Biochemistry Review

Lipids


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1. Lipids, defined by their solubility instead of their structure, are non-polar molecules and therefore tend to dissolve in fat soluble or organic solvents.

2. Most carbohydrates and proteins are hydrophilic ("water-loving") but lipids are characterized as hydrophobic or "water-fearing."

3. Provide an example of a lipid with the following biological roles:

a. energy storage: fats and oils
b. hormones: steriods
c. membrane structure: phospholipids
d. insulation: waxes, myelin sheath

4. All fats and oils are triglycerides --that is compounds made up of glycerol and three fatty acids.

5. Label the following molecular structures.

6. During the metabolic synthesis of a triglyceride three molecules of water are formed in the enzyme-mediated reaction.

7. Fatty acids occur most commonly in chains of 14, 16, 18, or 20 carbon atoms. The triglycerides with smaller fatty acid chains are liquids at room temperature. Larger chains are more likely to be fats (solids at room temperature).

8. Sodium and potassium salts of fatty acids are soluble in water and are known as soap or detergents.

9. A saturated fat is a triglyceride lacking double bonds.

10. Saturated fats tend to have higher melting points than unsaturated ones, that is they tend to remain solid at room temperature. As you might suspect this type of fat poses a health risk if it is deposited in your arteries and veins.

11. Unsaturated fatty acids are necessary in our diet because chemical processes in humans and other mammals cannot produce double bonds beyond the ninth carbon in a given fatty acid chain.

12. Compared to carbohydrates and proteins (4 kcal/gram) most lipids have nearly twice the energy content. Because oil is an ideal energy storage molecule plants often store it in their seeds.

13. Animals store body fat as an adaptation for lean times. Where is this fat commonly found?tJust below the skin and around some organs (like the kidneys).

14. Phospholipids are structurally similar to triglycerides. Two fatty acids are linked to a glycerol molecule but the third glycerol carbon is linked to a phosphate group.

15. Label the parts and bonds of the phospholipid below.

16. The phosphate group in a phospholipid is hydrophilic and the tail or fatty acid groups are hydrophobic.

17. The polar-nonpolar nature of phospholipids provides them with a detergent property because they can form a bridge between water and oil.

18. The ability of phospholipids to reduce the surface tension of water makes them a critical component in the lungs. They acts as wetting agents to promote the absorption of oxygen without the lungs collapsing under the force of surface tension.

19. What do waxes, steroids, lanolin, and cholesterol all have in common? All are lipids.