Cell Membrane and

Transport

The Cell Membrane

Cell membranes are

composed of two

phospholipid layers.

(bilayer)

The cell membrane has two

major functions.

1. Forms a boundary

between inside and

outside of the cell

2. controls passage of

materials

Present in all cells

•Phospholipid is a specialized lipid (fat) that has one

of it’s fatty acid tails removed so a phosphate can

be added.

•This causes a normal lipid that is ALWAYS

hydrophobic, to become partially hydrophilic.

•Terms that describe this are; hydrophilic/polar,

hydrophobic/non-polar

•Why do we want to have modified lipids (fats) in

the cell membrane?

Properties of the membrane

The fluid mosaic model describes the membrane.

cell membrane

There are other molecules embedded in

the membrane – this makes the surface

bumpy

protein

cholesterol

protein

carbohydrate

chain

protein channel

5 specialized proteins

Adhesion

Communication (cell to cell)

Receptor

Recognition

Passive Transport

Active Transport

The cell membrane is selectively

permeable. Some molecules can cross the

membrane while others cannot.

Chemical signals are

transmitted across the

cell membrane.

Receptors bind with

ligands and change

shape.

A ligand is a specific

molecule that binds

with a receptor to

make something

happen.

There are two types of receptors.

1) intracellular receptor

Ligand moves through the cell

membrane to reach receptor

on inside of cell.

Example: hormones

2) membrane receptor

Ligand on outside of cell binds

with a receptor within the cell

membrane.

Ex: Neurotransmitters, growth

factors

This is the end of the membrane lecture

that will be done in class on 9/16.

The remaining slides are the transport

lecture that will be done in class on 9/20.

Basic movement across cell membrane:

Materials move across the membrane in a variety of ways:

Passively: (no energy required) moved based on concentration

gradient.

Actively: moving items against a concentration gradient, energy is

required

Facilitated diffusion: No energy, just using helpers (like proteins) to move

things in or out of a cell that are large.

The two most common passive movement processes are diffusion

(solutions) and osmosis (water)

Solutions are substances (solutes) dissolved in a solvent (water) to form

a solution.

Diffusion

No solute likes to be crowded. Therefore, they will move from area that is

very saturated (crowded) to one that is not so saturated (uncrowded).

This process of widely spreading out is called diffusion.

Who has been in a room where someone sprays perfume? Does it stay in

just one area?

NO!! The perfume is moving from high concentration to low concentration

Diffusion takes no energy, so it is passive.

Osmosis is the passive movement of water.

Terms to describe solutionsHypo=less than Tonic =solute Iso = equal

Hyper=more than Osmotic = Water

Try these:

more solution (higher concentration of solute)

less solution (lower concentration of solute)

Equal amounts of solute

So if there is more solute then what does that say about the amount of water?

Now try these:

More solute = less water = ?

Less solute = more water = ?

Remember, you are comparing 2 environments! Inside the

cell(intracellular) and outside the cell (extra-cellular)

Effects of water movement:

If a cell loses to much water it will shrink and die! That’s called crenate or

plasmolyze.

If a cell gains to much water it will burst and die! This is called cytolysis.

(lysis for short)

Both are bad!

Cells try to maintain homeostasis when it comes to water and solutes

and solutions. Homeostasis means a stable internal environment.

(Biological balance)

Active Transport But what happens if we want solutes to go from an area of low

concentration to high concentration?

Must use ENERGY!

It’s like putting the smell back in the can! (Active transport-going from

low concentration to highly concentrated)

Movement by vesicle

What is a vesicle?

Endocytosis: Moving things into the cell using a vesicle

Exocytosis: Moving things out of the cell using a vesicle

Pinocytosis: Bringing in of or removing liquids

Phagocytosis: Bringing in or removing of solids or large particles.

These are not exclusive! You can combine them to describe the type of movement!!