One molecule of glycerol joins three fatty acid molecules to make one fat, a triglyceride…
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One molecule of glycerol joins three fatty acid molecules to make one fat, a triglyceride. (a) How many ester bonds does one fat molecule have? (b) How many molecules of water are given off in making one fat molecule? (c) A cell makes fat molecules. How many molecules of water are given off? (d) What reaction does the enzyme lipase carry out on a fat, and what does it need?
Need a reminder? The key ideaShow
Joining two monomers removes a molecule of water. Peptide bond: amino acids, between the carboxyl group of one and the amino group of the next. Glycosidic bond: monosaccharides. Ester bond: glycerol and fatty acids; a triglyceride has three. Phosphodiester bond: nucleotides, a phosphate that makes two ester bonds, linking the 3' carbon and the 5' carbon of neighbouring sugars. A chain of n monomers has n minus 1 bonds. Hydrolysis breaks a bond by adding water, as in digestion.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Ester bonds. Three fatty acids join the glycerol, so one fat has ester bonds.
Step 2. Water for one fat. One water molecule is given off for each bond, so molecules.
Step 3. Water for fats. molecules.
Step 4. Lipase. Lipase carries out hydrolysis. It breaks the ester bonds, and it needs water.
Answer: (a) ; (b) molecules; (c) molecules; (d) hydrolysis, which needs water.
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