3.1.2 Carbohydrates

Question 1

How many monomers does glucose have , name them and draw them ?

Answer 1

2 , Alpha and Beta glucose

Question 2

How are polysaccharides formed ?

Answer 2

Polysaccharides are formed by the condensation of many glucose
units.

Question 3

How are glycogen and starch formed ?

Answer 3

Glycogen and starch are formed by the condensation of
α-glucose.

Question 4

How is cellulose formed ?

Answer 4

Cellulose is formed by the condensation of β-glucose

Question 5

What three monosaccharides do you need to know the structure of ?

Answer 5

Glucose , Fructose and Galactose

Question 6

How do disaccharides form ?

Answer 6

Two monosaccharides are joined together by a
glycosidic bond. This is a condensation reaction which involves the removal of a
molecule of water

Question 7

What is a polysaccharide ?

Answer 7

A long chain of monosaccharides that are linked by glycosidic bonds are known as a
polysaccharide

Question 8

How is sucrose made ?

Answer 8

Glucose and Fructose

Question 9

What is the stucture and fucntion of cellulose ?

Answer 9

Cellulose is a polymer of β glucose - it’s made of long, unbranched chains of
beta-glucose.
‒ Condensation reactions link carbon atom 1 to carbon atom 4 on the next β
glucose.
‒ The glucose subunits in the chain are oriented alternately upwards and
downwards.
‒ The consequence of this is that the cellulose molecule is a straight chain rather
than curved.
The cellulose chains are linked together by hydrogen bonds to form strong fibres
called cellulose microfibrils.
‒ Because of those fibres, the tensile strength of cellulose provides structural
support for the cells (e.g the cell walls) and prevents plant cells from bursting -
even under very high (water) pressure.

Question 10

How is lactose made ?

Answer 10

glucose and galactose

Question 11

How is Maltose made ?

Answer 11

Glucose and glucose

Question 12

Where is starch found and what is it used for ?

Answer 12

Cells get their energy from glucose. Plants store excess glucose as starch.
‒ When a plant needs more glucose for energy, it will break down that starch to
release the glucose

Question 13

What are the two versions of starch ?

Answer 13

Amylose and Amylopectin

Question 14

What type of glucose is starch made of ?

Answer 14

Alpha glucose two variations amylose and amylopectin

Question 15

What is the struture and function of amylose ?

Answer 15

Amylose is a long, unbranched chain of α-glucose. The angle of the glycosidic
bonds give it a coiled, cylinder-like structure. This compact structure is good for
storage because more glucose can be stored in a small space

Question 16

What is the structure and function of amylopectin ?

Answer 16

Amylopectin is a long, branched chain of α-glucose. It has side branches which
allow the enzymes that break the molecule down to access glycosidic bonds
easily - meaning the glucose can be released quickly

Question 17

Why is starch good for energy storage ?

Answer 17

starch is insoluble, water cannot enter the cells by osmosis - which makes it
very good for storage.

Question 18

What number on carbons are the condensation links on ?

Answer 18

Condensation reactions link carbon atom 1 to carbon atom 4 on the next
α-glucose.

Question 19

Where is glycogen found and what is the main function of it ?

Answer 19

Glycogen is the main energy storage material in animals

Question 20

Where is glycogen stored in humans ?

Answer 20

it is stored in the liver and some muscles

Question 21

Where is glycogen used ?

Answer 21

It’s used in cells where large stores of dissolved glucose would cause osmotic problems

Question 22

What is the stucture of glycogen like ?

Answer 22

Glycogen has a similar structure to amylopectin but it has a lot more side
branches. These extra branches mean the stored glucose can be released very
quickly - something that is very important in animals.

Question 23

What are the adaptations that make glycogen a suitable energy source ?

Answer 23

As a result of the branches, glycogen is very compact which makes it very good
for energy storage.
‒ Glycogen does not affect the osmotic balance of cells - i.e. cause too much water
to enter them.

Question 24

What are reducing sugars ?

Answer 24

All monosachharides and some disaccharides including maltose and lactose

Question 25

How do you test for reducing sugars and what is the positive result ?

Answer 25

Add Benedict’s reagent (which is blue) to a sample and heat it in a water bath that
boils the mixture for 5 minutes.
‒ If the test is positive, it will form a coloured precipitate (solid particles suspended
in the solution).
blue to green, yellow, orange, or brick red

Question 26

How do you compare the amount of reducing sugars in different solutions ?

Answer 26

higher concentration of reducing sugar , further the colour change blue to green, yellow, orange, or brick red (more accurate way is to filter the solution and weigh the precipitate )

Question 27

How do you test for a non-reducing sugar ?

Answer 27

Following a negative Benedicts test
Take a fresh sample of the solution and either heat it with diluted hydrochloric
acid or hydrolyze using enzymes.
‒ You can then neutralise it with sodium hydrogencarbonate.
‒ Once you have done these, you can continue the Benedict’s test in the same way
you would for a reducing sugar.
‒ If the test is positive, it will form the coloured precipitate just the same as for a
reducing sugar. If the test is negative, the solution stays blue and it means the
solution does not contain any sugar

Question 28

How do you test for starch and what is the positive result?

Answer 28

Add iodine dissolved in potassium iodide solution to the test sample the colour changes from brown-orange to a dark blue-black