QUESTION 5 s and it has a flexible hinge My protease has a globular structure wi

Question

QUESTION 5 s and it has a flexible hinge My protease has a globular structure with beta sheets, alpha helix and ma that is regulated to cover the pocket so the enzyme can be turned off. Match the amino acid ny sharp turns It has a pocket where it binds amino acid to the MOST APPROPRIATE location in'on the open hihge closed hinge A none of these cysteine proline glycine histidine phenylalanine serine a sharp fixed turn in the protein backbone C a flexible hinge D the active site internal within the enzyme F external on the enzyme 0.5 poir QUESTION 6 If my protease is in lysosomes and works in the blood to attack un-engulfed invaders at which pH woulg the protein structure remain relatvely intact with the nge closed? 2.3 0 5 07.4 0 95 Click Save and Submit to save and submit. Click Save All Answers to save all answers. Save All Answers

Explanation / Answer

Ans. #5. Cysteine      - A. none of the above

            Proline            - B. a sharp fixed turn in the protein backbone

            Glycine           - C. a flexible hinge

            Histidine         - external on the enzyme

            Phenylalanine – E. internal within the enzyme

            Serine             - D. the active site    

# Glycine, having only an H-atom in its side chain provide greatest extent of movement along the dihedral angles. So, it’s most suited to form a flexible hinge in the protein.

# Note that the enzyme is a protease. Many proteases, say serine proteases, have serine residues at the active site.

# Being hydrophobic, phenylalanine is preferable buried in the hydrophobic core of protein (i.e. internal within the enzyme).

# Proline uniquely forms kink (a sharp fixed turn in the protein backbone).

# The external surface of enzyme is in direct contact with the hydrophilic, aqueous environment. So, polar as well as charged residues can be present on its surface. Serine (has –OH group) as well as histidine fulfil the criteria.

Note that the ring of histidine has 2 N-atoms in it. At physiology pH 7.4, though histidine bears (almost) no positive charge, it can form hydrogen bonds with H2O molecules more efficiently – because serine has only 2 atoms (-OH) serving as hydrogen bonding sites whereas histidine as 4 atoms [2 x (-NH)] that can serve as hydrogen bonding sites for water.

Therefore, since serine is preferred at the active site of proteases and histidine can well form H-bonds with aqueous environment, histidine shall be at the external surface of enzyme.

#6. Correct option. B. 5.

The optimal pH of lysosome is around 4.5 -5.0.

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