enzymes Flashcards
(21 cards)
What is a precipitating agent?
A substance that causes proteins to precipitate out of solution
Examples include ammonium sulphate, ferric chloride, trichloroacetic acid, and ethanol.
What effect does ammonium sulphate have on protein solubility?
Alters the ionic strength of the environment, leading to protein precipitation.
What is the isoelectric point (pI) of a protein?
The pH at which the net charge of the protein is zero.
At what pH is a protein least soluble?
When the pH of the solution equals the isoelectric point (pI) of the protein.
How does ionic strength affect protein solubility?
High concentrations of ions break protein-water interactions, causing protein precipitation.
What happens to proteins at alkaline pH?
Proteins tend to have negative charges on their surface at alkaline pH, which can react with positively charged heavy metal ions.
What role do heavy metals play in protein precipitation?
They can form larger complexes between proteins when multivalent.
What is the dielectric constant (ε)?
A measure of a substance’s ability to insulate charges from each other, indicating solvent polarity.
What is the dielectric constant of water compared to ethanol?
Water ~ 80; Ethanol ~ 25.
What is the effect of ethanol on protein solubility?
Ethanol decreases overall polarity, which can decrease interactions between proteins and water.
True or False: Ethanol can denature proteins.
True.
What determines the secondary and tertiary structure of a protein?
The amino acid sequence.
What is Levinthal’s paradox?
The concept that protein folding must be ordered due to the vast number of possible conformations.
How many conformations can a 100 amino acid polypeptide explore per second?
10^13 conformations.
What is the pH at which pepsin is active?
pH 2.0.
How does pepsin maintain activity at low pH?
Aspartic acid residues in the active site are fully protonated.
What happens to pepsinogen in the stomach?
It is activated at low pH through autocatalysis and cleavage of an inhibitory peptide.
What is the pKa of the aspartic acid side chain in pepsin?
3.86.
Fill in the blank: The _______ of a protein is the pH at which it has no net charge.
isoelectric point (pI).
How does decreasing pH affect enzyme activity?
It can alter the overall 3-D structure of the active site.
What can happen to groups on substrates involved in enzyme binding when pH changes?
Their charge can change, affecting enzyme activity.
