Monomers, Polymers and Carbohydrates

Question 1

What are monomers?

Answer 1

small units that are the components of larger molecules, e.g monosaccharides such as glucose, amino acids and nucleotides

Question 2

Give examples of monomers?

Answer 2

monosaccharides such as glucose, amino acids and nucleotides

Question 3

What are polymers?

Answer 3

molecules made from many monomers joined together.

Question 4

What are monomers joined by?

Answer 4

A chemical bond in a condensation reaction where by a water molecule is eliminated.

Question 5

What is a condensation reaction?

Answer 5

A reaction that joins two molecules together with the formation of a chemical bond and the elimination of a molecule of water.

Question 6

What is a hydrolysis reaction?

Answer 6

A reaction that breaks a chemical bond between two molecules and involves the use of a water molecule.

Question 7

What are monosaccarides?

Answer 7

A single monomer

Question 8

What is a disaccharide?

Answer 8

Two monomers joined together

Question 9

Name three monosaccarides?

Answer 9

Glucose, Galactose and fructose

Question 10

What is glucose?

Answer 10

A monosaccharide containing 6 carbon atoms in each molecule, and is the main substrate for respiration and therefore of great importance. It has two isomers – alpha and beta glucose with structures

Question 11

What is Maltose?

Answer 11

A disaccharide formed by the condensation of two glucose molecules.

Question 12

What is sucrose?

Answer 12

A disaccharide formed by condensation of glucose & fructose.

Question 13

What is lactose?

Answer 13

A disaccharide formed by condensation of glucose & galactose.

Question 14

What is a polysaccharide

Answer 14

Long chains of monosaccharides linked by glycosidic bonds.

Question 15

What do polysaccharides include?

Answer 15

• Glycogen and starch are both formed by the condensation of alpha glucose.
• Cellulose formed by the condensation of beta glucose

Question 16

What is Glycogen?

Answer 16

The main energy storage molecule in animals and is formed from many molecules of
alpha glucose joined together by 1, 4 and 1, 6 glycosidic bonds.

Question 17

Describe the components of glycogen?

Answer 17

• large number of side branches meaning that energy can be released quickly as enzymes can act simultaneously on these branches.
• relatively large but compact molecule thus maximising the amount of energy it can store.
• Insoluble means it will not affect the water the potential of cells and cannot diffuse out of cells.

Question 18

What is Starch?

Answer 18

A polysaccharide that stores energy in plants and is a mixture of two polysaccharides called amylose and
amylopectin

Question 19

What is Amylose?

Answer 19

Amylose is an unbranched chain of glucose molecules joined by 1, 4 glycosidic bonds, and as a result amylose is coiled and thus a very compact molecule storing a lot of energy.

Question 20

What is Amylopectin?

Answer 20

Amylopectin is branched and is made up of glucose molecules joined by 1, 4 and 1, 6 glycosidic bonds. Due to the presence of many side branches, these can be acted upon simultaneously by many enzymes and thus broken down to release their energy.

Question 21

What are the properties of starch?

Answer 21

• insoluble: so will not affect cell water potential,
• Compact: so a lot of energy can be stored in a small space
• When it is hydrolysed the released alpha glucose can be transported easily

Question 22

What is Cellulose?

Answer 22

A component of cell walls in plants and is composed of long, unbranched chains of beta glucose which is joined by glycosidic bonds.

Question 23

What are Microfibrils?

Answer 23

Strong threads are made of long cellulose chains running parallel to one another that are joined together by hydrogen bonds forming strong cross-linkages

Question 24

Why is Cellulose important?

Answer 24

Cellulose is important in stopping the cell wall from bursting under osmotic pressure:

• it exerts inward pressure that stops the
  the influx of water.
• Meaning: that cells stay turgid and rigid, helping to maximise the surface area of plants for photosynthesis.

Question 25

What are isomers?

Answer 25

Two molecules with the same molecular formula but differ structurally.

Question 26

What is Benedict’s reagent used for?

Answer 26

Used to test for the presence of reducing sugars

Question 27

What are reducing sugars?

Answer 27

Glucose, Galactose and fructose

Question 28

State the disaccharides?

Answer 28

Maltose, Lactose and Sucrose

Question 29

What is Benedict’s reagent?

Answer 29

Benedict’s reagent is an alkaline solution of Copper(II) Sulfate

Question 30

Summarise the Benedict test (reducing sugars)

Answer 30

1. Add 2cm3 of the food sample to be tested (needs to be in liquid form, to begin with).
2. Add 2cm3 of Benedict’s Reagent.
3. Heat the mixture gently in a water bath for five minutes. If the solution turns brick red (orange-brown) then a reducing sugar is present and it is a positive result.

Question 31

Summarise the Benedict test (non-reducing sugars)

Answer 31

1. 2cm3 of food sample (must be in liquid form) is added to 2cm3 of Benedict’s Reagent. This is then placed in a water bath for 5 minutes to gently warm.
2. If the colour does not change from blue to brick-red then a reducing sugar is not present.
3. Another 2cm3 of the same food sample is then taken and 2cm3 of dilute hydrochloric acid is added. The test tube is then placed in a water bath for 5 minutes. The dilute HCl will hydrolyse the disaccharides and polysaccharides into their constituent monosaccharides.
4. After this some sodium hydrogen carbonate is added in order to neutralise the test tube as Benedict’s Reagent will not work in acidic conditions. pH paper is used to check that the solution is neutralised.
5. The solution can now be retested by adding 2cm3 of Benedict’s Reagent to the solution and placing it in a water bath for 5 minutes.
6. If a non-reducing sugar is present in the original sample then a colour change from
   the blue Benedict’s Reagent to brick red (orange-brown) will be observed.

Question 32

What is the chemical test for starch?

Answer 32

A chemical test for starch is iodine/potassium iodide. If the solution turns blue/black in
colour from orange-brown then starch is present.

Question 33

What is a Glycosidic bond?

Answer 33

A bond formed as a result of a condensation reaction between saccharide molecules

Question 34

Name the disaccharides are reducing sugars

Answer 34

Maltose & Lactose

Question 35

What describes the Benedict’s solution

Answer 35

Clear blue liquid

Question 36

Describe the chain of a polysaccharide

Answer 36

Their chain may be branched or unbranched and could contain different types of monosaccharides.

Starch, glycogen, cellulose and chitin are examples of polysaccharide

Question 37

Which is structurally different between starch and cellulose gives them different physical properties

Answer 37

Cellulose is formed by 1-4 Beta-glycosidic linkages and cross links, making them rigid. Starch has 1-4 & 1-6 glycosidic linkages without the tight cross links of cellulose

Question 38

Chitin is a polysaccharide. What is it’s formula?

Answer 38

(C8H13O5N)n

Question 39

What is the major difference between chitin and other types of polysaccharide?

Answer 39

Chitin is nitrogenous

Question 40

Why is it impossible for humans to digest food that contain cellulose?

Answer 40

Human digestive enzyme cannot break the 1-4 beta glycosidic linkage in cellulose, which requires a special enzyme that is absent in humans