Question 1

You are attempting to crystallize the head group of a myosin-like muscle protein from a newly discovered vertebrate organism. Assuming that the protein structure is similar to other vertebrate myosins, which enzymes should you use to remove the myosin-like head group from the rest of the myosin-like protein?

Accepted Answer

Trypsin and papain are both proteolytic enzymes capable of cleaving proteins at specific sites, which can be used to isolate the myosin head group from the rest of the protein. Myosinase is not a commonly used enzyme for this purpose.

Question 2

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

Accepted Answer

The answer of What fraction of ligand binding sites are...

Question 3

Myosin obtains its high tensile strength due to its composition of:

Accepted Answer

Myosin's high tensile strength is due to its composition of F1F1F1S1F1F1F10 helices supercoiled around each other in a left-handed coiled coil.

Question 4

Which protein undergoes a conformational change upon interacting with Ca²⁺, leading to stimulation of muscle contraction?

Accepted Answer

Troponin is the protein that undergoes a conformational change upon interacting with Ca²⁺, leading to stimulation of muscle contraction. This is the mechanism by which skeletal muscle contraction is regulated.

Question 5

You are studying a muscle disorder where an individual's muscles have a higher tendency to be overextended due to a protein mutation. This mutation is likely to be in which protein?

Accepted Answer

The nebulin protein is located in the thin filament of skeletal muscle and helps regulate its length. Mutations in this protein can lead to muscle disorders and an increased tendency for muscles to be overextended.

Question 6

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

Accepted Answer

The answer of Describe the concept of "induced fit" in...

Question 7

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.

Accepted Answer

The answer of Explain why most multicellular organisms use an...

Question 8

Tropomyosin and troponin prevent muscle contractions in the absence of Ca²⁺ because they:

Accepted Answer

Tropomyosin and troponin bind to actin filaments and block the myosin binding sites in the absence of Ca²⁺. This prevents muscle contractions because myosin cannot bind to actin and perform the "power stroke" necessary for muscle contraction.

Question 9

If myosin head groups were unable to hydrolyze ATP due to an alteration in the protein structure but could still bind and release ADP and inorganic phosphate (P_i), which step in the actin-myosin cycle would NOT take place?

Accepted Answer

Repositioning of the myosin head group on the actin filament requires ATP hydrolysis to provide the energy needed for the myosin head to return to its original position after the power stroke.

Question 10

Myosin moves relative to actin filaments by using energy derived from the hydrolysis of which molecule?

Accepted Answer

Myosin uses the energy derived from the hydrolysis of ATP to move relative to actin filaments.

Question 11

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

Accepted Answer

The answer of Explain briefly why the relative affinity of...

Question 12

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.

Accepted Answer

The answer of Explain why the structure of myoglobin makes...

Question 13

Nerve impulses control muscle contractions by releasing which ion?

Accepted Answer

Nerve impulses control muscle contractions by releasing calcium ions, which bind to troponin on the thin filaments in muscle cells, causing a conformational change that allows myosin and actin to interact and initiate muscle contraction.

Question 14

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

Accepted Answer

The answer of Describe how you would determine the K_a...

Question 15

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?

Accepted Answer

The answer of For the binding of a ligand to...

Question 16

During muscle contraction, the _____ of myofibrils contract and the _____ move closer together due to the movement of myosin thick filaments along actin thin filaments.

Accepted Answer

During muscle contraction, the I bands of myofibrils contract and the Z disks move closer together due to the movement of myosin thick filaments along actin thin filaments.

Question 17

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

Accepted Answer

The answer of Why is carbon monoxide (CO) toxic to...

Question 18

Which class of proteins includes the LARGEST polypeptide chains discovered to date in humans?

Accepted Answer

Titins are giant proteins that can span half a micron in length, making them the largest polypeptide chains discovered to date in humans. Myosins, actins, troponins, and globins are all smaller protein classes than titins.

Question 19

Which event triggers a "power stroke" in myosin?

Accepted Answer

The release of inorganic phosphate (P_i) from the myosin head triggers the power stroke, which is the force-generating step in muscle contraction.

Question 20

Individual contractile units in muscle fibers are called:

Accepted Answer

The individual contractile units in muscle fibers are called sarcomeres. This is where the actin and myosin filaments interact to cause muscle contraction. Z disks are the borders of each sarcomere, myofibrils are bundles of sarcomeres, myomeres are segments of skeletal muscles in vertebrates, and porphyrins are organic compounds involved in heme synthesis.

Quiz 5: Protein Function

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

Myosin obtains its high tensile strength due to its composition of:

Which protein undergoes a conformational change upon interacting with Ca²⁺, leading to stimulation of muscle contraction?

You are studying a muscle disorder where an individual's muscles have a higher tendency to be overextended due to a protein mutation. This mutation is likely to be in which protein?

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

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.

Tropomyosin and troponin prevent muscle contractions in the absence of Ca²⁺ because they:

If myosin head groups were unable to hydrolyze ATP due to an alteration in the protein structure but could still bind and release ADP and inorganic phosphate (P_i) , which step in the actin-myosin cycle would NOT take place?

Myosin moves relative to actin filaments by using energy derived from the hydrolysis of which molecule?

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

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.

Nerve impulses control muscle contractions by releasing which ion?

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

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?

During muscle contraction, the _ of myofibrils contract and the _ move closer together due to the movement of myosin thick filaments along actin thin filaments.

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

Which class of proteins includes the LARGEST polypeptide chains discovered to date in humans?

Which event triggers a "power stroke" in myosin?

Individual contractile units in muscle fibers are called:

Quiz 5: Protein Function

What fraction of ligand binding sites are occupied ( θ\thetaθ ) when [ligand] = Kd? Show your work.

Myosin obtains its high tensile strength due to its composition of:

Which protein undergoes a conformational change upon interacting with Ca2+, leading to stimulation of muscle contraction?

You are studying a muscle disorder where an individual's muscles have a higher tendency to be overextended due to a protein mutation. This mutation is likely to be in which protein?

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

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.

Tropomyosin and troponin prevent muscle contractions in the absence of Ca2+ because they:

If myosin head groups were unable to hydrolyze ATP due to an alteration in the protein structure but could still bind and release ADP and inorganic phosphate (Pi) , which step in the actin-myosin cycle would NOT take place?

Myosin moves relative to actin filaments by using energy derived from the hydrolysis of which molecule?

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

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.

Nerve impulses control muscle contractions by releasing which ion?

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

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

During muscle contraction, the _____ of myofibrils contract and the _____ move closer together due to the movement of myosin thick filaments along actin thin filaments.

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

Which class of proteins includes the LARGEST polypeptide chains discovered to date in humans?

Which event triggers a "power stroke" in myosin?

Individual contractile units in muscle fibers are called:

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

Which protein undergoes a conformational change upon interacting with Ca²⁺, leading to stimulation of muscle contraction?

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.

Tropomyosin and troponin prevent muscle contractions in the absence of Ca²⁺ because they:

If myosin head groups were unable to hydrolyze ATP due to an alteration in the protein structure but could still bind and release ADP and inorganic phosphate (P_i) , which step in the actin-myosin cycle would NOT take place?

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

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?

During muscle contraction, the _ of myofibrils contract and the _ move closer together due to the movement of myosin thick filaments along actin thin filaments.