521. An essential amino acid is one that
A. is essentially easy to synthesize
B. is essential to flagella motion
C. the body cannot synthesize
D. the body can synthesize under essential conditions

522 .D-Alanine and L-Alanine are technically known as
A. anomers
B. enantiomers
C. epimers
D. polymer

523. Which of the following pairs of amino acids would carry a negative charge on their side chain at pH 8.0?
A. Asparagine & Glutamine
B. Leucine & Glycine
C. Histidine & Lysine
D. Aspartate & Glutamate

524. In a polypeptide average mass of an amino acid residue is
A. 110 daltons
B. 118 daltons
C. 80 daltons
D. 150 daltons

525. Which pair of amino acids absorbs the most UV light at 280 nm?
A. Threonine & Histidine
B. Trp& Tyrosine
C. Cystein& Asparagine
D. Phenylalnine& Proline

526. Which of the following is a nonstandard amino acid?
A. Cysteine
B. Isoleucine
C. Hydroxyproline
D. Histidine

527. Which of the following is an essential amino acid?
A. Tryptophan
B. Methionine
C. Lysine
D. All of these

528. Protein fluorescence arises primarily from which residue?
A. Arginine
B. Tryptophan
C. Tyrosine
D. Phenylalanine

529. Which of the following amino acid is known as half-cystine residue?
A. Cysteine
B. Isoleucine
C. Valine
D. Histidine

530. Which of the following is not an essential amino acid?
A. Aspartic acid
B. Glutamic acid
C. Glycine
D. All of these