Enzymes Flashcards
Explain catalase
It is a highly effective biological catalysts, each subunit of catalase contains a single iron ion which is as effective as several tons of iron filings. It is also highly specific
Why do we use enzymes (3C’s)?
Catalysis
Coupling
Control
Enzymes as catalysts
Not permanently changed during a reaction so one molecule can catalyse many reactant molecules.
low concentrations required
rate proportional to enzyme concentration (control speed)
cannot affect equilibrium position
Enzyme cofactors
Adds additional chemical reactivity over that provided by 20 amino-acid side chains.
e.g. carboxypeptidase: zinc ion is essential for enzymatic activity
cofactor types: metal ions (e.g. Zn2+, Mg2+)
NOT coenzymes
Prosthetic groups
Either organic or organometallic
tightly bound
sometimes covalently linked
removed by denaturation
undergo reversible changes whilst bound to the enzyme
How large is invertase enzyme and its substrate sucrose?
Enzyme invertase 100 000 Da
Substrate sucrose 360 Da
substrate(s) interact at specific site – interactions involved
active site (catalytic site)
enzyme and substrate(s) interact to form enzyme-substrate complete. The substrates bind to the enzyme
specificity for substrates.
Explain the induced fit theory
induced fit (Dan Koshland, 1959)
active site not quite the right ‘shape’
partial binding induces conformational change in enzyme (and substrate)
When does ATP bind?
ATP cannot bind until the protein has a conformational change due to the binding of a substrate molecule.
(The top part of the enzyme hinges down)
How do enzymes lower activation energy?
An enzyme will increase effective reactant concentration orientation with proximity 10^8 fold enhancement in rate possible
alternative reaction pathways
specific amino-acid side chains in active site involved
Specificity of serine proteases
Digestive enzymes chymotrypsin, trypsin and elastase
structurally related serine proteases because they have a serine residue in active site.
They catalyse hydrolysis of peptide bonds and are selective for peptide bonds on carboxyl side of specific amino-acid residues.
What is alpha chymotrypsin
Chymotrypsin with a tripeptide with alanine, glycine and tryptophan. To cut it up it forms a cleft called the specificity pocket which is where the enzyme decides by which amino acid side chains it’s going to cut. chymotrypsin will cut next to tyrosine tryptophan phenylalanine and methionine because they are either bulky or non-polar.
what amino acid does trypsin cut?
Lysine or arginine as positively charged side chains
what amino acid does elastase cut?
small uncharged side chains such as glycine or alanine
Are enzymes stereospecific?
Yes, they have a chiral centre carbon and stereospecific binding requires at least three ‘points of contact’
What drug can be used as anti-infammatory?
ibuprofen (cyclooxygenase)
