Biological Molecules- Carbohydrates

Question 1

What are polymers?

Answer 1

Large complex molecules composed of long chains of monomers

Question 2

What are monomers?

Answer 2

Small basic molecular units

Question 3

What are examples of monomers?

Answer 3

Monosaccharides, amino acids, nucleotides

Question 4

What elements do carbohydrates contain?

Answer 4

Carbon, hydrogen and oxygen

Question 5

What is glucose?

Answer 5

A hexose sugar

Question 6

What are examples of monosaccharides?

Answer 6

Glucose, fructose, galactose

Question 7

What are the two isomers of glucose?

Answer 7

Alpha and beta

Question 8

What’s the difference between an alpha and beta glucose molecule?

Answer 8

Alpha glucose- H at top, OH at bottom

Beta glucose- OH at top, H at bottom

Question 9

What happens when a condensation reaction occurs?

Answer 9

Two molecules join together to form a new chemical bond and a molecule of water is released

Question 10

How are monosaccharides joined together?

Answer 10

Condensation reactions

Question 11

What bond is formed between two monosaccharides?

Answer 11

Glycosidic bond

Question 12

How is a disaccharide formed?

Answer 12

Two monosaccharides join together

Question 13

How is maltose formed?

Answer 13

Two alpha glucose molecules join

Question 14

How is sucrose formed?

Answer 14

A glucose molecule and a fructose molecule join

Question 15

How is lactose formed?

Answer 15

A glucose molecule and a galactose molecule join

Question 16

How can polymers be broken down into monomers?

Answer 16

Hydrolysis reaction

Question 17

What happens in a hydrolysis reaction?

Answer 17

Breaks chemical bond between monomers using a water molecule

Question 18

How do you test for reducing sugars?

Answer 18

1. Add Benedict’s reagent
2. Heat in a water bath that’s been brought to boil
3. Positive result= colour change (green/yellow/orange/brick red)
4. Higher concentration of reducing sugar, closest to red precipitate colour goes

Question 19

How can you measure the concentration of reducing sugar?

Answer 19

Dry and weigh the precipitate or use a colorimeter

Question 20

How do you test for non-reducing sugars?

Answer 20

1. Add dilute hydrochloric acid
2. Heat in water bath that’s been brought to boil
3. Neutralise with sodium hydrogencarbonate
4. Carry out Benedict’s test as you would when testing for a reducing sugar
5. Positive result= forms coloured precipitate

Question 21

How are polysaccharides formed?

Answer 21

When more than two monosaccharides are joined together by a condensation reaction

Question 22

What is the structure and function of starch?

Answer 22

• Plants store excess glucose as starch
• Mix of amylose and amylopectin
• Amylose is a long, unbranched chain of alpha glucose, coiled structure which makes it compact so good for storage
• Amylopectin is a long, branched chain of alpha glucose, side branches allow enzymes that break down molecule to easily get at glycosidic bonds so glucose can be released quickly
• Insoluble in water and doesn’t affect water potential so water doesn’t enter cells by osmosis

Question 23

How do you test for starch?

Answer 23

Iodine test

1. Add iodine dissolved in potassium iodide solution
2. Positive result= colour change to blue-black

Question 24

What is the structure and function of glycogen?

Answer 24

• Animals store excess glucose as glycogen
• Similar structure to amylopectin
• Lots more side branches so glucose can be released quickly
• Very compact so good for storage

Question 25

What is the structure and function of cellulose?

Answer 25

• Made of long, unbranched chains of beta glucose
• Form straight cellulose chains
• Cellulose chains linked together by hydrogen bonds
• Form microfibrils (strong fibres) to form structural support