Introductory Biochemistry

Introductory Biochemistry Biological Membranes Fatty Acids, Triacylglycerols and Membrane Lipids Lipids are hydrophobic in nature 1. Fatty acids 2. Triacylglycerols Membrane lipids  glycerophospholipids  sphingolipids  cholesterol 3. Cholesterol The Structure of Fatty Acids monounsaturated saturated polyunsaturated Saturated Cis -unsaturated trans -unsaturated most naturally occurring double bonds are in the cis conformation Fatty acids are long-chain hydrocarbon carboxylic acids     3  3 Cis double-bond trans double-bond 6 5 4 3 2 1 Fatty Acids  Short/long chain hydrocarbon carboxylic acids.  Up to 24 carbons long (16 & 18 most common).  General formula CH 3 (CH 2 ) N COO -  “Amphipathic.” (“ Amphiphilic ”)  Polar and non-polar portions  May be saturated or unsaturated.  Saturated: No double bonds  Unsaturated: Double bonds  Mono- or polyunsaturated (one or more double bonds)  Usually “cis” ( Z ) double bonds Fatty Acid Nomenclature Worksheet Instructions: Fill in the blanks giving either the simple name or chemical formula. Symbol Draw the Structure Chemical Formula 12:0 CH 3 (CH 2 ) 12 COOH 16:0 CH 3 (CH 2 ) 16 COOH 20:2  9,11 22:0 CH 3 (CH 2 ) 22 COOH CH 3 (CH 2 ) 5 CH=CH(CH 2 ) 7 COOH 18:1  9 18:1  12 CH 3 (CH 2 ) 5 CH=CHCH=CH(CH 2 ) 3 COO - Cis Double-Bonds Alter the Shape of Fatty Acids Unsaturated Fatty Acids Cannot Pack Together Effectively  The two saturated fatty acids in the membrane lipid on the left are able to align closely, maximizing van der Waal’s interactions between them.  In contrast, the lipid on the right contains one saturated and one unsaturated fatty acid. These two groups cannot pack closely together because of the bend in the unsaturated hydrocarbon chain. Fatty Acid Melting Points  Affected by length and unsaturation  Length  Longer fatty acids melt at higher temperatures  Shorter fatty acids melt at lower temperatures  Unsaturation  Saturated fatty acids melt at higher temperatures  Unsaturated fatty acids melt at lower temperatures Melting temperature reflects the amount of energy required to separate individual molecules in the solid from one another.  Fatty acids are stored as fat (triacylglycerols, TAGS). TAG’s are NOT amphipathic Mixed TAGs most common Simple TAG- 3 identical fatty acids There are several distinct classes of membrane lipids  Glycerophospholipids  Sphingolipids  very large polar head group  Cholesterol polar head group hydrophobic tails

BIOCH | 200 | Introductory Biochemistry | lecture notes | Introductory Biochemistry Biol

10 31. Why is BPG essential for the delivery of O 2 to the tissues? A. BPG enables hemoglobin to bind O 2 . B. BPG enables hemoglobin to adopt the R state conformation. C. BPG enables hemoglobin to stabilize the R state conformation. D. BPG enables hemoglobin to adopt the T state conformation. E. B and C. 32. Which of the following statements is false? A. In fetal hemoglobin the central cavity is lined with less histidines than in adult hemoglobin, which results in preferential stabilization of the T-state. B. Fetal hemoglobin has a weaker affinity for BPG than maternal hemoglobin, resulting in a shift of the oxygen-binding curve to the left. C. As [H + ] decreases, the O 2 binding curve of hemoglobin shifts to the right, because a greater proportion of hemoglobin molecules exist in the T-state at a given ppO 2 . D. Actively respiring tissues have a relatively low pH and low ppO 2 , which favors the T-state of hemoglobin. E. A and B are both false 33. Which of the following methods of altering enzyme activity can be reversed? A. Enzyme denaturation. B. Binding of allosteric effectors to enzymes. C. Phosphorylation of enzymes. D. B and C E. All of the above. 34. Which one of the following statements regarding enzymes is/are TRUE? A. The substrate binding site of an enzyme contains residues without sidechains. B. Enzymes make the free-energy change for a reaction more favorable. C. Enzymes ensure that the transition state is preferentially stabilized compared to the substrate. D. B and C are true. E. All of the above statements are true. 11 35. A solution of a fatty acid (16:2) has an overall neutral charge at pH 3.5. This means: A. The pKa of the fatty acid is < 3.5. B. The pKa of the fatty acid is > 3.5. C. The pKa of the fatty acid is 3.5. D. The pKa may be any of the above choices. 36. In humans, the fatty acid composition of membrane lipids in skin cells is different from the fatty acid composition of membrane lipids in the internal organs, because the internal organs function at a slightly higher temperature. Which of the following differences in fatty acid composition is most likely to be observed? A. Skin cells show lower levels of 20:0 relative to 18:0 AND lower levels of 18:2 relative to 18:0. B. Skin cells show higher levels of 18:2 relative to 18:0 AND lower levels of 20:0 relative to 18:0. C. Skin cells show lower levels of 18:2 relative to 18:0 AND higher levels of 20:0 relative to 18:0. D. Skin cells show higher levels of 20:0 relative to 18:0 AND higher levels of 18:2 relative to 18:0. 37. If the molecule shown above is placed in an aqueous solution, the pH of that solution will A. Increase B. Decrease C. Stay the same

BIOCH | 200 | Introductory Biochemistry | exam | 10 31. Why is BPG essential fo

9._Glycolysis-eClass.pdf-Introductory Biochemistry Glucose Metabolism Glucose and

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BIOCH | 200 | Introductory Biochemistry | study guides | l_ /  7.d et 1 1h~fy 1-!Ae..~~

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