Cell Membrane WS

The Cell Membrane Insane in the membrane!!! PROTEIN The cell membrane regulates what enters and exits the cell. Let's look at the cell membrane and see how its' structure allows it to perform this important task. When you think about a membrane, imagine it is like a big plastic bag with some tiny holes. That bag holds all of the cell pieces and fluids inside the cell and keeps any nasty things outside the cell. The holes are there to let some things move in and out of the cell - this is called semi-permeable. The cell membrane is not one solid piece. Everything in life is made of smaller pieces and a membrane is no different. Three macromolecules combine to make cell membranes. Lipids called phospholipids make up most of the cell membrane. Proteins serve as channels, pumps or markers and make up another large portion of the cell membrane. Carbohydrates are also a part of the membrane so cells can recognize each other. Scientists describe this organization of the phospholipids and proteins as the fluid mosaic model. It is called fluid, because it moves. It is called a mosaic, because it has many macromolecules that combine to make it like mosaic tiles, Phospholipids are specialized lipids that are in a shape like a head with two tails. The heads love water (hydrophilic) and the tails fear water (hydrophobic). Since living things always have to have water inside and outside of the cell, the membrane is built in a manner that "hides" the hydrophobic tails. The tails bump up against each other and the heads are out facing the watery area surrounding the cell this double layer of phospholipids is called the lipid bi-layer! What about the proteins in the membrane? Scientists have shown that the proteins float in that bi-layer too. Some of them are found on the inside of the cell and some on the outside. Other proteins cross the bi-layer with one end outside of the cell and one end inside. Those proteins that cross the layer are very important in the active transport and facilitated diffusion of ions and small molecules. As you learn more about the organelles inside of the cell, you will find that most have a phospholipid membrane surrounding them. This is why many descriptions of eukaryote cells say they have membrane-bound organelles. Some organelles even have 2 membranes the mitochondria and the chloroplast both have double membranes surrounding them. Color the picture of the phospholipid bi-layer below and color the entire cell membrane on the following pages: Analysis Questions: 1. What is the job of the cell membrane? 2. Why is the cell membrane described as semi-permeable? 3. What are the 3 macromolecules that make up the cell membrane? 4. What is the primary roll of proteins in the cell membrane? What function do carbohydrates have in the cell membrane? 5. Why is the cell membrane described as the "fluid mosaic model"? 6. Why does the cell membrane have to form a lipid bi-layer? Why not a single layer? 7. What is meant by "membrane-bound" organelles? What types of cells have these? 8. Going Further: What is a polar molecule? What is a nonpolar molecule? How are these related to the structure of the cell membrane?