Biochemistry Study Notes: Proteins
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Questions and Answers

What is the difference between fibrous proteins and globular proteins in terms of their secondary structure?

Fibrous proteins have repeated identical secondary structures, while globular proteins have different structures inside.

What is the primary type of secondary structure found in myoglobin and hemoglobin?

  • Alpha helix (correct)
  • Random coil
  • Triple helix
  • Beta sheet

    • What is the driving force behind the formation of globular proteins?

    Hydrophobic interactions between non-polar amino acids inside the protein and polar amino acids on the outside.

    What is the function of myoglobin in the body?

    <p>Storage of oxygen in muscles and other tissues.</p> Signup and view all the answers

    Myoglobin has a higher affinity for oxygen than hemoglobin.

    <p>True</p> Signup and view all the answers

    What is the primary reason we breathe oxygen?

    <p>To provide oxygen for the electron transport chain in cellular respiration.</p> Signup and view all the answers

    What type of protein is myoglobin, and where is it primarily found?

    <p>Myoglobin is a monomeric protein primarily found in muscle tissue.</p> Signup and view all the answers

    What prosthetic group is found in myoglobin?

    <p>Heme group</p> Signup and view all the answers

    Describe the tertiary structure of myoglobin.

    <p>Myoglobin's tertiary structure consists of 8 alpha-helices connected by short non-helical regions, sequenced from A to H.</p> Signup and view all the answers

    What is the general rule for amino acid side chains in globular proteins?

    <p>Hydrophilic side chains are generally exposed on the surface of the molecule, while hydrophobic side chains are located in the interior.</p> Signup and view all the answers

    Which two histidine residues in myoglobin play a crucial role in oxygen binding?

    <p>E7 and F8</p> Signup and view all the answers

    Explain the two forms in which myoglobin can exist in terms of oxygen binding.

    <p>Myoglobin can exist as oxymyoglobin, when it is bound to oxygen, or deoxymyoglobin, when it is oxygen-free.</p> Signup and view all the answers

    Myoglobin and hemoglobin both have the same tertiary structure.

    <p>False</p> Signup and view all the answers

    What is the structure of the heme group, and what is its function in proteins?

    <p>The heme group is a large macrocyclic ring consisting of four pyrrole rings and a central iron atom. It functions as a prosthetic group, binding oxygen and other molecules.</p> Signup and view all the answers

    How many bonds can iron in the ferrous state form?

    <p>Iron in the ferrous state (Fe+2) can form up to 6 bonds.</p> Signup and view all the answers

    Explain the 4th, 5th, and 6th coordinate heme classification.

    <p>The classification refers to the number of bonds that iron in the heme group forms. A 4th coordinate heme is free, outside of a protein, while a 5th coordinate heme is bound to a protein, and a 6th coordinate heme is bound to both a protein and a ligand, such as oxygen.</p> Signup and view all the answers

    What happens to a heme molecule when iron is oxidized to the ferric state?

    <p>Oxidation of iron to Fe3+ renders the molecule incapable of normal oxygen binding.</p> Signup and view all the answers

    How does the heme group fit into the structure of myoglobin and hemoglobin?

    <p>The planar heme group fits into a hydrophobic pocket within the protein.</p> Signup and view all the answers

    The heme group is an amino acid.

    <p>False</p> Signup and view all the answers

    Explain how the hydrophobic pocket in myoglobin contributes to the stability of the heme group.

    <p>The hydrophobic pocket stabilizes the heme group by preventing its oxidation, ensuring the iron remains in the ferrous state and can bind oxygen.</p> Signup and view all the answers

    What is the role of the proximal histidine (F8) in myoglobin?

    <p>The proximal histidine (F8) binds to the iron in the heme group.</p> Signup and view all the answers

    What is the role of the distal histidine (E7) in myoglobin?

    <p>The distal histidine (E7) acts as a gate that opens and closes as oxygen enters the hydrophobic pocket to bind to the heme.</p> Signup and view all the answers

    The hydrophobic interior of myoglobin prevents the oxidation of iron.

    <p>True</p> Signup and view all the answers

    How does the hydrophobic interior of myoglobin or hemoglobin affect the affinity of oxygen binding?

    <p>It helps maintain a higher affinity for oxygen by preventing the oxidation of iron and ensuring it remains in the ferrous state, capable of binding oxygen.</p> Signup and view all the answers

    Explain the concept of P50 in relation to oxygen binding.

    <p>P50 refers to the partial pressure of oxygen required to saturate 50% of the myoglobin molecules.</p> Signup and view all the answers

    What is the typical value of P50 for myoglobin, and what does it tell us about its affinity for oxygen?

    <p>The typical P50 for myoglobin is around 2.8 torr. This indicates that myoglobin has a very high affinity for oxygen.</p> Signup and view all the answers

    Myoglobin is almost fully saturated with oxygen under normal tissue conditions.

    <p>True</p> Signup and view all the answers

    What is the shape of the oxygen binding curve for myoglobin, and why?

    <p>The oxygen binding curve for myoglobin is hyperbolic. This is because myoglobin has a high affinity for oxygen and readily binds it, even at low oxygen partial pressures.</p> Signup and view all the answers

    What is the significance of the steep slope of the oxygen binding curve for myoglobin?

