Carbohydrates

Question 1

What are the hexose sugars?

Answer 1

galactose, alpha glucose, beta glucose, fructose

Question 2

What are isomers?

Answer 2

molecules with the same chemical formula but different structural formula

Question 3

What is the chemical formula for all hexose sugars?

Answer 3

C6H12O6

Question 4

How does the structural formula of beta glucose differ from the structural formula of alpha glucose?

Answer 4

The formula is different because the hydroxyl group and H-atom are inverted at carbon-1

Question 5

How are disacchirides formed?

Answer 5

When two monosacchirides join in a condensation reaction

Question 6

What is meant by a condensation reaction?

Answer 6

A reaction where a molecule of water is also produced

Question 7

What does glucose and glucose form?

Answer 7

Maltose and water

Question 8

What does glucose and fructose form?

Answer 8

Sucrose and water

Question 9

What does glucose and galactose form?

Answer 9

Lactose and water

Question 10

What is the bond that joins the two monosacchirides called?

Answer 10

Glycosidic bond

Question 11

What is the chemical formula of maltose, sucrose and lactose?

Answer 11

C12H22O11

Question 12

What is a hydrolysis reaction?

Answer 12

A reaction that involves splitting a larger molecule into a smaller molecule by the chemical insertion of a water molecule

Question 13

How does the hydrolysis of sucrose work?

Answer 13

A water molecule is inserted. It breaks the glycosidic bond. The hydroxil group of H20 bonds with fructose to make it stable because it is left with a free bond. The H+ atom bonds with glucose to make it stable.

Question 14

How can hydrolysis happen?

Answer 14

Enzyme reactions (e.g. sucrase breaks down sucrose)
Heat with an acid (e.g. in stomach)

Question 15

What are the 4 important polysaccharides?

Answer 15

Starch, glycogen, cellulose and chitin

Question 16

What is starch a polymer of and where is it found?

Answer 16

Alpha glucose (in the form of amylose and amylopectin) found in plant cells

Question 17

Why does starch have a helical shape?

Answer 17

Because amylose contains only one type of bond (alpha 1-4 glycosidic bonds), therefore there is a strain on the chain

Question 18

Why is amylopectin a branched molecule?

Answer 18

It contains two types of bond - alpha 1-4 and alpha 1-6 glycosidic

Question 19

How do you test for starch?

Answer 19

Add 2-3 drops of iodine solution - a colour change for orange to blue/black

Question 20

What is glycogen a polymer of and what types of bonding does it have?

Answer 20

Alpha glucose, alpha 1-4 and alpha 1-6

Question 21

How does glycogen’s structure differ to amylopectin?

Answer 21

Although they are similar, amylopectin is more densely branched

Question 22

What 4 features make a good storage molecule?

Answer 22

Insolubility - osmotically inert 
Easily accessible (in respiration)
Compact shape (take up less space in cells)
Large molecules (can't leave through plasma membrane)

Question 23

What is cellulose a polymer of?

Answer 23

Beta glucose

Question 24

What happens during condensation reactions between molecules of ß glucose?

Answer 24

Alternate molecules rotate by 180 degrees so that glycosidic bonds can form on either side of the chain

Question 25

What forms between the parallel chains of ß glucose?

Answer 25

Hydrogen bonds which form microfibrils

Question 26

Why is it important that cellulose is strong?

Answer 26

It prevents osmotic lysis of the cells (they won’t burst)

Question 27

What is the monomer of Chitin?

Answer 27

Glucosamine (similar to beta glucose but some of the OH groups are replaced by amino acids)

Question 28

Where do you find chitin?

Answer 28

In fungi cell walls and exoskeletons of insects