Week 4 - Enzymes Flashcards
Describe globular protein structure
Polypeptide chain folds into compact ball-like structure
Describe fibrous protein structure
Individual protein molecule spanning a large distance, with quite a simple elongated 3D structure
Describe enzymes
Globular proteins which acts as biological catalysts to speed up metabolic reactions, without being used in the process
5 enzyme functions
Metabolism, Movement, Digestion, Cell signalling, Gene expression
Why can a single amino acid hugely change how an enzyme functions
Enzymes are highly specific, a single amino acid can change the protein shape, changing active site and no longer being able to catalyse a reaction
Name the two theories of enzyme binding
Lock and key, induced fit model
How is an enzyme so specific
Complimentary shape of substrate, charge and hydrophilic/hydrophobic interactions
What is an allosteric site
A distinct area away from active site which can induce a conformational change to the enzyme when something binds to it
Describe a cofactor
Any factor essentially needed for enzyme activity/protein function (inorganic)
Describe a coenzyme
A cofactor which is directly involved in catalysed reaction (organic)
Describe a prosthetic group
A covalently associated non-protein constituent needed for a specific function
Describe an apoenzyme
The protein segment of the enzyme
Describe a holoenzyme
The whole enzyme with any cofactors
Typically, how are enzymes classified
Name of substrate + ase ending
How do enzymes affect a reaction
Enzymes only affect rate of reaction, by reducing activation energy needed for reaction to occur
Name the four main catalytic mechanisms
Metal ion catalysis, catalysis by approximation, covalent catalysis, acid base catalysis
How do enzymes reduce activation energy
Binding to reactant and holding them in a way which the bond breaking or making process takes place much more easily and readily
How do we work out enzyme velocity
Amount of substrate converted to product per unit of time
Why do we take velocity at the start of a reaction
Fastest rate, highest S concentration, least amount of P and least amount of inhibition
Describe the relationship between [S] and enzyme velocity
Proportional increase between [S] and velocity, until there is more substrate than active sites readily available, where velocity will remain constant
Describe the relationship between [E] and enzyme velocity
Same as [S] except once active sites are higher than amount of [S] velocity remains constant
What is Michaelis constant
A measure of enzyme affinity for substrate, a high constant indicates weak binding, a low constant indicates strong binding
How do we get Michaelis constant
Half the Vmax and then concentration of substrate at that point on the graph
Explain how temperature affects an enzyme
Enzymes have a temperature range, with an optimum which they can work at.
Rise in T will increase rate until optimum surpassed, which will denature protein structure
Explain how pH affects enzymes
Small deviations in optimum pH result in decreased activity yet large deviations cause denaturation
Describe enzyme inhibition
Where certain products inhibit earlier pathway steps of an enzyme
Name 3 types of reversible inhibition
Competitive, Non-competitive and uncompetitive
Describe competitive inhibition
Competitive inhibitors have affinity for active site, competing for access with the substrate, reducing rate of activity
How can competitive inhibitors be overcome
Increasing [S]
How does competitive inhibition affect Vmax and Km
Vmax stays the same but Km increases , reducing affinity
Describe non competitive inhibition
Inhibitor binds to allosteric site to change active site so the substrate cannot bind
How does non competitive inhibition affect Vmax and Km
Vmax reduced and Km stays the same
Describe uncompetitive inhibition
Inhibitor binds to the enzyme substrate complex and inhibits catalysis
