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Flashcards in Enzymes Deck (52)

What are ribozymes?

Catalytic RNA molecules with no protein component


What is a cofactor?

A non-protein component needed for activity, usually metal ions


What is a co-enzyme?

A complex organic molecule, usually produced from a vitamin FAD NAD+


What is a prosthetic group?

A non-protein group forming part of or combined with a protein. 

i.e - A cofactor covalently bound to an enzyme or very tightly associated with an enzyme


What is an apoenzyme?

An inactive enzyme, activation of the enzyme occurs upon binding of an organic or inorganic cofactor.


What is a holoenzyme?

WHole enzyme, the apoenzyme plus the cofactor


Why isn't a spontaneous reaction instantaneous?

Because of the activation energy barrier


What is the activation energy used for?

Positioning chemical groups correctly


What is the transition state?

The moment that chemical bonds are formed and broken The reaction from this point could then go to products or reactants


What type of bonds occur between substrate and enzyme?



What is the active site complementary to?

The transition state


How do enzymes reduce activation energy?

Entropy reduction Desolvation Induced fit


How does entropy reduction reduce activation energy?

Molecules react by bumping into each other, enzymes orientate the substrates improving the chance of a successful collision and a resulting reaction


How does desolvation decrease the activation energy?

H bonds with the substrate and the solution are replaced by the weak bonds between the substrate and the enzyme.


How does induced fit decrease activation energy?

Conformational changes occur in the protein structure when the substrate binds


Which part of an enzyme reaction occurs more slowly?

The second part of the equation, producing E and P from the enzyme substrate complex


Which stage of an enzyme reaction is reversible?

The formation of ES from E and S K1 denotes the forward reaction K-1 denotes the reverse reaction


What is Km?

It is the substrate concentration when the reaction velocity is exactly half of the max velocity


On a lineweaver burke plot what does the y intercept represent?



On a lineweaver burke plot what does the X intercept represent?



What does Km measure?

The ration of rate constant for breakdown of ES to E+S compared to the rate constant for formation of ES from E+S It gives you a clue to the affinity of the enzyme with it's substrate


What does a large Km value indicate?

Less stable ES complex


Which enzyme activity fluctuates directly with blood glucose intake?

Glucokinase Catalyses Glucose + ATP to glucose - 6 - phosphate


What is used to determine normal enzyme activity?

Arbitrary values such as 1U/ml or 100%


How are enzymes separated?

Gel electrophoresis


Where can you find creatine kinase?

In the heart Elevation of plasma CK2 is diagnostic for myocardial infarction


What are the possible reaction mechanisms for enzymes with two or more substrates

Random or ordered with a ternary complex No ternary complex formation


Describe the reaction involving a ternary complex
Random order

Can bind to either substrate first

Eventually complexes with both substrates

Forms two products


Describe the reaction involving a ternary complex

Attaches to one substrate first, it is the fed the other substrate


Describe the reaction with no ternary complex formed

Reaction occurs with enzyme and substrate producing altered enzyme and a product


Second reaction occurs with the altered enzyme and the second substrate, producing a second product


What type of reactions have no ternary complex formation?

Transamination reactions


How does temperature affect the function of an enzyme?

Increase temperature will increase molecule collisions and it will increases the internal energy of molecules


Eventually denautres the enzyme


How does pH alter the function of an enzyme?

pH changes the charge of an amino acid, can stop the active site functioning if the amino acids in the active sites change charge.


Extreme pH will denature the enzyme


pH will affect the substrates


What effect does a competetive inhibitor have on the Vmax and Km?

Same Vmax

Km increases (since affinity active site has for the enzyme substrate complex decreases)


What is an example of a transition state anologue?



What does a catalytic antibody resemble?

It resembles the active site of the original enzyme, since it is specific to a transition state molecule


What effect do non-competitive inhibitors have on the Vmax and the Km values?

V max will decrease - inhibition remains the same regrdless of the change in substrate concentration

Km remains the same as the substrate is still able to bind to the active site


Which type of inhibitors bind in an rreversible manner?

Those that bind in a covalent manner


Which enzyme in a pathway holds the regulatory step for that pathway?

Often the first one in the pathway


What are the regulatory types of enzymes called?

Allosteric enzymes and covalently modified enzymes


What is feedback inhibition?

When there is a build up of an end product in a pathway or a key junction in a pathway that ultimately slows down the entire pathway


How is the change in the structure of an enzyme brought about in allosteric control?

An allosteric effector (usually a metabolite) binds non-covalently to a site on the enzyme that is not the active site, changing the enzymes structure


What are the two different types of allosteric effectors?

Activators and inhibitors


How does the concerted model show how a small amount of substrate increases an enzymes sensitivity to a substrate?

Concerted model suggests that enzyme sub-units are always flipping between two conformational formations

Binding of S to one substrate locks the other subunits in the same conformation


How do allosteric inhibitors and activators function in the concerted model?

Activators - stabilise the  the open conformation, allowing S to bind more effectively

Inhibitors - stabilise the ‘closed’ conformation and make it difficult for S to bind effectively


How does the sequential model show how a small amount of substrate increases an enzymes sensitivity to a substrate?

Substrate binding causes a change in ONE sub unit, this causes a change in another sub-unit allowing it to bind to S more readily


What enzymes are responsible for covalent modification?


Protein kinases (add phosphoryl groups to proteins)

Protein phosphatases (remove phosphoryl groups)


What do multiple phosphorylation sites allow?

Very fine control of enzyme funciton


What is an inactive precursor of an enzyme called?

A proprotein or a proenzyme


What can be produced when a proprotein is cleaved?



Give an example of a an enzyme that is regulated by proteolytic cleavage

Trypsin - activated in the small intestine

Its precursor trypsinogen is formed in the pancreas



Describe the bonding between a protein and :

  • A prosthetic group
  • A coenzyme

Prosthetic group - Tight bonding (sometimes even covalent bonds)

Coenzyme - Loose bonding