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Biology 2051 Quiz 5~.docx - LEARNING OUTCOMES Chapter 5...

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LEARNING OUTCOMES Chapter 5 Sections 5.1, 5.2, 5.3, 5.4 Describe the Fluid Mosaic Model by articulating how cellular membranes resemble a fluid and a mosaic. Fluid Mosaic Model – the accepted model of the plasma membrane a. Basic framework is the semifluid phospholipid bilayer with a mosaic of proteins b. Carbohydrates may be attached to the lipids of proteins c. Membrane exhibits properties that resemble a fluid because lipids and proteins can move relative to each other within the membrane d. Half of a phospholipid bilayer is termed a leaflet that faces a different region e. Best described: phospholipids, carbohydrates, proteins, semi-fluidity Biological membranes also contain proteins, and most membranes have carbohydrates attached to lipids and proteins a. The membrane is considered a mosaic of lipid, protein, and carbohydrate molecules Describe the polarity of a phospholipid. Are they polar, non-polar, or both (amphipathic)? Are they hydrophilic, hydrophobic, or both? Phospholipids are amphipathic a. Polar(hydrophilic) head b. Nonpolar (Hydrophobic) tail i. Composed of a string of carbons and hydrogens ii. One of the chains has a kink because of its double bond 1. Double bonds make tail more fluid because lipid is said to be unsaturated Insoluble in water Draw the way in which phospholipids are oriented in a phospholipid bilayer membrane. Phospholipids organize themselves in a bilayer to hide their hydrophobic tail regions and expose the hydrophilic regions to water Organization is spontaneous (natural process and does not require energy)
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Explain why phospholipids can move laterally in the membrane but require assistance in flipping from one leaflet to the other. Phospholipids can rotate freely around their long axes and move laterally within the membrane leaflet a. 2D type of movement because it occurs within the plane of the membrane b. Rotational and lateral movements keep the nonpolar tails within the hydrophobic interior, such movements are energetically favorable The Flip-flop of lipids from one leaflet to the opposite leaflet does not occur spontaneously a. Energetically unfavorable because the polar head of a phospholipid has to travel through the hydrophobic interior of the membrane b. Transport of lipids from one leaflet to the other requires action of enzyme flippase, which requires energy input in the form of ATP c. Lipid Raft – in a membrane, a group of lipids and proteins that float together as a unit in a larger sea of lipids i. Have high amount of cholesterol Describe what factors affect membrane fluidity and how cellular membranes react to changes in these factors. Biochemical properties of phospholipids affect the fluidity of the phospholipid bilayer a. Length of nonpolar tails : shorter tails are less likely to interact with each other which makes the membrane more fluid b. Presence of double bonds : double bonds make a membrane more fluid i. When a double bond is present, the lipid is said to be unsaturated with respect to the number of hydrogens that are bound to carbon atoms
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