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ENZYMES AND THEIR MECHANISMS - Coggle Diagram
ENZYMES AND THEIR MECHANISMS
WHAT ARE ENZYMES?
proteins that speed up( catalyse) chemical reactions
functions- digestion: carbohydrates, proteins lipids
Blood clotting: e.g fibrin clot catalysed by thrombin
movement- muscle actomyosin is an ATPase
Nerve conduction- membrane pumps K+, Ca2+,Na+
protease, nucleases, polymerases and kinases catalyses a certain type of reaction
ENZYME DEFECTS CAUSE DISEASE
phenylketonuria: cannot convert Phe to Tyr.
• glycogen storage disease- cannot mobilise glucose
• Tay-Sachs disease-defect in processing a membrane
ganglioside- neuronal damage and death
ENZYMES ARE DRUG TARGETS
Antibiotics: e.g penicillin inhibit cell wall synthesis
Antiinflammatory agents e.g aspirin block prostaglandin synthesis
Anticancer drug e.g methoxtrexate is a folate analogue- interferes with synthesis of DNA precursors
KEY PROPERITES
UNCHANGED AT END OF REACTION
SHOW SPECIFICITY
INCREASE RATE BY UP TO 10 BILLION PER FOLD
DO NOT ALTER REACTION EQUILIBRIUM
FACILLITATE REACTION BY DECREASING THE FREE ENERGY OF ACTIVATION
THE ACTIVE SITE IS A 3D CAVITY THAT BINDS SUBSTRATES WITH SPECIFICTY DUE TO ELECTROSTATIC, HYDROPHOBIC, HYDROGEN BONDING AND VAN DER WAALS INTERACTIONS.
EVIDENCE OF ACTIVE SITE COMES FROM XRAY CRYSTALLOGRAPHY AND KINETIC STUDY OF ENZYME SCTIVITIES
LOCK AND KEY VS INDUCED FIT
LOCK AND KEY- ENZYME ACTIVE SITE HAS VERY SPECIFIC SHAPE TO THE SUBSTRATE- FITS PERFECTLY. THEY BIND TO FORM ENZYME SUBSTRATE COMPLEX REACTION IS CATALYSED FORMING ENZYME PRODUCT COMPLEX.
INDUCED FIT- SHAPE OF SUBSTRATE SLIGHTLY DIFFERENT TO THAT OF ENZYMES, ACTIVE SITE CHANGES SHAPE SLIGHTLY TO FIT SUBSTRATE- MOST ENZYMES FOLLOW INDUCED FIT MODEL
ENZYMES REDUCE ACTIVATION ENERGY AND SPEED UP REACTION BY USING ENZYME SUBSTRATE BINDING ENERGY
TO CONSTRAIN SUBSTRATE MOVEMENT E.G LYSOSOMES USE STRAIN TO CLEAVE ITS BACTERIAL SUBSTRATE
TO BRING MOLECULES TOGETHER IN THE ACTIVE SITE
TO STRAIN PARTICULAR SUBSTANCES IN SUBSTRATEMAKING BREAKAGE EASIER
Vmax- maximum saturation at active site of enzyme
Vmax/2- when active site is half saturated. Km- concentration of Substrate at Vmax/2
turnover number- max no. of substrate handled per active site per second
ENZYME INHIBITION
NON-COMPETITIVE
Inhibitor I binds at site on enzyme not active site therefore in the presence of non-competitive inhibitor Km is unaltered but Vmax is reduced
COMPETITIVE
INHIBITOR COMPETES WITH SUBSTRATE FOR ACTIVE SITE IN THE PRECENCE OF INHIBITOR KM IS INCREASED TO ACHIEVE Vmax/2 however Vmax is unaffected as the effects of inhibitor can be counteracted by increasing substrate concentration
ALLOSTERIC
changes the conformation of active site allosteric inhibitor like non-competitive found on enzyme but not at active site
examples
DNA gyros used in DNA replication can be inhibited by Novobiocin
fluroquinolnes inhibit DNA gyros resealing
