Question 1

A prosthetic group of a protein is a non-protein structure that is:
A)a ligand of the protein.
B)a part of the secondary structure of the protein.
C)a substrate of the protein.
D)permanently associated with the protein.
E)transiently bound to the protein.

Accepted Answer

A prosthetic group is a non-protein structure that is permanently associated with a protein. This association is usually through covalent bonding and helps to carry out the function of the protein. Examples of prosthetic groups include heme in hemoglobin or flavin in flavoproteins.

Question 2

The predominant structural feature in myosin molecules is:
A)a$\beta$structure.
B)an$\alpha$ helix.
C)the Fab domain.
D)the light chain.
E)the meromyosin domain.

Accepted Answer

B

Question 3

An allosteric interaction between a ligand and a protein is one in which:
A)binding of a molecule to a binding site affects binding of additional molecules to the same site.
B)binding of a molecule to a binding site affects binding properties of another site on the protein.
C)binding of the ligand to the protein is covalent.
D)multiple molecules of the same ligand can bind to the same binding site.
E)two different ligands can bind to the same binding site.

Accepted Answer

An allosteric interaction involves a ligand binding to a protein at one site (the allosteric site) and affecting the binding properties of another site on the protein (the active site). This is different from multiple molecules of the same ligand binding to the same site (which would be a non-allosteric interaction) or covalent binding (which is not necessarily allosteric). Option E is also incorrect, as two different ligands binding to the same site would be a non-allosteric interaction.

Question 4

The interactions of ligands with proteins:
A)are relatively nonspecific.
B)are relatively rare in biological systems.
C)are usually irreversible.
D)are usually transient.
E)usually result in the inactivation of the proteins.

Accepted Answer

Ligand-protein interactions are usually transient, meaning they are reversible and not permanent. This allows for regulation and flexibility in biological processes. Additionally, ligand-protein interactions can be highly specific, depending on the ligand and protein involved.

Question 5

When oxygen binds to a heme-containing protein,the two open coordination bonds of Fe²⁺ are occupied by: A)one O atom and one amino acid atom. B)one O₂ molecule and one amino acid atom. C)one O₂ molecule and one heme atom. D)two O atoms. E)two O₂ molecules.

Accepted Answer

When oxygen binds to a heme-containing protein, the iron atom (Fe) in the heme group forms a bond with one oxygen molecule (O2) and one atom from an amino acid (usually the imidazole ring of a histidine residue), thus occupying the two open coordination bonds of the iron.

Question 6

In hemoglobin,the transition from T state to R state (low to high affinity)is triggered by: A)Fe²⁺ binding. B)heme binding. C)oxygen binding. D)subunit association. E)subunit dissociation.

Accepted Answer

The transition from T state to R state in hemoglobin is triggered by oxygen binding, which induces a conformational change in the protein and results in a higher affinity for oxygen binding. This is known as the allosteric effect.

Question 7

Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)?
A)It binds at a distance from the heme groups of hemoglobin.
B)It binds with lower affinity to fetal hemoglobin than to adult hemoglobin.
C)It increases the affinity of hemoglobin for oxygen.
D)It is an allosteric modulator.
E)It is normally found associated with the hemoglobin extracted from red blood cells.

Accepted Answer

2,3-bisphosphoglycerate (BPG) actually decreases the affinity of hemoglobin for oxygen, allowing for easier release of oxygen in tissues with lower oxygen concentrations. Thus, choice C is not correct. The other choices are all correct: A) BPG binds at a distance from the heme groups of hemoglobin, B) BPG binds with lower affinity to fetal hemoglobin than to adult hemoglobin, D) BPG is an allosteric modulator, and E) BPG is normally found associated with the hemoglobin extracted from red blood cells.

Question 8

Patients with chronic hypoxia (low O₂ levels)due to decreased lung function may adapt by increasing their circulating BPG levels.Predict which of the following will be true for such a patient. A)p₅₀ for O₂ will be decreased. B)p₅₀ for O₂ will be increased. C)The R-state of hemoglobin will be favored. D)O₂ binding to hemoglobin will be hyperbolic. E)None of the above

Accepted Answer

Patients with chronic hypoxia due to decreased lung function may adapt by increasing their circulating BPG levels. BPG binds to hemoglobin and stabilizes the T-state, which promotes the release of oxygen to tissues. Therefore, an increase in BPG levels would lower the affinity of hemoglobin for oxygen, shifting the oxygen dissociation curve to the right. This means that at any given oxygen partial pressure, hemoglobin will release more oxygen to the tissues. As a result, pO2 for O2 saturation will be decreased (choice A is incorrect), pO2 for O2 saturation will be increased (choice B is correct), the R-state of hemoglobin will be disfavored (choice C is incorrect), and the oxygen dissociation curve will be more sigmoidal due to the lower oxygen affinity of hemoglobin (choice D is incorrect).

