Enzymes Flashcards
(32 cards)
What are enzymes?
Proteins that catalyse specific chemical reactions
What functions are enzymes involved in?
Digestion, blood clotting, defence, movement, nerve conduction
List 5 properties of allosteric enzymes
They’re multisubunit complexes.
They have regulatory sites and catalytic sites on different subunits.
Regulation occurs via conformational changes.
They exhibit non-Michaelis-Menten kinetics- V vs S plots are sigmoidal.
They’re involved in feedback inhibition of metabolic pathways
Give an example of how an enzyme can be a drug target for antibiotic treatment
Penicillins inhibit cell wall synthesis by inhibiting the enzymes that make pentapeptide links
Give an example of how an enzyme can be a drug target for anti-inflammatory agents?
Aspirin blocks prostaglandin
Give an example of how an enzyme can be a drug target for anticancer drugs
Methotrexate is a folate analogue which interferes with synthesis of DNA precursors
Give the general 5 properties of enzymes
Increase reaction rate by up to 10 billion times
Enzymes show specificity
They remain unchanged at the end of the reaction
They do not alter reaction equilibrium
They facilitate reactions by decreasing free energy of activation of the reaction
What’s the name of the point of the reaction where free energy is highest?
The transition state
What are active sites?
3D cavities that bind substrates using electrostatic, hydrophobic, and hydrogen bonding and van Der Waal’s interactions.
What are 4 ways in which enzyme activity is regulated?
Control of gene expression
Compartmentation
Allosteric regulation
Covalent modification
What’s allosteric regulation of enzymes?
The regulation of an enzyme by binding an effector molecule at a site other than the active site, termed an allosteric site
What are the 2 types of allosteric regulators?
Allosteric inhibitors and allosteric activators
What is Michaelis constant?
KM is the substrate concentration where the rate is Vmax divided by 2, hence being where half the active sites are bound by substrate
What enzyme cleaves fructose 1,6-bisphosphate in glycolysis and what into?
Aldolase cleaves fructose 1,6-bisphosphate into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate
What converts dihydroxyacetone phosphate into glyceraldehyde 3-phosphate?
Triosephosphate isomerase (TIM)
Give a definition for a perfect enzyme
One for which the rate of the reaction it catalyses is limited by diffusion rate, not by the enzymes activity
What are the 4 categories of proteases?
Serine proteases, cysteine proteases, aspartyl proteases and metalloproteases
What allows serine proteases to function?
They have a very reactive serine amino acid which is able to directly participate in peptide bond hydrolysis
What are 3 important serine proteases?
Chymotrypsin, trypsin (pancreas) and elastase (lungs)
How does chymotrypsin affect peptide hydrolysis?
The very reactive serine attacks peptide bonds to form acyl-enzyme intermediates, which are much more prone to hydrolysis
What makes the serine amino acid so reactive in serine proteases?
There’s a catalytic triad of serine, histidine and aspartic acid in sequence. A proton is removed from the serine onto the histidine side chain, and then a proton on a nitrogen of the histidine can be moved away onto the negatively charged aspartic acid carboxyl group. This makes the serine oxygen very nucleophilic.
What amino acids does trypsin work specifically on?
Lysine and arginine
Why does trypsin work specifically on lysine and arginine?
Trypsin has a negatively charged pocket which accommodates the positive side chain of lysine and arginine, which gives tighter binding
What amino acids is chymotrypsin specific to?
Phenylalanine, tryptophan and tyrosine