    <p>The steep slope indicates that a small change in oxygen partial pressure results in a significant change in myoglobin's oxygen saturation level. This high affinity ensures that myoglobin can efficiently bind and store oxygen even in low oxygen environments.</p> Signup and view all the answers

    What is the role of the heme group in stabilizing the tertiary structure of myoglobin?

    <p>The heme group stabilizes the tertiary structure of myoglobin by binding the proximal histidine (F8) and creating a hydrophobic pocket that prevents oxidation of iron.</p> Signup and view all the answers

    The distal histidine (E7) acts as a gate for oxygen by directly binding to the iron in the heme.

    <p>False</p> Signup and view all the answers

    Explain the difference in oxygen binding affinity between the most stable and the less stable positions of oxygen in relation to the heme group.

    <p>The most stable position of oxygen binding is perpendicular to the heme group (90 degrees), resulting in the highest affinity. The less stable position is angled (around 120 degrees), leading to a lower affinity. This difference is due to the influence of the distal histidine (E7).</p> Signup and view all the answers

    How does myoglobin's high affinity for oxygen relate to its function in muscle tissue?

    <p>Myoglobin's high affinity for oxygen allows it to bind and store oxygen, providing a readily available oxygen reservoir for muscle cells during periods of intense activity or oxygen deprivation.</p> Signup and view all the answers

    Carbon dioxide binds to the same site on myoglobin as oxygen.

    <p>False</p> Signup and view all the answers

    Why is carbon monoxide a dangerous gas, and how does its binding to myoglobin affect oxygen transport?

    <p>Carbon monoxide is dangerous because it binds to the heme group with a much higher affinity than oxygen, effectively displacing oxygen and preventing its transport to tissues.</p> Signup and view all the answers

    What are the potential implications of carbon monoxide binding to myoglobin for oxygen transport?

    <p>Carbon monoxide's high affinity for myoglobin displaces oxygen, leading to a reduction in oxygen delivery to tissues and potential hypoxia or even death.</p> Signup and view all the answers

    Hemoglobin also has a heme group, like myoglobin, but it can carry four molecules of oxygen.

    <p>True</p> Signup and view all the answers

    What are the main differences between myoglobin and hemoglobin?

    <p>While both have heme groups and bind oxygen, myoglobin is primarily a storage protein with high oxygen affinity, while hemoglobin is a transport protein with a cooperative binding mechanism allowing it to bind four oxygen molecules.</p> Signup and view all the answers

    The oxygen binding curve for hemoglobin is hyperbolic.

    <p>False</p> Signup and view all the answers

    What is the significance of the sigmoidal shape of the oxygen binding curve for hemoglobin?

    <p>The sigmoidal shape reflects hemoglobin's cooperative binding behavior, where the binding of one oxygen molecule increases the affinity for the following oxygen molecules, leading to more efficient oxygen transport.</p> Signup and view all the answers

    Study Notes

    Biochemistry Study Notes

    • Globular Proteins: Myoglobin and hemoglobin are globular proteins, unlike fibrous proteins. They are an exception, containing only one type of secondary structure (alpha helix). The driving force for their globular structure is hydrophobic interactions.

    • Myoglobin Function: Myoglobin stores oxygen in muscles and other tissues. It releases oxygen during oxygen deprivation.

    • Hemoglobin Function: Hemoglobin transports oxygen and carbon dioxide, and helps buffer blood. The difference between myoglobin and hemoglobin is their affinity for oxygen, myoglobin has a higher affinity, due to its oxygen storage function, allowing it to hold oxygen longer.

    • Myoglobin Structure: Myoglobin is a monomeric protein primarily located in muscle tissue. It contains a heme group, a prosthetic group covalently bonded. Its tertiary structure is comprised of 8 alpha-helices connected by short non-helical regions.

    • Heme Group Structure: Large macrocyclic ring with iron in the middle. It consists of 4 pyrrole rings. Heme is a prosthetic group (non-protein) that's strongly attached to the protein. Heme gives hemoglobin and myoglobin a deep red color when light is absorbed.

    • Iron in Heme: Iron in the ferrous state (Fe+2) can form 6 bonds (maximum). Iron in heme forms four bonds with the nitrogen in the center of the rings, one with a nitrogen of a Histidine imidazole, and a sixth with oxygen. Oxidation of iron to the ferric state (Fe+3) makes the molecule incapable of normal oxygen binding.

    • Heme Classification: Heme is classified according to the number of bonds iron forms. Heme outside a protein has 4 coordinate bond. Heme inside a protein is 5 coordinate, and when in proteins like myoglobin/hemoglobin a 6th coordinate bond is possible.

    • Structure-Function Relationship: Heme fits into a hydrophobic pocket of myoglobin and hemoglobin; the interaction is stabilized by hydrophobic attractions. This pocket stabilizes the heme. The structure of the protein folds to accommodate the heme which is not an amino acid.

    • Oxygen Binding to Myoglobin: Myoglobin binds oxygen with high affinity. The P50 (partial pressure of oxygen where 50% of myoglobin is saturated) for myoglobin is approximately 2.8 torr or mm Hg. This high affinity means myoglobin is almost fully saturated at normal tissue oxygen levels.

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    Description

    Explore the essential functions and structures of globular proteins, specifically myoglobin and hemoglobin. This quiz focuses on their roles in oxygen transport and storage, as well as their distinct affinities for oxygen. Gain a deeper understanding of the biochemical principles that underpin these vital proteins.

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