Enzymes Flashcards
What are globular proteins?
Polypeptide chains folded into a compact shape like a ball with an irregular surface
Complex tertiary and quaternary structure
What are fibrous proteins?
Individual molecules that span a large distance
Simple 3D structure
What is an enzyme?
A globular biological catalyst that speeds up metabolic reactions without being changed in the process
What are enzymes needed for?
Metabolism, movement, digestion, cell signalling and gene expression
What is a kinase enzyme?
These add phosphate ions to molecules
How are enzymes involved in disease?
May disrupt homeostasis e.g. PKU - rare genetic disorder caused by mutation leading to seizures and behavioural problems
What is the active site?
It is a cleft on the protein
It is non polar
Has specific amino acids that allow substrate to bind and others for catalysis
What is the induced fit model?
when substrates bind to the enzyme active site it will change its shape slightly so the chemical reaction can occur with the lowest energy possible
What is the allosteric site?
Away from the active site and is where regulatory molecules bind which can activate or inhibit a molecule
What is a co-factor?
Any inorganic factor required for enzyme activity e.g. metal ions for metalloenzymes
What is a coenzyme?
An organic molecule that is directly involved in enzyme catalysis e.g. lactate dehydrogenase
What is an apoenzyme?
Inactive - no coenzyme added
What is a holoenzyme?
Active - coenzyme added
What is a prosthetic group?
Non protein molecules that are associated with the enzyme via covalent bonds
What do oxidoreductases do?
Transfer oxygen or hydrogen atoms or electrons from one substrate to another
What do transferases do?
Transfer a functional group form one substrate to another
What do hydrolases do?
Hydrolysis of substrate
What do lyases do?
Addition or removal of a group to form a double bond
What do isomerases do ?
Transfer of groups within a molecule
What do ligases do?
Bond formation coupled with ATP hydrolysis
What is activation energy?
Amount of energy needed to start a reaction
What is the transition state?
Highest energy level as the substrate is in the process of being converted to products (most unstable)
What are 7 ways enzymes reduce activation energy?
Binding(collision theory) - substrates need to collide with each other with enough energy
Spatial complementarity- reactants in the right orientation
Induced fit- a.s. adjusts shape so substrate bound in best way
Chemical complementarity- specific a/a allow catalysis
Specific r groups - define shape of a.s
Exclude water
Weak forces- release enery
What are the catalytic mechanisms?
Metal ion catalysis - metal ion aids catalysis
Catalysis by approximation- brings reactants closer together
Covalent catalysis- enzyme uses a transient bond to bind the substrate
Acid base catalysis- Hydrogen added or taken away for reaction to occur
What is the RoR / velocity ?
Amount of substrate converted to products per unit time
Outline the initial velocity
Units are µmol/min
Fastest rate, high concn of substrate, low products, low feedback inhibition
What is the Michaelis constant?
Measure of affinity of the substrate to the enzyme- how readily the substrate binds to enzyme
How to calculate Km
- Vmax line to Y axis
- Half of Vmax line - line down to the x axis
- Km- concn of substrate when Vmax is at its half point
What does a high Km mean?
Weak binding
Low affinity
High concn of substrate to reach Vmax
What is the effect of temperature on RoR?
Increase in thermal energy so overcomes the Ae which increases rate
BUT beyond optimal
Rapid decrease in RoR as weak bonds broken altering active site
enzyme denatured
How does pH impact enzyme activity?
Ionisation of groups in the active site
How are enzymes regulated?
- Controls how molecules of each enzyme it makes by regulating the expression of the gene that encodes that enzyme
- Confining sets of enzymes to particular subcellular compartments
- Covalently modified to control activity
- Rate of protein destruction
- Binding of small molecules
What is feedback regulation?
End products inhibit earlier pathway steps to prevent the build up of unnecessary metabolites
What is competitive inhibition?
Inhibitor is a similar shape to the substrate so it binds to the active site of the, blocking the binding of substrates. Can be overcome by increasing substrate concn
Km increases
Affinity decreases
Vmax same
What is non competitive inhibitors?
Inhibitor binds to the allosteric site causing conformational changes to the active site the binding of the substrate is the same BUT catalytic activity is decreased
Km is the same
Vmax is reduced
What is an uncompetitive inhibitor?
An inhibitor binds to the e.s complex thus inhibiting catalysis
Km is reduced
Vmax is reduced
