Topic 1 - Year 1 - Biological Molecules - Carbohydrates

Question 1

Which type of reaction joins biological monomers in order to create biological polymers?

Answer 1

Condensation reactions join monomers to create biological polymers which are larger more complex molecules. In the condensation reaction two things happen

1. A chemical bond is made
2. A water molecule is produced

Question 2

Which type of reaction breaks biological polymers down into their biological monomers?

Answer 2

Biological polymers are usually broken down by hydrolysis reactions , hydrolysis use molecules of water to break chemical bonds.

Question 3

What does the term ‘sugars’ refer to?

Answer 3

The term sugars refer to monosaccharides and disaccharides.

Question 4

Which elements do carbohydrates contain?

Answer 4

Hydrogen
Carbon
Oxygen

Question 5

Name 3 Monosaccharides

Answer 5

Glucose
Fructose
Galactose

Question 6

There are two different isomers of glucose what are the names of these two isomers?

Answer 6

Alpha Glucose

Beta Glucose

Question 7

Explain the orientation of the H and OH groups on the first carbon in the hexose sugars Alpha Glucose and Beta Glucose

Answer 7

Alpha Glucose – the H group is ontop and the OH group is on the bottom

Beta Glucose – the OH group is ontop and the OH group is on the bottom

Question 8

What is a Monosaccharide?

Answer 8

A monosaccaride is a monomer for a polysaccharide which is a carbohydrate hence a monosaccharide is a monomer of carbohydrate

Question 9

What is created when two monosaccharides are joined in a condensation reaction?

Answer 9

A disacchaaride

Question 10

If a disaccharide is hydrolysed what happens?

Answer 10

The chemical bond that holds the disaccharide together is broken by a water molecules and the disaccharide becomes two separate monosaccharides

Question 11

Which disaccharide is produced when two monosaccharides of glucose join in a condensation reaction?

Answer 11

Maltose

Question 12

Which disaccharide is formed if monosaccharides glucose and fructose join by condensation reaction?

Answer 12

Sucrose

Question 13

Which disaccharide is formed if monosaccharides glucose and galactose join by condensation reaction?

Answer 13

Lactose

Question 14

What is a reducing sugar ?

Answer 14

A reducing sugar is a sugar that readily looses electrons to another substance. reducing sugars reduce other substances by giving them electrons (reduction is gain)

Question 15

How do you test for a reducing sugar ?

Answer 15

To test for a reducing sugar you use the Benedict’s test, Benedicts test is conducted by:

1) first the sample being tested must be put into solution
2) Benedicts reagent is then added in an excess to the solution an excess is added so that all the sugar reacts
3) the sample is then placed in a water bath and boiled
4) a positive test result will show a colour change and a precipitate will form
5) the Benedicts test has a semi-quatative nature the closer the colour change to brick red the more reducing sugar that was found in the sample , colour changes from blue to something like green may suggest only small amounts of reducing sugar were present.

Question 16

How do you test for non-reducing sugar ?

Answer 16

To test for non-reducing sugars you must also use the Benedictus test however you must complete some additional steps:

1) first the sample being tested must be put into solution
2) too this solution hydrochloric acid must be added , the solution containing the sample must be heated with this hydrochloric acid in a water bath
3) this mixture must then be mixed with sodium hydrogen carbonate to neutralise the acid.
4) Benedicts reagent is then added in an excess to the solution an excess is added so that all the sugar reacts
5) the sample is then placed in a water bath and boiled
6) a positive test result will show a colour change and a precipitate will form
7) the Benedicts test has a semi-quatative nature the closer the colour change to brick red the more reducing sugar that was found in the sample , colour changes from blue to something like green may suggest only small amounts of reducing sugar were present.

Question 17

What is a Polysaccharide?

Answer 17

A polysaccharide is a large chain of monosaccharides that are held together by glycosidic bonds which form in condensation reactions. Polysaccharides are carbohydrates.

Question 18

Name 3 polysaccharides

Answer 18

Starch
Cellulose
Glycogen

Question 19

What is the monomer of Starch

Answer 19

alpha glucose

Question 20

Explain the structure of Starch

Answer 20

Starch is a polysaccharide , the monosaccharide that builds the polymer is alpha glucose (glucose with the h on the first carbon in the ring orientated on top) . the monomers are organised in two ways , straight chains and branches , to form the straight chains (amylose) alpha glucose molecules form 1,4 glycosidic bonds. As starch has a branched structure branches must also be formed (amylopectin) , these branches are created when when alpha glucose molecules for 1,6 glycosidic bonds. Starch has a coiled structure hence is a great storage molecule as it is compact so can store a lot of energy in a small space. The branched nature of starch also means its easily hydrolysed.

Question 21

Explain the purpose of Starch

Answer 21

starch is a storage molecule in plants , plants get energy from glucose and store their excess glucose as starch and then hydrolyse this starch if at a later point they require energy.

Question 22

Where is the polysaccharide starch found?

Answer 22

Plants

Question 23

Starch is insoluble in water , why is this important?

Answer 23

starch is insoluble in water hence it docent affect the water potential of cells. this means that water doesn’t move into the cell by osmosis and cause them to swell. the insolubility of starch is therefore a good thing as it makes it an ideal storage molecule.

Question 24

What is the monomer of glycogen?

Answer 24

Alpha glucose

Question 25

Explain the structure of Glycogen

Answer 25

The monomer of glycogen is alpha glucose , the chains of alpha glucose which are bonded by glycosidic bonds are branched they are more branched than you would find in starch . as the chains are branched you find both 1,4 and 1,6 glycosidic bonds. As glycogen is heavily branched it can be quickly hydrolysed meaning energy in the form of glucose can be taken from it quickly.

Question 26

Explain the function of Glycogen

Answer 26

Glycogen is a storage molecule it is found in animal cells , animals store their excess glucose as glycogen.

Question 27

Where is Glycogen found?

Answer 27

glycogen is found in animals , primarily in the muscles and the liver.

Question 28

Glycogen is insoluble why is this important?

Answer 28

Glycogen is insoluble hence it does not change the water potential in cells this is important as it means water does not enter the cell and cause it to become hemolysed as this could cause death . Therefore the insolubility of glycogen allow it to be an ideal storage molecule

Question 29

Where is the polysaccharide cellulose found?

Answer 29

Cellulose is found in plant cell walls.

Question 30

Explain the structure of cellulose

Answer 30

Cellulose is made up by monomers of beta glucose. The monosaccharides of beta glucose are joined in 1,4 glycosidic bonds. In order to align the 1 and 4 groups on the beta glucose molecules the monosaccharide must continually alienate in orientation. there are no 1,6 glycosidic bonds in cellulose as the polysaccharide is made up of LONG STRAIGHT CHAINS of beta glucose. These many long straight chains are linked together by hydrogen bonds to form strong fibres called microfibrils. These strong fibres create a cross hatch structure by weaving together p ultimately providing structural support in the cell wall.

Question 31

Explain the function of Cellulose

Answer 31

cellulose keeps plant walls stable and keeps them intact by preventing them from bursting

Question 32

How would you test for starch?

Answer 32

Firstly you would put your sample in solution , you would then add iodine to this solution , if there is starch present there will be a colour change from brown-yellow too blue-black.