Cell Membrane & Function

The Plasma Membrane The Plasma Membrane is the boundary that separates the inside of the cell, from its’ watery external environment. It regulates what enters and exits the cell. The cell membrane is selectively permeable allowing only certain molecules to move through the membrane. This ability facilitates the transport of materials needed for cell survival.

The Plasma Membrane’s main goal is to maintain Homeostasis The cell is a place of constant activity even when you are sleeping. Chemical reactions are taking place, and materials are moving in and out of the cell. Because of all of this activity, the membrane works hard to maintain a stable internal environment in spite of external change. (Body temperature, oxygen and water levels, etc.)

In general, small cells work more efficiently than larger cells in moving materials in and out of the cell. If homeostasis is not maintained, the cell/organism may become sick or die.

Fluid Mosaic Model The Membranes are “Fluid Mosaics” ◦Proteins Move Within Layers of Lipids. Phospholipids are “grout” & membrane proteins, are the “tiles”.

The Bilayer Plasma Membrane is made up of a double layer of phospholipids, proteins, and cholesterol

Bilayer of Phospholipids The tails point in toward each other, and the heads point toward the outside, or inside of the cell. The phosphate head of the phospholipid is polar making it hydrophilic. The fatty acid tails of the phospholipid is nonpolar making it hydrophobic.

Phospholipids have: “phosphate head” (polar) and two “fatty acid tails” (nonpolar) Double bonds in the tail increase fluidity of membrane

Cholesterol Cholesterol is found between phospholipids, stabilizing the membrane and keeping it fluid.

Types of Proteins Integral Proteins (Intrinsic) Transport proteins ◦receptor proteins ◦recognition proteins ◦Glycoprotein- have a carbohydrate group attached. Peripheral proteins (Extrinsic) - attached to the cytoskeleton

This is a Foldable * Use 4 sheets of paper. It should look like this.. ( Next slide )

How to make a flip book.. LAYERED-LOOK BOOK Collect 4 sheets of paper and layer them about 1.5 cm apart vertically. Keep the edges even. Fold up the bottom edges of the paper to form 8 equal tabs. Fold the papers and crease well to hold the tabs in place. Staple along the fold. Label each tab.

Tabs for Foldable Title= Plasma membrane Functions of Cell membrane Fluid mosaic model ◦Phospolipid ◦Bilayer ◦Layer structure ◦Membrane structure ◦Proteins

Plasma Membrane Membrane function is dependent on membrane structure.

Biomolecules in the Plasma Membrane Label the components of the membrane in your foldable under: “Plasma/Cell Membrane Structure”

Make sure to include: ◦Phospholipids ◦Cholesterol ◦ makes the bilayer stronger. ◦more flexible, less fluid, and less permeable to water-soluble substances. ◦Proteins ◦Integral (Intrinsic) Proteins ◦Peripheral (Extrinsic) Proteins

Read and study picture

Glue the Phospholipid molecule on the flap of the “Phospholipid Bilayer” section.

Phospholipids Phospholipids have a phosphate head and two fatty acid tail. The phosphate head is hydrophilic (polar) The fatty acid tail is hydrophobic (nonpolar) Phospholipids can move from side to side.

Functions of the Plasma Membrane

3 Major General Functions. 1.Isolates internal environment (cytoplasm) from external environment. 2.Determines what enters and leaves the cell 3.Communicates with other cells.

The Plasma Membrane The membranes are selectively permeable - only certain substances can pass through.(H 2 O, CO 2, O 2 ) It is made up of a double layer of phospholipids, proteins, and cholesterol. Proteins regulate the movement of substances across the membrane communicate with the environment

Look at What Happens!!- (You don’t write this down) Phospholipid bilayer selectively isolates internal environment from external environment Most biological molecules are hydrophilic and cannot easily pass through the membrane Some very small molecules or uncharged, lipid-soluble molecules can freely pass through membrane

Concentration Gradient If you go with the concentration gradient you don’t need ATP (energy) If you go against the concentration gradient you need ATP

Let’s Review !!