Macromolecule Lab

Question 1

Test for protein

Answer 1

Xanthoproteic test : adding nitric acid to unknown solution ( if their is aromatic amino acid then it will turn yellow)

Question 2

Test for lipid

Answer 2

Placing substance on unglazed paper ( The presence of lipids will make the paper dry transparent)

Question 3

Test for simple sugar

Answer 3

Benedict test : Heating the sample with basic solution containing cupric copper ( reduce to red cuprous oxide)

Question 4

Positive results for simple sugar test

Answer 4

Series of color changes : green to yellow to orange ( color depends on the amount of glucose from least to most respectively)

Question 5

Example of simple sugars (monosaccharides)

Answer 5

Glucose, fructose, galactose

Question 6

What forms a disaccharide?

Answer 6

Dehydration synthesis of 2 monosaccharides ( forms a glycosidic bond)

Question 7

Test for complex sugars

Answer 7

Drops of iodine solution in samples (positive results yellow to blue-black)

Question 8

How does the complex sugar test work?

Answer 8

The iodine becomes embedded in the center of a coil of glucose monomers = electrons are forced together into a configuration of particular energy levels ( allows them to absorb certain wavelengths of light resulting in color)

Question 9

Why do lipids float on water?

Answer 9

• They are hydrophobic
• Non polar molecules ( can’t interact with water because they cant form hydrogen bonds )
• Hydrocarbons ( carbon and hydrogen ) chain = non polar

Question 10

Why is paper opaque before you add oil?

Answer 10

Air and cellulose dont have the same refractive index and causes the light to scatter. When you add oil, fills the air gab ( same refractive index as the cellulose) allows light to pass through = transparency.

Question 11

What is the proportion of protein : lipid in high density lipoprotein ( HDL) ?

Answer 11

The proportion of protein to lipid is higher in HDL.
- Denser
- Carry less lipids
- Higher protein content = more compact
- Lower quantity of lipids to transport

Question 12

Why does the amino acid turn yellow in the xanthoproteic test ?

Answer 12

The aromatic ring of the amino acid becomes nitrated

Question 13

Why are Tyrosine and Tryptophan ( amino acids with aromatic rings) hydrophobic?

Answer 13

• Their side chains (aromatic rings) are large and non polar
• Contain many carbon-hydrogen bonds ( C-H) = non polar so they do not form hydrogen bonds with water molecules

Question 14

Example of polysaccharides

Answer 14

Starch, cellulose, Glycogen