MODULE #3 HW

If curve 3 represents the binding of oxygen to normal hemoglobin, which curve would represent the binding behaviour of a single α-globin subunit? 1 2 3 4 None of the above

1

Which of the curves does NOT show cooperative binding? 1 2 3 4 None of the above

1

Which of the curves in the graph represents the binding of oxygen to a monomeric oxygen binding protein? 1 2 3 4 None of the above

1

If curve 3 represents the binding of oxygen to Hb at pH 7.2, which curve represents the binding of oxygen to Hb at pH 7.6? 1 2 3 4 None of the above

2

If curve 3 represents the binding of oxygen to Hb at pH 7.4, which curve represents the binding of oxygen to Hb at pH 7.2? 1 2 3 4 None of the above

4

Which of the following is TRUE for a β-pleated sheet? A, B, and C are correct. A and C only are correct. B. The polypeptide chain is almost fully extended. A. There are hydrogen bonds perpendicular to the direction of the polypeptide chain. C. The polypeptide chains may be hydrogen bonded together in parallel or anti-parallel orientation.

A, B, and C are correct.

Which of the following series of amino acids is most likely to be buried in the center of a water-soluble globular protein? Glu, Asp, Lys Gly, Asn, Ser Ala, Leu, Phe Pro, Gln, His

Ala, Leu, Phe

The binding of one O2 to a molecule of hemoglobin results in: The movement of hemoglobin to an organism's muscle tissue. The release of any other O2 that may have bound earlier. Dissociation of the hemoglobin subunits. A decrease in hemoglobin's ability to bind a second O2. An increased affinity for O2 in the remaining subunits (which have not yet bound O2).

An increased affinity for O2 in the remaining subunits (which have not yet bound O2).

Which of the following is NOT a conservative amino acid substitution in a protein structure? Asp to Glu Ala to Val Asn to Gln Arg to Phe Ser to Thr

Arg to Phe

Which of the following statements about 2,3-bisphosphoglycerate (BPG) binding is FALSE? BPG requires a binding site containing multiple positively charged groups. BPG binds less tightly to fetal hemoglobin than to adult hemoglobin, thereby aiding oxygen transfer to a fetus. BPG binds to hemoglobin at one site and lowers hemoglobin's affinity for oxygen at another site. BPG aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen.

BPG aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen.

Which group of the 3rd residue is used to make its hydrogen bond in the alpha-helix? side chain N-H C-H C=O

C=O

One of the amino acids that is classified as having a polar side chain is typically found buried in the hydrophobic core of soluble globular proteins. Which of the following amino acids is it? Cys Gly Gln Ser

Cys

Which of the following sequences of amino acids is most likely to be at the surface of a water-soluble globular protein? Pro-Phe-Thr Ile-Ser-Met Ala-Leu-Phe Glu-Asp-Lys Gly-Tyr-Val

Glu-Asp-Lys

Which of the following stabilizes the folding of a polypeptide backbone into regular secondary structure? Electrostatic interactions. Hydrogen bonds. Disulphide bridges. Covalent bonds. Hydrophobic interactions.

Hydrogen bonds

Which of the following best describes the tertiary structure of myoglobin? It contains 8 α-helices. It contains heme, which is slotted into a hydrophobic pocket between α-helix E and α-helix F. It contains heme, which is loosely associated via hydrophobic interactions with amino acid side chains in the heme pocket. It contains no β-sheet. It Is a heterotetramer.

It contains heme, which is slotted into a hydrophobic pocket between α-helix E and α-helix F.

Why does a decrease in pH alter/disrupt the tertiary structure of an enzyme? It reduces disulphide bonds. It disrupts ion pairs/salt bridges. It promotes proteolytic cleavage of peptide bonds. It reduces hydrophobic interactions. It deprotonates prosthetic groups.

It disrupts ion pairs/salt bridges.

Which one of the following sequences of five amino acids would most likely be located in the interior of a globular soluble protein? Tyr-Phe-Glu-Asn-Leu Glu-Asn-Ser-Thr-Gln Val-Ala-Val-Glu-Val Met-Cys-Pro-His-Tyr Met-Phe-Pro-Ile-Leu

Met-Phe-Pro-Ile-Leu

Which of the following statements about the structure of myoglobin is FALSE? Myoglobin contains all three types of secondary structure. A heme prosthetic group is tightly bound to myoglobin via a coordination bond. The tertiary structure of myogobin is a compact, roughly spherical shape. Myoglobin contains a heme prosthetic group that is slotted into a hydrophobic pocket between α-helix E and α-helix F.

Myoglobin contains all three types of secondary structure.

Which of the following statements most accurately explains why hemoglobin is able to deliver oxygen to myoglobin in the tissues? The pH of tissue/muscle is always higher than that of blood, which aids hemoglobin in giving up its oxygen. The iron in the heme group of myoglobin is Fe3+, which has a higher affinity for oxygen. The presence of BPG in the red blood cells shifts the equilibrium towards the R state of hemoglobin. Myoglobin has a hyperbolic oxygen binding curve, whereas hemoglobin has a sigmoidal oxygen binding curve.

