Question 1

Based on the plot of oxygen saturation versus partial pressure of oxygen, which of the following statements is true?

Accepted Answer

A) at oxygen pressure >100 mm Hg, hemoglobin dissociates into individual subunits so that it is able to bind oxygen similar to myoglobin 
B) at typical resting capillary oxygen pressure of ~30 mm Hg, hemoglobin has only 1 of its 4 oxygen binding sites filled while myoglobin is nearly saturated with oxygen 
C) under periods of extreme muscle exertion, capillary oxygen pressure can drop to 10 mm Hg, allowing release of ~90% of oxygen carried by hemoglobin 
D) the structure of hemoglobin allows for complete release of oxygen in capillary beds at all times 
E) none of the above 
A) at oxygen pressure >100 mm Hg, hemoglobin dissociates into individual subunits so that it is able to bind oxygen similar to myoglobin 
B) at typical resting capillary oxygen pressure of ~30 mm Hg, hemoglobin has only 1 of its 4 oxygen binding sites filled while myoglobin is nearly saturated with oxygen 
C) under periods of extreme muscle exertion, capillary oxygen pressure can drop to 10 mm Hg, allowing release of ~90% of oxygen carried by hemoglobin 
D) the structure of hemoglobin allows for complete release of oxygen in capillary beds at all times 
E) none of the above C

Question 2

Changes in hemoglobin's oxygen affinity are primarily the result of changes in the _________ structure of the protein.

Accepted Answer

A) primary 
B) secondary 
C) tertiary 
D) quaternary 
E) all of the above 
A) primary 
B) secondary 
C) tertiary 
D) quaternary 
E) all of the above D

Question 3

Which of the following occurs when hemoglobin switches from the T (deoxy)state to the R (oxy)state?

Accepted Answer

A) the heme group goes from a slightly puckered conformation to a flat conformation 
B) the ferrous ion is pulled into the plane of the heme group 
C) the F8 (proximal)histidine rotates about 8$\circ$ to better align with the ferrous ion 
D) movement of the F8 histidine causes a shift in the F helix, thus weakening interactions with other subunits 
E) all of the above 
A) the heme group goes from a slightly puckered conformation to a flat conformation 
B) the ferrous ion is pulled into the plane of the heme group 
C) the F8 (proximal)histidine rotates about 8$\circ$ to better align with the ferrous ion 
D) movement of the F8 histidine causes a shift in the F helix, thus weakening interactions with other subunits 
E) all of the above E

Question 4

Which of the following reversible reactions of carbon dioxide explains how hemoglobin serves as a transporter of carbon dioxide?

Accepted Answer

A) reaction with the imidazole group of the distal histidine where oxygen would normally be bound 
B) reaction with the carboxyl group of glutamic acid to form a carbonic acid anhydride 
C) reaction with the N-terminal amino groups to form a carbamate 
D) reaction with the hydroxyl group of serine to form a carbonate 
E) none of the above 
A) reaction with the imidazole group of the distal histidine where oxygen would normally be bound 
B) reaction with the carboxyl group of glutamic acid to form a carbonic acid anhydride 
C) reaction with the N-terminal amino groups to form a carbamate 
D) reaction with the hydroxyl group of serine to form a carbonate 
E) none of the above

Question 5

Recent studies have shown that the H-bond between the distal histidine and oxygen molecule in myoglobin has a strength of ~ 15 kJ/mol, but in hemoglobin, the strength of the bond is only ~8 kJ/mol. What does this suggest about the differences between myoglobin and hemoglobin?

Accepted Answer

A) myoglobin binds oxygen more strongly than hemoglobin 
B) hemoglobin binds oxygen more strongly than myoglobin 
C) the iron in myoglobin is more easily oxidized than in hemoglobin 
D) the iron in hemoglobin is more easily oxidized than in myoglobin 
E) none of the above 
A) myoglobin binds oxygen more strongly than hemoglobin 
B) hemoglobin binds oxygen more strongly than myoglobin 
C) the iron in myoglobin is more easily oxidized than in hemoglobin 
D) the iron in hemoglobin is more easily oxidized than in myoglobin 
E) none of the above

Question 6

2,3-Bisphosphoglycerate is known to interact with hemoglobin in the following ways:
carboxylate with Lys
C-2 phosphate with protonated His
C-3 phosphate with N-terminal amino acid
Using the structure of 2,3-bisphosphoglycerate, show these interactions and identify what type of interaction occurs.

