Amino Acids Flashcards
At pH 7.0, converting a glutamic acid to y-carboxyglutamate, will have what effect on the overall charge of the protein containing it?
It will become more negative
At pH 7.0, converting a proline to hydroxyproline, will have what effect on the overall charge of the protein containing it?
It will stay the same
At pH 7.0, converting a proline to a hydroxyproline, will have what effect on the overall charge of the protein containing it?
It will stay the same
What is the approximate charge difference between glutamic acid and a-ketoglutarate at pH 9.5?
1/2
The formation of a peptide bond between two amino acids is an example of a(n)
Condensation reaction.
The peptide alanylglutamylglycylalanylleucine has:
four peptide bonds
An octapeptide composed of four repeating glycylalanyl units has:
one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue
At the isoelectric pH of a tetrapeptide
The total net charge is zero
Which of the following is correct with respect to the amino acid composition of proteins?
Proteins with different functions usually differ significantly in their amino acid composition
The average molecular weight of the 20 standard amino acids is 138 , but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight. Why?
The number 110 reflects the higher proportion of small amino acids in proteins, as well as the loss of water when the peptide bond forms.
In a conjugated protein, a prosthetic group is:
A part of the protein that is not composed of amino acids
Prosthetic groups in the class of proteins known as glycoproteins are composed of:
Carbohydrates
For the study of a protein in detail, an effort is usually made to first:
Purify the protein
In a mixture of the five proteins listed below, which should elute second in size-exclusion (gel-filtration) chromatography?
immunoglobulin G Mr= 145,000
By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to:
separate proteins exclusively on the basis of molecular weight
To determine the isoelectric point of a protein, first establish that a gel:
exhibits a stable pH gradient when ampholytes become distributed in an electric field.
The first step in two-dimensional gel electrophoresis generates a series of protein bands by isoelectric focusing. In a second step, a trip of this gel is turned 90 degrees, placed on another gel containing SDS, and electric current is again applied. In this second step:
Proteins with similar isoelectric points become further separated according to their molecular weights.
The term specific activity differs from the term activity in that specific activity:
is the activity ( enzyme units ) in a milligram of protein.
Which of the following refers to particularly stable arrangements of amino acid residues in a protein that give rise to recurring patterns?
Secondary Structure
Which of the following describes the overall three dimensional folding of a polypeptide?
Quaternary structure
The functional differences, as well as difference in three-dimensional structures, between two different enzymes from E. Coli result directly from their different:
Amino acids sequences.
One method used to prevent disulfide bond interference with protein sequencing procedures is:
reducing disulfide bridges and preventing their re-formation by further modifying the -SH groups
A nonapeptide was determined to have the following amino acid composition: (Lys)2, (Gly)2, (Phe)2, His, Leu, Met. The native peptide was incubated with 1-fluoro-2,4-dinitrobenzene (FDNB) and then hydrolyzed; 2,4-dinitrophenylhistidine was identified by HPLC. When the native peptide was ezxposed to cyanogen bromide (CNBr), an octapeptide anad free glycine were recovered. Incubation of the native peptide with trypsin gave pentapeptide, a tripeptide, and free Lys. 2,4- Dinitrophenyl-histidine was recovered from the pentapeptide, and 2,4- dinitrophenylphenylalanine was recovered from the tripeptide. Digestion with the enzyme pepsin produced a dipeptide, a tripeptide. Digestion with the enzyme pepsin produced a dipeptide, a tripeptide, and a tetrapeptide. The tetrapeptide was composed of (Lys) 2, Phe, and Gly. The native sequence was determined to be:
His-Leu-Phe-Gly-Lys-Lys-Phe-Met-Gly
Even when a gene is available and its sequence of nucleotides is known, chemical studies of the protein are still required to determine:
the location of the disulfide bonds.