Enzyme properties and enzyme regulation Flashcards
Describe what enzymes are?
Biological Catalysts- increase the rate of reaction whilst not altering the final equilibrium between products and reactants. The decrease the time for the transition state
They are ere extremely efficient- eg. catalase with hydrogen peroxide breakdown
Enzymes are proteins ( and share similar properties- stabilised by weak non covalent bonds)
They are sensitive to pH changes and temperature changes
The active site contains functional groups that stabalise the Transition state of the reaction
NB this is done by providing an alternative reaction pathway - makes the reaction more kinetically favourable
Why is important the product has low affinity for active site
less time in the Enzyme-Product complex- greater turnover for enzyme-substrate complex
What is an active site?
A cleft/groove with a defined shape only substrate can fit in
The active site contains functional groups that stabalise the Transition state of the reaction
What does specificity spend on?
It depends on the shape of the active site where only the substrate of the correct shape and charge can fit
Describe how specific enzymes can be
Enzymes will catalyse one type of reaction
e.g Alcohol dehydrogenase oxidising primary alcohol to aldehydes
Will act on a few related molecules
Will act only on one substrate - absolute specificity
When stereoisomers exists with a natural compound
e.g. D glucose and L-glucose only the enzyme concerned with metabolism in the cell will usually act on one isomer
When can specificity be useful?
When a group of enzymes are together in one compartment-
eg. cytoplasm of a muscle cell
The initial substance D glucose converted through a sequence of enzyme catalysed reactions to produce lactic acid
Name the types of classes enzymes can be organised in
Hydrolyses Oxidoreductases Ligases Transferases Isomerases Lysases
Hydrolyse
catalyse the cleavage of bonds by addition of water
Oxidoreductases
catalyse the removal of Hydrogens and electrons
eg. lactate dehydrogenase
Ligases
use ATP to catalyse the formation of new covalent bonds
Transferases
catalyse the transfer of functional groups from donors to acceptors eg. Alanaine amino transferase
Isomerases
catalyse the transfer of functional group within the same molecule eg. phosphoglucose isomerase
Lyases
catalyse the cleavage of C - C , C - O , C -N
eg. ATP citrate lyase
Explain what is meant by the Lock and Key model
Enzyme has a defined rigid active site- substrate with the right shape will be complementary and fit perfectly
Explain what is meant by the Modified Lock and Key model
Similar to the original, the substrate changes shape ( conformational change) making the substrate more reactive BUT the active site still remains rigid
Explain what is meant by the Induced fit model
The active site is flexible making the shape of substrate and active site more complementary
What is a catalytic triad
A catalytic triad is a set of three coordinated amino acids that can be found in the active site of some enzymes. Catalytic triads are most commonly found in hydrolase and transferase enzymes.
eg. Chymotyrpsin - Ser, His, Asp all linked via hydrogen bonds
Explain the catalysis of peptide bond hydrolysis by chymotrypsin
see notes
How does temperature effect enzymes?
20-40 degrees celsius- Increases the rate of product formation- by increasing the kinetic energy and increases the rate of formation of E- S complex rate
more likely to meet the activation energy
40-50 degrees celsius- less product formed as increasing the KE increases the distance between Ser and His in catalytic triad which means that theres no formation of H bonds- NO TS formed
Comment on pH in regards to enzymes
Different enzymes will have different optimum pH.
What are co factors?
a substance whose presence is required for the activity of enzymes
Give examples of co factors
Inorganic elements-
Cu2+ -cytochrome oxidase
Fe2+/3+ - cytochrome oxidase, catalase and peroxidase
K+ - pyruvate kinase
Mg2+ - hexokinase, G-6-phosphate, pyruvate kinase
Se - gluthione peroxidase
Zn 2+ - carbonic anhydrase, alcohol dehydrogenase
Ni 2+ - Kinase
What are coenzymes?
They can help transfer compounds between enzymes.
Coenzymes also help attract the correct compounds and repel incorrect compounds to the active site of their enzyme.
Enzymes are a type of cofactor that can attach itself to the active site temporarily- this means that the enzyme is activated
What are Isoenzymes?
Enzymes with different protein structures catalyse the same reaction-
these enzymes are coded by different genes
and are often found in different compartments in cells
eg. Lactate dehydrogenase- heart vs muscle- different functions