Accepted Answer

All intera

Question 7

Using the following sequence from the coding strand of DNA, determine the amino acid sequence of the corresponding protein. Make three different mutations: (1)silent, (2)missense with little or no effect upon the protein structure (indicate the amino acid substitution)and (3)nonsense.
CATTTATATGAAAGC

Accepted Answer

His-Leu-Tyr-Glu-Ser
Silent with mutation

Question 8

Which of the following mutations in the coding strand of DNA would be the most likely to cause a serious mutation?

Accepted Answer

A) AGA $\rarr$ CGA 
B) ATA $\rarr$ TTA 
C) GAA $\rarr$ AAA 
D) TAA $\rarr$ TGA 
E) ACT $\rarr$ AGT 
A) AGA $\rarr$ CGA 
B) ATA $\rarr$ TTA 
C) GAA $\rarr$ AAA 
D) TAA $\rarr$ TGA 
E) ACT $\rarr$ AGT

Question 9

Which of the following is a homotropic effector of hemoglobin-oxygen binding?

Accepted Answer

A) O2 
B) H+ 
C) CO2 
D) Cl- 
E) 2,3-bisphosphoglycerate (2,3-BPG) 
A) O2 
B) H+ 
C) CO2 
D) Cl- 
E) 2,3-bisphosphoglycerate (2,3-BPG)

Question 10

The binding of oxygen to hemoglobin is said to be _______________.

Accepted Answer

A) high affinity 
B) low affinity 
C) sigmoidal 
D) cooperative 
E) sequential 
A) high affinity 
B) low affinity 
C) sigmoidal 
D) cooperative 
E) sequential

Question 11

The ability of some bacteria to resist the cytotoxic effects of macrophages is most likely due to which of the following?

Accepted Answer

A) they have high levels of flavohemoglobin that allows for the destruction of nitric oxide, a potent cytotoxic compound produced by macrophages 
B) they possess a protein called cytoglobin that causes macrophages to undergo apoptosis 
C) they have high levels of a myoglobin-like protein that tightly binds oxygen, preventing proper activity of the macrophage 
D) they possess the protein neuroglobin which enables them to specifically target nerve cells and thus evade macrophages 
E) none of the above 
A) they have high levels of flavohemoglobin that allows for the destruction of nitric oxide, a potent cytotoxic compound produced by macrophages 
B) they possess a protein called cytoglobin that causes macrophages to undergo apoptosis 
C) they have high levels of a myoglobin-like protein that tightly binds oxygen, preventing proper activity of the macrophage 
D) they possess the protein neuroglobin which enables them to specifically target nerve cells and thus evade macrophages 
E) none of the above

Question 12

Which of the following methods could be used to produce a Fab fragment from an IgG?

Accepted Answer

A) treatment with reducing agent, isolation of the light chain, removal of reducing agent 
B) treatment with reducing agent, isolation of the heavy chain, removal of reducing agent 
C) treatment with papain, separation of the Fab fragment from the rest of the heavy chain 
D) treatment with papain, separation of the Fab fragment from the rest of the light chain 
E) none of the above 
A) treatment with reducing agent, isolation of the light chain, removal of reducing agent 
B) treatment with reducing agent, isolation of the heavy chain, removal of reducing agent 
C) treatment with papain, separation of the Fab fragment from the rest of the heavy chain 
D) treatment with papain, separation of the Fab fragment from the rest of the light chain 
E) none of the above

Question 13

Which of the following is responsible for the immense diversity of antibodies?

Accepted Answer

A) recombination of introns 
B) recombination of exons 
C) variable domain recombination 
D) epitope recombination 
E) none of the above 
A) recombination of introns 
B) recombination of exons 
C) variable domain recombination 
D) epitope recombination 
E) none of the above

Question 14

Which of the following is true regarding the effectors of hemoglobin-oxygen binding?

