Enzymes II Flashcards
what are perfect enzyme reaction rates limited by
Diffusion
Rate of reaction =
Kcat [ES]
Turnover number, Kcat =
Vmax / [enz]
whats on a serine protease active site and how does it work
A very reactive serine group, CH2OH
They attack the peptide bond to form an acyl-chloride so its more easily hydrolysed by water
What enzymes have serine active sites
Chymotryspin and tryspin
What is the catalytic triad
Ser 195, His 57 and Asp 102
How does the catalytic triad work
- The positive charge is moved from the serine to the aspartate making the serine very negatively charged
- The negative oxygen in the serine group will attack the ketone group in the peptide bond resulting in half of the polypeptide being protonated and released but the other half links onto the enzyme creating an ester intermediate
- Water attacks the acyl-enzyme releasing the second half of the polypeptide, leaving the enzyme unchanged
Where does chymotrypsin cleave at
Aromatic tissues
Why does chymotrypsin cleave here
Its active site pocket is lined by hydrophobic residues therefore they have an attraction to the hydrophobic side chains of the aromatic residues
Where does trypsin cleave at
Lysine and arginine
Why does trypsin cleave here
Its active site pocket has a negatively charged side chain therefore will form an electrostatic attraction with the positive residues
Where does elastase cleave at
Small substrates
Why does elastase cleave at
Its active site pocket is very narrow since its constricted by other residues so only small side chains can enter
What is the electron transport chain
Cytochromes that take electrons and pass them along other cytochromes. Eventually they pass the electrons to oxygen to make water.
What is the net effect of the electron transport chain
Protons are generated and they are exported out of the mitochondria
