1. Which of the following amino acids is likely to be soluble in water?
a) Leucine
b) Alanine
c) Glycine
d) Aspartic acid
Explanation: Aspartic acid is a negatively charged amino acid. Thus, it has a negative charge to interact with water, hence it is likely to be soluble in water. Leucine, alanine, and glycine are neutral non-polar amino acids, therefore insoluble in water.
2. Proteins are made of _______
a) deoxyribonucleotides
b) ribonucleotides
c) glucopyranose
d) amino acids
Explanation: Proteins are made of amino acids. Amino acids are structural monomers of proteins. There are around 20 standard amino acids in nature. Deoxyribonucleotides are the monomers of DNA. Ribonucleotides are the monomers of RNA. Glucopyranose is a monomer of few polysaccharides.
3. Amino acids are also known as ‘dipolar ions’ or ‘zwitterions’
a) false
b) true
Explanation: At physiological pH, the amino group present in amino acids is protonated, whereas the carboxyl group is deprotonated. This forms two charges (one positive and one negative) within an amino acid. Therefore, amino acids are also known as ‘dipolar ions’ or ‘zwitterions’.
4. The common amino acids are also called as alpha-amino acids because they contain their amino group attached to the alpha carbon.
a) false
b) true
Explanation: The carbon next to carbonyl carbon in amino acids is called as alpha carbon. This alpha carbon contains an amino group as a substituent. Hence, the statement is true.
5. William C. Rose discovered the twentieth amino acid. Which amino acid is that?
a) Tyrosine
b) Tryptophan
c) Serine
d) Threonine
Explanation: William C. Rose discovered the last and twentieth amino acid, threonine. Rose wanted to identify the nutritional content of individual amino acids. Out of the 20 amino acids, 10 are nutritionally essential. The other 10 amino acids are considered “dispensable”.
6. The pH at which an amino acid has no net charge on it is known as its isoelectric point (pI).
a) false
b) true
Explanation: Amino acids have two or more than two ionizable groups. At low values of pH (acidic), these groups are protonated whereas, at higher values of pH (basic), these groups are deprotonated. There is an intermediate pH value, for which the amino acid will have no net charge. This pH is called its isoelectric point (pI). Hence, the above statement is true.
7. Find the odd one out.
a) Alanine
b) Aspartic acid
c) Serine
d) Glycine
Explanation: Glycine contains hydrogen atom as its side chain; therefore, its alpha-carbon is achiral. The rest of the amino acids have side chain groups other than the hydrogen atom, hence contain a chiral carbon atom. Therefore, glycine is the only amino acid that is optically inactive.
8. ______ stereochemical configuration of amino acids is present in proteins.
a) Only D
b) Both D and L
c) Either D or L
d) Only L
Explanation: Only the L stereochemical configuration of amino acids is present in proteins. Therefore, the relative configuration around the alpha carbon atoms of all the amino acids is the same. L amino acids can either be dextrorotatory or laevorotatory.
9. The bioluminescent jellyfish Aequorea victoria, has a protein called Green Fluorescent Protein (GFP) that fluoresces with a peak wavelength of ________, under UV or blue light radiation.
a) 808 nm
b) 708 nm
c) 408 nm
d) 508 nm
Explanation: The wavelength 508 nm is the correct answer as it lies in the green light spectrum of electromagnetic radiation. The wavelength 808 nm, 708 nm, and 408 nm lie in the infrared region, red light region, and blue light region respectively.
10. Which of the following is the correct sequence of the three consecutive amino acids present in the light-emitting group of green fluorescent protein?
a) Asp-Ser-Glu
b) Ser-Gly-Asn
c) Ser-Thr-Gly
d) Ser-Tyr-Gly
Explanation: Ser-Tyr-Gly is the correct sequence. The green fluorescent protein is made up of 238 amino acids. Once this protein is synthesized, these three amino acids undergo spontaneous cyclization and oxidation. The structure thus formed contains a system of double bonds that show conjugation and give this protein its fluorescent property.