Carbohydrates

Question 1

What enzyme allows use to break down alpha linkages?

Answer 1

alpha-amylase

Question 2

Why can’t we break down beta linkages?

Answer 2

We do not have beta-cellulase

Question 3

T or F: L isomers are naturally occurring isomers of glucose.

Answer 3

False. D isomers are naturally occurring isomers of glucose.

Question 4

What are 3 key dietary disaccharides and their subunits?

Answer 4

• Lactose - glucose and galactose
• Maltose - glucose and glucose
• Sucrose - glucose and fructose

Question 5

What are the two components of starch?

Answer 5

• Amylose

- Amylopective

Question 6

What are the main differences between amylose and amylopectin?

Answer 6

Amylose is a straight-chain alpha 1-4 polymer. Amylopectin consists of alpha 1-4 linked monomers and alpha 1-6 branch points.

Question 7

How does branching in amylopectin assist in its breakdown?

Answer 7

More branch points allow for more binding sites for amylase to latch on to and initiate breakdown (essentially reaction surface area).

Question 8

What are the four types of resistant starch and their characteristics?

Answer 8

• RS1: Digestible but inaccessible
• RS2: Naturally-occurring semi-crystalline granules
• RS3: Formed during cooking and cooling of foods (retrogradation)
• RS4: Processed to make resistant

Question 9

What structural components in plants are considered fibrous?

Answer 9

Cellulose, hemicellulose and pectin

Question 10

What is the difference between soluble and insoluble fibers?

Answer 10

• Soluble takes up water, and insoluble does not.
• Soluble - pectins
• Insoluble - cellulose and hemicellulsose

Question 11

What is the main difference between starch and cellulose?

Answer 11

Starch is easily digestible because it has an alpha-linkage at the bond site.

Question 12

What are the characteristics of hemicellulose?

Answer 12

• Heteropolymer
• Multiple hexoses and pentoses
• Indigestible, but fermentable

Question 13

T or F: Like hemicellulose, pectin is indigestible, but fermentable.

Answer 13

True. Both hemicellulose and pectin are indigestible, but fermentable.

Question 14

Why eat fiber?

Answer 14

It binds metal and cholesterol which help to increase fecal bulk. Alters viscosity of gut contents.

Question 15

Why are we eating the same amount of carbs, but not as much carb fiber as we were in 1900?

Answer 15

Eating a lot more sugar now.

Question 16

What are the recommendations for carb and fiber intake?

Answer 16

• Can make up 50% of calories, but less than 25% should come from sweeteners
• Fiber - 25-40 g/d