2: Carbohydrates

Question 1

What are ‘monosaccharides’?

Answer 1

sugars that consist of a single sub-unit (monomer)

Question 2

Which atoms do monosccharides contain? What is the ratio between these atoms?

Answer 2

• carbon, hydrogen, and oxygen

- 1:2:1

Question 3

Give an two exampls of monosaccharides. How many, and of what sort, of atoms are in your two examples?

Answer 3

ribose - C5 H10 O5

glucose - C6 H12 O6

Question 4

Draw a ribose molecule (technically a D-ribose). (p20)

Answer 4

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Question 5

What sort of ribose and glucose do living organisms use? What is the other sort called? What is the difference between them?

Answer 5

• liv org use: right handed versions or glucose/ribose
• other called: left handed version…
• difference: ?

Question 6

Draw an a-D-glucose molecule. Draw a b-D-glucose molecule. (p20)

Answer 6

-

Question 7

How are pairs of monosaccharides linked together? What do they form?

Answer 7

• condensation reactions

- disaccharides

Question 8

Give 3 common examples of monosaccharides.

Answer 8

• glucose
• galactose
• fructose

Question 9

Give 3 common examples of disaccharides.

Answer 9

• maltose
• lactose
• sucrose

Question 10

How can disaccharides be recognised?

Answer 10

by their double ring structure

Question 11

What would a condensation reaction involving 2 glucose molecules form?

Answer 11

maltose + H2O

Question 12

What would a condensation reaction involving a glucose molecule and a galactose molecule form?

Answer 12

lactose + H2O

Question 13

What would a condensation reaction involving a glucose molecule and a fructose molecule form?

Answer 13

sucrose + H2O

Question 14

Give 3 common examples of polysaccharides. What are all these molecules composed of?

Answer 14

• cellulose
• glycogen
• starch
• all made up from glucose

Question 15

What is used to help describe the structure of polysaccharides?

Answer 15

a numbering system for the carbon atoms in glucose molecules

Question 16

Draw an a-D-glucose molecule with the right numbers by the carbon atoms (numbers from the numbering system). (p20)

Answer 16

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Question 17

What is the basic linkage between glucose subunits in polysaccharides called? Between which carbon atoms do most form? What, therefore, is this bond called?

Answer 17

• glycosidic bond
• forms between C1 of one glucose molecule, and C4 of the next
• called “1,4 glycosidic bond”

Question 18

Most glycosidic bonds form between C1 of one glucose molecule, and C4 of the next. Where else can they form? What, therefore, is this bond called?

Answer 18

• between C1 of one glucose molecule, and C6 of the next

- 1,6 glycosidic bond

Question 19

Describe cellulose.

Answer 19

1) unbranched polymer of B-D-glucose
2) orientation of glucose units alternates (up-down-up…)
- which makes the polymer straight, rather than curved
- and means groups of cellulose molecules can be arranged in parallel with hydrogen bonds forming cross links
3) these structures (parallel cellulose molecules with hydrogen bonds forming cross links) are called cellulose microfibrils
4) they have enourmous tensile strength and are the basis of plant cell walls

Question 20

Draw a cellulose molecule. (p20)

Answer 20

-

Question 21

Describe starch.

Answer 21

1) polymer of a-D-glucose
2) all of glucose units in same orientation = helical shape
3) two forms of starch:
- amylose: 1,4 linkages = unbranched
- amylopectin: some 1,6 linkages = branched
4) starch used by plants to store glucose in an insoluble form (that does not cause osmotic problems)
5) branched molecule = possible to load/unload glucose more rapidly as there are more points on starch molecules to which glucose can be added/detached

Question 22

Draw a branched starch molecule. (p20)

Answer 22

-

Question 23

Describe glycogen.

Answer 23

1) branched polymer of a-D-glucose (similar to amylopectin)
2) more 1,6 linkages than amylopectin = more branched
3) glycogen used by mammals to store glucose in liver and muscle cells
4) glyocen = insoluble, so large amounts can be stored (if glycogen was soluble it would cause water to enter cells by osmosis and there would be a danger of them bursting)