Carbohydrates

Question 1

What happens in a condensation reaction?

Answer 1

a chemical bond forms between 2 molecules and a molecule of water is produced

Question 2

What happens in a hydrolysis reaction?

Answer 2

a water molecule is used to break a chemical bond between 2 molecules

Question 3

What’s the difference between a disaccharide and polysaccharide?

Answer 3

disaccharide - 1 chemical bond and 2 monomers
polysaccharide - many chemical bonds and multiple monomers

Question 4

What’s the name for 1 chemical bond and 2 monomers?

Answer 4

disaccharide

Question 5

What’s the name for many chemical bonds and multiple monomers?

Answer 5

polysaccharide

Question 6

What type of bond forms between monosaccharides?

Answer 6

glycosidic (1,4 or 1,6)

Question 7

How do disaccharides form?

Answer 7

When a condensation reaction forms a glycosidic bond between 2 monocsaccharides

Question 8

What are 3 disaccharides?

Answer 8

maltose, sucrose, lactose

Question 9

What monosaccharides make up maltose?

Answer 9

glucose + glucose

Question 10

What monosaccharides make up sucrose?

Answer 10

glucose + fructose

Question 11

What monosaccharides make up lactose?

Answer 11

glucose + galactose

Question 12

Draw the structure of alpha-glucose

Answer 12

(look at notes)

Question 13

Draw the structure of beta-glucose

Answer 13

(look at notes)

Question 14

What is starch?

Answer 14

storage polymer of alpha-glucose in plant cells

Question 15

What are 2 functions of starch?

Answer 15

insoluble - no osmotic effect on cells
large - does not diffuse out of cells

Question 16

What are the 2 types of starch?

Answer 16

amylose and amylopectin

Question 17

What is the structure of amylose?

Answer 17

1,4 glycosidic bonds
H-bonds = compact

Question 18

Describe amylopectin

Answer 18

1,4 and 1,6 glycosidic bonds
branches = many terminal ends for hydrolysis into glucose

Question 19

What is glycogen?

Answer 19

main storage polymer of alpha-glucose in animal cells (also found in plant cells)

Question 20

What bonds does glycogen contain?

Answer 20

1,4 and 1,6 glycosidic bonds

Question 21

What are the structures related to their functions of glycogen?

Answer 21

branched = many terminal ends for hydrolysis
insoluble = no osmotic effect
large = does not diffuse out of cells
compact

Question 22

What is cellulose?

Answer 22

polymer of beta-glucose

Question 23

What is the function of cellulose?

Answer 23

keeps plant cell walls rigid as it:
- prevents bursting under turgor pressure
- holds stem up
H-bond crosslines between parallel strands form microfibrils = high tensile strength

Question 24

What is the structure of cellulose?

Answer 24

1,4 glycosidic bonds
straight-chained, unbranched molecule
alternate glucose molecules are rotated 180 degrees

Question 25

What is the test for reducing sugars?

Answer 25

benedict’s test

Question 26

What is the benedict’s test for reducing sugars

Answer 26

1) add an equal volume of benedict’s reagent to a sample
2) heat mixture in an electric water bath at 100 degrees for 5 mins
3) positive result = blue to orange/brick-red

Question 27

What is the test for non-reducing sugars?

Answer 27

benedict’s test

Question 28

What is the benedict’s test for non-reducing sugars?

Answer 28

1) hydrolyse non-reducing sugars by adding 1cm3 of hydrochloric acid
2) heat in boiling water bath for 5 mins
3) neutralise mixture using sodium carbonate solution
4) proceed with benedict’s test as usual

Question 29

How do you test for starch?

Answer 29

1) add iodine solution
2) positive result = orange to blue-black

Question 30

How can colorimetry be used to show presence of sugars and starch?

(5 points)

Answer 30

1) make standard solutions with known concentrations
2) record absorbance or % transmission values
3) plot calibration curve (y = absorbance/% transmission, x = concentration)
4) record absorbance or % transmission values of unknown samples
5) use calibration curve to read off concentration

Question 31

How do beta-glucose and alpha-glucose differ structurally?

Answer 31

alpha-glucose OH group on C1 is below plane whilst beta-glucose OH group on C1 is above plane