Carbohydrates

Question 1

List some carbohydrates in our diet

Answer 1

Starch (cereal, potatoes, rice)
Maltose (breakdown product of starch)
Sucrose (table sugar)
Lactose (milk)
Cellulose and hemicellulose (plant cell wall, we can’t digest this)
Glucose
Fructose
Glycogen (meat but when the animal dies, enzymes degrade much of the glycogen stores)
Oligosaccharides (not digested, peas, beans, lentils)

Question 2

Define the 3 types carbohydrates

Answer 2

Monosaccharides - monomers. E.g glucose, fructose, galactose

Disaccharides - two monomers joined by glycosidic bond. E.g maltose, lactose, sucrose

Polysaccharides - polymers, 3 or more monomers joined by glycosidic bonds.
E.g starch, glycogen

Question 3

How do plants and animals store glucose?

Answer 3

Plants - store glucose in the form of starch. Starch contains 2 polymers of glucose, amylose (unbranched, a1-4 linkages) and amylopectin (branched, a1-4 linkages with a1-6 branches).

Animals - store glucose in the form of glycogen. Polymer of glucose with a1-4 linked subunits and a1-6 branches. (Highly branched).

Question 4

How are carbohydrates digested?

Answer 4

Mouth- salivary amylase hydrolyses the alpha 1-4 (branches) bonds of starch.

Stomach- no carbohydrate digestion takes place here

Duodenum- pancreatic amylase hydrolyses glycosidic alpha 1-4 bonds, releasing free glucose (same as in mouth)

Jejunum- final digestion or carbohydrate takes place here.
Isomaltase - hydrolyses alpha1-6 bonds
Glucoamylase - removes glucose from non-reducing ends
Sucrase - hydrolyses sucrose
Lactase - hydrolyses lactase

Question 5

What are the main products of carbohydrate digestion?

Answer 5

Glucose, galactose, fructose