a selectively permeable phospholipid bilayer that

surrounds all cells.

The Cell membrane is …

Selectively Permeable

• It chooses or selects specific substances

Permeable means to pass pass through

A selectively permeable membrane is selective about what it allow to pass through

Cell membrane diagram

Inside

cell

Outside cell

Cell membrane

Polarity• Polar: has opposite charges

at opposite ends of molecule

* Example: Water

Non-polar: Balanced molecule with charges evenly spaced around molecule

* Example: fats and oils

Phospholipid diagrams

Outside cell

Inside cell

A picture of the cell membrane using a transmission election microscope

T.E.M.

Membrane proteins are imbedded in plasma membrane.

Outside cell

Inside

cell

nucleus

Organelles are surrounded by membranes!

Golgi Apparatus

Lysosomes

Mitochondria

Membrane proteins do the following 4 things

1) Recognition proteins: Identify the cell! (recognize the cell)

2) Receptor proteins: React to stimulation and cause cell to function (react).

3) Transport Proteins: transport substances across plasma membrane.

4) Enzymes: Catalyze reactions on membrane surface

Recognition Proteins

Passive Transport

• Not requiring energy or ATP

• When substances diffuse from a high to a low concentration

• When they diffuse down their concentration gradient

                                                                   

Types of Transport Proteins

Facilitated Diffusion: a passive form of transport using membrane proteins

Before After

Active Transport

• Requires Energy or ATP

• When something large or difficult needs to pass through the membrane

• When substances have to be pushed or “pumped” backwards from a low to a high concentration.

• Proteins that do this are called protein pumps

Active transport

Adapted from Campbell, Reece & Mitchell, Biology 6 th edition, 2002with permission of Pearson Education, Inc.

1 2

Active transport (cont.)

Adapted from Campbell, Reece & Mitchell, Biology 6 th edition, 2002with permission of Pearson Education, Inc.

3 4

Active transport (cont.)

Adapted from Campbell, Reece & Mitchell, Biology 6 th edition, 2002with permission of Pearson Education, Inc.

5 6

Endocytosis: when the cell membrane must move to engulf larger

substances that cannot fit through

• There are 3 different types that will be discussed

Phagocytosis: when very large substances are engulfed into the cell. (pac-man)

Pinocytosis• Same as phagocytosis but with smaller

substances and liquids

• “cell slurping”

                                              

Exocytosis• When substances leave the cell (saliva,

sweat, oils, digestive juices, tears)

                                                                  

• The same cell is a hypertonic environment will loose water, shrivel, and probably die.

• A cell in a hypotonic solution will gain water, swell, and burst.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 8.12