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 biuret 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

Question 33

Relate Glycogen’s structure to its function

Answer 33

-it’s extensive branching allows enzymes to work on many ends at the same time. This allows a quick release of glucose when animals need immediate energy.
-it’s highly branched structure allows for compact storage.

Question 34

Relate Amylose’s structure to its function

Answer 34

-it’s unbranched structure makes it resistant to digestion
-its helical shape enables it to be more compact.

Question 35

Relate Amylopectin’s structure to its function

Answer 35

-it’s branched structure makes it more easily hydrolyzed for use during cellular respiration or added to for storage.

Question 36

Relate Cellulose’s structure to its function

Answer 36

-the linear arrangement of b glucose glucose molecules and extensive hydrogen bonding gives it a rigid, fibrous structure. And provides high tensile strength which allows it to stretch without breaking making it possible for cells to withstand turgor pressure.
-the tensile strength of cellulose helps resist mechanical stress and prevents cells from bursting.
-the tightly packed hydrogen bonds make cellulose insoluble in water.

Question 37

Relate Triglycerides structure to its function

Answer 37

-they are hydrophobic so they do not cause osmotic water uptake in cells so more can be stored.
-they compose part of the adipose tissue layer which acts as insulation against heat loss
-low density of fat tissue increases ability of animals to float more easily
-the adipose tissue contains stored triglycerides and this tissue helps protect organs from damage risk.

Question 38

Relate the structure of hemoglobin to its function.

Answer 38

-The haem group with its central iron ion is essential for the reversible binding of oxygen.
-hemoglobin’s cooperative binding is another important aspect of its function. When one oxygen molecule binds to a haem group it causes a conformational change.

Question 39

Relate the structure of collagen to its function.

Answer 39

-the triple helix of collagen provides great tensile strength which is crucial for tissues that need to withstand pulling forces.
-The staggered ends of the collagen molecule within the fibrils provide strength.
-the cross linking between collagen fibrils strengthens tissues making them more rigid and able to withstand compressive forces.
-the presence of glycine in every third position and hydrogen bonds between chains help maintain the structural integrity of collagen

Question 40

Differences between collagen and hemoglobin?

Answer 40

1. Collagen has 3 polypeptide chains forming a triple helix
   Hemoglobin has 4- a-globin and b-globin
2. Collagen is a fibrous protein and hemoglobin is a globular protein
3. Collagen has structural functions and hemoglobin has functional functions
4. Collagen is insoluble in water and hemoglobin is soluble in water.

Question 41

Explain how hydrogen bonding occurs between water molecules.

Answer 41

It arises due to the polarity of the water molecule where the oxygen atom attracts the hydrogens of neighboring water molecules leading to the formation of hydrogen bonds.

Question 42

Relate the properties of water to its roles in living organisms.

Answer 42

1. Solvent action- as water is a polar molecule many ions and covalently bonded polar substances will dissolve in it. Substances like nutrients, gases, and waste in fluids such as blood, lymph and cytoplasm.
2. High specific heat capacity- it allows it to act as a temperature buffer. In living organisms it helps maintain homeostasis.
3. High latent heat of vaporization- means it takes a lot of energy to turn water from a liquid into a gas.
   Only little water is required to evaporate for the organism to lose a great amount of heat.
   This provides a cooling effect for living organisms.