Life’s Guardian… Cell Membranes …their Structure & Function

How do things enter and leave living cells? How does oxygen get into our cells? How does carbon dioxide and other waste products leave our cells? How do nutrients enter our cells? How do white blood cells engulf foreign invaders? Do cells drink and eat?

All living cells are surrounded by an extracellular fluid (ECF).

SMALL HYDROPHOBIC MOLECULES O 2, CO 2, N 2, benzene SMALL UNCHARGED POLAR MOLECULES LARGER UNCHARGED POLAR MOLECULES amino acids, glucose, nucleotides H 2 O, alcohols N +, Na +, HCO 3-, K +, Ca 2+, Cl -, Mg 2+ IONS Besides other organisms, there are many chemicals in the ECF.

Solutions where the water is the solvent such as the ECF and blood are called aqueous solutions. Solution solvent

Solution solvent A solution is a combination of a solvent with one or more solutes. solute If this solution was blood the solvent would be called plasma and the solute would be red and white blood cells.

An organism's chemical processes are carried out inside cells and/or it’s organelles. Biochemical reactions require raw materials from outside the cell and generate waste products inside that the cell must discharge back into its environment.

In order to do this and remain alive a cell must maintain CHEMICAL HOMEOSTASIS. Homeostasis is the maintenance of a steady state or balance within the cell or organism.

The PLASMA MEMBRANE plays a major role in the maintenance of homeostasis as it determines what enters and leaves the cell.

Life’s Hangout Plasma membrane Embedded Proteins Phospholipids

Life’s Hangout Phospholipids hydrophillic or water loving head hydrophobic or water fearing end Gk: phil – loving phob – fear ~75-95% of the cell’s plasma membrane

Life’s HangoutEmbedded Proteins Carrier proteins that regulate transport and diffusion Marker proteins that identify the cell to other cells And receptor proteins that allow the cell to receive instructions ~5-25% of the cell’s plasma membrane

Life’s Hangout Embedded Proteins Diffusion Embedded proteins provide the cell with a pore for the passive transport of solute particles. concentration gradient

Life’s Hangout Carrier proteins provide the cell with a means of active transport. Embedded Proteins facilitated diffusion concentration gradient

Life’s Hangout Embedded Proteins Symport carrier proteins provide the cell with a means of two-way diffusion. Sodium-Na+ Glucose Active Transport ATP concentration gradient

Life’s Hangout Marker proteins extend across the plasma membrane and serve to identify the cell. The immune system uses these proteins to tell friendly cells from foreign invaders. Embedded Proteins

Life’s Hangout Receptor proteins are used in intercellular communication. In this animation a hormone binds to the receptor. This causes the receptor protein to release a chemical signal to perform a specific action. Embedded Proteins

Life’s Hangout Embedded Proteins The passive transport of solvent molecules like water is called …. concentration gradient A B

Life’s HangoutReview Cells are essentially a selectively permeable sack of particles dissolved in water with larger complex structures suspended in the resulting solution. For this reason, it is important to know what a solution is before attempting to understand how cells respond to changes in their environments.

Simple Diffusion