Carbohydrates 1.1

Question 1

What are monomers? e.g.s?

Answer 1

small basic molecular units

e.g. monosaccharides (e.g. glucose, fructose and galactose), amino acids, nucleotides

Question 2

What are polymers? e.g.s?

Answer 2

Polymers are large complex molecules composed of long chains monomers joined together. e.g. carbohydrates, proteins and nucleic acids.

Question 3

What are the chemical elements in all carbohydrates?

Answer 3

C, H and O

Question 4

What are isomers?

Answer 4

Molecules with the same molecular formula as each other but with a different arrangement of atoms.

Question 5

What are the two types (isomers) of glucose?

Answer 5

Question 6

What is a condensation reaction?

Answer 6

when two molecules join together to form a new chemical bond, and a water molecule is released.

Question 7

What type of bond forms between monosaccharides?

Answer 7

a glycosidic bond

Question 8

Draw a diagram to show the formation of maltose

Answer 8

Question 9

What are the three main diasaccharides made up of?

Answer 9

glucose + glucose → maltose

glucose + fructose → sucrose

glucose + galactose → lactose

Question 10

What type of reaction breaks down disaccharides?

Explain how and give an e.g.

Answer 10

Disaccharides are broken down by hydrolysis reactions. This is where the chemical bond between two monsaccharides in a disaccharide is broken by the addition of a molecule of water. e.g. maltose is hydrolysed into two molecules of α glucose.

Question 11

Draw a diagram of the hydrolysis of maltose

Answer 11

Question 12

How do you perform the test for reducing sugars?

Answer 12

To perform the Benedict’s test, add an excess of benedict’s reagent to the sample and heat it to a boil in a water bath. If the test is +ve a coloured precipitate will form. the colour of the precipitate will change (B-G-Y-O-R) depending on the concerntration of the reducing sugar present in the sample. The higher the concerntration of the reducing sugar, the further the colour change goes.

Question 13

How do you test for non-reducing sugars?

Answer 13

If you test for reducing sugars, non-reducing sugars could stillbe present. To test for non-reducing sugars, like sucrose, you first need to break them down into monosaccharides.

To do this heat a new solution (of the sample and benedicts reagent) with dilute HCl in a water bath. Then neutralise it with sodium hydrocarbonate - the B. reagent dosn’t work in acidic conditions.

Then carry out the B. test as you would for a reducing sugar.

Question 14

What is a +ve result for the non-reducing sugar test?

Answer 14

If +ve, it will form a coloured precipitate (as with the reducing sugar test). If the test’s negative, the solution will stay blue. this means it dosen’t contain any sugar (either reducing or non-reducing).

Question 15

What is a polysaccharide?

Answer 15

A polysaccharide is a chain of two or more monosaccharides joined together by condensation reactions. e.g. amylose

Question 16

Draw the structure of amylose

Answer 16

Question 17

Describe the structures of the two different polysaccharides in starch and explain how these structures help starch carry out its function of energy storage.

Answer 17

The two polysaccharides found in starch are amylose and amylopectin.
Amylose is composed of a long, unbranched chain of alpha-glucose. It has a coiled, cylinder-like structure that allows it to be tightly packed. This makes it good for storage as more can fit into a small space.

Amylopectin is made from a long, branched chain of alpha-glucose. It has side branches that allow enzymes easy access to break the glycosidic bonds and quickly release stored glucose.

Question 18

How does the solubility of starch make it a good storage molecule?

Answer 18

Insoluble in water and dosen’t affect the water potential so it dosen’t cause water to enter the cells by osmosis, which would make them swell. = good for storage

Question 19

What is the test for detecting starch? Describe how it works.

Answer 19

Iodine test: dissolved in potassium iodide is added to a test sample. +ve: browny-orange colour to a dark blue-black colour.

Question 20

What properties does glycogen have that make it a good energy storage molecule?

Answer 20

Glycogen, another ploysaccharide of alpha glucose, is very compact, which allows a large amount of it to be stored in a small space.
It also has a large number of side branches, which means that stored glucose can be released quickly.

Question 21

What is the function of cellulose in plants? Explain how its structure accomplishes its function.

Answer 21

The function of cellulose is to provide structural support in cells, for example, in plant cell walls.
Long, unbranched chains of beta-glucose form cellulose chains. These chains can then link together via hydrogen bonds to make strong, rigid microfibrils.