Enzymes Flashcards
What is an enzyme?
It is a biological catalyst that increases the rate of a reaction and can be reused.
What is the enzymes catalytic centre?
The active site
What are the 2 models of enzyme action?
Lock and Key
Induced Fit
Explain the Lock and Key Hypothesis.
The substrate is like a “key” whose conformation is complementary to the enzyme active site or “lock”. When enzyme and substrate collide in correct orientation, enzyme-substrate complex is formed. Once products formed, products no longer fit in active site and are released into surrounding.
Explain the Induced Fit Model.
Substrate enters enzyme active site, inducing a change in shape of protein causing active site to enfold and hold substrate in place. This change in conformation allows active site to be moulded into a more precise fit for the substrate.
What are the factors affecting rate of reaction?
Temperature, pH levels, enzyme concentration and substrate concentration.
How does temperature affect rate of reaction?
As temperature increases, kinetic energy of enzyme and substrate molecules increases, increasing the frequency of effective collisions between substrate and enzyme active sites, increasing rate of enzyme-subtrate complex formation
As temperature increases past optimum temperature, the increase in kinetic energy causes intramolecular vibrations to increase, breaking the bonds that stabilises conformation of enzyme resulting in denaturation of enzyme. Hence substrate no longer complementary in conformation to active site of enzyme and fewer enzyme-substrate complex is formed.
How does pH affect rate of reaction?
Deviation from optimum pH results in lowering of rate of reaction. Excess [H+] or [OH-] ions may afffect ionisation of R-groups, disrupting formation of ionic or hydrogen bonds which determines specific conformation of enzyme active site, hence enzyme is denatured, reducing rate of enzyme-substrate complex formation, causing a reduced rate of reaction.
How does enzyme concentration affect rate of reaction?
With increased enzyme concentration, frequency of effective enzyme-substrate collisions increases resulting in increased rate of formation of enzyme-substrate complex and reaction rate will increase.
How does substrate concentration affect rate of reaction?
With increasing substrate concentration, frequency of effective enzyme-substrate collisions increases resulting in increased rate of formation of enzyme-substrate complex and reaction rate will increase. When enzymes are fully saturated, an increase in substrate concentration does not change rate of reaction.
What are the 2 modes of enzyme inhibition
Competitive and Non-competitive inhibitors
Explain competitive inhibition.
Competitive inhibitors prevent substrate molecules from binding to enzyme active site. Competitive inhibitors bear similar conformation and charge to substrate thus competes with substrate for active site. This reduces availability of enzyme active site for substrate binding and hence reduces rate of reaction. Competitive inhibition can be overcomed by increasing substrate concentration.
Explain non-competitive inhibition.
Non-competitive inhibitors bind to a site other than the enzyme active site, altering the conformation of the specific enzyme active site thus substrate cannot bind to active site and rate of reaction is decreased.
What are the different amino acid residues found in an enzyme?
Contact residues, Catalytic residues, Structural residues
What is the function of contact residues in an enzyme?
They are found in the active site and help to position substrate in correct orientation via weak interactions (hydrogen bonds, ionic bonds & hydrophobic interactions).
