Carbohydrates: Starch

What polymers is starch made up of?

• Amylose

• Amylopectin

Give the monomer and the bonds in amylose

• alpha-glucose

• 1-4 glycosidic bonds

Give the monomer and the bonds in amylopectin

• alpha-glucose

• 1-4 and 1-6 glycosidic bonds

Describe the structure of amylose

• Compact helix with hydrogen bonds forming between glucose molecules along the chain

• Unbranched

Describe the structure of amylopectin

• Every 25-30 glucose molecules, amylopectin chains have a branch

• Branch consists of glycosidic bond between carbon one of a glucose molecule and carbon 6 of another glucose molecule

• Creates 1-6 glycosidic bond

• Highly branched molecule

What is the function of starch?

• Store of glucose

• Glucose is extremely soluble in water (as it has large number of hydroxyl groups)

• If cell contains a large amount of dissolved glucose water can move into the cell via osmosis

• So plants store glucose as insoluble starch

Where is starch located?

Plant cells (e.g: chloroplasts)

How does the structure of starch lead to its function? (3 points)

• Amylose forms a tight helix which means starch is compact, so starch can store a large amount of glucose for its size

• Insoluble in water so does not cause water to enter the cell by osmosis. Amylose and amylopectin are polymers so are too large to pass through the cell membrane,

• Amylopectin is highly branched. The enzymes which break glycosidic bonds act at end of molecules. So enzymes can break down starch rapidly and glucose is released quickly.

How do you test for starch?

1. Add a few drops of iodine in potassium iodide solution to the sample

2. If starch is present solution will turn from orange/brown to blue-black