Exam 2 Flashcards
Ammonium sulfate is a common reagent to use for salting out of proteins. Consider three theoretical proteins that are largely identical except for their given sequences below.
Protein 1: Gly-Trp-Val-Ile-Ala-Tyr-Phe-Phe
Protein 2: Gly-Trp-Val-Gln-Ala-Tyr-Asn-Phe
Protein 3: Gly-Ser-Thr-Gln-Ala-Gln-Asn-Phe
In which order would you expect these proteins to salt out?
Protein 1 first, Protein 3 last
More hydrophobic proteins salt out first (those with more nonpolar regions), therefore those with more polar regions would salt out last.
An extremely efficient enzyme has a ____________ KM and a _____________ kcat.
Small, large
In a 1/V vs. 1[S] plot,
x-intercept =
y-intercept =
slope = KM/Vmax
x-intercept = -1/KM
y-intercept = 1/Vmax
slope = KM/Vmax
You want to use a cation-exchange column to separate out three amino acids: Ala, Arg, and Asp.
a. You start with a pH of 2.7. Which amino acid do you expect to elute?
b. How would you elute the next amino acid? Specify a new pH and which amino acid would elute.
c. How would you get the last amino acid to elute? Be as specific as possible.
The first amino acid to elute is Asp due to its negative charge.
Raise the pH to at least 6 to bring Alanine to an overall negative charge (once pH goes above PI it will elute)
The last amino acid will be eluted by the addition of a large amount of salts to displace it from the resin.
You are going to use salt fractionation to separate proteins in a mixture. Start with a ________ concentration of salt and then _______ salt concentration.
Which would you expect to precipitate first, the protein that is more hydrophobic or the protein
that is more hydrophilic?
low, increase
More hydrophobic. It is less water-soluble and will require much less salt to get rid of its hydration shells.
Reaction A–>B is catalyzed by an enzyme. The rate law would be rate = k[A]x. In which case would
this reaction be most likely to exhibit zero-order kinetics?
[A]»>[enzyme]
When enzymes are completed saturated, adding more substrate will not increase velocity.
Which of the following amino acid side chains is most likely to participate in acid-base catalysis?
Met
Gly
His
Phe
His
ATCase is the enzyme that catalyzes the first reaction in the pathway for the synthesis of CTP. CTP is a known inhibitor of ATCase. This is an example of
Feedback inhibition
In the concerted model, which state binds the substrate more tightly?
the relaxed (R) state
Homotrophic effects for allosteric enzymes involve the _____ binding to ______ in the enzyme.
same molecule, different sites
Chymotrypsin cleaves a peptide with a Phe residue at the ______ on the _____ side of Phe
amide bond
carbonyl
A Lineweaver-Burk plot will change when a mixed non-competitive inhibitor is added by:
y-intercept increases (because Vmax decreases)
Slope and x-intercept should change from original.
For an allosteric
Sphingolipids are commonly found in neural tissue as ______
sphingomyelin
Steroids have three _______ rings and one _______ ring fused together.
cyclohexane, cyclopentane
