Term
| Describe the fluid-mosaic model of membrane structure as well as the models that preceded it. Cite evidence that either disprove or supports these models. |
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Definition
| Fluid-mosaic model proposes that the membrane is a fluid phospholipid bilayer in which protein moleculse are either partially or wholly embedded. This was proven through a freeze-fracture of the membrane and viewing under an electron micrograph. Other models include the sandwich model and the unit membrane model. |
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Term
| Tell how the phospholipids are arranged in the plasma membrane. What other lipids are present in the membrane and what function do they serve? |
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Definition
| The hydrophilic polar heads of the phospholipid molecule face the ouside and inside of the cell where water is found. The hydorphobic non-polar tails face each other. Cholesterol is another lipid found in animal plasma membrane that stiffens and strengthens the membrane and thereby helping to regulate it fluidity. |
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Term
| Describe how proteins are arranged in the plasma membrane. Describe an expirement indicating that proteins can literally drift in the membrane. |
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Definition
| Peripheral proteins are on the inside surface of the membrane held in place by cytoskeletal filaments. Integral proteins are embedded in the membrane but they can move back and forth. some integral proteins protrude from only one surface of the bi-layer, but most span the membrane with a hydorphilic and hydrophobic region. A mouse cell and a human cell were fused toghther, after 40 minutes both mouse and human proteins had diffused across the cell. |
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Term
| What are the various functions of proteins? |
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Definition
| Receptor protein, Enzymatic Protein, Carrier protein, Channel Protein, Cell Recognition Protein |
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Term
| Define diffusion. What substances can diffuse through a differentially permeable membrane. |
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Definition
| Diffusion is the movement of molecule from a higher concentration to a lower concentration--down their concentration gradient. Water, gases, and non-charged molecules can diffuse through a differentially permeable membrane. |
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Term
| Define Osmosis. Discribe verbally what happen to an animal cell with placen in isotonic, hypotonic, and hypertonic solutions. |
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Definition
| Osmosis is the diffusion of water across a differentially permable membrane due to concentration differences. An animal cell placed in a isotonic solution has neither a net gain or loss of water so nothing happens. An animal cell placed in a hypotinic solution will have a net gain of water and the cell may burst (lysis). An animal cell placed in a hypertonic solution will have a net loss of water and the cell shrivles (crenation). |
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Term
| Why do most substances have to be assisted through the plasma membrane? Contrast movement by facilitated transport with movement by active transport. |
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Definition
| Most substances must be assisted across the plasma membrane because the plasma membrane impedes all but a very few substances. In facilitated transport, no energy is required for the molecule to pass through the plasma membrane. They are simply following their concentration gradient. In active transport molecules move to a region of higher concentration, exactly the opposite of diffusion. |
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Term
| Explain how a sodium potassium (Na+) (K+) pump works. |
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Definition
| 1. Carrier protein has a shape that allows it to take up 3Na+ 2. ATP is split and phosphate group attaches to the carrier protein. 3. Change is shape results and causes carrier to release 3Na+ outside the cell. 4. Carrier protein now has a shape that allows it to take up 2K+. 5. Phosphate group is release from the carrier protein. 6. Change in shape results and causes carrier to release 2K+ inside the cell. Back to #1. |
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Term
| Describe and contrast three methods of endocytosis. |
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Definition
| Phagocytosis-- when large material such as food, or antother cell is taken by endocytosis. Pinocytosis -- occurs when vesicles form around a liquid or around a very small particle. Receptor-Mediated Endocytosis-- a form of pinocytosis that is quite specific because it uses a receptor protein shaped in such a way that a specific molecule can bind to it. |
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Term
| Give examples to show that cell surface modifications help plant and animal cells communicate. |
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Definition
| Adhesion junctions -- internal cytoplasmic plaques, firmly attached to the cytoskeleton within each cell are joined by intercellular filaments. The result is a sturdy, but flexible, sheet of cells such as the stomach, bladder and heart. Tight Junctions--plasma membrane proteins actually attached to each adjecent cell producing a zipper-like fastening Cells of tissues that serve as barriers are held together in tight junctions. (intestine, kidneys) Gap Junction--lends strength to the cells, but allows molecules and ions to pass between them. Gap junction are important in the heart. |
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Term
Electron micrograph following freeze-fracture of the plasma membrane indicate.
