1. MA Biology 2.1 Structure and function of cell membranes – makeup of a cell membrane and its role as a highly selective barrier CELL MEMBRANES

2. *two page notebook format* Do Now: 1) What are the jobs performed by the cell membrane? 2) Think about security workers at a concert or sporting event. What do they need to do, to keep the crowd safe and under control? Tuesday, Sept 29, 2015 Topic: Cell Membranes Objectives: Describe what a cell membrane is made of Explain the membrane’s role as a highly selective barrier Make and analyze a model of a cell membrane Page 24Page 25

3. Phospholipid phospholipid

4. Cell membranes are composed to two phospholipid layers A phospholipid has 3 basic parts: 1) a charged phosphate group water and electricity DO mix! The charge makes this hydrophilic or water loving! 2) glycerol 3) two fatty acid chains water and oil DO NOT mix! The fats make this hydrophobic or water fearing!

5. Figure 3.1, page 78 Sketch and label the illustration of the Cell Membrane found on page 78. Include: Proteins Carbohydrate chain Cholesterol Protein channel Cytoskeleton proteins Phospholipids

6. Quick Lab – Modeling the Cell Membrane Complete the Quick Lab as listed on the top of page 79. Problem: How does the cell membrane regulate what moves into and out of the cells? Analyze and Conclude (left side of notebook) 1) Explain: How do the swabs represent the polar and nonpolar characteristics of the cell membrane? 2) Apply: In this model, the swabs and proteins can be moved around. Explain whether this is an accurate representation of a real cell membrane. Homework: How could you improve this model to make it more realistic?

7. Selective Permeability A semipermeable or selectively permeable membrane allows some, but not all, molecules to cross. The cell maintains control over the concentration of most substances inside and outside the cell. Size, polarity, and the concentration gradient influence how well molecules cross the cell membrane.

8. Chemical signals are transmitted across the cell membrane by RECEPTORS Intracellular Receptors are located inside the cell. When the correct ligand binds to the receptor, it signals the cell to do something. Membrane Receptors allow molecules that are too large to enter the cell to send signals to the inside of the cell. When the ligand binds to the membrane receptor, the entire receptor protein changes shape, even on the inside of the membrane, to transmit the signal.

9. 3.3 Formative Assessment page 80 1) Why do phospholipids form a double layer? 2) Explain how membrane receptors transmit messages across the cell membrane. 3) Compare: Describe the similarities between enzymes and receptors. 4) Infer: If proteins were rigid, why would they make poor receptors? 5) Insulin helps cells take up sugar from the blood. Explain the effect on blood sugar levels if insulin receptors stopped working. Homework: How could you improve the cell membrane model to make it more realistic?