1.2 Carbohydrates

Question 1

What are monosaccharides?

Answer 1

The monomers from which larger carbohydrates are made (eg/glucose, fructose, galactose)

Question 2

What are disaccharides?

Answer 2

Formed by the condensation of 2 monosaccharides

Question 3

Glucose + glucose?

Answer 3

Maltose

Question 4

Glucose + fructose = ?

Answer 4

Sucrose

Question 5

Glucose + galactose = ?

Answer 5

Lactose

Question 6

What does a condensation reaction between 2 monosaccharides form?

Answer 6

Glycosidic bonds

Question 7

What do isomers of glucose look like?

Answer 7

OH group is below C1 for a-glucose
OH group is above C1 for β-glucose

Question 8

What is a polysaccharide?

Answer 8

Formed by the condensation of many monosaccharides

Question 9

What is the function and structure of glycogen?

Answer 9

FUNCTION: energy store in animal cells

STRUCTURE: polysaccharide of a-glucose with C1-C4 and C1-C6 glycosidic bonds so branched

Question 10

Structure of glycogen related to its function:

Answer 10

• Branched: can be rapidly hydrolysed to release glucose for respiration to provide energy
• Large polysaccharide molecule; can’t leave cell
• Insoluble in water: water potential of cell not affected

Question 11

What is the function and structure of starch?

Answer 11

FUNCTION: energy store in plants

STRUCTURE: polysaccharide of a-glucose. Mixture of amylase (C1-C4 glycosidic bond therefore unbranched) and amylopection (C1-C6 therefore branched)

Question 12

Structure of starch related to its function:

Answer 12

• Helical: compact for storage in cell
• Large polysaccharide molecule: can’t leave cell
• Insoluble in water: no osmotic effect

Question 13

What is the function of cellulose?

Answer 13

FUNCTION: provides strength and structural support to plant cell walls

Question 14

Structure of cellulose related to its function:

Answer 14

• Every other beta-glucose molecules is inverted in a long, straight, unbranched chain
• Many hydrogen bonds link parallel strings to form microfibrils
  - Form a tough wall that resits expansion
• H bonds are strong in high numbers
• Provides structural/strength support to plant cell walls

Question 15

What is the Benedict’s test for reducing sugars?

Answer 15

• All monosaccharides, and some disaccharides
  1. Add Benedict’s reagent (blue) to sample
  2. Heat in boiling water bath
  3. Positive = green/yellow/orange/red precipitate

Question 16

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

Answer 16

• No monsaccharides, some disaccharides
  1. Add a few drops of hydrochloric acid
  2. Heat in boiling water bath
  3. Neutralise with sodium bicarbonate
  4. Add Benedict’s reagent and heat again
  5. Non-reducing sugar present = green/yellow/orange/red precipitate

Question 17

How do you determine glucose concentration?

Answer 17

1. Produce a dilution series of glucose solutions of known concentration
2. Perform a Benedict’s test on each sample
3. Using a colorimeter, measure the absorbance of each sample and plot a callibration curve
   
   • Calibrate colorimeter using unreacted Benedict’s
   • Use a red filter
   • Less absorbance of filtrate = more sugar present
   • Plot absorbance against glucose concentration
4. Repeat with unknown sample and use graph to determine glucose concentration

Question 18

What is the iodine test?

Answer 18

1. Add iodine dissolved in potassium iodide to solution and shake
2. Blue-black colour = starch present