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CHEM 4600: BIOCHEM TEST 2
oxidoreductase |
enzyme that catalyzes oxi-reduc rxn using NAD+/FAD
eg: dehydrogenases
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transferases |
enzymes that catalyze transfer of functional groups
eg: transaminase,
transcarboxylase, hexokinase
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Hydrolyases
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enzymes that cleave bonds with the addition of water (ex: proteases: trypsin, thrombin, chymotrypsin) carboxypeptidase A
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Lyases |
Catalyze carbon-carbon bond and carbon-nitrogen bond cleavage
Release CO2 from a b-keto acid
Some are reversible
eg pyruvate decarboxlyase
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Isomerase
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An enzyme that rearranges the atom in a molecule.
change from one isomer to another, eg cis-trans isomerism
eg maleate--fumarate
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ligase |
enzyme that catalyzes joining of 2 large molecules by forming chemical bond
-couples 2 substrates w/ splitting of ATP
S + S + ATP---> S + ADP + P
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enzyme catalysis
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-protiens that enhance rxn rate by lowering EA
-E recognizes S & induces the TS
-E changes shape when S bound (tighter fit, chem groups into position to catalyze, creates fav cond)
-S held in active site by IMF
-E provides catalytic surface
-Enyzyme surface stabilizes the TS
-transforms TS to P
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steady state theory
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theory in enzyme kinetics
-the production = consumption of TS [ES] remains constant
-persists until almost all S is consumed
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V(max)
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hypothetical maximum rate: when all substrate is bound to enzyme
hypothetical because continuously binding and converting to product, then unbinding
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Km
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enzyme's "affinity" with substrate
-measure of [S] required for effective enzyme catalysis
-[S] @ 1/2 Vmax
-constant for a given enzyme
-small Km= tight binding, needs less S
-large Km=weak binding, needs more S to obt Vmax
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Kcat
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turnover #
-# S--P per E per unit of time
-1/sec
-measure of catalytic production under saturated Substrate(optimum conditions)
-with S excess K2=Kcat
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Kcat/ Km
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catalytic or enzyme efficiency
-measure of how perfect an E is
-apparent 2nd order rate constant
-large Kcat/ Km value= more P made per S per time
-measuers eff of transformation of bound P and eff of productive S binding
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specific activity
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measure of enzyme purity
-activity units/ protein
-mmole/min per mg
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enzyme inhibitors
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competitive
reversible, competes with S at active site
Km ↑ Vmax ∅
noncompetitive
irreversible, I binds to E or ES at diff site
Km Ø Vmax↓
uncompetitive
irreversible, I binds to ES at diff site, alters E structure to make I site available
Km↓ Vmax ↓
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Ordered Sequential
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Substrate binding order and product release order are constant
ex. Pyruvate >>> Lactate; NADH binds first, Lactate released first
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double displacement
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catalytic mechanism
one S binds 1 P released
ping pong mechanism
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Catalytic residue
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-alter pka of a residue or H20
-activate part of S
-stabilize TS
-in active site and weaken bondes
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protease
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an enzyme that cleaves peptide bonds via hydrolysis
-cleavage is slow due to resonance in bond
so enzyme must facilitate Nu attack at normally unreactive C=O
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general acid-base catalysis
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catalysis in which a protein is transferred in the transition state
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chymotrypsin |
pancreatic enzyme that cleaves on C-term side of AA WYFML
-covalent and AB catalysis
-Nu becomes briefly covalently attached
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List the types of proteases.
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Serine protease (OH), Aspartic protease (COO), cysteine protease (SH) and metalloproteases. (Zn)
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isozymes |
related proteins with similar but not identical catalytic activity
-eg LDH and H/M subunits
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reversible covalent modification
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a mechanism of enzyme regulation in which the enzyme's activity is either incr or decr by the reversible covalent addition of a group such as phosphate or AMP to the protein
-eg phosphorylation
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Proteolytic Activation
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Enzymes that cycle between active and inactive forms. Hydrolysis of peptide bonds in inactive enzymes produce active enzymes. Chymotrypsin, trypsin, and pepsin are all activated this way.
-irreversible converstion btw inactive (zymogen) to active enzyme
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chymotrypsinogen
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chymotrypsinogen (inactive) is activated by trypsin via proteolytic cleavage to form π chymotrypsin
-π chymo is cleaved by itself to make α chymo (3 chains)
α chymotypsin - A B C chains linked by disulfide bonds
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cofactors
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-any molecule (org or inorganic) that aids in catalysis, (protein fxn)
-two types
coenzyme : nonprotein org that aids in catalysis, binds with IMF
prosthetic group: nonprotein org molecule that aids, binds convalently (stuck)
enzyme + cofactor= haloenzyme
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serine proteases
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chymotrpysin: cuts WYFML
trypsin: cuts RK
elastase: cuts AG
all have catalytic triad
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