Question

Determine the PI of peptide AEGK (Ala-Glu-Gly-Lys).

Answer #1

PI is the average of the pKa values representing the protonation and deprotonation of the neutral form of the peptide.

The pH range where the peptide has a net charge of 0 is between pH 4.2 and pH 9.7.

Below pH 4.2, which represents the pKa value for the glutamic acid carboxyl group, the peptide gains a net charge of +1.

Above pH 9.7, which represents the pKa value for peptide N-terminus, the peptide has a net charge of -1.

Therefor, PI = (4.2+9.7)/2 = 6.95

Can you calculate the pI for the following peptide?
Phe-Lys-Glu-Asp-Lys-Ser-Ala (note: there is one alpha carboxyl at
the C-terminus and one alpha-amino group at the N- terminus and
don't forget to take into account the ionizable side chain
groups!)

Calculate the net charge on this polypeptide:
Glu-Gly-Ala-Lys.
What is the charge at a pH of 1? Please show work, I'm so
confused!

For the peptide Ala-His-Glu-Val-Asp-Cys-Lys-Leu what is the net
charge at pH 3? Please explain how you get the charge of each amino
acid.

Consider the following short peptide:
Ala-Gly-Lys-Ser-Asp
What is the difference in the number of primary amines this
peptide would yield after it was fully hydrolyzed versus when it
was intact as shown (report the absolute/positive value)?

Based off of the one letter abrev. for the amino acids, are any
of these peptide chains hydrophobic? Please explain why or why not
***each peptide chain has a NH3+ at the N-terminus and COO- at the
C-terminus***
1 = MWQINAGP....Met, Trp, Gln, Ile, Asn, Ala, Gly, Pro
2 = GGVYAR..... Gly, Gly, Val, Tyr, Ala, Arg
3 = HIFPCK ......... His, Ile, Phe, Pro, Cys, Lys

Polyglutamate (a peptide consisting of all GLU residues) assumes
an alpha helical structure at pH = 1.75 but a random coil
arrangement at a pH greater than 5.0. Explain why this peptide
assumes different structural conformations at the different
pHs.

Give the amino acid sequence of an octapeptide that contains the
amino acids Phe, Lys, Thr, Trp, His (2 equiv), Gly, Ser, and forms
the following fragments when partially hydrolyzed with HCl:
Thr―Phe―Lys―Gly, Trp―His―Ser, and Ser―His―Thr―Phe.

The His operon though having a different sequence, utilizes a
similar mechanism for regulation. Its leader peptide has the
sequence
Met-His-Ala-Ile-Phe-His-Ile-His-Gly-Trp-Trp-His-Ser-Thr-Stop. In an
experiment you substitute the His leader sequence for the Trp
leader peptide (purple region) in the Trp operon. What effect do
you think this will have on amino acid attenuation, if any? Provide
your rationale.

The Pi Theorem is a method to convert a dimensional equation
into a
nondimensional equation. It determines the number of
nondimensional Pi groups
needed. Can you determine the number of Pi groups for a given
starting
functional form? Can you go through the process of finding the
nondimensional
Pi groups associated with the original dimensional equation?
From this you can
write a “generic” equation that relates the Pi groups

A test of hypotheses for one proportion has the following Null
Hypothesis: pi = 0.79, and uses 0.01 for the level of significance.
a. If the calculated value for the associated test statistic equals
-2.71, determine the p-VALUE for the test:
0.0068
0.0034
0.0272
0.0136

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