Myoglobin has a hyperbolic oxygen binding curve, whereas hemoglobin has a sigmoidal oxygen binding curve.

Which of the following statements is true because of the hydrophobic effect? Charged polar residues R, H, K, E, and D are usually found on the surfaces of proteins. Uncharged polar residues S, T, N, Q, and Y are usually found on the surface of proteins, but may also be found in the interior. The interior of proteins is packed very densely. Nonpolar residues V, L, I, M, and F are found in the interior of proteins.

Nonpolar residues V, L, I, M, and F are found in the interior of proteins.

What is the major factor that "drives" the folding of proteins into their tertiary structure? Formation of the maximum number of hydrophilic interactions. Placement of hydrophobic amino acid residues within the interior of the protein. Formation of the maximum number of ionic interactions. Placement of polar amino acid residues on the surface of the protein.

Placement of hydrophobic amino acid residues within the interior of the protein.

Which of the following statements about quaternary structure is TRUE? Quaternary structure is stabilized by the same types of noncovalent interactions as tertiary structure. Quaternary structure is defined as the 3D structure of proteins with four subunits. Quaternary structure exists only in proteins containing prosthetic groups. Quaternary structure requires covalent interactions between polypeptide chains.

Quaternary structure is stabilized by the same types of noncovalent interactions as tertiary structure.

Structurally, myoglobin and hemoglobin are very similar proteins. In which of the following levels of structure do they differ most? Primary structure. Secondary structure. Tertiary structure. Quaternary structure.

Quaternary structure.

Which of the following is an example of a conservative amino acid substitution in a protein structure? Gly to Trp Ser to Thr Cys to Met Asp to Arg

Ser to Thr

Which of the following describes the entire three-dimensional structure of a single polypeptide? Secondary structure Primary structure Tertiary structure Quaternary structure

Tertiary structure

One of the adaptations to high altitude is an increase in the concentration of BPG in red blood cells. What effect does this have on the oxygen binding curve of hemoglobin and why? The curve is shifted to the left because hemoglobin has a lower K (dissociation constant). The curve is shifted to the right, because hemoglobin has tighter oxygen binding. The curve is shifted to the right, because hemoglobin has a lower affinity for oxygen. The curve is shifted to the left because hemoglobin binds oxygen more tightly.

The curve is shifted to the right, because hemoglobin has a lower affinity for oxygen.

What is the primary driving force in the formation of protein tertiary structure? The formation of van der Waals interactions between neighbouring groups. Energy released when additional hydrogen bonds are formed. Energy released when additional ion pairs are formed. The exclusion of non-polar substances from aqueous solution.

The exclusion of non-polar substances from aqueous solution.

What ultimately determines the unique three dimensional structure of soluble globular proteins? The exact number of disulfide bonds. The exact number of H-bonds. The prosthetic groups. The number of subunits.

The number of subunits.

A newly-identified protein has a sigmoidal curve in a graph of fractional saturation versus ligand concentration. What can be deduced about this protein? The protein has a constant high affinity for the ligand. The protein has primary, secondary and tertiary structure, but not quaternary. The protein binds the ligand cooperatively. The dissociation constant (K) of the ligand is low.

The protein binds the ligand cooperatively.

β-sheets can be parallel or antiparallel. The β-sheet is a type of regular secondary structure. The side chains in a β-sheet alternate between the two sides of the sheet. The β-sheet is a type of secondary structure that fulfills the hydrogen bonding requirements of amino acid side chains. The β-sheet contains hydrogen bonds between the carbonyl oxygen of one residue and an amide hydrogen of a residue on an adjacent strand.

The β-sheet is a type of secondary structure that fulfills the hydrogen bonding requirements of amino acid side chains.

Which of the following statements is TRUE regarding the R-groups of amino acid residues in an α-helix? They are found on the exterior of the helix. They form the hydrogen bonds that produce the helix. They alternate between the outside and the inside of the helix. They are found in the interior of the helix. They cause the helix to be right handed.

They are found on the exterior of the helix.

Why does the concentration of BPG in red blood cells increase when humans are exposed to high altitudes? To allow hemoglobin to release more oxygen at lower partial pressures of oxygen. To induce the production of more red blood cells. To neutralize the increased concentration of hydrogen ions produced when muscle works harder at high altitudes. To allow hemoglobin to bind more oxygen at lower partial pressures of oxygen.

To allow hemoglobin to release more oxygen at lower partial pressures of oxygen.

A newly-identified protein shows the following behaviour in ligand binding. Which of the statements about this protein is FALSE? The protein exists in two conformational states which have different affinities for the ligand. When the ligand binds to one subunit, the affinity of the other subunits for the same ligand is reduced. The protein binds the ligand cooperatively. The ligand binds reversibly at a specific site on the protein, causing a global change in conformation.

When the ligand binds to one subunit, the affinity of the other subunits for the same ligand is reduced.

Which of the following amino acids has the most significant role in the molecular mechanisms of hemoglobin's function? tyrosine histidine lysine glycine glutamate

histidine