Period+2+ch+7


 * ​​AP Biology**
 * Chapter 7 Guided Reading Assignment**

1. What does selective permeability mean and why is that important to cells?

[[image:http://www.columbia.edu/cu/psychology/courses/1010/mangels/neuro/neurosignaling/AfterDiffusionSmall.gif]]
2. What is an amphipathic molecule? It is a phosphilipid that has both a hydrophobic region 3. What were the ideas concerning the plasma membrane models below: a. Gorter and Grendel -cell membrane must be made of phospholipid bilayer -layer could be a stable boundary between two aqueous compartments because the molecular arrangement shelters hydrophobic tails from water and exposes the hydrophilic heads Davson and Danielli -the difference in structure is that phospholipid bilayer between tow layers of protiens -Sandwich model: structure of plasma membrane and all internal membranes of all cells -this model had issues c. Singer and Nicolson - membrane protiens are dispersed individually inserted into phospholipid bilayer with hydophilic regions protruding far enough to be exposed to water -maximizes contact of hydrophilic with water and hydrophobic regions with nonaqueous solutions 4. Describe the freeze fracture technique and why is it useful in cell biology. -the freeze fracture technique is a method used for preparing cells for electron microscopy -splits a cell membrane along the middle of the phospholipid bilayer -when halves are viewed on the electron microscope, the interior bilayer appears cobblestoned with protiens interspersed in a smooth matrix as in the fluid mosaic model -demonstrates that proteins are imbedded in the phospholipid bilayer

5. How is the fluidity of cell membrane’s maintained?

The kinks in the hydrocarbon tails of the phospholipid bilayer and the cholesterol in animal cells maintain fluidity. 6. Label the diagram below – for each structure – briefly list it’s function:

Will add picture in class. Won't upload for some reason. Functions: **Fibers of extracellular matrix:** Attaches cells together and holds them in place. **Glycoprotein:** Bonded to glycolipids. **Glycolipid:** Used in cell-cell recognition. It tells other cells what kind of cell it is or specifically who the individual person is. **Cytoskeleton:** Helps keep the cell up **Cholesterol**: Reduces membrane fluidty but also helps the membrane not break at low temperatures. **Peripheral Protein:** Proteins that are loosely bound to the surface of the membrane. (See #7 for the types of proteins) **Integral protein**: Proteins that penetrate the hydrophobic area of the lipid bilayer.(See #7 for the types of proteins)

7. List the six broad functions of membrane proteins.

· ** Transport proteins: ** they allow substances to pass through the membrane that cannot pass through the phospholipid bilayer. They act as a selective channel across membranes. They change shape in order to shuttle substances across · ** Enzymatic activity: ** a protein built into the membrane may be an enzyme with tits active site exposed to substances in the adjacent solution. Enzymes can join as a team and carry out sequential steps of a metabolic pathway · ** Signal transduction: ** a membrane protein may have a binding site with a specific shape that fits the shape of a chemical messenger (i.e. a hormone). The external messenger may cause a conformational change in the protein that relays the message to the inside of the cell · ** Cell-cell recognition: ** they serve as identification tags that are specifically recognized by other cells · ** Intercellular joining: ** membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions · ** Attachment to the cytoskeleton and extracellular matrix (ECM): ** help maintain cell shape and stabilizes the location of certain membrane proteins.

8. How do glycolipids and glycoproteins help in cell to cell recognition? They are covalently bonded to carbohydrates. The fuse with the membrane and release secretory proteins from the cell. They are important because they provide energy and serve as markers. When the cells try to recognize each other, the glycolipids and glycoproteins serve as indicators.

9. Why is membrane sidedness an important concept in cell biology?

 It is important because the synthesis of membrane components is dependent on their orientation on the resulting membrane. For example, the plasma membrane has distinct cytoplasmic and extracellular sides, or faces, with the extracellular face arising from the sinside face of ER, Goldgi, and vesicle membranes.

