CELL BOUNDARIES

The Cell Membrane and Transport Processes

I. The Structure and Function of the Cell Membrane

Components of the cell membrane: Phospholipid bilayer – nonpolar fatty acid

tails turn inside, polar phosphate heads turn outside – forms a flexible structure as a boundary

Proteins – can be integral proteins or peripheral proteins. They can act as enzymes, receptors, transport and binding molecules

Carbohydrates – Identification tags outside of the cell membrane (glycolipids and glycoproteins)

Cholesterol – helps stabilizing the membrane by making it more solid – animal cells

The Function of the Cell Membrane

Surrounds the cell. Regulate the transport of molecules

in and out of the cell -- semipermeable

Immune response Attaches the cells to other cells or

surfaces. The model that describes cell

membrane, the Fluid Mosaic Model http://www.youtube.com/watch?v=GW0lqf4Fqpg http://www.youtube.com/watch?v=Qqsf_UJcfBc

Cell membranes control what goes in and out of the cell

It allows some substances to cross more easily than others

Selective Permeability

II. Passive Transport Processes

Transport means the movement of molecules from one side of the cell membrane to the other

Transport is influenced by: The size of substances The polarity of substances The concentration of substances The permeability of the cell membrane

Passive transport: requires no energy from the cell, the energy comes from the difference in concentration not ATP (energy from the cell).

Moves smaller substances from the higher to the lower concentration area.

Important in transporting O2, CO2, water, small molecules.

http://bcs.whfreeman.com/thelifewire/content/chp05/0502001.html

Types of Passive Transport

Diffusion – moving substances within the cell and small nonpolar molecules across the phospholipid bilayer.

http://www.stolaf.edu/people/giannini/

flashanimat/transport/osmosis.swf Osmosis: the movement of water

across the cell membrane by using the phospholipid bilayer or transport proteins.

Tonicity: Describes the tendency of a cell in a given

solution to lose or gain water. Isotonic, hypertonic, and hypotonic

Osmosis in action Isotonic solutions – when cells are put

into solutions that have equivalent salt concentration, visible osmosis does not take place.

Hypotonic solutions – Cells in very dilute solutions will take in water and eventually can burst (animal cells).

Hypertonic solutions – Cells in very concentrated solutions will lose water and shrink.

Facilitated Diffusion – a special type of diffusion in which the transported molecules are moved by the help of a transport protein.

http://bcs.whfreeman.com/thelifewire/

content/chp05/0502001.html

III. Active Transporthttp://bcs.whfreeman.com/thelifewire/content/chp05/0502002.html

Transport processes that can move substances from the lower concentration area to the higher by using energy.

Energy is gained by using ATP molecules.

A type of active transport is the Na-K ion pump

3 sodium ions move out of the cell with the help of a transport protein, while 2 potassium ions move into the cell.

H + ion pump – this active transport moves hydrogen ions (protons) from low to high concentration area by using energy from the cell (ATP).

IV. Bulk Transport Bulk transport – transport of large substances

through the cell membrane by using vesicles. Endocytosis – a process by which large particles can

move into the cell Types of endocytosis:

Phagocytosis – engulfing solid particles Pinocytosis – engulfing liquids, solutions Receptor-mediated endocytosis – moving

into the cell by first binding with receptor molecules on the cell’s surface.

http://www.youtube.com/watch?v=4gLtk8Yc1Zc http://academic.brooklyn.cuny.edu/biology/bio4fv/page/rectpr.htm

Exocytosis – the process by which the cell releases large molecules through its cell membrane