CELL MEMBRANE

Hi students:

The following week we will be working on a really nice organelle. The cell membrane.

First of all, print the worksheet clicking in the following link.

WORKSHEET ON BUBBLES MEMBRANES

I need that you read the following information about cell membrane. and take some notes in you notebook as a summery to get extra points.

The cell membrane (plasma membrane) is a thin semi-permeable membrane that surrounds the cytoplasm of a cell. Its function is to protect the integrity of the interior of the cell by allowing certain substances into the cell, while keeping other substances out. It also serves as a base of attachment for the cytoskeleton in some organisms and the cell wall in others. Thus the cell membrane also serves to help support the cell and help maintain its shape. Another function of the membrane is to regulate cell growth through the balance of endocytosis and exocytosis. In endocytosis, lipids and proteins are removed from the cell membrane as substances are internalized. In exocytosis, vesicles containing lipids and proteins fuse with the cell membrane increasing cell size. Animal cells, plant cells, prokaryotic cells, and fungal cells have plasma membranes. Internal organelles are also encased by membranes.

Cell Membrane Structure

The cell membrane is primarily composed of a mix of proteins and lipids. Depending on the membrane’s location and role in the body, lipids can make up anywhere from 20 to 80 percent of the membrane, with the remainder being proteins. While lipids help to give membranes their flexibility, proteins monitor and maintain the cell's chemical climate and assist in the transfer of molecules across the membrane.

Cell Membrane Lipids

Phospholipids are a major component of cell membranes. Phospholipids form a lipid bilayer in which their hydrophilic (attracted to water) head areas spontaneously arrange to face the aqueous cytosol and the extracellular fluid, while their hydrophobic (repelled by water) tail areas face away from the cytosol and extracellular fluid. The lipid bilayer is semi-permeable, allowing only certain molecules to diffuse across the membrane.

Cholesterol is another lipid component of animal cell membranes. Cholesterol molecules are selectively dispersed between membrane phospholipids. This helps to keep cell membranes from becoming stiff by preventing phospholipids from being too closely packed together. Cholesterol is not found in the membranes of plant cells.

Glycolipids are located on cell membrane surfaces and have a carbohydrate sugar chain attached to them. They help the cell to recognize other cells of the body.

Cell Membrane Proteins

The cell membrane contains two types of associated proteins. Peripheral membrane proteins are exterior to and connected to the membrane by interactions with other proteins. Integral membrane proteins are inserted into the membrane and most pass through the membrane. Portions of these transmembrane proteins are exposed on both sides of the membrane. Cell membrane proteins have a number of different functions. 

Structural proteins help to give the cell support and shape.

Cell membrane receptor proteins help cells communicate with their external environment through the use of hormones, neurotransmitters, and other signaling molecules.

Transport proteins, such as globular proteins, transport molecules across cell membranes through facilitated diffusion. 

Glycoproteins have a carbohydrate chain attached to them. They are embedded in the cell membrane and help in cell to cell communications and molecule transport across the membrane.

OBSERVE AND IF YOU CAN PRINT THE FOLLOWING IMAGE.

Cell Membranes

The picture above (click image to enlarge) shows a small section of the animal cell membrane or cell 'skin' 

(though the membranes of most cells of other organisms are similar). Above the membrane is outside the cell and 

below the membrane is inside the cell.

A - phospholipid molecule

  A1 - hydrophilic phosphate head group of phospholipid

  A2 - Fatty acid tail (x 2) of phospholipid

B - glycolipid (a phospholipid with a carbohydrate chain attached to it)

C - glycoprotein (a protein with a carbohydrate chain attached to it)

  D - carbohydrate chain of glycoprotein

E - cholesterol

F - protein

G - a protein channel (pore)

Finally, this is the video we will use in the class to observe the parts and functions of cell membrane.

See you at class!!!!