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BCHS 3304

Terms in this set (28)

At 10°C, Keq for a reaction is 20. At 30°C, Keq is 100. In the standard state, would this reaction release or absorb heat?
...
Which of the following statements about water is incorrect?
Cations are solvated by shells of water molecules oriented with their oxygen atoms pointed toward the ions.
The pKa of citric acid is 3.09. What is the citric acid : monosodium citrate ratio in a 1.0 M citric acid solution with a pH of 5.09?
pH=pKa+log([A-]/[HA])
log([A-]/[HA])=pH-pKa=5.09-3.09=2
[A-]/[HA]=100
[HA]/[A-]=1/100
A student at UH wants to measure the activity of an enzyme at pH 7.5. To buffer her reaction, she will use a buffer system based on one of the acids listed below, which acid is most appropriate for the experiment?
HEPES (Ka 3.39 × 10−8)

pKa= -logKa
for HEPES, pKa= -log(3.39x10-8)=8-log3.39=7.47, closest to pH7.5
The net charge of Lysine at pH=12 is approximately
-1
The oligopeptide ALKFDR contains five ionizable groups with pKas of 3.0 (for C-ter COOH), 3.9, 8.5 (for N-ter NH3+), 10.5 and 12.5. Calculate the pI for this oligopeptide
...
The following peptide is rapidly digested by trypsin or chymotrypsin. Trypsin will yield _____fragments, while chymotrypsin will yield _____fragments.
2, 4
Treatment of a polypeptide by DTT (same function as β-ME) yields 2 polpeptides that have the following aa sequences:
Ala-Phe-Cys(C1)-Met-Tyr-Cys(C2)-Leu-Trp-Cys(C3)-Asn
and
Val-Cys(C4)-Trp-Val-Ile-Phe-Gly-Cys(C5)-Lys
Determine the positions of the disulfide bonds in the original polypeptide knowing that chymotrypsin treatment of the original polypeptide yields fragments with compositions as follows:
...
We have a synthetic peptide with the sequence of QLPIDSPAGYTRPGK. The m/z of this peptide at a singly protonated ion is 1599.85. What mass/charge would you observe for the +2 charge state?
m/z=(M+z)/z
1599.85=(M+1)/1
Therefore, M=1598.85

At +2 charge state, m/z=(M+2)/2=(1598.85+2)/2=800.43
Which of the following can best be related to tertiary protein structure?
myoglobin
Which of the following technology can be used to obtain information about protein 3-D structure?
X-ray crystallography
In what order would Asp, Arg and Ala be eluted from a carboxymethyl column (Hint: this is an ion exchange chromatography column) at pH8?
Asp, Ala, Arg

(Carboxymethyl (CM) is negatively charged. Therefore, this is cation exchange chromatography. Negatively charged Asp elutes first, followed by neutral Ala, then cation Arg)
In hemoglobin (Hb), the ligand for the 6th coordinate of Fe (II) is ________.
an O2 molecule
What of the following is NOT part of the Bohr Effect?
the decrease in affinity of Hb for O2 when the BPG concentration goes u
The following shows the structure of the heavy chains and light chains of IgG. They are connected by disulfide bonds. On SDS-PAGE in the presence of beta mercaptoethanol, purified IgG will show ____ bands.
2

(Beta mercaptoethanol cleaves disulfide bond (black lines), resulting 4 fragments. The 4 fragments have only two unique peptides.)
Like Hemoglobin S, Hemoglobin C is a single residue substitution variant that affects Glu6beta. The following is a chromatograph of several Hemoglobin variants on a commercial cation-exchange column. We have learned that HbSS (two copies of Hemoglobin S gene, "homozygous") patients suffer from Sickle Cell anemia.
Individuals with sickle cell-hemoglobin C (HbSC), have the gene for HbS inherited from one parent and the gene for HbC is inherited from the other parent: they are "heterozygous".
HbC has a Glu to Lys mutation, and HbSC will have less sickling than HbSS.

(The only difference among Hemoglobin,
Hemoglobin S, and Hemoglobin C is on residue 6β.
In Hemoglobin: Glu6β.
In Hemoglobin S: Val6β.
In Hemoglobin C: Lys6β, why?)
Trypsin is an example of a _____.
hydrolase
Within the lysozyme active site, Glu35 is in a hydrophobic environment and Asp52 is in a polar environment. During the early stages of catalysis, _____.
based on the local environment, Asp52 has a lower pKa than Glu35
Glu 35 transfers its proton to the O1 atom bridging the D and E rings, thereby facilitating cleavage of the C1-O1 bond

This step converts the D ring to a resonance-stabilized oxonium ion transition state whose formation is facilitated by the strain distorting it to the half-chair conformation

The positively charged oxonium ion is stabilized by the presence of the nearby negatively charged Asp 52 carboxylate group
general acid catalysis

catalysis by the preferential binding of the transition state

electrostatic catalysis
8.Among the following amino acid residues, which one is likely to carry out nucleophilic attack?
pentagon NH, double bonded on sides, N in left corner, 6 peaks long, 2 O bonds (one O-), and NH3+
Some enzymes are produced as zymogens because_____.
the reactions they catalyze are undesirable at the site of production.
To describe enzyme kinetics, Michaelis and Menten made several assumptions which include______.
a. The enzyme-substrate complex concentration remains in steady state.
b. The formation of ES is at equilibrium.

a and b
An enzyme is near maximum efficiency when____.
the catalytic efficiency is close to the rate of diffusion.
An uncompetitive inhibitor of a reaction has a KI=2.5mM. At [I]=2.5 mM, what will be the KMapp?
0.5KM

α`=1+ [I]/KI=1+ 1mM/1mM=2

KMapp=KM/α`=KM/2
24.Shown below are kinetics data for an enzyme that were collected in the presence and absence of an inhibitor. The enzyme concentration used in both experiments was 1.5 μM. The concentration of the inhibitor was 3 μM. vo is the initial rate of the catalyzed reaction, and [S] is the substrate concentration. Please calculate α (or α' as appropriate).
2
Khan et al. (RSC Adv., 2015, 5, 64404-64413) have developed new inhibitors of alkaline phosphatase. One of the inhibitors displayed the following patterns in double reciprocal plots. The data were collected in the absence or presence of increasing concentrations of the inhibitor. According to these data, you can conclude that in the presence of this inhibitor, _____.
both KM and Vmax decrease
For an enzyme that follows simple Michaelis-Menten kinetics, what is the value of Vmax if Vo is equal to 1 micromolar per minute at 10KM
1.1 µM/min
Below is the structure of glucose. If you have to come up with an accurate and long name for it, what will it be?
β-D-glucopyranose
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