Biological Molecules

Question 1

What are carbohydrates made of?

Answer 1

Monosaccharides

Question 2

How do monosaccharides join together?

Answer 2

By a condensation reaction.

Question 3

Sucrose is made from:

Answer 3

Glucose and fructose

Question 4

Lactose is made from;

Answer 4

Glucose and galactose

Question 5

Maltose is made from:

Answer 5

Glucose and glucose

Question 6

What type of reaction breaks polymers?

Answer 6

Hydrolysis reaction.

Question 7

State the Benedict’s Test for Sugars:

Answer 7

1) Reducing sugars include all monosaccharides and some disaccharides.
2) Add Benedict’s reagent (blue coloured) to a sample and heat it in a water bath.
3) If the test is positive a coloured solution will form.

The more Reducing it is the more red the precipitate is.
A more accurate way to do this would be to filter the solution and weigh the precipitate.

Question 8

State the Benedict’s test for non-Reducing sugars:

Answer 8

1) Add dilute HCl to the solution
2) Heat in water bath then add equal volume of Na2CO3
2) Add Benedict’s reagent (blue coloured) to a sample and heat it in a water bath.
3) If the test is positive a coloured solution will form.

The more Reducing it is the more red the precipitate is.
A more accurate way to do this would be to filter the solution and weigh the precipitate

Question 9

Definition of a polysaccharide:

Answer 9

A carbohydrate (e.g. starch, cellulose, or glycogen) whose molecules consist of a number of sugar molecules bonded together.

Question 10

What is starch made from?

Answer 10

Alpha glucose.

Question 11

What are the 2 types of polysaccharides present in starch?

Answer 11

Amylose

Amylopectin

Question 12

Describe the structure of amylose:

Answer 12

A long, unbranched chain of alpha-glucose. The angles of the glycosidic bonds give it a coiled structure. This makes it compact, and is so good for storage as you can fit more in a small space.

Question 13

Describe the structure of amylopectin:

Answer 13

A long, branched chain of alpha-glucose. It’s side branches allow the enzymes to easily break down the molecule to get at the glycosidic bonds easily. This means glucose is quickly released.

Question 14

Suggest a benefit of starch:

Answer 14

Starch is insoluble in water and doesn’t affect water potential so it doesn’t cause water to enter cells by osmosis, which would make them swell. This makes starch a good for storage.

Question 15

What is glycogen made from?

Answer 15

Alpha-Glucose

Question 16

Describe the structure of glycogen:

Answer 16

A long, highly branched chain of alpha-glucose. Side branches allow the enzymes that break down the molecule to break the glycosidic bonds quickly.
Lots of branches means energy can be quickly released.
Compact molecule.

Question 17

What is glycogen the main energy store of?

Answer 17

Animals

Question 18

What is starch the main energy source of?

Answer 18

Plants

Question 19

What is cellulose used as?

Answer 19

It is used in plants cell walls.

Question 20

Describe the iodine test for starch:

Answer 20

Add iodine dissolved in potassium iodide solution to the test sample.
If there is any starch present, the sample changes from a browny-orange colour to a blue-black colour.

Question 21

What is cellulose made from?

Answer 21

Beta-Glucose

Question 22

Describe the structure of cellulose and describe why this is:

Answer 22

Cellulose is made of long, unbranded chains of beta-glucose.
When the glucose molecules bind, they form straight cellulose chains.
These chains are linked by H bonds to form strong divers called microfibres. The strong fibres mean cellulose provides structural support for cells.

Question 23

Maltose is a sugar. Describe how a molecule of maltose is formed:

Answer 23

Two molecules of alpha-glucose are joined by a glycosidic bond. A molecule of water is released/a condensation reaction takes place.

Question 24

Describe the structure of a triglyceride:

Answer 24

Triglycerides have one molecule of glycerol with 3 fatty acid attached to it.

Question 25

What are there properties of a triglyceride?

Answer 25

They’re hydrophobic (repel water).

Question 26

Describe how triglycerides are formed:

Answer 26

A glycerol molecule comes into contact with the fatty acid, an ester bond is formed between the two OH groups on the glycerol and fatty acid forming an ester bond.
A molecule of water is released.
This occurs another 2 times as triglycerides have 3 fatty acid groups.

Question 27

Define an unsaturated fatty acid:

Answer 27

An unsaturated fatty acid has at least 1 double bond between carbon atoms.

Question 28

Define a saturated fatty acid:

Answer 28

Saturated fatty acids don’t have any double bonds between their carbons atoms.

Question 29

Describe the structure of a phospholipid:

Answer 29

There are 2 fatty acids attached to a glycerol molecule and one phosphate molecule attached.

Question 30

Describe the properties of phospholipids:

Answer 30

They’re hydrophobic (attracts water (the phosphate group)).

They’re hydrophilic (repels water(the fatty acid)).

Question 31

How does the structure of a triglyceride relate to its function?

Answer 31

Mainly used as energy storage molecules because:
• long hydrocarbon chains of the fatty acid release lots of chemical energy when broken down.
• they’re insoluble and so don’t affect water potential.

Question 32

Why are triglycerides insoluble?

Answer 32

The triglyceride ms clump together as insoluble droplets in cells because the fatty acid tails are hydrophobic - the tails face inwards, shielding themselves from water.

Question 33

How does the structure of a phospholipid relate to its function?

Answer 33

Phospholipids make up the bilayer of cells because:
• Their heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on each side.
• The centre of the bilayer is hydrophobic so water-soluble substances can’t easily pass through it - the membrane acts as a barrier to those substances.

Question 34

Describe the emulsion test for lipids:

Answer 34

1) shake the substance in a test tube with ethanol until the substance dissolved.
2) pour the solution into water
3) any lipid present will form a milky emulsion. The more lipid the more noticible milky colour.

Question 35

What type of bond is made from a condensation reaction between a glycerol and a fatty acid molecule?

Answer 35

Ester bond.