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Cell Membrane Structure and Function - revision questions and answers.

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Introduction

Chapter 4 - Membrane Structure and Function 4.1 Plasma Membrane Structure and Function What is the main function of the plasma membrane? The plasma membrane separates the internal environment of the cell from the external and regulates the entrance and exit of molecules of it. What are the main structural components of the plasma membrane and how does each function? The plasma membrane is made up of glycolipids and glycoproteins (which are phospholipids and proteins with attached carbohydrate sugar chains). The proteins allow substances to move across the membrane (channel proteins), combine with substances to help it move across a membrane (carrier proteins), allow molecules to bind to it so that its shape changes and triggers a cellular response (receptor protein), and enzymatic proteins which catalyze a specific reaction. 4.2 The Permeability of the Plasma Membrane Can substances freely pass across the plasma membrane? If so, what types? Yes they can, but usually its passage requires some sort of transport (either through diffusion, facilitated transport, active transport, exocytosis, or endocytosis). Small noncharged molecules like carbon dioxide, oxygen, glycerol, water, and alcohol can diffuse across the membrane freely, as they can slip between the hydrophilic heads of the phospholipids and pass through the hydrophobic tails of the membrane. What does it mean for a plasma membrane to be differentially permeable? Differentially permeable simply means that the membrane only allows certain substances to pass in and out of the membrane. ...read more.

Middle

Figure 4.8 Facilitated Transport What is facilitated transport? How is it different from active transport? Facilitated transport allows the passage of molecules such as glucose and animo acids across the plasma membrane (as they're not lipid soluble) through the use of carrier proteins. In facilitated transport the substances follow their concentration gradient, wheras in active transport substances are moved against it. Not only that, but active transport also requires a carrier protein and energy for it to occur. Figure 4.10 - The Sodium-potassium Pump What is the sodium-potassium pump? The sodium-potassium pump uses active transport to move sodium ions to the outside of a cell and potassium ions to the inside of a cell. The carrier protein that allows for these substances to be pumped is known as the sodium-potassium pump. Figure 4.12 - Three Methods of Endocytosis What are the three methods of endocytosis? The three methods of endocytosis are phagocytosis, pinocytosis, and receptor-mediated endocytosis. Testing Yourself 1. Label this diagram of the plasma membrane A. Glycolipid B. Glycoprotein C. Carbohydrate (sugar) Chain D. Hydrophilic Heads E. Hydrophobic Tails F. Phospholipid Bilayer G. Filaments of Cytoskeleton H. Peripheral Protein I. Cholesterol J. Integral Protein 2. The fluid-mosaic model of the membrane structure refers to B. The fluidity of phospholipids and the pattern of proteins in the membrane. 3. A phospholipid molecule has a head and two tails. ...read more.

Conclusion

2. What is the glycocalyx? The glycocalyx are the carbohydrate chains of cell recognition proteins that give the cell a 'sugar coat' that protects it, facilitates adhesion between cells, allows for the reception of signal molecules, and cell-to-cell recognition. 3. What is meant by "differentially permeable?" Differentially permeable means that some substances can move across the plasma membrane of a cell and some can't (it is selective). 4. How does passive transport differ from active transport? Passive transport doesn't use chemical energy, whereas active transport does (i.e. in the form of ATP). Passive transport involves diffusion and facilitated transport, whereas active transport involves exocytosis and endocytosis. 5. Why does oxygen diffuse from the lungs into the blood and not in the opposite direction? Oxygen diffuses from an area of greater concentration to an area of lesser concentration. It is assumed that oxygen concentration is greater in the lungs. 6. If a cell is placed into a hypotonic solution, in what direction will there be movement of water? Water will move into the cell from the surrounding solution. 7. What does it mean when membrane carrier proteins are "specific?" Membrane carrier proteins can each combine with only one type of molecule. 8. What is the sodium-potassium pump? The sodium-potassium pump is a carrier protein that uses energy to actively transport sodium ions to the outside of the cell and potassium ions to the inside. 9. Pinocytosis differs from phagocytosis in what way? Pinocytosis occurs when vesicles form around very small particles or liquids, while phagocytosis occurs when the cell takes in larger particles. ...read more.

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