Chapter 4 Practice Problems Flashcards
(17 cards)
Which of the following is least likely to result in protein denaturation?
change the salt concentration
disruption of weak interactions by boiling
exposure to detergents
altering net charge by changing pH
mixing the organic solvents such as acetone
change the salt concentration
Roughly how many amino acids are there in one turn of an alpha helix?
1
3.6
10
2.8
4.2
3.6
Which of the following pairs of bonds within a peptide backbone show free rotation around both bonds?
C(alpha)–C and N–C(alpha)
N–C and C(alpha)–C
C=O and N–C
C=O and N–C(alpha)
N–C(alpha) and N–C
C(alpha)–C and N–C(alpha)
Amino acid residues commonly found in the middle of beta-turn are:
Ala and Gly
Pro and Gly
hydrophobic
two Cys
those with ionized R- groups
Pro and Gly
Which of the following is not an appropriate description for van der Waals’s interactions?
-An individual van der Waals interaction does not contribute significantly to the stability of a protein
-They involve dipole-dipole interactions
-They can involve hydrophobic amino acids
-They are highly specific
-Their strength on the distance between the two interacting atoms
-They are highly specific
In an alpha helix, the R groups on the amino acid residues:
are found on the outside of the helix spiral
alternate between the outside and the inside of the helix
cause only right-handed helices to form
generate the hydrogen bonds that form the helix
stack within the interior of the helix
are found on the outside of the helix spiral
All of the following are considered “weak” interactions in proteins except:
hydrophobic interactions
van der Waals forces
ionic bonds
hydrogen bonds
peptide ponds
peptide ponds
The most important contribution to the stability of a protein’s conformation appears to be the:
-stabilizing effect of hydrogen bonding between the carbonyl group of one peptide bond and the amino group of another
-sum of free energies of formation of many weak interactions among the hundreds of amino acids in a protein
-entropy increase from the decrease in ordered water molecules forming a solvent shell around it
-sum of free energies of formation of many weak interactions between its polar amino acids and surrounding water
-maximum entropy increase from ionic interactions between the ionized amino acids in a protein
-entropy increase from the decrease in ordered water molecules forming a solvent shell around it
In the alpha helix the hydrogen bonds between N-H and C=O groups in the polypeptide chain:
occur mainly between electronegative atoms of the R groups
are roughly perpendicular to the axis of the helix
are roughly parallel to the axis of the helix
occur only near the amino and carboxyl termini of the helix
occur only between some of the amino acids of the helix
are roughly parallel to the axis of the helix
The three-dimensional conformation of a protein may be strongly influenced by amino acid residues that are very far apart in sequence. This relationship is in contrast to secondary structure, where the amino acid residues are:
generally near each other in sequence
often on different polypeptide strands
usually near the polypeptide chain’s amino terminus or carboxyl terminus
invariably restricted to about 7 of the 20 strand amino acids
always side by side
generally near each other in sequence
Proteins often have regions that can fold and function as an independent entity from the whole protein. These regions are called:
subunits
peptides
domains
sites
oligomers
domains
Proteins are classified within families or superfamilies based on similarities in:
physio-chemical properties
evolutionary origin
subunit structure
structure and /or function
subcellular location
structure and /or function
The major reason in antiparallel beta-stranded protein structures is more stable than parallel beta-stranded structures is that the latter:
do not have as many disulfide crosslinks between adjacent strands
do not stack in sheets as well as antiparallel strands
have weaker hydrogen bonds laterally between adjacent strands
are in a slightly less extended configuration than antiparallel strands
have fewer lateral hydrogen bonds than antiparallel strands
have weaker hydrogen bonds laterally between adjacent strands
Which of the following statements is false?
Gly residues are particularly abundant in collagen
Collagen is a protein in which the polypeptides are mainly in the alpha-helix conformation
Silk fibroin is a protein in which the polypeptide is almost entirely in the beta conformation
Disulfide linkages are important for keratin structure
Alpha-keratin is a protein in which the polypeptides are mainly in the alpha-helix conformation
Collagen is a protein in which the polypeptides are mainly in the alpha-helix conformation
A sequence of amino acids in a certain protein is found to be -Ser-Gly-Pro-Gly-. The sequence is most probably part of a(n):
alpha sheet
beta turn
parallel beta-sheet
alpha helix
antiparallel beta sheets
beta turn
Protein S will fold into its native conformation only when protein Q is also present in the solution. However, protein Q can fold into its native conformation without protein S. Protein Q therefore, may function as a ___ for protein S.
protein precursor
structural motif
molecular chaperone
proteasome
supersecondary structural unit
molecular chaperone
A d-amino acid would interrupt an a helix made of I-amino acids. Another naturally occurring hindrance to the formation of an a helix is the presence of:
a Pro residue
a nonpolar residue near the carboxyl terminus
a positively charged Lys residue
a negatively charged Arg residue
two Ala residues side by side
a Pro residue
