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

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 B

Question 3

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 C

Question 4

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

Question 5

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 6

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

Question 7

In sickle cell hemoglobin,a Glu is mutated to a _______.This causes the formation of _______ between hemoglobin molecules,ultimately forming large aggregates.

Accepted Answer

A) Arg;salt bridges 
B) Cys;disulfide bonds 
C) Val;hydrophobic interactions 
D) Pro;disrupted $\alpha$-helix,resulting in several H-bonds and salt bridges 
E) none of the above 
A) Arg;salt bridges 
B) Cys;disulfide bonds 
C) Val;hydrophobic interactions 
D) Pro;disrupted $\alpha$-helix,resulting in several H-bonds and salt bridges 
E) none of the above

Question 8

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 9

Why do individuals who are heterozygous for sickle cell anemia have a resistance to malaria?

Accepted Answer

A) formation of hemoglobin aggregates makes red blood cells impervious to parasitic infection 
B) shortened life span of red blood cells does not allow sufficient time for the parasite to mature in the red blood cell 
C) diminished blood flow to the skin as a result of sickled red blood cells blocking capillaries prevents mosquitoes from actually transferring the malaria parasite to individuals 
D) sickle cell hemoglobin fibers have both decreased O2 and CO2 carrying capacity;since CO2 is a mosquito attractant,diminished CO2 exhalation does not attract mosquitoes 
E) none of the above 
A) formation of hemoglobin aggregates makes red blood cells impervious to parasitic infection 
B) shortened life span of red blood cells does not allow sufficient time for the parasite to mature in the red blood cell 
C) diminished blood flow to the skin as a result of sickled red blood cells blocking capillaries prevents mosquitoes from actually transferring the malaria parasite to individuals 
D) sickle cell hemoglobin fibers have both decreased O2 and CO2 carrying capacity;since CO2 is a mosquito attractant,diminished CO2 exhalation does not attract mosquitoes 
E) none of the above

Question 10

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 11

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 12

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

Question 13

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 14

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 15

Which of the following mutations is correctly defined?

Accepted Answer

A) silent: change of a single base in the non-coding intron region of a gene 
B) missense: substitution of a single base results in a premature stop codon 
C) nonsense: substitution of a single base results in a complete change of amino acid sequence 
D) frameshift: deletion of a single base results in a single amino acid change 
E) permissive: results in a protein that has greater thermodynamic stability 
A) silent: change of a single base in the non-coding intron region of a gene 
B) missense: substitution of a single base results in a premature stop codon 
C) nonsense: substitution of a single base results in a complete change of amino acid sequence 
D) frameshift: deletion of a single base results in a single amino acid change 
E) permissive: results in a protein that has greater thermodynamic stability

Question 16

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 17

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 18

A typical Hill plot (log [YO2/(1- YO2)] vs log PO2)for hemoglobin-oxygen binding does not yield a straight line as it does for myoglobin.Which of the following is the best explanation for this?

Accepted Answer

A) at high oxygen pressures,hemoglobin is in a low oxygen affinity state 
B) at low oxygen pressures,hemoglobin is in a high oxygen affinity state 
C) hemoglobin undergoes a transition from low affinity state under low oxygen pressure to a high affinity state under high oxygen pressure 
D) hemoglobin undergoes a transition from high affinity state under low oxygen pressure to a low affinity state under high oxygen pressure 
E) none of the above 
A) at high oxygen pressures,hemoglobin is in a low oxygen affinity state 
B) at low oxygen pressures,hemoglobin is in a high oxygen affinity state 
C) hemoglobin undergoes a transition from low affinity state under low oxygen pressure to a high affinity state under high oxygen pressure 
D) hemoglobin undergoes a transition from high affinity state under low oxygen pressure to a low affinity state under high oxygen pressure 
E) none of the above

Question 19

When oxygen is bound to myoglobin,the amino acid _____ is complexed to the iron ion of the heme group while _______ forms a hydrogen bound to the oxygen.

Accepted Answer

A) cysteine;serine 
B) cysteine;histidine 
C) serine;cysteine 
D) histidine;histidine 
E) histidine;cysteine 
A) cysteine;serine 
B) cysteine;histidine 
C) serine;cysteine 
D) histidine;histidine 
E) histidine;cysteine

Question 20

One would expect that defects in the globin genes would be so serious as to cause death in utero.Which of the following explains how some thalassemias are found in living people?

Accepted Answer

A) in $\beta$-thalassemia,the use of the $\gamma$ subunit allows individuals to live a normal lifespan 
B) individuals who completely lack functional $\alpha$ subunits can live if placed in a hypobaric chamber to induce hypoxia 
C) since humans have 4 copies of the $\alpha$ chain gene,effects are only seen when at least 3 of the genes are nonfunctional 
D) individuals with nonfunctional $\alpha$ chain genes can make $\beta$2$\gamma$2 tetramers that function normally 
E) none of the above 
A) in $\beta$-thalassemia,the use of the $\gamma$ subunit allows individuals to live a normal lifespan 
B) individuals who completely lack functional $\alpha$ subunits can live if placed in a hypobaric chamber to induce hypoxia 
C) since humans have 4 copies of the $\alpha$ chain gene,effects are only seen when at least 3 of the genes are nonfunctional 
D) individuals with nonfunctional $\alpha$ chain genes can make $\beta$2$\gamma$2 tetramers that function normally 
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?

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

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

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

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

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

In sickle cell hemoglobin,a Glu is mutated to a _______.This causes the formation of _______ between hemoglobin molecules,ultimately forming large aggregates.

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

Why do individuals who are heterozygous for sickle cell anemia have a resistance to malaria?

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

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?

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

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

Which of the following mutations is correctly defined?

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

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

A typical Hill plot (log [YO2/(1- YO2)] vs log PO2)for hemoglobin-oxygen binding does not yield a straight line as it does for myoglobin.Which of the following is the best explanation for this?

When oxygen is bound to myoglobin,the amino acid _____ is complexed to the iron ion of the heme group while _______ forms a hydrogen bound to the oxygen.

One would expect that defects in the globin genes would be so serious as to cause death in utero.Which of the following explains how some thalassemias are found in living people?

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?

In sickle cell hemoglobin,a Glu is mutated to a _.This causes the formation of _ between hemoglobin molecules,ultimately forming large aggregates.

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.

A typical Hill plot (log [Y_O₂/(1- Y_O₂)] vs log P_O₂)for hemoglobin-oxygen binding does not yield a straight line as it does for myoglobin.Which of the following is the best explanation for this?

When oxygen is bound to myoglobin,the amino acid _ is complexed to the iron ion of the heme group while ___ forms a hydrogen bound to the oxygen.