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
What drives ATP synthase
The electrochemical proton gradient
What is the structure of ATP synthase
has 3 active sites activated by a rotating spindle
Every time it rotates 120 degrees an ADP and Pi molecule is bound together forming ATP
What does topoisomerase II do
Its an enzyme that untangles the mitotic spindle so that chromosomes can be separated
How does topoisomerase II work
- Binds to a segment of one chromosome, the gate segment
- Binding of ATP causes a segment perpendicular to the gate segment, the transport segment, to be clamped into position
- The enzyme makes a transient break in the gate segment so the transport segment passes through into holder on the other side
- The break in the gate segment is resealed and the transport segment is resealed
- Hydrolysis of the ATP resets the cycle
Why is this enzyme targeted
Anti-cancer drugs can interfere with enzyme as it can interfere with DNA replication
