The document discusses cell membranes and membrane proteins. It begins by describing the cell membrane as the boundary that separates internal and external environments of the cell, and controls movement of materials in and out through selective permeability. The membrane is a phospholipid bilayer with hydrophobic tails facing inward and hydrophilic heads forming the inner and outer surfaces. It then explains the structure of phospholipids as amphipathic molecules with hydrophobic fatty acid tails and a hydrophilic phosphate head. Proteins and cholesterol are embedded throughout the flexible phospholipid bilayer. Integral proteins span the membrane while peripheral proteins attach to the inner or outer surface. Finally, it lists several types of membrane proteins and their functions, including channel proteins for passive diffusion

1. THE CELL PART 2
CELL MEMBRANE AND MEMBRANE PROTEINS
UNIVERSITY OF HEALTH EDUCATION

2. THE CELL MEMBRANE
 Cell Membranes
 The boundary of the cell, sometimes called the plasma
membrane, separates internal metabolic events from the
 external environment and controls the movement of materials
into and out of the cell. This membrane is very
 selective about what it allows to pass through; this
characteristic is referred to as "selective permeability." For
 example, it allows oxygen and nutrients to enter the cell while
keeping toxins and waste products out. The plasma
 membrane is a double phospholipid membrane, or a lipid
bilayer, with the nonpolar hydrophobic tails pointing
 toward the inside of the membrane and the polar hydrophilic
heads forming the inner and outer surfaces of the
 membrane.

3. PHOSPHOLIPID
BILAYER
 Each phospholipid is amphipathic, with two
hydrophobic tails and a hydrophilic head.
The hydrophobic tails face inward towards
one another, and the hydrophilic heads face
outwards.
 The hydrophilic head is composed of a
choline structure (blue) and a phosphate
(orange). This head is connected to a
glycerol (green) with two hydrophobic
tails (purple) called fatty acids.
 The hydrophilic heads are facing the
intra and extra cellular space.
 The hydrophobic tails consists of fatty
acids
 The hydrophobic tails face inward
towards one another,

4. KEY TERMS
TERM EXPLANATION
CELL MEMBRANE Specialized structure that surrounds the
cell and its internal environment; controls
movement of substances into/out of cell
HYDROPHOBIC Molecule that repels water (“water-
fearing”)
HYDROPHILIC Molecule that is attracted to water (“water-
loving”)
AMPHIPATHIC Molecule that contains both a
hydrophobic and a hydrophilic end
PHOSPHOLIPID Amphipathic lipid made of glycerol, two
fatty acid tails, and a phosphate group
PHOSPHOLIPID BILAYER A biological membrane involving two
layers of phospholipids with their tails
pointing inward

5. PROTEINS AND CHOLESTEROL
 Proteins and cholesterol molecules are scattered throughout the flexible
phospholipid membrane. Peripheral proteins attach loosely to the inner or
outer surface of the plasma membrane. Integral proteins lie across the
membrane, extending from inside to outside. A variety of proteins are
scattered throughout the flexible matrix of phospholipid molecules,
somewhat like icebergs floating in the ocean, and this is termed the fluid
mosaic model of the cell membrane.
 The phospholipid bilayer is selectively permeable. Only small, uncharged
polar molecules can pass freely across the membrane. Some of these
molecules are H2 O and CO2 , hydrophobic (nonpolar) molecules like O2 ,
and lipid soluble molecules such as hydrocarbons. Other molecules need
the help of a membrane protein to get across.

6. MEMBRANE PROTEINS
 THERE ARE A VARIETY OF MEMBRANE PROTEINS THAT SERVE VARIOUS
FUNCTIONS.
1. Channel proteins : Proteins that provide passageways through the
membranes for certain hydrophilic or water-soluble substances such as
polar and charged molecules. No energy is used during transport, hence
this type of movement is called facilitated diffusion.
2. Transport proteins : Proteins that spend energy (ATP) to transfer materials
across the membrane. When energy is used to provide passageway for
materials, the process is called active transport.
3. Recognition proteins : Proteins that distinguish the identity of
neighbouring cells. These proteins have oligosaccharide or short
polysaccharide chains extending out from their cell surface.
4. Adhesion proteins : Proteins that attach cells to neighbouring cells or
provide anchors for the internal filaments and tubules that give stability to
the cell.

7. MBRANE PROTEIN
5. Receptor proteins : Proteins that initiate specific cell responses once
hormones or other trigger molecules bind to them.
6. Electron transfer proteins: Proteins that are involved in moving electrons from
one molecule to another during chemical reactions.

8. MEMBRANE PROTEINS. video
presentation