Chapter 4 Flashcards
(24 cards)
The variations in the physical characteristics between different proteins are influenced by
the overall amino acid compositions, but even more important is the unique amino acid _______
Sequence
β sheets can participate in the formation of amyloid fibers, which are insoluble protein
aggregates. What drives the formation of amyloid fibers?
β-sheet stabilization of abnormally folded proteins
Protein structures have several different levels of organization. The primary structure of a
protein is its amino acid sequence. The secondary and tertiary structures are more
complicated.
Consider the definitions below and select the one that best fits the term “protein
domain.
a protein segment that folds independently
Proteins bind selectively to small-molecule targets called ligands. The selection of one ligand
out of a mixture of possible ligands depends on the number of weak, noncovalent interactions
in the protein’s ligand-binding site. Where is the binding site typically located in the protein
structure?
inside a cavity on the protein surface
The order in which amino acids are linked is unique for each protein and is the most
important factor in determining overall protein structure
True
Peptide bonds are planar amide bonds that are central to the polypeptide backbone
True
The chemical properties of amino acid side chains include charged, uncharged polar, and
nonpolar
True
The relative distribution of polar and nonpolar amino acids in a folded protein is determined
largely by hydrophobic interactions, which favor the clustering of nonpolar side chains in
the interior.
True
Knowing that there are 20 different possible amino acids that can be used at each position in a
polypeptide, calculate the number of different polypeptides that could theoretically be
produced for a protein that is 180 amino acids in length
20^180
No, we would not expect all of the
theoretically possible proteins to be made
Natural selection favors the retention of genes that encode
proteins with stable conformations.
A newly synthesized protein generally folds up into a __________ conformation
Stable
All the
information required to determine a protein’s conformation is contained in its amino acid
__________
Sequence
On being heated, a protein molecule will become __________ as a result of
breakage of __________ bonds.
denatured, covalent
On removal of urea, an unfolded protein can become
__________.
renatured
The final folded conformation adopted by a protein is that of __________
energy.
Lowest
Why might high concentrations of urea unfold proteins?
-Urea can squeeze between H bonds, destabilizing protein structures
-H bonded network of water molecules becomes disrupted & molecule falls apart
Arrangement of Amino acids in B pleated sheet
Amino acid sequence consists of alternating nonpolar & charged amino acids. Therefore one side polar and the other hydrophobic.
-Hydrophobic side would face protein interior
Why don’t cells contain millions of proteins that aren’t in use?
Natural selection provides a strong driving force that eliminates both useless/harmful proteins.
What would happen if your hair was treated w/ strong reducing agents that broke all the disulfide bonds
Keratin filaments would separate and individual hairs would become weakened
What are the advantages of protein phosphorylation or binding of a nucleotide to regulate protein activity.
-Fast rate at which small nucleotide can diffuse to protein
-Phosphates can be added to many different side chains on a protein, increasing complexity of regulation
Do noncovalent bonds influence the three-dimensional shape of macromolecules?
Yes
What common features of of a helices and B sheets make them universal building blocks for proteins?
All of N-H and C=O groups are engaged in H bonds. Provides stability
Would you expect any fragment of a polypeptide chain would fold the same way as an intact protein?
Yes
What happens at the molecular level to a mutant enzyme as the temp increases?
The mutation causes the enzyme to have a less stable structure & therefore gets turned off at higher temps.
How is it possible that a change in a single amino acid can destroy protein function?
Small changes in protein core can disrupt protein functioning by altering the conformation at a binding site.