A. the membrane is a phospholipid bilayer
B. Some proteins span the membrane
C. Protein is found only on the surface
D. Glycolipids and Glycoproteins are antigenic |
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Definition
| B. some proteins span the membrane |
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Term
A phospholipid molecule has a head and two tails. The tails are found.
A. at the surface of the membrane
B. In the interior of the membrane
C. Spanning the membrane
D. Where the envrioment is hydrophilic
E. Both a and C |
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Definition
| B. in the interior of the membrane |
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Term
During diffusion:
A. Solvents move from the area of higher to lower concentration
B. Ther is a net movement of molecules from the area of higher to lower concetration.
C. A cell must be present for any movement of molecules to occur
D. molecules move |
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Definition
| There is a net movement of molecules from the area of higher to lower concentration. |
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Term
| When a cell is placed in a hypotonic solution: |
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Definition
| Water enters the cell toward the area of higher solute concentration |
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Term
| When a cell is placed in a hypertonic Solution |
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Definition
| Water exits the cell toward the area of higher solute concentration. |
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Term
Active transport
A. require a carrier protein
B. moves a molecule against its concentration gradient
C. requires chemical energy
D.Does not occur during facilitated transport.
E. All |
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Definition
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Term
The Sodium-Potassium Pump
A. helps establish an electrochemical gradient across the membrane
B. concentrate sodium on the outside of the membrane.
C. Utilizes a carrier protein and chemical energy
D. is present in teh plasma membrane
E. All |
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Definition
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Term
Receptor-mediated endocytosis
A. is no different from phagocytosis
B. brings specific solutes into the cell
C. helps concentrate proteins in vesicles
D. results in high osmotic pressure
E. All |
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Definition
| B bring specific solutes into the cell |
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Term
Plant Cells
A. always have a secondary cell wall, even though the primay one may disappear
B. have channels between cells that allow strands of cytoplasm to pass from cell to cell
C. develop turgor pressure when water enters the nucleus
D. do not have |
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Definition
| B. have channels between cells tha allow strands of cytoplasm to pass from cell to cell |
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Term
| The fluid-moasic model of membrane structure refers to |
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Definition
| Teh fluidity of phospholipies and the patter of proteins in the membrane. |
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Term
| The fluid-moasic model of membrane structure refers to |
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Definition
| The fluidity of phospholipids and the patter of proteins in the membrane. |
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Term
Which is not a function of proteins present in the membrane
A. assist the passage of material into the cell.
B. interact and recognize other cells
C. bind with specific hormones
D. carry out specific metabolic reactions
E. produce lipid molecules |
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Definition
| E. Produce lipid molecules |
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Term
The carbohydrate chain projection for the plasma membrane are involved in
A. adhesion between cells
B. Reception of molecules
C. Cell to cell recognition
D. All |
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Definition
| B. reception of molecules |
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Term
Plants wilt on a hot summer day because of a decrease in
A. turgor pressure
B. evaporation
C. condensation
D. diffusion |
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Definition
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Term
| _____Characteristic of the plasma membrane due to its ability to allow certain molecues, but not others to pass through. |
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Definition
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Term
| _____Diffusion of water throug the plasma membrane of cells |
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Definition
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Term
| ____higher solute concentration(less water)than the cytoplasm of a cell; causes cell to lose water by osmosis |
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Definition
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Term
| _____Protein in plasma membrane that bears a carbohydrate chain. |
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Definition
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Term
| _____Process by which a cell engulf a substance forming an intracellular vacuole |
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Definition
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