Enzymes I Flashcards
What are enzymes?
Enzymes are proteins that speed up (catalyse) specific chemical reactions.
List some functions of enzymes.
- DIGESTION: carbs, fats, proteins
- BLOOD CLOTTING: fibrin clot, activation by thrombin
- DEFENCE: immune system, activation of complement
- MOVEMENT: muscle actomyosin is an ATPase
- NERVE CONDUCTION: membrane ion pumps for Na+, Ca2+
Give examples of diseases caused by enzyme defects.
- PHENYLKETONURIA: can’t convert Phe to Tyr, too much Phe can be broken down into toxic byproducts that affect brain development
- TAY-SACHS DISEASES: can’t make a membrane unit called cerebroside
Give examples of how bacterial enzymes are drug targets.
- ANTIBIOTICS: eg. penicillins inhibit cell wall synthesis
- ANTI-INFLAMMATORY DRUGS: aspirin blocks prostaglandin (a hormone-like substance that participates in a wide range of bodily functions such as the contraction/relaxation of smooth muscle, dilation/constriction of blood vessels, etc.)
- ANTI-CANCER DRUGS: methotrexate is a folate analogue (it interferes with the synthesis of DNA precursors)
List some key enzyme properties.
- they increase the reaction rate up to 10 billion fold
- they show specificity (only catalyse certain reactions)
- they’re unchanged at the end of the reaction
- they don’t alter the reaction equilibrium
- they facilitate the reaction by decreasing the free energy of the activation of the reaction
What is an enzyme active site?
It’s a 3D cavity/cleft that binds substrate(s) using electrostatic, hydrophobic, hydrogen bonding and van der Waals interaction.
What evidence do we have for enzyme active sites?
We have evidence of that from X-ray crystallography and kinetic studies of enzyme activity.
What does the induced fit model entail?
With the induced fit model, the substrate isn’t complementary to the active site, so the active site changes its shape to fit the substrate.
What is enzyme-substrate binding energy used for?
- to bring molecules together in the active site
- to constrain substrate movement
- to stabilise the positive and negative charges int he t-state
- to strain particular bonds in the substrate, making breakage easier (the substrate is distorted on binding to resemble the transition state)
- to use cofactors (they bring new chemistry to the active site)
What is Km?
Km stands for the Michaelis Constant, and it’s a measure of how ‘sticky’ the substrate is. If it’s sticky enough, that means that it binds really tightly to the active site, so not much of the substrate is needed.
What are the two versions of the equation we need to know for Km?
V = Vmax ( [S] / ([S] + Km) )
or
(1/V) = (1/Vmax) + (Km/Vmax)x(1/[S])
(can’t figure out any other way to represent the equations without paying, cba)
What is the turnover number?
Turnover number is the maximum number of chemical conversions of substrate molecules per second that a single catalytic site will execute for a given enzyme concentration.
What is the equation for turnover number?
Turnover number = Vmax/ [enz]total
again, sorry
How are these measurements affected with non-competitive inhibition?
With non-competitive inhibition, Vmax decreases but Km is unaltered.
In what ways is enzyme activity regulated?
- control of gene expression by controlling the amount of enzymes available
- compartmentation: where the sequence in the enzyme helps it get targeted to its destination
- allosteric regulation: regulatory molecules control protein shape to increase/decrease activity
- covalent modification of the enzyme where the enzyme’s shape is changed and thus it’s activity (eg. phosphorylation)
