Lesson #3: The Cell Membrane

Question 1

Membrane Structure

Answer 1

The cell membrane is
composed of a
phospholipid bilayer

Question 2

The Phospholipid
Bilayer

Answer 2

Each phospholipid
consists of two regions:

Polar
(hydrophilic)
“head”

Non – polar
(hydrophobic)
“tail”
The “head” region is composed of glycerol bonded to a phosphate group.

This gives the “head” region a negative charge which allows it to dissolve in
water.

(hydrophilic = water loving)

The “tail” region is composed of two fatty acid chains. One saturated and one
unsaturated.

This region carries an overall positive charge making it not able to dissolve in
water.

(hydrophobic = water fearing)
The fact that the lipids
do not dissolve in
water creates a border
around the cell.

The phospholipid
bilayer allows water
molecules small
enough to fit between
the phospholipids to
pass through the
membrane.

Question 3

The Fluid – Mosaic
Model

Answer 3

The phospholipid bilayer is
the basis of the cell
membrane.

This layer also contains
many other molecules that
are necessary for the cell to
maintain homeostasis.

These molecules scattered
throughout the membrane
led researchers to name it
the fluid – mosaic model.

Question 4

Cholesterol

Answer 4

Cholesterol is found
between some of the
phospholipid molecules.

Keeps the membrane fluid
and flexible.

Question 5

Integral Proteins

Answer 5

These are protein
molecules embedded in
the membrane

Provide channels for larger
ions and molecules to
enter and leave the cell.

Question 6

Peripheral Proteins

Answer 6

These are structural proteins on the
membrane inside the cell.

These are connected to the cytoskeleton
filaments that give structure and support to
the cell.

Question 7

Alpha Helix Protein

Answer 7

Coil like proteins that
extend through the
membrane

Act as channels for
nutrients entering the
cell.

Question 8

Glycoprotein

Answer 8

Proteins with
carbohydrates
attached that stick out
of the cell

These act as receptors
for hormones and
other body cells.