Heme and Hemoglobin

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What is the primary role of the coordinated nitrogen atoms in the porphyrin ring system of heme?

Promoting the release of oxygen from Fe^2+.
Facilitating the conversion of Fe^2+ to Fe^3+.
Enhancing the binding of oxygen to Fe^3+.
Preventing the conversion of Fe^2+ to Fe^3+. (correct)

Iron in the Fe^3+ state can reversibly bind oxygen.

False (B)

What structural feature of heme-containing proteins prevents the irreversible oxidation of Fe^2+ to Fe^3+ by oxygen?

Sequestering of the heme deep within the protein structure.

In heme-containing proteins, one of the coordination bonds of iron is occupied by a side-chain nitrogen of a _______ residue.

His Signup and view all the answers

Match the following characteristics with either Fe^2+ or Fe^3+.

Binds oxygen reversibly = Fe^2+ Does not bind oxygen = Fe^3+ Signup and view all the answers

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

It binds to heme iron with greater affinity than oxygen, excluding O<del>2</del>. (C) Signup and view all the answers

What change causes the color difference between oxygen-depleted venous blood and oxygen-rich arterial blood when oxygen binds to heme iron?

The electronic properties of heme iron change. Signup and view all the answers

What type of organic ring structure is bound to an iron atom in heme?

Protoporphyrin IX (C) Signup and view all the answers

Which of the following statements accurately describes the T state of hemoglobin?

His HC3 residues are involved in ion pairs. (A) Signup and view all the answers

The transition from the T state to the R state in hemoglobin widens the pocket between subunits.

False (B) Signup and view all the answers

What term describes a protein in which the binding of a ligand to one site affects the binding properties of another site on the same protein?

allosteric protein Signup and view all the answers

In the R state of hemoglobin, the His HC3 residues rotate toward the ______ of the molecule.

center Signup and view all the answers

What structural change facilitates oxygen binding in myoglobin?

Rotation of the side chain of the distal Histidine (His E7). (A) Signup and view all the answers

Match the hemoglobin state with its oxygen affinity.

T state = Low oxygen affinity R state = High oxygen affinity Signup and view all the answers

Why is a transition from a low-affinity state (T state) to a high-affinity state (R state) necessary for hemoglobin function?

To bind oxygen efficiently in the lungs and release it effectively in the tissues. (C) Signup and view all the answers

Erythrocytes are fully functional cells capable of reproduction due to the presence of a nucleus and other organelles.

False (B) Signup and view all the answers

Which factor primarily induces conformational changes in allosteric proteins?

Binding of modulators (C) Signup and view all the answers

What is the approximate percentage of oxygen saturation in arterial blood as it leaves the lungs?

96% Signup and view all the answers

A single-subunit protein with one ligand-binding site can produce a sigmoid binding curve.

False (B) Signup and view all the answers

Normal human erythrocytes are shaped like __________ disks.

biconcave Signup and view all the answers

Match the following proteins with their primary function in oxygen transport or storage:

Hemoglobin = Oxygen transport in blood Myoglobin = Oxygen storage in muscle tissue Signup and view all the answers

Why is carbon monoxide (CO) binding to hemoglobin weaker than its binding to free heme?

The distal histidine (His E7) sterically hinders the preferred perpendicular binding of CO. (D) Signup and view all the answers

What volume of O2 gas is released by each 100 mL of blood passing through tissue?

6.5 mL (C) Signup and view all the answers

What precursor stem cells are erythrocytes formed from?

Hemocytoblasts (A) Signup and view all the answers

How does 2,3-bisphosphoglycerate (BPG) affect the affinity of hemoglobin for oxygen?

BPG greatly reduces the affinity of hemoglobin for oxygen. (B) Signup and view all the answers

The pKa of a certain residue in hemoglobin remains constant in both the R and T states.

False (B) Signup and view all the answers

What is the effect of increasing H+ concentration on oxygen release from hemoglobin?

Increasing H+ concentration promotes the release of oxygen. Signup and view all the answers

Carbon dioxide binds to the α-amino group at the amino-terminal end of each globin chain, forming ________.

carbaminohemoglobin Signup and view all the answers

Which of the following best describes the allosteric modulation by BPG on hemoglobin?

Heterotropic inhibition (D) Signup and view all the answers

BPG binds to hemoglobin at the same site as oxygen.

False (B) Signup and view all the answers

What role does BPG play in adapting to lower pO2 levels at high altitudes?

BPG increases in concentration, promoting oxygen release to tissues. Signup and view all the answers

At pH 7.6, which state is favored by hemoglobin?

R state (B) Signup and view all the answers

What is the primary function of class I MHC proteins?

To bind and display peptides derived from intracellular protein degradation. (C) Signup and view all the answers

All individuals have the same set of class I MHC protein variants.

False (B) Signup and view all the answers

Which cells of the immune system recognize the complexes of peptides and class I MHC proteins?

T cells Signup and view all the answers

The maturation of TC cells in the ______ includes a stringent selection process.

thymus Signup and view all the answers

Match the following descriptions to the correct MHC protein class:

Class I MHC Protein = Displays peptides from intracellular proteins Class II MHC Protein = Regions of high variability near the amino-terminal ends of both alpha and beta chains. Signup and view all the answers

What is the purpose of the stringent selection process in the thymus during TC cell maturation?

To eliminate T<del>C</del> cells that might attack normal cells of the body. (C) Signup and view all the answers

Which of the following is a characteristic of class I MHC proteins?

The small chain is invariant while the large chain exhibits high variability. (D) Signup and view all the answers

Class II MHC proteins present peptides derived exclusively from intracellular proteins.

False (B) Signup and view all the answers

What is the primary function of helper T cells (TH cells) within the immune system?

To produce soluble signaling proteins called cytokines, including interleukins. (C) Signup and view all the answers

The humoral immune system targets intracellular viruses and fungal infections within the body's cells.

False (B) Signup and view all the answers

What type of protein interaction is typically involved in protein-ligand binding, especially when a prosthetic group is not involved?

Reversible binding Signup and view all the answers

The immune response is facilitated by various types of __________ (white blood cells), which include macrophages and lymphocytes.

leukocytes Signup and view all the answers

Match the component of the immune system with its respective function.

Humoral Immune System = Targets bacterial infections and extracellular viruses. Cellular Immune System = Destroys infected host cells. Helper T Cells = Produce cytokines to signal other immune cells. Macrophages = Patrol tissues and recognize molecules that signal infection. Signup and view all the answers

Which of the following best describes how the immune system distinguishes between 'self' and 'nonself'?

By recognizing and binding to specific chemical structures on pathogens and foreign molecules. (D) Signup and view all the answers

How do most protein-ligand interactions achieve high specificity?

Via a binding site that is a cleft lined with amino acid residues arranged to render the binding interaction highly specific. (A) Signup and view all the answers

Humans are capable of producing fewer than 100 different antibodies with distinct binding specificities.

False (B) Signup and view all the answers

Porphyrin Ring

A flat ring system with an iron atom at its center, crucial for oxygen binding in proteins.

Iron Coordination Bonds

Iron's ability to form six bonds, four to nitrogen in the porphyrin ring, and two perpendicular to it.

Electron-Donating Nitrogen Atoms

Nitrogen atoms in the porphyrin ring that donate electrons, helping to keep iron in the Fe^2+ state.