2. Biological Molecules

Question 1

Describe the Benedict’s test for reducing sugars

Answer 1

-add equal volume of Benedict reagent to the sample to be tested.
-heat the mixture in a water bath at 100 degrees for 5 minutes
Positive result- blue to a green to yellow to orange to brick red

Question 2

Describe the iodine test for starch

Answer 2

-add a few drops of iodine to the sample
-if starch is present, iodide ions in the solution interact with the Centre of starch molecules, producing with a distinctive blue-black colour

Question 3

Describe the Benedict test for non-reducing sugars

Answer 3

1. hydrolyse non reducing sugars into their monomers by adding an equal volume of HCl
2. Heat in a boiling water bath for 5min
3. Neutralize the mixture using sodium hydrogen carbonate solution
4. Proceed with the Benedict’s test as usual.

Question 4

Describe the emulsion test for lipids.

Answer 4

-add ethanol to the sample to be tested, shake to mix then add the mixture to a test tube of water
-if lipids are present, a milky emulsion will form
-if no lipid is present, the solution remains clear.

Question 5

Describe the outer test for proteins.

Answer 5

-a liquid solution of sample is treated with sodium or potassium hydroxide to make the solution alkaline.
-a few drops of copper(II) sulfate is added to the sample
-if protein is present, a color change from blue to lilac/purple will be observed

Question 6

Describe a semi-quantitative Benedict’s test on a reducing sugar solution.

Answer 6

-can be carried out by setting up standard solutions with known concentrations of reducing sugar
-using serial dilution.
-each solution is then treated in the same way; add the same volume of Benedict’s solution to each sample and heat in a water bath that has been boiled.
-any color change observed for each solution of a known concentration of reducing sugars is then compared to the stock solution colors.

Question 7

Define the term monomer

Answer 7

A single subunit that is used to build large polymers

Question 8

Define the term polymer

Answer 8

A large molecule comprised of repeating subunits

Question 9

Macromolecule

Answer 9

A large biological molecule
Eg: polysaccharides
Proteins (polypeptides)
Nuclei acids (polynucleotides)

Question 10

What is the difference between alpha and beta glucose?

Answer 10

The OH group on carbon 1 for alpha glucose is below the ring, while that for the beta glucose is above the ring.

Question 11

Define a monosaccharide

Answer 11

A single sugar monomer, all of which are reducing sugars

Question 12

What is a disaccharide

Answer 12

A sugar formed from two monosaccharides joined by a glycosidic bond in a condensation reaction

Question 13

What is a polysaccharide

Answer 13

A polymer formed by many monosaccharides joined by a glycosidic bond in a condensation reaction

Question 14

Why are triglycerides energy reserves ?

Answer 14

Because they store more energy per gram due to their hydrocarbon chains.

Question 15

What is a condensation reaction?

Answer 15

A chemical reaction involving the joining together of two molecules by removal of a water molecule

Question 16

What is a hydrolysis reaction?

Answer 16

A chemical reaction in which a chemical bond is broken by the addition of a water molecule; commonly used to break down complex molecules into simpler molecules.

Question 17

Equation for sucrose

Answer 17

Glucose+fructose

Question 18

Equation for maltose

Answer 18

Glucose+ glucose

Question 19

Equation for lactose

Answer 19

Glucose+galactose

Question 20

Functions of triglycerides

Answer 20

1. They make excellent energy stored because they are richer in carbon-hydrogen bonds than carbohydrates
2. They act as an insulator against loss of heat just below the skin
3. Metabolic source of water- when triglycerides are oxidized in respiration, they are converted to carbon dioxide and water.

Question 21

What is the primary structure in a protein?

Answer 21

The sequence of amino acids in a polypeptide or protein.

Question 22

What is a secondary structure in proteins?

Answer 22

The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids (an ą-helix or B-pleated sheet)

Question 23

What is the tertiary structure of a protein?

Answer 23

The compact structure of a protein resulting from the three-dimensional coiling of the chain of amino acids.

Question 24

What is the quaternary structure of a protein?

Answer 24

The three-dimensional arrangement of two or more polypeptides, or of a polypeptide and a non-protein component such as haem, in a protein molecule.

Question 25

What is a globular protein?

Answer 25

A protein whose molecules are folded into a spherical shape, it is often water-soluble.

Question 26

Why do globular proteins usually curl up?

Answer 26

So that their non-polar hydrophobic R groups point into the centre of the molecule, away from the watery surroundings.

Question 27

What is a fibrous protein?

Answer 27

A protein whose molecules have a relatively long, thin structure that is generally insoluble and whose function is usually structural.

Question 28

What is the latent heat of vaporization?

Answer 28

A measure of the heat energy needed to vaporize a liquid changing it from a liquid to a gas.

Question 29

Disulphide bonds

Answer 29

Strong covalent bonds that form between two cysteine R groups
Strongest bonds in a protein molecule

Question 30

Ionic bonds

Answer 30

Form between positively charged and negatively charged R groups
Stronger than hydrogen bonds

Question 31

Hydrogen bonds

Answer 31

Form between strongly polar R groups

Question 32

Hydrophobic interactions

Answer 32

Form between the non-polar (hydrophobic) R groups