Enzymes Flashcards
Will an unfavourable reaction proceed in the presence of a catalyst
No, they make sure that reactions that can go, will go
What is PEPCK and what is it used for
Phosphophenolpyruvatecarboxykinase
Involved in gluconeogenesis, producing glucose for the bloodstream
Involved in glyceroneogenesis, producing triglycerides to power muscles
Explain the induced fit mechanism for enzymes
Substrate enters active site
This triggers a comfortmative change in the enzyme which distorts the substrate
This distortion puts stress on the substrates bonds, eventually breaking them
What is the transition period during enzyme function
The period when the substrate is being distorted by the enzyme
In some enzymes, the active site is complimentary to the distorted substrate during this phase as opposed to the initial substrate
What is binding energy
There are lots of small and weak interactions between the active site and the substrate. Each of these interactions produce a small amount of free energy into the environment which stabilises the reaction and lowers the activation energy. This is referred to as binding energy
What are the different mechanisms for enzyme catabolism
Proximity and strain
Electrostatic effects
Acid/base catalysis
Covalent intermediates
Cofactors and coenzymes
What happens during covalent catalysis
Active site contains catalytic residues
These residues form a temporary covalent bond which hold the substrate in place and forms a covalent intermediate molecule
The breakdown of this molecule provides a new reaction pathway with a lower activation energy
What happens during catalysis by proximity
The reaction will only take place when the substrate molecules collide in the correct orientation with the required energy.
The active site creates a micro environment that helps to orient these substrates for the reaction to take place
What happens during acid-base catalysis
Some active site residues (e.g. histidine) are able to accept or donate protons.
Transferring a proton often creates a strong nucleophile which may be required to lower the activation energy
Transferring a proton may stabilise charged groups in the substrate, lowering the activation energy
Transferring a proton may increase the amount electrostatic interactions that are stabilising the transition state
What happens during metal ion catalysis
Metal ions have a positive charge making them good at stabilising transient and intermediate structures in the reaction
The positive charge helps form strong nucleophilic species
The positive charge may form ionic bonds that help hold the substrate in place
In Michealis-Menten kinetics, what is V-max and Km
V-max is the maximum velocity that the enzyme can achieve at a set concentration (assuming infinite substrate)
Km is the substrate concentration that will produce half the V-max. It shows the tightest affinity a substrate has for its enzyme
