Deck 5: Protein Function

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.

Answer 1

permanently associated with the protein.

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.

Answer 2

an $\alpha$ helix.

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.

Answer 3

binding of a molecule to a binding site affects binding properties of another site on the protein.

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.

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.

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.

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.

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

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.

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.

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

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

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.

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.

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).

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.

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

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.

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.

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.

Question 21

Describe how you would determine the K_a (association constant)for a ligand and a protein.

Question 22

(a)What is the effect of pH on the binding of oxygen to hemoglobin (the Bohr Effect)?
(b)Briefly describe the mechanism of this effect.

Question 23

Describe how immunoaffinity chromatography is performed.

Question 24

What fraction of ligand binding sites are occupied ( $\theta$ )when [ligand] = K_d? Show your work.

Question 25

During muscle contraction,hydrolysis of ATP results in a change in the:

A)conformation of actin.
B)conformation of myosin.
C)structure of the myofibrils.
D)structure of the sarcoplasmic reticulum.
E)structure of the Z disk.

Question 26

Explain why most multicellular organisms use an iron-containing protein for oxygen binding rather than free Fe²⁺.Your answer should include an explanation of (a)the role of heme and (b)the role of the protein itself.

Question 27

Describe briefly the basic structure of an IgG protein molecule.

Question 28

Describe briefly the two principal models for the cooperative binding of ligands to proteins with multiple binding sites.

Question 29

Fetal hemoglobin binds BPG with lower affinity than adult hemoglobin.How does this property facilitate tranfers of O₂ from mother to fetus?

Question 30

Describe the concept of "induced fit" in ligand-protein binding.

Question 31

Explain why the structure of myoglobin makes it function well as an oxygen-storage protein,whereas the structure of hemoglobin makes it function well as an oxygen-transport protein.

Question 32

Why is carbon monoxide (CO)toxic to aerobic organisms?

Question 33

The energy that is released by the hydrolysis of ATP by actin is used for:

A)actin filament assembly.
B)actin filament disassembly.
C)actin-myosin assembly.
D)actin-myosin disassembly.
E)muscle contraction.

Question 34

What is the concept of "induced fit" as it applies to antigen-antibody binding?

Question 35

Why is it likely that the immune system can produce a specific antibody that can recognize and bind to any specific chemical structure?

Question 36

What is the chemical basis for the specificity of binding of an immunoglobin antibody to a particular antigen?

Question 37

Explain briefly why the relative affinity of heme for oxygen and carbon monoxide is changed by the presence of the myoglobin protein.

Question 38

How does BPG binding to hemoglobin decrease its affinity for oxygen?

Question 39

For the binding of a ligand to a protein,what is the relationship between the K_a (association constant),the K_d (dissociation constant),and the affinity of the protein for the ligand?

Question 40

What properties of antibodies make them useful biochemical reagents? Describe one biochemical application of antibodies (with more than just the name of the technique).

Question 41

What is the relationship between G-actin and F-actin?

Question 42

What is the role of ATP and ATP hydrolysis in the cycle of actin-myosin association and disassociation that leads to muscle contraction?

Question 43

Describe the cycle of actin-myosin association and disassociation that leads to muscle contraction.

Question 44

Although the myosin molecule "walks" along actin in discrete steps,you are able to make smooth motions using your muscles.Explain how this is possible.

Question 45

Describe briefly the structure of myosin.