Carbohydrates 3.1.2

Question 1

What is a monosaccharide and give examples

Answer 1

A monosaccharides are the monomers which make up larger carbohydrates. Some examples of monosaccharides are glucose, galactose and fructose

Question 2

What is the disaccharide maltose made up of?

Answer 2

glucose + glucose

Question 3

What is the disaccharide lactose made up of?

Answer 3

glucose + galactose

Question 4

What is the disaccharide sucrose made up of?

Answer 4

glucose + fructose

Question 5

What bond is formed between the condensation of two monosaccharides?

Answer 5

glycosidic bond

Question 6

What two isomers does glucose have?

Answer 6

alpha-glucose

beta-glucose

Question 7

What is the structure of starch, how does this relate to its function?

Answer 7

• made from a-glucose, which is easily transported and can be used as a respiratory substrate
• has a helical structure, making it compact so more can be stored taking up less space
• contains glycosidic bonds between carbon 1-4
• it is insoluble in water so won’t affect osmosis in plats and water potential
• branched, lots of places for enzymes to act on and release glucose for respiration

Question 8

What is the structure of glycogen, how does the structure relate to its function?

Answer 8

• made up of a-glucose which is a respiratory substrate
• helical structure, making it compact so easily stored in cells
• highly branched (more so than starch) so lots of places enzymes can act upon to release the glucose
• insoluble so doesn’t affect water potential and excess water isn’t drawn into cells by osmosis
• it is found in animal cells

Question 9

What is the structure of cellulose and how does this relate to its function?

Answer 9

• made up of b-glucose with every alternate monomer rotating 180 to form straight uniform chains
• linked by a multitude of h bonds, providing strength and rigidity to the cell wall
• no branches
• cellulose molecules group together with the formation of microfibrils
• it is able to resist digestion and osmotic pressure

Question 10

How do you test for the presence of starch?

Answer 10

iodine test for starch

• you add iodine dissolves in potassium iodide to the sample
• if starch is present the solution will turn from orange/brown to blue/black

Question 11

What is a reducing sugar?

Answer 11

A less complex sugar with a free aldehyde or ketone functional group e.g.

• glucose
• fructose
• maltose
• lactose
• galactose

Question 12

How do you test for reducing sugar?

Answer 12

• Add Benedict’s reagent (blue) to a sample and heat it in a water bath boiling the mixture for 5 minutes
• If the test is positive, it will form a coloured precipitate (from green to red)
• higher concentrations of reducing sugar, mean the further the change of colour
• this a qualitative way of measuring concentration of sugars

Question 13

What is a non-reducing sugar?

Answer 13

A sugar that is unable to be oxidised and doesn’t reduce other substances e.g. sucrose

Question 14

How do you test for non-reducing sugars?

Answer 14

-you first need to break them down
into monosaccharides.
-take a fresh sample of the solution and heat it with diluted hydrochloric acid
-then neutralise it with sodium hydrogencarbonate.
-now continue the Benedict’s test in the same way
you would for a reducing sugar.
-if the test is positive, it forms a coloured precipitate (green to red). If the test is negative, the solution stays blue so solution does not contain any sugar (either reducing or non-reducing).

Question 15

How do you determine an unknown glucose concentration?

Answer 15

• produce a dilution series of know glucose concentrations
• perform benedict’s test on each solution
• using a colorimeter measure the absorbance and use the results to plot a calibration curve
• Repeat the test with the unknown samples and use the calibration curve to determine the glucose concentration