Accepted Answer

A) an increase in blood pH will cause hemoglobin to bind more tightly to oxygen 
B) increased CO2 from increased muscle activity will result in an increase in the R state of hemoglobin 
C) increased Cl- will cause the formation of a salt bridge between two Lys residues, one on an $\alpha$ subunit, the other on a $\beta$ subunit 
D) the binding site of 2,3-BPG contains several Asp and Glu residues which are repelled by the similar charge, pushing the two $\beta$ subunits away from each other 
E) all of the above 
A) an increase in blood pH will cause hemoglobin to bind more tightly to oxygen 
B) increased CO2 from increased muscle activity will result in an increase in the R state of hemoglobin 
C) increased Cl- will cause the formation of a salt bridge between two Lys residues, one on an $\alpha$ subunit, the other on a $\beta$ subunit 
D) the binding site of 2,3-BPG contains several Asp and Glu residues which are repelled by the similar charge, pushing the two $\beta$ subunits away from each other 
E) all of the above

Question 15

Myoglobin without a heme group would be considered a(n)_______.

Accepted Answer

A) apoprotein 
B) holoprotein 
C) apoenzyme 
D) holoenzyme 
E) none of the above 
A) apoprotein 
B) holoprotein 
C) apoenzyme 
D) holoenzyme 
E) none of the above

Question 16

Which immunoglobulin is the only one to occur in a dimeric form?

Accepted Answer

A) IgA 
B) IgD 
C) IgE 
D) IgG 
E) IgM 
A) IgA 
B) IgD 
C) IgE 
D) IgG 
E) IgM

Question 17

Which of the following explains why the ferrous ion is not oxidized to the ferric state in the globin proteins even though free heme in solution is readily oxidized?

Accepted Answer

A) when bound to globins, the heme is always planar; when free in solution, heme adopts a non-planar configuration which allows the oxidation of the iron 
B) the globin proteins provide a hydrophobic environment that prevents oxidation 
C) coordination with the proximal histidine allows any oxidized iron to be rapidly reduced back to the ferrous state 
D) since the oxygen is hydrogen bound to the distal histidine, if oxidation of iron does occur, the distal histidine allows for rapid reduction 
E) none of the above 
A) when bound to globins, the heme is always planar; when free in solution, heme adopts a non-planar configuration which allows the oxidation of the iron 
B) the globin proteins provide a hydrophobic environment that prevents oxidation 
C) coordination with the proximal histidine allows any oxidized iron to be rapidly reduced back to the ferrous state 
D) since the oxygen is hydrogen bound to the distal histidine, if oxidation of iron does occur, the distal histidine allows for rapid reduction 
E) none of the above

Question 18

Which of the following interactions causes a change from the R state (oxy form)to the T state (deoxy form)of hemoglobin?

Accepted Answer

A) interactions between heme groups 
B) protonation of the R-group of His146 on the $\beta$ subunit to allow formation of a salt bridge with Lys40 on the $\alpha$ subunit 
C) salt bridge formed by $\alpha$ 1-Arg141 to the carboxylate of $\alpha$ 2Asp126 
D) protonation of the $\alpha$ 1 subunit terminal carboxyl group disrupts a salt bridge with $\alpha$ 2Lys 127 
E) none of the above 
A) interactions between heme groups 
B) protonation of the R-group of His146 on the $\beta$ subunit to allow formation of a salt bridge with Lys40 on the $\alpha$ subunit 
C) salt bridge formed by $\alpha$ 1-Arg141 to the carboxylate of $\alpha$ 2Asp126 
D) protonation of the $\alpha$ 1 subunit terminal carboxyl group disrupts a salt bridge with $\alpha$ 2Lys 127 
E) none of the above

Question 19

Given the following plot of oxygen binding versus pressure of O2 for myoglobin and hemoglobin, (1)draw a curve that shows what happens when the pH is increased to about 7.6 and (2)draw a curve that shows what happens when the pH is decreased to about 6.8.

Accepted Answer

Question 20

Which of the following models of allosteric transitions best applies to hemoglobin?

