing
chemicals(neurotransmitters)

7. THE STRUCTURE OF MEMBRANES
 Two major components of all membranes are:
 1. Phospholipids
 2. Proteins

8. PHOSPHOLIPIDS
 Phospholipids are the most abundant lipid in the plasma
membrane
 Phospholipids are amphipathic molecules, containing
hydrophobic and hydrophilic regions
 The fluid mosaic model states that a membrane is a fluid
structure with a “mosaic” of various proteins embedded in
it

9.  In a phospholipid, two fatty acids and a phosphate group are
attached to glycerol
 The two fatty acid tails are hydrophobic, but the phosphate group
and its attachments form a hydrophilic head

10. MONOLAYER, MICELLE

11. BILAYER FORMATION
 With water in each side phospholipids form a bilayer.

12. MEMBRANE MODELS
 In 1935, Hugh Davson and James Danielli proposed a sandwich
model in which the phospholipid bilayer lies between two layers of
globular proteins
 Later studies found problems with this model, particularly the
placement of membrane proteins, which have hydrophilic and
hydrophobic regions
 In 1972, J. Singer and G. Nicolson proposed that the membrane is a
mosaic of proteins dispersed within the bilayer, with only the
hydrophilic regions exposed to water

13. CONTROL OF MEMBRANE FLUIDITY

14.  Cholesterol is a more rigid molecule than many of the
phospholipids and so makes the membrane more stable and
stronger.

15. MEMBRANE PROTEINS
 A membrane is a collage of different proteins embedded in the fluid
matrix of the lipid bilayer
 Proteins determine most of the membrane’s specific functions

16.  Two major groups
proteins:
 1. Integral
proteins –
channel, carrier
proteins
 2. Peripheral
proteins are
bound to the
surface of the
membrane

17. INTEGRAL PROTEINS
 Types of integral proteins are:
 1. Gated channels
 2. Channel proteins
 3. Carrier proteins

18. MEMBRANE PROTEIN FUNCTIONS
 Six major functions of membrane proteins:
• Transport
• Enzymatic activity
• Signal transduction
• Cell-cell recognition
• Intercellular joining
• Attachment to the cytoskeleton and extracellular matrix (ECM)

20. BUILDING A MODEL OF THE
MEMBRANE
 Charles Ernest Overton - In 1900, he proposed a biomembrane
model "Overton Biomembrane Model" which stated that
biomembranes are made up of lipids.
 Irving Langmuir – in 1917 demonstrated lipid monolayer.
 Evert Gorter and Francois Grendel – in 1925 used RBCs, proposed
that lipid is bilayer.
 Davson and Danielli – in 1935, sandwich model.