In attempting to define the subunit composition of an unknown protein, you decide to subject the protein to SDS-PAGE in the presence or absence of the reducing agent DTT. The results of this analysis are shown below.

Lane 1: molecular weight marker ladder.

Lane 2: protein sample without DTT

Lane 3: protein sample with DTT.

From this analysis, what is the subunit composition of the original native protein?

The following peptide sequence was deemed too long to be easily assessed by mass spectrometry. Therefore, any disulphide bonds were reduced and the peptide was digested with trypsin. In the box below, enter the amino acid sequence (use the single letter code; do not enter spaces or non-amino acid characters) of any ONE possible tryptic peptide that may have been detected by the mass spectrometer.

VSANSVYGFTGAQVGKLPCLEISQSVTGFGRQMIEKTKQLVESKYTVENGYSTSA

In attempting to define the subunit composition of an unknown protein, you decide to subject the protein to SDS-PAGE in the presence or absence of the reducing agent DTT. The results of this analysis are shown below.

Lane 1: molecular weight marker ladder.

Lane 2: protein sample without DTT

Lane 3: protein sample with DTT.

From this analysis, what is the subunit composition of the original native protein?

The Zwitterionic form of an amino acid can act as a base because:

Consider that you wish to separate a mixture of glutamate, glycine and lysine by ion exchange chromatography.

Using a cation exchange column at pH 5, which amino acid would you expect to elute first and which last?

pKa and pI values are as follows:

Glutamate: pK₁ = 2.19, pK₂ = 9.67, pK_R = 4.25, pI = 3.22

Glycine: pK₁ = 2.34, pK₂ = 9.62, pI = 5.97

Lysine: pK₁ = 2.18, pK₂ = 8.95, pK_R = 10.53, pI = 9.74

The image below is a representation of an acid-base titration of a diprotic amino acid, labelled at specific points (i through v).

Which region corresponds to the pH being equal to the pKa of the protonated amino group?

A sample containing an unknown polypeptide of 20 amino acids was assessed through a combination of Edman degradation and tryptic digest with mass spectrometry.

The Edman degradation result showed a peptide sequence of: MSIKNVC

The tryptic digest and mass spectrometry result showed peptide sequences of: 

NVVVW and NVCLK and MSIK and FGGAHR

What is the complete polypeptide sequence?

(Use the single letter amino acid code, with no spaces or non-amino acid characters)

Which ONE of the following statements applies to Edman degradation?

The following peptide sequence was deemed too long to be easily assessed by mass spectrometry. Therefore, it was first digested with trypsin. In the box below, enter the amino acid sequence (use the single letter code; do not enter spaces or non-amino acid characters) of any ONE possible tryptic peptide that may have been detected by the mass spectrometer.

IDISQLVITKELTRAASDYAGKQAHVELAERMAGLDPGSAPSLGDRVPYV

Proteins can be separated according to their net charge. Which type of separation technique would result in positively charged proteins being eluted earlier than negatively charged proteins?