Carbohydrates

Question 1

State the elements present in carbohydrates.

Answer 1

Carbon, Hydrogen, oxygen

Question 2

State the general formula of carbohydrates.

Answer 2

(CH2O)x

where x is any number between three and eight

Question 3

Define the term monosaccharide

Answer 3

A monomer of carbohydrates, a single sugar

Question 4

Define the term disaccharide

Answer 4

A molecule comprising two monosaccharides, joined together by a glycosidic bond

Question 5

Define the term polysaccharide

Answer 5

A polymer made up of many sugar monomers (monosaccharides)

Question 6

Define pentose sugar

Answer 6

a monosaccharide composed of 5 carbons

Question 7

Define hexose sugar

Answer 7

a monosaccharide composed of 6 carbons

Question 8

Define the term “triose sugar” and name an example.

Answer 8

a monosaccharide composed of 3 carbons

e.g L-Glyceraldehyde and D-Glyceraldehyde

Question 9

Draw a molecule of alpha, beta glucose and ribose

Answer 9

look at book

Question 10

Draw a simplified molecule of alpha- and beta-glucose.

Answer 10

look at book

Question 11

Define the term isomer

Answer 11

Isomers are molecules that have the same molecular formula, but have a different arrangement

Question 12

Describe the difference between alpha- and beta-glucose.

Answer 12

Alpha glucose has an -OH (hydroxyl group) that points “downwards”, away from the ring, whereas the -OH on carbon 1 of beta glucose is above the ring.

Question 13

Draw a table listing the properties and differences between alpha-glucose and ribose.

Answer 13

Similarities:
1. They are both carbohydrates
2. Both monosaccharides
3. Both have the same general formula
4. Both very soluble in water
Differences:
1. Glucose has 6 carbons whereas ribose has 5 carbons
2. Glucose is a hexagon and ribose is a pentagon
3. Glucose main function- production of ATP during aerobic R .
4. Ribose main function- Forms a component of nucleotide DNA and RNA. and also a component of ATP

Question 14

List 3 examples of disaccharides and for each state which monosaccharides they are composed of. (F)

Answer 14

1. Sucrose- alpha-glucose and Fructose
2. Lactose- Alpha- glucose and galactose
3. Maltose- Alpha glucose and Alpha-glucose

Question 15

State the properties and functions of glucose

Answer 15

1. Glucose is a hexose sugar and can either be alpha or beta glucose which both have a ring structure.
2. It’s structure makes it soluble so it can be easily transported - because hydrogen bonds from between the hydroxyl groups and water molecules
3. And its chemical bonds contain a lot of energy
4. this relates to its function as the main energy source in animals and plants
5. It is polar so hydrogen bonds can form.

Question 16

State the properties and functions of fructose

Answer 16

1. A hexose monosaccharide

2. It is the sugar in fruits and is used as a sugar substitute for diabetics

Question 17

State the properties and functions of galactose

Answer 17

1. A hexose monosaccharide

2. It is used to make lactose ( the sugar in milk)

Question 18

State the properties and functions of maltose

Answer 18

1. A disaccharide made of two alpha- glucose molecules

2. Found in intestines and germinating seeds is an intermediate in the formation of starch.

Question 19

State the properties and functions of sucrose

Answer 19

1. A disaccharide made of alpha-glucose and fructose and is table sugar
2. In plants carbohydrate is moved from one region to another as sucrose.

Question 20

State the properties and functions of lactose

Answer 20

1. A disaccharide made from alpha-glucose and galactose
2. It is the main sugar in milk
3. It is difficult to hydrolyse providing a slow release of sugars to baby

Question 21

Draw a labelled diagram demonstrating how two molecules of glucose form a disaccharide in a condensation reaction, showing the location of a 1,4-glycosidic bond and from where a water molecule is generated.

Answer 21

Look at book

Question 22

Describe, using a diagram, how hydrolysis of maltose occurs and why water is needed.

Answer 22

1. Hydrolysis of maltose occurs when a water molecule is added to maltose disaccharide
2. the addition of water results in the breakdown of maltose to two alpha- glucose monosaccharides.
3. The 2 hydrogen atoms and the oxygen atom bond with the oxygen joining the monomers.
4. This forms two hydroxyl groups on each monosaccharide (OH)

Question 23

Explain why alpha-glucose links together to form starch whereas beta-glucose links together to form cellulose.

Answer 23

1. Because beta-glucose has a hydroxyl group pointing up. This means the hydroxyl group on carbon-1 and carbon-4 would be too far way from each other to react
2. So the only way beta-glucose can join together and from a polymer is if alternate beta-glucose molecules are turned upside down.
3. This means that the polysaccharide is unable to coil or form branches so is a straight chain molecule- cellulose
4. Starch has branches and coils- amylopectin 1-6 bonds as well as 1-4 glycosidic bonds

Question 24

List the two different polysaccharides that make up starch.

Answer 24

1. Amylopectin

2. Amylose

Question 25

Explain with the use of diagrams why glycosidic bonds are called 1,4 or 1,6.

Answer 25

1. because the bond either happens with the hydroxyl group from the 1st carbon in the structure and the 4th carbon.
2. or with the 1st carbon and the 6th carbon

Question 26

Explain how to calculate the number of glycosidic bonds in a carbohydrate given the number of monosaccharides it is made up from.

Answer 26

It will be one less
c-c-c-c-c-c
6 monosaccharides but only 5 bonds

Question 27

Explain how to calculate the chemical formula for a carbohydrate given the number of hexose sugars it is made up from.

Answer 27

Multiply c6h12o6 by n=number of hexose sugars

and then minus h2o*(n-1)

Question 28

Describe the structure of a cellulose fibre.

Answer 28

1. cellulose molecules make hydrogen bonds with each other forming microfibrils.
2. these microfibrils join together forming macrofibrils, which combine to produce fibres
3. these fibres are strong and insoluble and are used to make cell walls.
4. cellulose is an important part of our diet, it is very hard to break down into monomers and forms the fibre necessary for a healthy digestive system.

Question 29

State the properties and functions of cellulose

Answer 29

1. A straight chain molecule of beta- glucose.
2. because it is straight chain the chains can lie parallel to each other. numerous hydrogen bonds link the parallel chains producing strength- means it provides structural support for cells.

Question 30

State the properties and functions of starch

Answer 30

1.Starch is the main energy storage material in plants
2. Starch is insoluble in water- so it doesn’t cause water to enter the cell by osmosis which would make them sell- good storage
3. Amylose- long unbranched chain of alpha-glucose
the angles of the glycosidic bonds give it a coiled structure- making it compact so it’s very good storage as it can fit a lot in a small space.
4. Amylopectin- long branched chain of alpha-glucose. its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily. - it releases glucose quickly.

Question 31

State the properties and functions of glycogen

Answer 31

1. It is a polysaccharide of alpha-glucose, with a very similar structure to amylopectin except with a lot more side branches coming off it.
2. loads of branches mean that stored glucose can be released quickly which is important for energy release in animals.
3. it is also a very compact molecule so it’s good fro storage.