SHSU Spring 2013
BIO 2440
Essential Cell Biology 3e, (Alberts, et al)
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| 686289313 | plasma membrane | Fatty film so thin and transparent that it cannot be seen directly in the light of the light microscope. Structure is based on a two-ply sheet of lipid molecules about 5 nm - or 50 atoms - thick. Is penetrated by highly selective channels and pumps - protein molecules that allow specific substances to be imported and others to be exported. Is also involved in cell communication as well as cell growth and motility. | |
| 686289314 | internal membranes | In eucaryotic cells, additional membranes that enclose intracellular compartments to form the various individual organelles, including the endoplasmic reticulum, Golgi apparatus, and mitochondria. Prevents molecules on one side from mixing with molecules on the other. Subtle differences in the composition of these membranes, especially in their resident proteins, gives each organelle its distinctive character. | |
| 686289315 | cell membranes | Regardless of their location, all are composed of lipids and proteins and share a common general structure: the lipids are arranged in two closely apposed sheets, forming a lipid bilayer. (Refers to both plasma and internal membranes.) | |
| 686289316 | lipid | Molecule that combines two very different properties: a hydrophilic ("water-loving") head and one or two hydrophobic ("water-fearing") hydrocarbon tails. | |
| 686289317 | phospholipid | Most abundant lipids in a cell. | |
| 686289318 | phosphotidylcholine | Most common type of phospholipid in most cell membranes which has five parts: the small molecule choline attached to a phosphate as its hydrophilic head which is linked to a glycerol, which in turn is linked to two long hydrocarbon chains that form its hydrophobic tails.The two hydrocarbon tails originate as fatty acids - that is, hydrocarbon chains with a -COOH group at one end - which become attached to glycerol via their -COOH groups. A kink in one of the hydrocarbon chains occurs where there is a double bond between two carbon atoms. | |
| 686289319 | sterols | Amphipathic molecules (such as cholesterol found in animal cell membranes). | |
| 686289320 | glycolipids | Amphipathic molecules which have sugars as part of their hydrophilic head. It is a carbohydrate attached to a phospholipid. Located mainly in the plasma membrane and found only in the noncytosolic half of the bilayer - which ensures that they will be on the exterior of the cell when vesicle fuses with the plasma membrane. | |
| 686289321 | hydrophilic molecules | Dissolve readily in water because they contain charged atoms or polar groups, that is, chemical groups with an uneven distribution of positive and negative charges; these charged atoms can form electrostatic attractions or hydrogen bonds with water molecules, which are themselves polar. | |
| 686289322 | hydrophobic molecules | Insoluable in water because all - or almost all - of their atoms are uncharged and nonpolar; they therefore cannot form favorable interactions with water molecules. Instead, these nonpolar atoms force adjacent water molecules to reorganize into a cagelike structure around the hydrophobic molecule. | |
| 688618332 | properties that affect fluidity of membranes | 1. length of hydrophobic tails 2. level of undaturation; the number of double bonds in fatty acids 3. presence of sterols/steroids | |
| 688618333 | hydrophobic tails | Do not like water because they are uncharged and nonpolar, they cannot form bonds with water | |
| 688618334 | hydrophilic heads | Like water because they contain charged atoms or polar groups that can form electrostatic bonds or hydrogen bonds with water | |
| 688618335 | amphipathic | Have both hydrophilic and hydrophobic properties | |
| 688618336 | phospholipids | Provide basic structure and serve as a permeability barrier. What a cell makes in higher temps to reduce fluidity because it has more carbons and more saturation. | |
| 688618337 | proteins | Provide most of the other functions of the membrane and give different membranes their individual characteristics | |
| 688618338 | all membranes | Have similar structure. | |
| 688618339 | Davson and Danielli model | In 1935 took all of the available information and said this is what we think membrane structures are made of: phospholipids that form a bilayer sandwiched between an outer layer of proteins. | |
| 688618340 | Singer and Nicholson | In 1972 came up with the Fluid Mosaic model (fluid like salad dressing): phospholipid bilayer that has proteins with very stable structures inserted in it. | |
| 688618341 | properties that affect permeability | 1. Length of hydrophobic tails 2. Level of unsaturation or the number of double bonds in fatty acids. | |
| 688618342 | Shorter fatty acids | Reduce the tendency of the tails to interact with one another -> increase fluidity, increase permeability (usually have 18-20 carbons, range is 14-24) | |
| 688618343 | decreased temperatures | Results in a less fluid bilayer (think cold butter) | |
| 688618344 | increased temperatures | Results in a more fluid bilayer (think hot butter) | |
| 688618346 | several double bonds | Results in bilayers are more fluid than those with more saturation, increased permeability. | |
| 688618347 | bacterial cells | Are procaryotic. | |
| 688618348 | yeast cells | Are a fungus that are eucaryotic | |
| 688618349 | bacterial and yeast cells | Will have to adapt to varying temperatures and constantly adjusting the length of the fatty acids and their saturation to maintain membrane at constant fluidity (i.e. add carbons to make it longer, removing carbons to make shorter, or introducing or removing double bonds.) | |
| 688618350 | presence of sterols | In animal cells: fluidity can be regulated with the inclusion of cholesterol. | |
| 688618351 | cholesterol | Fills space between fatty acid tails which are saturated and those which are unsaturated, making it more rigid and less permeable | |
