[Unit 1.2/3/4] | Carbohydrates

Question 1

List 3 Monosaccharides

Answer 1

“FGG”: Fructose, Glucose, Galactose

Question 2

List 3 Disaccharides

Answer 2

“SLM”: Sucrose, Lactose, Maltose

Question 3

List 4 Polysaccharides

Answer 3

“CAGS”: Celluose, Amylopectin, Glycogen, Starch

Question 4

What does -saccharide classify?

Answer 4

Classifies carbohydrates containing sugars

Question 5

How many monosaccharides form a disaccharide and how many form a polysaccharide?

Answer 5

2 form a disaccharide
3+ form a polysaccharide

Question 6

On a diagram of an alpha/beta glucose molecule is carbon 1 found on the left or right of the oxygen atom?

Answer 6

Right.
Carbon 1-6 can be found clockwise from the oxygen atom.

Question 7

What is the difference between an alpha and a beta glucose molecule?

Answer 7

Bonded to the carbon 1 atom, the alpha glucose molecule will have a hydrogen atom above and a hydroxyl group below.
The beta glucose molecule has the opposite: the hydroxyl group is above and the hydrogen atom is below.

Question 8

Describe the colour change observed within a solution containing a reducing sugar when Benedict’s Solution & 70°C of heat are added.

Answer 8

Brick Red

Question 9

List the products of the condensation of Glucose + Glucose.

Answer 9

“GluGluM”: Maltose + Water

Question 10

List the products of the condensation of Fructose + Glucose.

Answer 10

“FruGluS”: Sucrose + Water

Question 11

List the products of the condensation of Glucose + Galactose.

Answer 11

“GluGaL”: Lactose + Water

Question 12

Explain what occurs between the C1 and C4 of 2 glucose molecules to form maltose.

Answer 12

A condensation reactions occurs and from the 2 hydroxyl groups, 2 hydrogen atoms and 1 oxygen atom are taken to form a water molecule.
This leaves a single oxygen atom forming a bond between the 2 glucose molecules which is called a glycosidic bond.

Question 13

• Explain the alterations made to the reducing sugar test to account for non-reducing sugars.
• What molecules are non-reducing sugars?

Answer 13

An acid must be used to break down non-reducing sugars into reducing monosaccharides.
It must then be neutralised as the Benedict’s test cannot function in acidic conditions.

Polysaccharides and some disaccharides are non-reducing sugars, meaning they do not produce a colour change when mixed with Benedict’s solution.

Question 14

Why do polysaccharides make good storage molecules?

Answer 14

They are long polymers of monosaccharide units. Due to their size, they are insoluble which means they do not affect the water potential of a cell. They are therefore valuable for storage.

Question 15

Where is starch stored?
Where is glycogen stored?

Answer 15

Starch is stored as intracellular grains in plastids.
Glycogen is mainly stored as small granules in the muscles and liver.

Question 16

Compare the structure of amylose to amylopectin.

Answer 16

Amylose is helically coiled with only alpha 1-4 glycosidic bonds.
Amylopectin is less coiled due to the presence of 1-6 bonds and is also more soluble than amylose.

Question 17

Describe 4 features of Starch that make it suitable for its function (storage).

Answer 17

• Coiled so compact.
• Insoluble so does not affect the water potential of a cell
• Branched so glucose can easily be released for respiration
• Large molecule so cannot travel across membranes / leave the cell

Question 18

Explain how glycogen differs from starch.

Answer 18

• It is found in animals & bacteria, unlike starch which is found in plants.
• It is more highly branched to allow for more glucose to be released faster.
• This is necessary as animals have higher metabolic rates.

Question 19

Describe 4 features of cellulose that make it suitable for its function.

Answer 19

• It is a long, linear chain of beta glucose molecules (joined by C1-4 glycosidic bonds after a condensation reaction).
• Layers are stacked in parallel, held together by bridging hydrogen bonds.
• Molecules form microfibrils & macrofibrils (which form cell walls when embedded in pectins).
• Strength is provided due to the abundance of bonds.

Question 20

How do the hydroxyl groups line up for a condensation reaction between 2 beta glucose monomers?

Answer 20

Like with alpha glucose molecules, the bonds are C1-4. Every 2nd beta glucose molecule is flipped upside down in order to align the hydroxyl groups to form a glycosidic bond.