3.3 Carbohydrates

Question 1

What is the general formula for a cabohydrate?

Answer 1

(CH2O)x x being from 3-8 (inclusive)

Question 2

What is the term for a single sugar unit? (Give examples)

Answer 2

Monosaccharide E.g. glucose, fructose, ribose

Question 3

What is the term for 2 single sugar units joined together? (Give examples)

Answer 3

Disaccharide E.g. lactose, sucrose

Question 4

What is the term for more than 2 single sugar units joined together? (Give examples)

Answer 4

Polysaccharide E.g. glycogen, starch, cellulose

Question 5

What type of monosaccharide is glucose?

Answer 5

Hexose monosaccharide (Has 6 carbon atoms, hence hex-ose) C6H12O6

Question 6

How does glucose become a hexagonal shape?

Answer 6

C1 joins C5, the hydroxyl group on C1 is either aboveor below the plane If the hydroxyl is above the plane it is beta-glucose If it is below the chain it is alpha-glucose

Question 7

Give characteristics of glucose.

Answer 7

• Polar and soluble in water (this is because water is a polar solvent) - Hydroxyl groups are electronegative (tendency to attract electrons of a bond) - Hydrogen bonds form between water and hydroxyl groups

Question 8

Describe the formation of the disaccharide, maltose.

Answer 8

Condensation reaction 2 glucose monomers involved The 2 hydroxyl groups at C1 and C4 of the two glucose monomers give up 2 hydrogens and 1 oxygen between them to eliminate a water molecule A bond is formed between C1 and C4 C-O-C This is called a 1-4 glycosidic link.

Question 9

Give the two monosaccharides involved with sucrose and lactose.

Answer 9

Fructose + glucose > sucrose (normal sugar) Galactose + glucose > lactose (milk sugar)

Question 10

What are examples of pentose monosaccharides.

Answer 10

5 carbons Ribose (in RNA nucleotide) Deoxyribose (in DNA nucleotide)

Question 11

What are the 2 types of polysaccharides under the umbrella term starch?

Answer 11

Amylose and amylopectin

Question 12

Describe the bonding and structure of amylose.

Answer 12

• Alpha-glucose 1-4 glycosidic links - Bond angles with helixical structure - Compact polysaccharide

Question 13

Describe the bonding and structure of amylopectin.

Answer 13

• Alpha-glucose with 1-4 glycosidic links - Every 25 glucose subunits, there is a 1-6 glycosidic link, this gives a branched structure - More compact than amylose

Question 14

Describe the solubility of amylose and amylopectin.

Answer 14

Amylose - less soluble in water Amylopectin - insoluble in water

Question 15

What is the function of glycogen?

Answer 15

Animal glucose store (and in fungi)

Question 16

Describe the structure of glycogen.

Answer 16

• More branched than amylopectin - More compact, therefore less storage space needed - Branching leaves free ends meaning glucose can be added and/or removed quicker speeding up the releasing or storing of glucose where required.

Question 17

What is hydrolysis?

Answer 17

Essentially reverse condensation. Add a water molecule to the starch, e.g. glycogen, to release glucose for respiration. It is an ADDITION reaction, water is added and the reaction is catalysed by the enzyme maltase.

Question 18

How is cellulose formed?

Answer 18

Beta-glucose polysaccharide - Thy hydroxyl groups at C1 and C4 of the respective monomers are too far apart to react so one of the molecules flips on a horizontal plane to from 1-4 glycosidic bonds. - It is a straight chain and cannot coil or form branches

Question 19

How are cellulose fibres made and what are they used for?

Answer 19

Cellulose -(hydrogen bond)- cellulose = microfibril Microfibril + microfibril = macrofibril Macrofibril + macrofibril = cellulose fibre Used to make cell walls Important in diet as they are difficult to break down into monomers, they support the digestive system.