Proteins and Enzymes Flashcards
What does it mean if an amino acid is in the zwitterionic form?
- Both amine and carboxylic acid group are charged
- Amine group has been protonated to form NH3+
- Carboxylic acid group has been deprotonated to form COO-
- Leads to an overall neutral charge
What is meant by the isoelectric point?
It’s the pH at which an amino acid has no overall net charge and therefore won’t move when placed in an electrical field
What are the chemical properties used to classify amino acids?
- Hydrophobic / Hydrophilic
- Polar / Non-Polar
- Acidic / Basic
What are the physical properties used to classify amino acids?
- Aliphatic
- Aromatic
What is the equation for pKa?
pKa = -log10Ka
What is pKa?
- The pH at which a chemical species will accept or donate a proton in aqueous solution
- Low pKa (2-4) means its acidic
- High pKa (10-12) means its basic
What is the equation for Ka?
Ka = [H+][A-] / [HA]
In the Henderson-Hasselbalch equation, what does it mean if pH is greater than pKa?
Solution is more alkaline so chemical compound will be deprotonated as it wants to donate its proton to make the solution more acidic
In the Henderson-Hasselbalch equation, what does it mean if the pH is less than the pKa?
Solution more acidic so chemical compound acts as a base and accepts a proton so exists more in protonated form
What are globular proteins?
- More compact
- Often contain more than one secondary structure
- E.g. enzymes
What are fibrous proteins?
- More extended structure
- Only contains one type of secondary structure
- E.g. collagen
How can protein misfolding cause disease?
Altered conformation of a normal human protein can cause existing proteins to change into diseased form.
E.g. Mad cow disease in humans caused the change of a normally soluble protein to become insoluble. These insoluble proteins then formed insoluble amyloid fibres in the brain
What is the Michaelis-Menten equation?
Initial rate (V0) = Vmax [S] / Km + [S]
What is Km?
The substrate concentration at which you get half maximal velocity (km = half vmax)
What is Vmax?
The maximum rate of the reaction
What is the universal unit of enzyme activity?
U where 1 unit is the amount of enzyme that produces 1 micromol of product per min under standard physiological conditions
What is the Lineweaver-Burk plot and why is it useful?
Puts the Michealis-Menton equation into the form of a straight line graph (y=mx+c)
It makes it easier to derive Vmax and Km
What are competitive inhibitors?
They bind at the active site of enzyme to reduce the proportion of free enzyme that the substrate can bind to
What is the effect on Km and Vmax with competitive inhibition?
Adding enough substrate will always overcome the effect of the inhibitor so has no effect on Vmax but a higher substrate concentration is needed so Km increases
What are non-competitive inhibitors?
Bind at a site away from the active site which changes the shape of the enzyme so the substrate can’t bind as effectively
What is the effect on Vmax and Km with non-competitive inhibition?
The Vmax is reduced as there is less functional enzyme so increasing the substrate concentration won’t make a difference. Km is unaffected
What are irreversible inhibitors?
Form a covalent bond with the enzyme causing it to be chemically modified so it no longer functions. E.g. toxins. Only way to overcome is to synthesise new enzymes
List 4 major regulatory mechanisms
- Isoenzymes
- Allosteric regulation
- Phosphorylation
- Proteolytic activation
What are isoenzymes?
They are different forms of the same enzyme. Same function but different genetic sequence and shape. They have different activity and different regulatory properties. E.g. they have different Km’s so different affinities for the substrate
