Enzymes Flashcards
Enzymes properties and functions
Globular Biological catalyst Can be regulated Increase rates of spontaneous reactions Lower activation energy Accelerate movement towards reaction equilibrium
Ribozymes
catalytic RNA molecules with no protein component
Cofactor
Non-protein component needed for activity
Coenzyme
organic molecule produced by vitamins and is involved in the reaction
Prosthetic Group
Cofactor covalently bound to enzyme or very tightly associated
Apoenzyme
Component of enzyme that contains cofactor
Holoenzyme
Whole enzyme
Active site
Part of the enzyme in which the substrate binds and is acted upon
Transition state
moment that chemical bonds are formed and broken
How is the Michaelis Menton constant calculated
from the hyperbolic reaction curve as half vmax= substrate concentration at half vmax
[S]
Substrate concentration
V0
Initial reaction velocity
Vmax
Maximum reaction velocity
Km
Affinity
Large Km
less stable E-S complex
Smaller Km
More stable E-S complex
Glucokinase
High Km, High Vmax
Hexokinase
Low Km, Low Vmax
Double displacement
Amino group being transferred from an amino acid
Allosteric
enzyme that contains many active sites and subunits
Reversible attachment
uncompetitive inhibitor
Stops enzyme carrying out reaction once substrate has bound to the enzyme
enhances the binding of substrate (so reducing Km), but the resultant enzyme-inhibitor-substrate complex only undergoes reaction to form the product slowly, so that Vmax is also reduced
Non-competitive inhibitor
Binds before and changes shape of enzyme preventing the reaction taking place
Vmax is reduced
Km remains unchnaged
2 models of allosteric enzyme kinetics
Concerted Model
Sequential Model
Concerted Model
Each subunit consist in 2 different confirmation
Allosteric activators stabilise the open conformation
Allosteric inhibitors will stabilise the closed confirmation
Sequential Model
No flipping between conformational states
Binding of first substrate causes a conformational change that allows the second substrate to bind more easily
Covalent modification
Enzymes can be regulated by phosphorylation
Enzymes that catalyse the phosphorylation of enzymes
Protein kinases
Protein phosphatases
Multiple phosphorylation sites
allow very fine control of enzyme function, enzyme never in off state
Proteolytic Cleavage
Enzymes can exist as inactive precursor proteins that are cleaved to give active enzymes such as insulin
Irreversible inhibitors
Cyanide binds to Fe3+ in cytochrom C oxidase and starves the cells of ATP and disrupts terminal respiration
Competitive inhibitors
Increase in Km, Vmax unchanged
AZT
Nucleotide analogue
Competitive inhibition of reverse transcriptase
Mimics the ordinary DNA pre-cursor
Feedback Inhibition
A build up of end product can slow down the whole pathway
Isoenzyme
each of two or more enzymes with identical function but different structure
Competetive Inhibitor
Increase Km by interfering with the binding of the substrate, but they do not affect Vmax because the inhibitor does not change the catalysis in ES because it cannot bind to ES
Haem Group
The Fe2+ ion lies in the middle of a complex nitrogen and carbon containing (porphyrin) ring structure
