carbohydrates

Question 1

what elements does carbohydrates contain? ratio of the elements?

Answer 1

CHO, with H:O is 2:1

Question 2

3 main classes of carbo

Answer 2

monosaccharides, disaccharides and polysaccharides

Question 3

why does monosaccharides dissolve easily in water

Answer 3

due to their many polar hydroxyl (-OH) groups which readily forms hydrogen bonds with water

Question 4

3 types of monosaccharides

Answer 4

glucose, fructose, galactose

Question 5

3 types of disaccharides

Answer 5

maltose, sucrose, lactose

Question 6

what bond is formed when 2 monosacc join to form a disacc?

Answer 6

glycosidic bond

Question 7

formation of α-1,4 glycosidic bond

Answer 7

• btw -OH group of carbon 1 of one α-glucose monomer and -OH group of carbon 4 of another α-glucose monomer
• removal of a water molecule
• catalysed by enzymes

Question 8

3 types of polysaccharides

Answer 8

starch, cellulose, glycogen

Question 9

what is starch used for

Answer 9

main storage polysaccharide in plants

Question 10

what type of glucose is starch made of

Answer 10

α-glucose

Question 11

what are 2 polymers of α-glucose

Answer 11

amylose and amylopectin

Question 12

structure of amylose (3)

Answer 12

• unbranched chain structure that consists several hundred α-glucose residues linked by α-1,4 GB
• angle of bonds causes chain to coil helically into a more compact shape, allowing packing of many glucose molecules per unit volume
• most -OH groups projected into interior of helix, hence no free -OH groups to form HB with water, resulting in insoluble molecule

Question 13

function of structure of amylose (3)

Answer 13

• large no. of glucose molecules present so it serves as a GOOD ENERGY SOURCE in plants, as glucose is oxidised during resp to produce atp [OR]
• GB in amylose can be hydrolysed easily, resulting in release of a large no. of glucose monomers which can be oxidised during resp to produce large amt of atp. hence it acts as an ACCESSIBLE SOURCE OF GLUCOSE
• insoluble nature of starch (amylose) prevents its diffusion out of cell, therefore does not change the wp within the cell, making starch a GOOD STORAGE MOLECULE

Question 14

structure of amylopectin (2)

Answer 14

• backbone of α-glucose residues held tgt by α-1,4 GB
• highly branched w side chains formed by α-1,6 GB

Question 15

why is starch a good storage polysaccharide (2)

Answer 15

• GB in starch can be hydrolysed easily, releasing large number of glucose monomers, which can be oxidised during resp to produce large amt of atp. hence it acts as an ACCESSIBLE SOURCE OF GLUCOSE
• the large and insoluble nature of starch prevents its diffusion out of cell and thus does not change the wp within cell, making it a GOOD STORAGE MOLECULE within the cell

Question 16

what is glycogen used for

Answer 16

main storage polysaccharide in animals

Question 17

structure of glycogen (4)

Answer 17

• backbone of α-glucose residues held tgt by α-1,4 GB
• highly branched w side chains formed by α-1,6 GB
  (compared to amylopectin, glycogen has shorter chains and is more highly branched)
• GB in glycogen can be hydrolysed easily
• it is a large polysacc, which makes it insoluble in water

Question 18

function of structure of glycogen (3)

Answer 18

• large amt of glucose molecules present, it serves as a GOOD ENERGY SOURCE in animals, as glucose is oxidised during resp to produce atp
• the many branched ends allow many hydrolytic enzymes to act on the branched ends at any one time, so glycogen can be easily broken down into its glucose monomers to be used as resp substrates. thus it serves as an accessible source of glucose
• large and insoluble nature prevents its diffusion out of cell and thus does not change the wp within the cell, making it a GOOD ENERGY STORAGE MOLECULE

Question 19

what is cellulose used for

Answer 19

it is the structural polysaccharide in plants

Question 20

structure of cellulose (3)

Answer 20

• long chain of β-glucose residues linked by β-1,4 GB which makes cellulose chain straight
• successive β-glucose residues are rotated 180° with respect to its adjacent residue, resulting in -OH groups projecting outwards from each cellulose chain in all directions
• HB are formed btw the -OH groups of neighbouring cellulose chains lying in parallel, resulting in cross-linking that binds the chains rigidly together to form microfibrils and macrofibrils which confer high tensile strength, stability and support

Question 21

what type of glucose is cellulose made of
(alpha or beta)

Answer 21

β-glucose

Question 22

function of structure of cellulose (3)

Answer 22

• it is the main structural component of plant cell walls. the high tensile strength of microfibrils prevents plant cell from bursting when water enters by osmosis
• as a plant cell inflates with water, pressure develops inside it and cell becomes turgid. turgid cells help support plants which lack wood
• the arrangement of fibres around the cell helps determine the shape of plant cell as it grows

Question 23

what is maltose the product of

Answer 23

glucose + glucose

Question 24

what is sucrose the product of

Answer 24

glucose + fructose

Question 25

what is lactose the product of

Answer 25

glucose + galactose

Question 26

describe test for reducing sugar and observation (3)

Answer 26

benedict’s test:
1. add 2cm3 of benedict’s solution into test tube containing 2cm3 of sample solution
2. put test tube into a boiling water bath for 2 minutes
observation: brick red ppt formed if reducing sugars are present

Question 27

describe test for non-reducing sugar (2 test - 4)
(hint: 1,2,3)

Answer 27

acid hydrolysis:
1. add 1cm3 of dilute HCl into a boiling tube containing 2cm3 of sample solution
2. place boiling tube into a boiling water bath for 3 minutes
3. add a spatula of sodium hydrogencarbonate powder to boiling tube
benedict’s test:
4. add 2cm3 of benedict’s solution into test tube containing 2cm3 of sample solution
5. put test tube into a boiling water bath for 2 minutes