Week 2 Review Sheet answers

Week 2 Review Sheet answers - Final Review Sheet Week 2...

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Final Review Sheet – Week 2 Lecture 4 - 1/14/08 Main Points Lipids: fats, phospholipids, steroids not polymers. Primary characteristic is high number of nonpolar groups, therefore, not water soluble. Parts of a fat Saturated vs. unsaturated bonds. With saturated bonds, there is free rotation about the bond, with unsaturations there is not. Therefore, when unsaturated bonds are present, it puts kinks in the chain. This has important consequences for melting point. Cis isomers are naturally occurring, trans created during partial hydrogenation processes. It is the trans forms which stimulate production of LDL. Soaps are amphipathic . Form micelles in water. Phospholipids – some similarities to fats, some to soaps (What are they?) Cholesterol – different transport mechanisms are LDL, HDL. Why are these particles necessary for cholesterol transport? Proteins: structure of amino acid, sterioisomers, formation of a dipeptide. You will be expected to draw a dipeptide. Primary structure: what it is, what kinds of bonds stabilize? Sample Questions: 1. Compare the structures of a triglyceride and a phospholipids, noting similarities and differences. Similarities: Both have a gycerol backbone, both have esterified fatty acids linked to the glycerol. Differences: The triglyceride has three fatty acid chains, all of which are nonpolar. Therefore, these molecules are entirely non-polar and insoluble in water. Phospholipids have two fatty acids and at the third position a charged (polar) group. Thus, they are amphipathic. They can form micelles or bilayers in water as the polar groups interact with the water while the non- polar groups interact with each other. 2. What is the effect of a cis double bond on the melting point of a fat? Why? What about the effect of a trans bond? Why the difference? A cis double bond lowers the melting point because the “kink” it puts in the chain as a result of the fact that there is no rotation about the double bond means that it is harder for the fatty acid tails to line up and form a solid. A trans bond puts much less of a kink in the chain and doesn’t really reduce the melting point. It stays more or less like the melting point of a saturated fatty acid.
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Final Review Sheet – Week 2 3. What is the difference between HDL and LDL in terms of their composition? HDL is smaller and contains a higher ratio of protein to lipid. Which is the one that causes plaques? LDL 4 What does amphipathic mean? Name a molecule besides soap that is amphipathic. Amphipathic means that a molecule has a polar end and a nonpolar end. An example is the phospholipids as described above. 3. Draw the structure of a dipeptide at pH 7, circling the peptide bond. 6.
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Week 2 Review Sheet answers - Final Review Sheet Week 2...

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