b) Plant cell wall
d) Both plant cell wall and collagen
17. Peptide bonds between amino acids are highly stable and have a half-life of seven years in intracellular condition. This is due to
a) High activation energy required for hydrolysis
b) Low activation energy required for hydrolysis
c) Peptide bond is a covalent bond
d) Peptide bond is rigid and planar
18. Tri-peptide consists
a) 3 amino acids and 3 peptide bonds
b) 2 amino acids and 3 peptide bonds
c) 3 amino acids and 2 peptide bonds
d) 3 amino acids and 4 peptide bonds
19. All the following statements are true except
a) Ornithine and citrulline are uncommon aminoacids
b) Ornithine is an intermediates in Urea cycle
c) Ormithine and citrulline are uncommon amino acids present in many proteins
d) Both ornithine and citrulline are intermediates in urea cycle
20. The characteristic strong absorbance of 280nm of proteins is due to
a) All amino acids can absorb at 280nm
b) Only Tryptophan and tyrosine can absorb at 280 nm
c) Tryptophan is responsible for the absorbance
d) Tryptophan, tyrosine and phenylalanine can absorb at 280 nm
21. The formation of cystine occurs at
a) Covalent bond
b) Ionic bond
c) Hydrophobic interaction
d) Vander walls interaction
23. Which of the following aminoacid has pKa near neutrality
24. Desmosine is an unusual amino acid found in
25. How many small peptides are formed upon cleavage by trypsin if a protein has 5 lysine residues
26. EF-1α and EF-Tu are
27. All the statements regarding peptide bond are true except
a) Peptide bond is a co-valent bond
b) Peptide bond is rigid and planar
c) Peptide bond has partial double bond character
d) Peptide bond is formed by non-condensation reaction
28. Αlpha-helix has
a) 3.6 residues/turn and is a right handed helix
b) 3.8 residues/turn and is a right handed helix
c) 3.6 residues/turn and is a left handed helix
d) 3.8 residues/turn and is a left handed helix
29.Which of the following amino acids are rarely present in alpha helix
a) Glycine and proline
b) Proline and tryptophan
c) Tryptophan and glycine
d) Proline only
30. PDI is an enzyme involve in
a) Protein synthesis
b) Protein degradation
c) Protein folding
d) Protein quaternery structure formation
Both plant cell wall and collagen
Explanation: 4-hydroxyproline, 5-hydroxy lysine, selenocysteine, desmosine, carboxy glutamate all are uncommon amino acids
18.c) amino acids and 2 peptide bonds
Ormithine and citrulline are uncommon amino acids present in many proteins
Remember, these two amino acids are not present in any proteins.
Tryptophan, tyrosine and phenylalanine can absorb at 280 nm. These are aromatic amino acids. Tryptophan and tyrosine absorbs strongly at 280nm where as phenylalanine has comparatively low absorbance.
Two cysteine amino acids are linked by di-sulphide bond to form cystine. Di-sulphide bonds are formed only in the highly oxidizing environment of ER.
22.c Hydrophobic interaction (Bonds in Proteins)
23.c histidine has a pKa of 6.0 and has buffering capacity
25.c) 6 Trypsin cleave at C-terminal of lysine or arginine residue
EF-Tu elongation factor is involved in protein synthesis of bacteria. The protein counterpart in eukaryote is EF-1α. Both are members of the same family with a common ancestry.
27.d Peptide bond is formed by non-condensation reaction. Actually Peptide bond is formed by condensation reaction.
28.a) 3.6 residues/turn and is a right handed helix in all proteins. You have to read the options carefully before picking one.
29.a) glycine and proline.
Proline is an alpha helix terminator as it cannot form H- bond with other residues. Glycine is the simplest amino acid and has high conformational flexibility. Polymers of glycine form coiled structures entirely different from alpha helix.
PDI (protein di sulphide isomerase) is an enzyme involved in shuffling of di sulphide bonds in protein folding. Refer our post protein folding.