10. How has our understanding of membrane permeability changed since the discovery of aquaporins? 11. What is diffusion and how does a concentration gradient relate to passive transport? **Diffusion is the tendency for molecules of any substance to spread out evenly into the available space. A concentration gradient (increase or decrease in the density of a chemical substance in an area) requires no energy. Because it is spontaneous and requires no energy, it's passive transport.** 12. Why is free water concentration the “driving” force in osmosis? **Water molecules need to be freely moving, not clustered around other molecules, in order to move across a membrane.**
 * Aquaporins are transport proteins in the plasma membrane that specifically facillitate the diffusion of water across the membrane. They allow water to travel through the hydrophobic center of the membrane because they are hydrophilic channels. **

Ariel, Tyler, Kyle, Anthony 13. Why is water balance different for cells that have walls as compared to cells without walls? A cell without walls is an an isotonic environment. This means there is no not movement of water across a membrane. Water flows across the membrane, however, it is in both directions at the same rate. A cell with a wall is turgid when healthy. This means that water acts on the cell to make it more firm.

14. Label the diagram below: A)Animal cells are best within an isotonic environment, unless it has adaptations to offset the osmotic uptake or loss of water. B)Plant cells are turgid and generally healthier in a hypotonic environment; where uptake of water is eventually balanced by an elastic wall. 15. What is the relationship between ion channels, gated channels and facilitated diffusion – write 1 -2 sentences using those terms correctly. Ion channels can act as gated channels which help facilitated diffusion occur. 16. How is ATP specifically used in active transport? ​ Active transport needs energy to work. The energy provided in this transport is provided by ATP. The ATP can power the active transport by transferring its terminal phosphate group directly to the transport protein, giving the passage energy to allow bigger substances to enter and leave the cell. 17. Define and contrast the following terms: membrane potential, electrochemical gradient, electrogenic pump and proton pump. Membrane Potential- charge difference between the cytoplasm and extracellular fluid becuase of the unequal distribution of anions and cations on opposite sides of membrane. Electrochemical Gradient- diffusion gradient of an ion; representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential. Electrogenic Pump- An ion transport protein that generates voltage across a membrane. Proton Pump- An active transport mechanism in cell membranes that uses ATP to force hydrogen ions out of a cell, generating a membrane potential in the process. Membrane potential is like a battery it is an energy source that affects the ttraffic of all charged substances across the membrane and the Electrochemical gradient is a combination of a chemical force and an electrical force. In an animal cell and a plant cell there is a different electrogenic pump, for example in an animal cell the major electrogenic pump is the sodium-potassium pum and in plant cell the major elecctrogenic pump is the proton pump. 18. What is cotransport and why is an advantage in living systems? Cotransport occurs when pump proteins in the membrane of a cell transport one substance across the membrane by active transport, and during their diffusion back across the membrane, carry something else with them, theu getting two active transports for the price of one. For example, when a plant cell ejects a hydrogen ion, that hydrogen atom is brought back in by another protein, this one not requiring energy. however, another chemical, in this case sucrose, attaches to the same rtransport molecule as the hydrogen ion, thus getting a free ride into the cell. A video showing cotransport: []

19. What is a ligand? A ligand is a substance that binds specifically to a receptor in a cell membrane, triggering an event. An in context example is LDL, a combination of lipids and proteins which act to carrry cholesterol in our bodies. when the LDL molecules come into contact with receptors on our cell membranes, the membrane engulfs the recptor and the LDL, as well as anything in the vicinity, in a process known as receptor mediated endocytosis. 20. Contrast the following terms: phagocytosis, pinocytosis and receptor-mediated endocytosis. Phagocytosis, or "cell eating" occurs when a cellular membrane rears out towards something, effectively food molecules, by extending pseudopodia, surrounding it, following which it absorbs the molecules in a vacuole. Pinocytosis or "cell drinking" is the opposite, when the cell divets in to capture droplets of extra cellular fluid, inorder to capture the fluids solute. Receptor-mediated endocytosis occurs when certain trigger moleculescome into contact with certain receptor protein in the cell membrane, triggering what is effectively pinocytosis