-+90% 1. An amino acid will have the form shown at NH3 A) a pH less than its iso
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-+90% 1. An amino acid will have the form shown at NH3 A) a pH less than its isoelectric point. B) any pH other than 7.0. C) a pH greater than its isgelectric point. D) its isoelectric point 2. Amino acids are least soluble in water at A) their isoelectric point. B) low pH. C) neutral pi. D) high pH 3. The beta-pleated sheet is an example of A) primary structure. B) secondary structure. C) tertiary structure. D) quaternary structure 4. The type of bonding that maintains the secondary structure in a protein is the A) hydrogen bonds between the carbonyl and amino groups of the backbone. B) covalent bond between the carbonyl and amino groups of the amino acids. C) hydrogen bonds between two amino acids. D) disulfide bonds that hold two polypeptide chains together. 5. Which protein is considered to be a globular protein? A) albumin B) keratinC) collagen D) myosin 6. Which pair of amino acids can have hydrophobic interactions? A) arginine and glutamic acid B) aspartic acid and lysine C) leucine and alanine D) glutamic acid and serine 3Explanation / Answer
1) The isoelectric point (pI), is the pH at which a particular molecule carries no net electrical charge in the statistical mean.
The given amino acid has protonated amino group and carboxylic group as well. When pH is below pI, amino acid will have protonated amino group and carboxylic group. Hence, given molecule will be present when pH less than its pI. Answer is option A.
2) At pH higher than pI amino acid will be in H2N-R-COO-
At pH lower than pI amino acid will be in HOOC-R-NH3+
Thus in either case, the molecules gets solubalized due to Coulombian repulsion.
Wheras, at the pH where their charge is zero (pI), they can stick together more easily, and therefore the overall amino acid is less soluble.
Answer is option A: their isoelectric point.
3) The ?-sheet (also ?-pleated sheet) is a common motif of regular secondary structure in proteins.
Thus answer is: Option B.
4) Secondary structure is formally defined by the pattern of hydrogen bonds between the amino hydrogen and carboxyl oxygen atoms in the peptide backbone.
Answer is option A.
5) An albumin (a type of globular protein) found in vertebrate blood.
Answer is option A.
6) Following are the Hydrophobic:
• Alanine - Ala - A
• Isoleucine - Ile - I
• Leucine - Leu - L
• Methionine - Met - M
• Phenylalanine - Phe - F
• Valine - Val - V
• Proline - Pro - P
• Glycine - Gly - G
Hence Leucin and alanine can have hydrophobic interactions.
Answer is C.
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