| 688618352 | asymmetry | Describes the structure of a phospholipid bilayer because both saturated and unsaturated phospholipids are present. Is established when the membrane is synthesized. | |
| 688618353 | cytosolic side of ER | Where enzymes for membrane synthesis are located. | |
| 688618354 | membrane synthesis | Occurs especially when a cell has just divided or is dividing. | |
| 688618355 | vesicles | In eukaryotic cells allow membranes to move from one part of the cell to another. Because they pinch off and fuse with other parts of cell, the membrane has a distinct "inside" and "outside" face. | |
| 688618356 | cytosolic face | Is always adjacent to the cytosol. | |
| 688618357 | noncytosolic face | Is exposed to either the cell exterior or the interior space of an organelle. | |
| 688618358 | golgi | Where enzymes which add the carbohydrates to the lipid are located. | |
| 688618359 | integral membrane proteins | Directly attach to membranes, need to disrupt the phospholipid bilayer to extract these proteins. | |
| 688618360 | peripheral membrane proteins | Not directly attached to membranes and the phospholipid bilayer does not need to disrupted to extract. May be bound to an integral membrane protein by an ionic, hydrophobic, or hydrogen bond. | |
| 688618361 | cell cortex | Framework of proteins attached to the membrane with transmembrane proteins to provide support by reinforcing the extremely thin and fragile plasma membrane. This protein framework is important for the cell to have proper shape. | |
| 688997852 | functional classes of membrane proteins | 1. TRANSPORTERS - transport particular nutrients, metabolites, and ions across the lipid bilayer 2. ANCHORS - some anchor the membrane to macromolecules such as microtubules, microfilaments, or members of the cytoskeleton on either side 3. RECEPTORS - detect chemical signals in the cell's environment and relay them to the cell interior 4. ENZYMES - catalyze specific reactions | |
| 688997853 | types of associations between membrane proteins and the lipid bilayer | 1. TRANSMEMBRANE - extend across the bilayer as a single α helices, or as a rolled-up β sheet (called a β barrel). 2. MONOLAYER-ASSOCIATED - Anchored to cytosolic surface by an amphipathic alpha helix. 3. LIPID-LINKED - peripheral proteins that have a strong, covalent attachment to a phospholipid. 4. PROTEIN-ATTACHED - peripheral proteins that have a weak, noncovalent interactions (ionic, hydrophobic, or hydrogen bonded) with other transmembrane proteins. | |
| 688997854 | alpha helix | Most common part of protein to span the membrane. Its hydrophobic amino acid side chains don't like water and stay in contact with the hydrophobic hydrocarbon tails of the phospholipid molecules, while the hydrophilic parts of the polypeptide backbone form hydrogen bonds with one another on the interior of the helix. An α helix containing approximately 20 amino acids are required to transverse the membrane. | |
| 688997855 | transmembrane hydrophilic pore | Can be formed by multiple α helices. The hydrophobic amino acid side chains on one side of each helix contact the hydrophobic hydrocarbon tails, while the hydrophilic side chains on the opposite side of the helices forma water-filled pore. | |
| 688997856 | porin proteins | Transmembrane proteins that form water-filled channels in the outer membrane of a bacterium. It is a β pleated sheet spanning the membrane, curved into a cylinder. | |
| 688997857 | detergent molecules | Used to extract membrane proteins. They have both a hydrophobic tail and hydrophilic head and can dissolve membranes. It disrupts the lipid bilayer and brings the proteins into solution as protein -detergent complexes. The phospholipids in the membrane are also solubilized by them. (Ex: laundry and dish soaps.) | |
| 688997858 | micelles | Small clusters, as opposed to a bilayer, of detergent molecules that are shaped like cones which have a hydrophilic head and a single hydrophobic tail. | |
| 688997859 | spectrin | A long, think, flexible rod about 100 nm in length. It forms a meshwork that provides support for the plasma membrane and maintains the cell's shape. The meshwork is connected to the membrane through intracellular attachment proteins that link it to specific transmembrane proteins. Found in human red blood cells. | |
| 688997860 | oligosaccharides | Short chains of sugars linked to proteins called glycoproteins in the plasma membrane. (Approx. 12 monomers, maybe 15-20 at most, but not usually more.) | |
| 688997861 | proteoglycans | Plasma membrane proteins that have one or more long polysaccharide chains attached to them. | |
| 688997862 | glycoproteins | Plasma membrane proteins that have short chains of sugars, called oligosaccharides, liked to them. | |
| 688997863 | carbohydrate layer (composition) | It is a sugar coating formed by all of the carbohydrate on the glycoproteins, proteoglycans, and glycolipids and is located on on the external, noncytosolic, side of the membrane. (Made of the oligosaccharide side chains attached to the membrane glycolipids and glycoproteins, and of the polysaccharide chains on membrane proteoglycans.) | |
| 688997864 | carbohydrate layer (function) | 1. Helps to protect the cell from mechanical and chemical damage. 2. Allows cell to have a slimy surface which allows it to squeeze through narrow spaces, involved in cell lubrication. 3. Is important in cell-cell recognition and adhesion. 4. Often described as sticky oligosaccharides because it helps keep cells in contact with each other. | |
| 688997865 | ways of restriction of lateral mobility of plasma membrane proteins | 1. Proteins can be tethered to the cell cortex inside the cell. 2. Proteins can be tethered to the extracellular matrix molecules outside the cell. 3. Proteins can be tethered to proteins on the surface of another cell. 4. Diffusion barriers can restrict proteins to a particular membrane domain. |
