ENZYMES Flashcards
what are enzymes?
biological catalyst, usually a protein, synthesized by living organisms that speed up rate of reaction w/o being used up or permanently altered at the end of the reaction
what is a catalyst?
substance that speeds up the rate of reaction by lowering the amount of energy needed for the reaction to occur
- reactant binds to a catalyst and change into products which then dissociate from the catalyst
what is the importance of enzymes?
w/o it, biochemical reactions in cells will either not occur at all or occur at a rate that is too slow for life to be sustained
what are the 7 characteristics of enzymes?
- substrate specifity
- regulated enzyme activity
- speeds up reaction
- temperature
- pH
- salt concentration
- cofactor
what is substrate specifity?
enzymes are highly specific for the reactants or substrates that they act on and the products that they form
- properties and spatial arrangement of the amino acid residues forming the active site of an enzymes will determine which molecules can bind and serve as substrates for that enzyme
what is regulated enzyme activity?
enzyme is regulated and the can be enhance or suppressed by the very same molecules whose reaction they catalyse
what is speeding up of the reaction?
speeds up the rate of reaction w/o being used up/permanently altered
what affects enzymes?
temp, pH, salt conc.
what is cofactor?
some enzymes require other organic compound molecules, coenzymes to be bound to them before they can catalyse any reactions
what is the structure of enzymes?
usually proteins w complex 3D shapes or conformation in which each enzymes have a groove/pocket called an active site to which reactant bind to
- structure of an enzyme determines its specifity, hence determining its functions which determines the type of reaction that the enzyme catalyse
what is binding and active site?
binding site : bind and orient substrates
catalytic site : reduce chemical activation energy
what are the two model of enzymes actions?
1 ) Lock and key model
- two shapes are considered as rigid and fixed and perfectly complement each other when brought tgt in the right alignment
2 ) Induced fit model
- binding of substrate to the active site induces a conformational change in the enzyme to fit the shape of an enzymes
what bonds hold the substrates and enzymes together?
hydrogen bonds and reversible covalent bonds, van der waals, hydrophobic and electrostatic interactions
what are the 6 classes of enzymes?
OXIDOREDUCTASES : catalyse redox reactions
TRANSFERASE : catalyse group transfer reactions which requires the presence of co-enzymes
HYDROLASES : catalyse hydrolysis ; water serving as the receptor of the group transfer
LYASES : catalyse lysis of a substance, generating a double bond
ISOMERASES : catalyse structural change within a single molecule
LIGASES : catalyse ligation ; joining of two substrates which require the input of the c.p.e of ATP
what are enzyme assays?
measure the rate of conversion of substrate to product, under conditions of cofactos, pH and temp at which the enzyme is optimally active
- rate of appearance of product/rate of disappearance of substrates is measured in the change in absorbance using a spectrophotometer or by linking enzymes to another enzymes-catalysed reaction that does involve a change in absorbance
what is enzyme kinetics?
study of rates of enzyme-catalysed reactions
how does substrate concentration\ affect enzyme activity?
- at low [S] , 2x [S] will lead to 2x Vo
at high [S] , enzyme becomes saturated and there is no further increase in Vo
how does enzyme concentration affect enzyme activity?
when enzyme concentration is saturating, a 2x of the enzyme conc. will lead to a 2x of Vo
how does temperature affect enzyme activity?
higher temperature, higher thermal energy of the substrate molecules hence, increasing the proportion of molecules with sufficient energy to overcome the activation energy barrier, hence increasing the rate of reaction
- each enzyme has its own optimal temp in which it works best at
how does pH affect enzyme activity?
each enzymes has an optimum pH at which the rate of the reaction that it catalyses is a max/fastest speed
- small deviations in pH from the optimum lead to a decrease in enzyme activity due to changes in the ionisation of groups at the active site of the enzyme
- larger deviation in pH will lead to the denaturation of the enzyme protein due to interference with many weak non-covalent bonds
how does salt concentration affect enzyme activity?
too high of a salt conc. will interfere with the 3D structure of the enzyme thereby destroying the enzyme activity
how does cofactors affect enzyme activity?
some enzymes require the presence of cofactors to help weaken the bonds of the substrate, allowing it to react with the enzymes
- Holoenzymes : catalytically active form of the enzyme with its cofactor
apoenzyme : protein portion of an enzymes that has no activity
what are isoenzymes?
diff. forms of an enzyme which catalyse the same reaction but exhibit different physical or kinetic properties
what are cofactors?
can be essential ions, coenzymes and coenzyme classification
what are essential ions?
1 ) metal activated enzymes
- have an absolute requirement for the added metal ion or are simulated by the addition of metal ions
2 ) Metalloenzymes
- contain firmly bound metal ions at their active site ; usually transition metals
what are coenzymes?
1 ) cosubstrates
- cosubstrate is altered in the course of the reaction and dissociates from the active site and its orginal structure will be regenerated in a subsequent reaction catalysed by another enzyme ; cosubstrate is recycled repeatedly
2 ) Prosthetic group
- remains bound to the enzyme during the course of the reaction
what are coenzymes classification?
1 ) Metabolite coenzymes
- synthesized from common metabolites which includes a no. of ATP
2 ) Vitamin-derived coenzymes
- vitamins required for the synthesis of coenzymes must be obtained as nutrients usually in small amounts
- mammals and other animals rely on other organism to supply these nutrients such as plants and microorganisms
