2 - ICH - Carbohydrates

Question 1

Elements that make up carbohydrates and their approximate ratio

Answer 1

Carbon, hydrogen, oxygen

C:H:O = 1:2:1

Question 2

General formula of a carbohydrate

Answer 2

C_x(H₂O)_y

Or alternatively: (CH₂O)_n

Question 3

What is a:

Triose, tetrose, pentose, hexose, heptose

Answer 3

Monosaccharides that have this number of carbons:

Triose = 3

Tetrose = 4

Pentose = 5

Hexose = 6

Heptose = 7

Question 4

Name for 4 compounds that have the formula C₆H₁₂O₆

Answer 4

Alpha glucose

Beta glucose

Fructose

Galactose

Question 5

Name 2 pentoses and their formulas

Answer 5

Deoxyribose = C₅H₁₀O₄

Ribose = C₅H₁₀O₅

Question 6

Difference between deoxyribose and ribose

Answer 6

In ribose there’s 1 hydrogen bond and a hydroxyl bond.

In deoxyribose there’s 2 hydrogen atoms attached to a carbon.

Question 7

Name a triose and give it’s chemical formula

Answer 7

Glyceraldehyde = C₃H₆O₃

Question 8

SUCROSE = ?

MALTOSE = ?

LACTOSE = ?

Answer 8

Sucrose = alpha glucose + fructose

Maltose = alpha glucose + alpha glucose

Lactose = alpha glucose + galactose

Question 9

Source of:

Sucrose

Maltose

Lactose

Answer 9

Sucrose = Sugar cane and sugar beet

Maltose = Barley

Lactose = Milk

Question 10

Define reducing sugar

Answer 10

A carbohydrate monomer or dimer that gives a positive result in Benedict’s test because it is able chemically to reduce copper sulphate in solution

Question 11

Results for Benedict’s test

Answer 11

Blue = Little to non of reducing sugar

Green

Yellow

Orange

Brick red = Lots of reducing sugar

Question 12

Why Sucrose is no a reducing sugar

Answer 12

Sucrose = alpha glucose + fructose

When alpha glucose and fructose bond together to make sucrose the part of the compound that has the ability to reduce (the OH and the H) has been condensed in the reaction.

Question 13

Name 2 types of starch that’s found in plants

Answer 13

Amylose - 20%

Amylopectin - 80%

Question 14

Properties of Amylose (5)

Answer 14

• Present in plants
• Condensation
• Monomer = α glucose
• 1,4 glycosidic bonds only
• Forms an alpha helix, held together by hydrogen bonds

Question 15

Properties of Amylopectin (5)

Answer 15

• Present in plants
• Condensation
• Monomer = α glucose
• Many 1,4 glycosidic bonds, some 1,6 glycosidic bonds
• Branched

Question 16

Properties of Cellulose (5)

Answer 16

• Present in plants & animals
• Monomer = ß glucose
• Different orientation of the monomer
• Can’t form a helix
• Builds plant walls

Question 17

Properties of Glycogen (3)

Answer 17

• Food store in animals and fungi
• Monomer = α glucose
• Much like amylopectin

Question 18

Microfibril

Macrofibril

Answer 18

Microfibril = Bundle of cellulose molecules bonded together

Macrofibril = Several microfibrils bonded together by intramolecular hydrogen bonds

Question 19

Function of carbohydrates (4)

Answer 19

• Build cell walls in plants
• Pentose sugars are important for DNA and RNA
• Broken down for respiration to supply energy
• Energy storage (starch in plants, glycogen in animals/fungi)

Question 20

Homoglycan

Hetroglycan

Answer 20

Homoglycan = Molecule that only contains 1 type of monomer

Hetroglycan = Molecule that contains more than 1 type of monomer

Question 21

Why is starch good for storage? (4)

Answer 21

Compact

Insoluble

Resistant to change e.g. hydrolysis

Readily hydrolysed

Question 22

Describe a test for Reducing Sugars

Answer 22

Add Benedict’s solution and heat to 80ºC in a hot water bath.

O = Solution turns from blue → Orange red

Question 23

Describe a test for Non-reducing Sugars

Answer 23

Test for a reducing sugar first (Boil sample at 80ºC and add Benedict’s reagent).

If it’s negative: O = Blue solution

Boil with HCl, cool and neutralise with either Na₂CO₃ solution or NaHCO₃ solution.

Repeat Benedict’s test.

O = Blue → Orange red (final test)

Question 24

Describe a test for starch

Answer 24

Add a few drops of iodine solution to sample.

O = Blue-black ppt formed.