Flashcards
Intro to Enzymes
Cards in this deck (24)
- 1What are enzymes?Proteins which act a biological catalysts by lowering the activation energy required for a chemical reaction by forming complexes with their substrates & stabilising the transition state
- 2Under what conditions do enzymes operate?Normal physiological condition
• moderate temperature
• approx pH 7
• low substrate concentration
• aqueous environment - 3Catalytic power is determined by what equation?Rate enhancement = catalysed rate / un-catalysed rate
i.e the factor by which a catalyst enhances the rate of a reaction - 4How does enzymology influence medicine?• Enzyme deficiencies caused by 'inborn errors' cause disease - to determine a diagnosis you need to be able to measure the relative concentration & activity of enzymes e.g. MI or indigestion?
• Many drugs are enzyme inhibitors & so the specific dosage will be related to the inhibition mechanism - 5Why is product accumulation not linear?• Substrate concentration falls throughout the reaction
• Products may inhibit the enzymes
• Enzymes may become denatured
• Reverse reactions can become more favourable - 6How is enzyme activity (Vo) measured?By increasing the [substrate] and measuring the accumulation of product over time - enzyme activity depends on how rapidly it den process the substrate
- 7How is Vmax calculated?Plotting a Lineweaver-Burke Plot
• a double reciprocal of the data - 8Equation of a Lineweaver-Burke Plot
- 9What is the Km & how is calculated?Michaelis-Menten Constant
The substate concentration required for 50% Vmax
- 10Michaelis-Menten Equation
- 11Discuss the difference in the Km value of Hexokinase & GlucokinaseNOTE--> Blood glucose level = 5mM
Hexokinase Km = 0.1mM
• works at lower glucose concentrations
• lower Km ensures all glucose is utilised for energy production
Glucokinase Km = 50mM
• works at higher glucose concentrations
• ensures glucose is not removed from the blood for storage at low conc.
• Glucokinase is mainly found in the liver & phosphorylates glucose when conc. is high allowing glycogen production - 12What are the two main types of enzyme inhibitors?Irreversible - inactivators
Reversible - competitive or allosteric - 13Action of: Irreversible inhibitorsReact with the enzyme & form a covalent adduct with the protein
- 14Action of: Organophosphate Diisopropyl Fluorophosphate (DIPE - a pesticide)Inhibition of AChE an enzyme which degrades ACh into choline & acetic acid
• inactivates AChE by phosphorylating the serine hydroxyl group locate at the active site
• once inactivated ACh accumulates throughout the nervous system resulting in overstimulation of the receptors --> kills pest - 15Action of: Aspirin (Acetylsalycilic acid - an NSAID)Irreversible inhibits COX-1 enzyme which catalyses the conversion of arachidonic acid to prostaglandins
• aspirin reacts with the serine residue close to the active site preventing the substrate from binding - 16Action of: Competitive inhibitorsCompetes with the normal substrate for the enzymes active site, as it has a similar structure, slowing down the action of the enzyme
• the drug will occupy the active site & then leave it unchanged - 17Action of: SulphonamidesAntibiotics which starve bacteria of essential folic acid
• bacteria cannot use readily made folic acid but must synthesis it themselves from 4-amino benzoic acid which is structurally similar to sulphonamides & so they competitively inhibit their action - 18How do competitive inhibitors alter the kinetics of an enzyme?Cause a higher concentration of substrate to be required in order to reach Vmax --> increased Km
NOTE --> they do not alter Vmax - 19Action of: Allosteric inhibitorsBind to the enzyme at the same time a a substrate at a secondary binding site - not the active site
• causes a conformational change which changes the shape of the active site hence rendering the enzyme & enzyme-substrate complex inactive
• allosteric inhibitors cannot be driven off the enzyme even by higher substrate concentrations - 20How do allosteric inhibitors alter the kinetics of an enzyme?Vmax is decreased & often Km increases (but not always)
- 21What are the 2 types of allosteric inhibition?Mixed inhibition
Non-competitive inhibition - 22How do mixed inhibition & non-competitive inhibition differ?• Allosteric changes affect substrate binding & activity in mixed but only affect binding in non-competitive
• Mixed inhibition can be reduced by an increased i [S] but has no affect on non-competitive inhibition
• Vmax decreases due to inhibition in mixed but decreases due to deceased reaction efficiency in non-competitive
• Km increases with decreased substrate affinity in mixed but is unchanged by non-competitive - 23Action of: Phosphofructokinase (PFK)PFK catalyses the transfer of phosphate to fructose-6-phosphate:
F-6-P + ATP --> F-6-biphosphate + ADP
• PFK binds to ATP at 2 sites - active & inhibitory - in the presence of high levels of ATP the inhibitory site is occupied & F-6-P binding is inhibited --> glycolysis does not proceed as ATP is not required - 24How is Ethylene Glycol poisoning treated & why?Administration of a 'near-intoxicating' dose of ethanol
• ethanol competes with ethylene glycol for the active site of alcohol dehydrogenase & slows the oxalate (toxin) production
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- MD2001 Flashcards on Intro to Enzymes, created by Lareyna Mcmenemy on 21/07/2018.
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- Lareyna Mcmenemy
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