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Flashcards in Enzymes Deck (23):

What is a cofactor?

A non protein component needed for activity


What is a Coenzyme?

A complex organic molecule such as NADH


What is a prosthetic group?

A cofactor bound to the enzyme or tightly associated with it


What sort or protein is an enzyme?



How does an enzyme catalyse a reaction?

Lowers activation energy

Accelerates movement towards reaction equilibria


How does an enzyme lower activation energy?

Force substrates into correct orientation

Desolvination - forms weak bonds with substrates replacing the substrate-aqueous bonds

Changes shape once substrate is bound creating an induced fit - tigher fit


What is the active site complementary to?

The transition state of the substrate - not the actual substrate!


What happens if you increase substrate levels?

Faster reaction rate till all enzyme sites are being used - known as Vmax


What does the M-M equation state?

Everything after the enzyme-substrate complex is bound is the rate determining step


What does a high Km show?

Shows a less stable ES complex so a low affinity


What does a low Km show?

Shows a stable ES complex - high affinity


What can electrophoresis be used as?

A diagnostic tool to separate complex mixtures of enzymes


What is an ordered sequential mechanism?

When the enzyme has two or more substrates and they can only bind and leave in a specific order.


What is a random seqeuntial mechanism?

Enzyme has 2 ore more substrates and they can bind and leave in any random order


What does pH effect?

Charge of amino acids


What is a Competitive inhibitor?

Inhibitor that is similar in shape to substrate and binds non-covalantly to the active site.

This increases Km as affinity for substrate decreases until there is a high conc of substrate to kick out inhibitor.


What is a non competitive inhibitor?

Bind non- covalntly allosterically decreasing Vmax but leaving Km unchanged


What is an irreversible inhibitor?

Binds to the enzyme covalently and cannot be removed


What is feedback inhibition?

If the end product/ key mid-product in a pathway gets too large the product will bind to the enzyme inhibiting it till there is a lower concentration again letting pathway proceed normally. Example of homeostatic control.


What is the concerted model of allosteric enzyme kinetics?

Each subunit of an enzyme can have a high or low Km,

All units need to be in the same conformation so flip together.

When one substrate binds, it looks all other to low Km affinity.


What is the sequential model?

No flipping between states, one subunit binds which causes only ONE other subunit to change conformation and make binding easier in only that subunit - occurs until all subunits binded.


Example of covalent modification?

Phosphorylation of enzyme - makes it more fined tuned


What is proteolytic cleavage?

Enzyme is in an inactive state as a proenzyme.

Proenzyme cleaved by proteases giving active enzyme.