Accepted Answer

A) sequential (KNF)model 
B) concerted (MW
C) model 
C) tertiary two-state model 
D) tense versus relaxed model 
E) none of the above 
A) sequential (KNF)model 
B) concerted (MW
C) model 
C) tertiary two-state model 
D) tense versus relaxed model 
E) none of the above

Exam 7: Protein Function and Evolution

Based on the plot of oxygen saturation versus partial pressure of oxygen, which of the following statements is true?

Changes in hemoglobin's oxygen affinity are primarily the result of changes in the _________ structure of the protein.

Which of the following occurs when hemoglobin switches from the T (deoxy)state to the R (oxy)state?

Which of the following reversible reactions of carbon dioxide explains how hemoglobin serves as a transporter of carbon dioxide?

Recent studies have shown that the H-bond between the distal histidine and oxygen molecule in myoglobin has a strength of ~ 15 kJ/mol, but in hemoglobin, the strength of the bond is only ~8 kJ/mol. What does this suggest about the differences between myoglobin and hemoglobin?

2,3-Bisphosphoglycerate is known to interact with hemoglobin in the following ways: carboxylate with Lys C-2 phosphate with protonated His C-3 phosphate with N-terminal amino acid Using the structure of 2,3-bisphosphoglycerate, show these interactions and identify what type of interaction occurs.

Which of the following mutations in the coding strand of DNA would be the most likely to cause a serious mutation?

Which of the following is a homotropic effector of hemoglobin-oxygen binding?

The binding of oxygen to hemoglobin is said to be _______________.

The ability of some bacteria to resist the cytotoxic effects of macrophages is most likely due to which of the following?

Which of the following methods could be used to produce a Fab fragment from an IgG?

Which of the following is responsible for the immense diversity of antibodies?

Which of the following is true regarding the effectors of hemoglobin-oxygen binding?

Myoglobin without a heme group would be considered a(n)_______.

Which immunoglobulin is the only one to occur in a dimeric form?

Which of the following explains why the ferrous ion is not oxidized to the ferric state in the globin proteins even though free heme in solution is readily oxidized?

Which of the following interactions causes a change from the R state (oxy form)to the T state (deoxy form)of hemoglobin?

Given the following plot of oxygen binding versus pressure of O2 for myoglobin and hemoglobin, (1)draw a curve that shows what happens when the pH is increased to about 7.6 and (2)draw a curve that shows what happens when the pH is decreased to about 6.8.

Which of the following models of allosteric transitions best applies to hemoglobin?

The Scope of Biochemistry

The Matrix of Life: Weak Interactions in an Aqueous Environment

The Energetics of Life

Nucleic Acids

Introduction to Proteins: the Primary Level of Protein Structure

The Three-Dimensional Structure of Proteins

Contractile Proteins and Molecular Motors

Carbohydrates: Sugars, Saccharides, Glycans

Lipids, Membranes and Cellular Transport

Enzymes: Biological Catalysts

Chemical Logic of Metabolism

Carbohydrate Metabolism: Glycolysis, Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

Citric Acid Cycle and Glyoxylate Cycle

Electron Transport, Oxidative Phosphorylation, and Oxygen Metabolism

Photosynthesis

Lipid Metabolism I: Fatty Acids, Triacylglycerols, and Lipoproteins

Interorgan and Intracellular Coordination of Energy Metabolism in Vertebrates

Lipid Metabolism Ii: Membrane Lipids, Steroids, Isoprenoids, and Eicosanoids

Metabolism of Nitrogenous Compounds I: Principles of Biosynthesis, Utilization, and Turnover

Metabolism of Nitogenous Compounds II: Amino Acids, Porphyrins, and Neurotransmitters

Nucleotide Metabolism

Mechanisms of Signal Transduction

Genes, Genomes and Chromosomes

DNA Replication

DNA Restructuring: Repair, Recombination, Rearrangement, Amplification

Information Readout: Transcription and Post-Transcriptional Processing

Information Decoding: Translation and Post-Translational Protein Processing

Regulation of Gene Expression

Filters

Which of the following methods could be used to produce a F_ab fragment from an IgG?

Given the following plot of oxygen binding versus pressure of O₂ for myoglobin and hemoglobin, (1)draw a curve that shows what happens when the pH is increased to about 7.6 and (2)draw a curve that shows what happens when the pH is decreased to about 6.8.