Question 9

The fundamental cause of sickle-cell disease is a change in the structure of:
A)blood.
B)capillaries.
C)hemoglobin.
D)red cells.
E)the heart.

Accepted Answer

Sickle-cell disease is caused by a genetic mutation that affects the structure of hemoglobin, the protein in red blood cells that carries oxygen. The mutation results in the production of abnormal hemoglobin molecules that cause the normally round and flexible red blood cells to become stiff and take on a crescent or sickle shape. These sickle cells can get stuck in small blood vessels, blocking blood flow and leading to pain and damage to organs and tissues.

Question 10

Which of the following generalizations concerning motor proteins is correct?
A)They convert chemical energy into kinetic energy.
B)They convert chemical energy into potential energy.
C)They convert kinetic energy into chemical energy.
D)They convert kinetic energy into rotational energy.
E)They convert potential energy into chemical energy.

Accepted Answer

Motor proteins, such as myosin and kinesin, use the energy from the breakdown of ATP to generate kinetic energy and perform work, such as muscle contraction and intracellular transport. Therefore, they convert chemical energy into kinetic energy.

Question 11

Neuroglobin is a member of the globin family found in neurons.It is a monomeric protein that helps protect the brain from hypoxia (low O₂).Identify the correct statement(s)about neuroglobin below. a-It binds O₂ with a hyperbolic binding curve. b-It binds O₂ with a sigmoidal binding curve. c-It binds O₂ with higher affinity than hemoglobin. d-It binds O₂ with lower affinity than hemoglobin. A)a and c B)a and d C)b and c D)b and d E)None of the above

Accepted Answer

Neuroglobin, being a monomeric protein, binds O2 with a hyperbolic binding curve similar to myoglobin, and it has a higher affinity for O2 compared to hemoglobin.

Question 12

Which of the following parts of the IgG molecule are not involved in binding to an antigen?
A)Fab
B)Fc
C)Heavy chain
D)Light chain
E)Variable domain

Accepted Answer

The Fc region of the IgG molecule is not involved in binding to an antigen. Instead, it binds to various cell surface receptors and proteins to activate immune responses or to clear immune complexes from circulation.

Question 13

An individual molecular structure within an antigen to which an individual antibody binds is as a(n):
A)antigen.
B)epitope.
C)Fab region.
D)Fc region
E)MHC site.

Accepted Answer

An epitope is a specific part of an antigen that an antibody recognizes and binds to. It is also known as an antigenic determinant. The other answer choices are incorrect: 
A) Antigen refers to a substance that triggers an immune response and can include multiple epitopes. 
C) Fab region is the part of an antibody that recognizes and binds to the epitope on an antigen. 
D) Fc region is the part of an antibody that mediates effector functions and interacts with other immune components. 
E) MHC site refers to the binding site on a major histocompatibility complex molecule that displays a processed antigen to T cells.

Question 14

A monoclonal antibody differs from a polyclonal antibody in that monoclonal antibodies:
A)are labeled with chemicals that can be visualized.
B)are produced by cells from the same organism that produced the antigen.
C)are synthesized by a population of identical,or "cloned," cells.
D)are synthesized only in living organisms.
E)have only a single polypeptide chain that can recognize an antigen.

Accepted Answer

Monoclonal antibodies are synthesized by a population of identical, or "cloned," cells, whereas polyclonal antibodies are produced by multiple different cells in response to an antigen. This allows for monoclonal antibodies to be highly specific for a single epitope on an antigen, while polyclonal antibodies may recognize multiple epitopes. Monoclonal antibodies are also used extensively in research and therapeutics due to their specificity and reproducibility.

