Biological Molecules

Question 1

How do you test for proteins?

Answer 1

Biuret test - add sodium hydroxide to the liquid sample to make it alkaline. Then, add a few drops of copper sulphate solution, and if the substance becomes mauve, then a protein is present

Question 2

What is a glycosidic bond?

Answer 2

A chemical bond formed as a result of condensation between two monosaccharides e.g. bond between carbon-1 and carbon-4 of two alpha glucose molecules

Question 3

Name two molecules formed by the condensation of alpha glucose

Answer 3

Glycogen and starch

Question 4

What is the basic structure and function of glycogen?

Answer 4

Structure - alpha glucose chains with lots of 1-6 bonds, causing it to be very branched
Function - store for glucose in animals and used for respiration

Question 5

What is the difference between a saturated and an unsaturated fatty acid?

Answer 5

Saturated fatty acids have no carbon-carbon double bonds, giving them generally higher melting points and a straighter structure

Question 6

What role do hydrogen bonds have in tertiary, secondary and quaternary structures?

Answer 6

Form between the R-groups in amino acids, helping the proteins form their structures. They are not strong, but there are thousands of them, providing structure.

Question 7

What are the properties and function of triglycerides?

Answer 7

Fatty acid tails contain large amounts of chemical energy so they can be used as energy storage molecules. They are insoluble, so do not affect the water potential of the cell

Question 8

What are the basic roles of DNA and RNA?

Answer 8

DNA holds genetic information. and RNA transfers genetic information from DNA to the ribosomes

Question 9

What forms a peptide bond?

Answer 9

A condensation reaction between two amino acids

Question 10

What enzyme hydrolyses starch into maltose?

Answer 10

Amylase

Question 11

In a triglyceride, what reaction forms an ester bond?

Answer 11

Condensation reaction between a glycerol and a fatty acid

Question 12

What is the secondary structure in a protein?

Answer 12

The way that the polypeptide chain becomes folded up due to the hydrogen bonds, either into an alpha helix or a beta pleated sheet

Question 13

Why is water able to be a universal solvent?

Answer 13

Due to it’s polar structure, which means that one side has a slightly negative charge and the other a slightly positive charge.

Question 14

What does a carbohydrate contain?

Answer 14

Carbon, hydrogen and oxygen

Question 15

What does starch consist of and what are their structures?

Answer 15

Amylose and amylopectin
Amylose is a long chain that coils up into a spiral, whereas amylopectin has a branched molecular structure

Question 16

What role do ionic bonds have in formation of proteins?

Answer 16

Form between an amino acid with a positive charge and an amino acid with a negative charge if they are close. Helps to create the structure in tertiary and quaternary structures, but they are not strong.

Question 17

What is the basic structure and function of cellulose?

Answer 17

Structure - beta glucose chains with alternate bonding, making the cellulose very very straight. Hydrogen bonds also hold the layers together, and although they are weak individually, together they are strong
Function - supporting cells and limiting water intake in plants

Question 18

Describe the structures of the two isomers of glucose

Answer 18

Both have C6H12O6 formula
Alpha glucose has the OH group below the plane, and beta glucose has the OH group above the plane

Question 19

Which sugars turn orange when boiled with Benedict’s solution and why?

Answer 19

Reducing sugars - glucose, fructose, maltose, galactose
The Cu(II) ions in the Benedict’s are reduced to CU(I) ions due to the chemical formula of the sugars, making an orange precipitate

Question 20

What are the three components that are the same in every amino acid?

Answer 20

NH2 (amine group), COOH (carboxyl group) and a central carbon. Almost all also contain a hydrogen coming off of the central carbon.

Question 21

Give an example of a mono-, di- and poly- saccharide

Answer 21

Mono - glucose, fructose, galactose
Di - sucrose, maltose, lactose
Poly - starch

Question 22

Name the molecules that form maltose

Answer 22

Two glucose molecules

Question 23

How are triglycerides formed?

Answer 23

The condensation reaction between a molecule of glycerol and three molecules of fatty acid

Question 24

What is the structure of a phospholipid?

Answer 24

A central glycerol, with two fatty acids branching off and a phosphate head

Question 25

**What colour does iodine go when starch is present?**

Answer 25

Blue-black

Question 26

What is the primary structure in a protein?

Answer 26

Sequence of amino acids in a polypeptide, the order that the amino acids occur

Question 27

What is the quaternary structure of a protein?

Answer 27

The interaction and structure when a protein has more than one polypeptide chain, held together by hydrogen, ionic and disulphide bonds

Question 28

Name the molecules that form lactose

Answer 28

A glucose and a galactose molecule

Question 29

What are the properties and function of phospholipids?

Answer 29

Phosphate group is hydrophilic whereas the rest of the molecule is hydrophobic, so they naturally form bilayers of membranes, with the hydrophobic fatty acids facing in. This creates a barrier which can control what enters and leaves the cell.

Question 30

Where is a large store of glycogen found in the body?

Answer 30

Liver - continually breaks it down in order to maintain a stable blood concentration

Question 31

Name the molecules that form sucrose

Answer 31

A glucose and a fructose molecule

Question 32

**What is the basic structure and function of starch?**

Answer 32

Structure - alpha glucose chains with both 1-4 and 1-6 bonds Function - store for glucose in plants

Question 33

How should you test for lipids?

Answer 33

Add ethanol to the sample and shake, then add to a test tube of water - if lipids are present, then a milky emulsion will form. This is because lipids are a non polar molecule, so they dissolve in acids but not in water

Question 34

What is the tertiary structure of a protein?

Answer 34

The complex folding of the secondary structure, either into a fibrous or globular protein.

Question 35

What are the two types of tertiary protein structures and what are their functions?

Answer 35

Fibrous proteins are long, thin and insoluble. They have structural functions, and include collagen. Globular proteins are spherical and soluble. They have biochemical functions, such as enzymes.

Question 36

What role do disulphide bonds have in formation of proteins?

Answer 36

Form between amino acids with sulphur in their R-groups, assisting in creating the tertiary and quaternary structures. They are strong covalent bonds, so not easily borden.