Question 15

Which of the following statements about protein-ligand binding is correct? A)The K_a is equal to the concentration of ligand when all of the binding sites are occupied. B)The K_a is independent of such conditions as salt concentration and pH. C)The larger the K_a (association constant),the weaker the affinity. D)The larger the K_a,the faster is the binding. E)The larger the K_a,the smaller the K_d (dissociation constant).

Accepted Answer

The dissociation constant (K_d) is the inverse of the association constant (K_a). Therefore, the larger the association constant, the smaller the dissociation constant. This means that a larger association constant indicates a stronger binding affinity between the protein and ligand.

Question 16

In the binding of oxygen to myoglobin,the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as:
A)hyperbolic.
B)linear with a negative slope.
C)linear with a positive slope.
D)random.
E)sigmoidal.

Accepted Answer

The binding of oxygen to myoglobin follows a hyperbolic curve, indicating a direct and saturable binding relationship as oxygen concentration increases. This is because myoglobin has a single binding site for oxygen, leading to a simple, non-cooperative binding mechanism.

Question 17

The amino acid substitution of Val for Glu in Hemoglobin S results in aggregation of the protein because of ___________ interactions between molecules.
A)covalent
B)disulfide
C)hydrogen bonding
D)hydrophobic
E)ionic

Accepted Answer

The substitution of Val for Glu leads to the exposure of hydrophobic pockets on the surface of hemoglobin, which can then interact with hydrophobic pockets of other hemoglobin molecules, resulting in aggregation.

Question 18

Which of the following is not correct concerning cooperative binding of a ligand to a protein?
A)It is usually a form of allosteric interaction.
B)It is usually associated with proteins with multiple subunits.
C)It rarely occurs in enzymes.
D)It results in a nonlinear Hill Plot.
E)It results in a sigmoidal binding curve.

Accepted Answer

Cooperative binding is often associated with proteins with multiple subunits and is usually a form of allosteric interaction. It results in a nonlinear Hill plot and a sigmoidal binding curve. However, it can occur in enzymes, so statement C is incorrect.

Question 19

Carbon monoxide (CO)is toxic to humans because: A)it binds to myoglobin and causes it to denature. B)it is rapidly converted to toxic CO₂. C)it binds to the globin portion of hemoglobin and prevents the binding of O₂. D)it binds to the Fe in hemoglobin and prevents the binding of O₂. E)it binds to the heme portion of hemoglobin and causes heme to unbind from hemoglobin.

Accepted Answer

Carbon monoxide binds to the iron (Fe) in the heme group of hemoglobin, preventing oxygen (O2) from binding and thus reducing oxygen transport in the blood.

Question 20

Myoglobin and the subunits of hemoglobin have:
A)no obvious structural relationship.
B)very different primary and tertiary structures.
C)very similar primary and tertiary structures.
D)very similar primary structures,but different tertiary structures.
E)very similar tertiary structures,but different primary structures.

Accepted Answer

Myoglobin and the subunits of hemoglobin have very similar tertiary structures, which means their three-dimensional shapes are alike, allowing them to perform similar functions in oxygen binding. However, their primary structures, or the sequence of amino acids, are different.

Quiz 5: Protein Function

A prosthetic group of a protein is a non-protein structure that is:

The predominant structural feature in myosin molecules is:

An allosteric interaction between a ligand and a protein is one in which:

The interactions of ligands with proteins:

When oxygen binds to a heme-containing protein,the two open coordination bonds of Fe²⁺ are occupied by:

In hemoglobin,the transition from T state to R state (low to high affinity) is triggered by:

Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG) ?

Patients with chronic hypoxia (low O₂ levels) due to decreased lung function may adapt by increasing their circulating BPG levels.Predict which of the following will be true for such a patient.

The fundamental cause of sickle-cell disease is a change in the structure of:

Which of the following generalizations concerning motor proteins is correct?

Which of the following parts of the IgG molecule are not involved in binding to an antigen?

An individual molecular structure within an antigen to which an individual antibody binds is as a(n) :

A monoclonal antibody differs from a polyclonal antibody in that monoclonal antibodies:

Which of the following statements about protein-ligand binding is correct?

In the binding of oxygen to myoglobin,the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as:

The amino acid substitution of Val for Glu in Hemoglobin S results in aggregation of the protein because of ___________ interactions between molecules.

Which of the following is not correct concerning cooperative binding of a ligand to a protein?

Carbon monoxide (CO) is toxic to humans because:

Myoglobin and the subunits of hemoglobin have: