60 Questions
What is the term used to describe the reversible binding of other molecules by proteins?
Protein-ligand interactions
What characteristic of a binding site allows a protein to selectively bind only one or a few types of molecules?
Complementary in size, shape, charge, and hydrophobic or hydrophilic character
What is the term for the molecule bound reversibly by a protein?
Ligand
What allows an organism to respond rapidly and reversibly to changing environmental and metabolic circumstances?
The transient nature of protein-ligand interactions
What does a ligand bind to on a protein?
A binding site
What is the term used to describe a protein's ability to discriminate among the thousands of different molecules in its environment and selectively bind only one or a few types?
Specificity
What is the major class of antibodies?
IgG
Which antibody preparation is produced by many different B lymphocytes responding to one antigen?
Polyclonal antibodies
What is the molecular weight of Myosin?
520,000
Which protein binds to the thin filament and blocks the myosin-binding sites?
Tropomyosin
What causes a conformational change in a troponin-tropomyosin complex and exposes myosin-binding sites?
Binding of Ca2+ to troponin
What is the basis for a variety of important analytical procedures?
Antibody-antigen interaction
Which of the following is true about the Bohr effect?
It describes the effect of pH and [CO2] on the binding and release of O2 by hemoglobin.
What is the function of 2,3-bisphosphoglycerate (BPG) in hemoglobin?
It greatly reduces the affinity of hemoglobin for oxygen.
What is the primary difference between fetal hemoglobin and normal adult hemoglobin?
Fetal hemoglobin has a lower affinity for 2,3-bisphosphoglycerate (BPG).
In the immune system, what is the role of cytotoxic T cells (TC cells)?
Destroying infected host cells, parasites, and foreign tissues.
What is the purpose of a vaccine in the immune system?
To teach the immune system what viral particles look like, stimulating the production of memory cells.
What is an antigen?
A molecule or pathogen capable of eliciting an immune response.
What is the primary reason for myoglobin's distal His enhancing heme's O2 affinity?
Stabilizing the Fe-O2 complex via hydrogen bonding
What prevents CO poisoning from metabolism and industrial sources?
Selective O2 affinity enhancement in globins
What is the primary function of erythrocytes in relation to hemoglobin?
Transporting O2
What stabilizes hemoglobin's quaternary structure?
Strong interactions between unlike subunits
What triggers a conformational change in hemoglobin from T to R state?
O2 binding
What influences the hybrid sigmoid binding curve of hemoglobin?
pO2 levels in lungs and tissues
Which type of protein shows conformational changes in one subunit affecting others?
Hemoglobin
What is the coordination number of iron in heme?
Six
Which type of iron in heme binds O2 reversibly?
Fe2+
What does the dissociation constant (Kd) measure?
Equilibrium constant for release of ligand
Which ligand binds free heme much better than O2?
Carbon monoxide (CO)
What affects the binding geometries of carbon monoxide (CO) and O2 to heme?
Orbital structures
What is the term used to describe the reversible binding of other molecules by proteins?
Ligand
What allows an organism to respond rapidly and reversibly to changing environmental and metabolic circumstances?
Transient nature of protein-ligand interactions
What is the term for the molecule bound reversibly by a protein?
Ligand
What is the primary function of erythrocytes in relation to hemoglobin?
Transporting oxygen to tissues
What is the term used to describe a protein's ability to discriminate among the thousands of different molecules in its environment and selectively bind only one or a few types?
Specificity
What influences the hybrid sigmoid binding curve of hemoglobin?
Cooperative binding of oxygen
What is the coordination number of iron in heme?
6
What is the primary reason for myoglobin's distal His enhancing heme's O2 affinity?
Modulating the binding geometry of oxygen
What does the dissociation constant ($K_d$) measure?
Equilibrium constant for ligand release
What allows an organism to respond rapidly and reversibly to changing environmental and metabolic circumstances?
Reversible protein-ligand binding
What is the term used to describe the reversible binding of other molecules by proteins?
Protein-ligand interaction
What is the basis for a variety of important analytical procedures?
Protein-ligand binding equilibrium
What is the coordination number of iron in heme?
6
What is the primary function of erythrocytes in relation to hemoglobin?
Transporting oxygen to body tissues
What causes a conformational change in a troponin-tropomyosin complex and exposes myosin-binding sites?
Binding of Ca2+ to troponin
What is the major class of antibodies?
IgG
What is the molecular weight of Myosin?
520,000
What is the basis for a variety of important analytical procedures?
Antibody-antigen interaction
What is the primary function of erythrocytes in relation to hemoglobin?
Transporting O2 and carrying high concentrations of hemoglobin
What influences the hybrid sigmoid binding curve of hemoglobin?
pO2 levels in lungs and tissues
What is the primary difference between fetal hemoglobin and normal adult hemoglobin?
Fetal hemoglobin has a higher affinity for O2
What prevents CO poisoning from metabolism and industrial sources?
Selective O2 affinity enhancement in globins
What is the function of 2,3-bisphosphoglycerate (BPG) in hemoglobin?
Regulating O2 binding and release
What stabilizes hemoglobin's quaternary structure?
Strong interactions between unlike subunits
What is the primary function of 2,3-bisphosphoglycerate (BPG) in hemoglobin?
BPG binds to a site distant from O2-binding site and greatly reduces the affinity of hemoglobin for oxygen
What is the primary role of fetal hemoglobin?
Fetal hemoglobin has a higher affinity for oxygen than normal adult hemoglobin
What is the primary function of the humoral immune system?
The humoral immune system is directed at bacterial infections and extracellular viruses
What is the primary role of T lymphocytes in the cellular immune response?
T lymphocytes destroy infected host cells, parasites, and foreign tissues
What is the primary function of a vaccine in the immune system?
A vaccine stimulates the production of memory cells for rapid response to pathogens
What is the primary characteristic of haptens in the context of immune response?
Haptens are small molecules that can elicit an immune response when covalently attached to large proteins
Study Notes
Principles of Protein Function and Reversible Interactions
- Protein-ligand binding involves conformational changes in the protein structure, with induced fit being a specific adaptation.
- Multisubunit proteins show conformational changes in one subunit affecting others, and interactions between ligands and proteins may be regulated.
- Myoglobin and hemoglobin are extensively studied oxygen-binding proteins, crucial for the evolution of oxygen transport in multicellular organisms.
- Heme is a protein-bound prosthetic group consisting of a complex organic ring structure with a bound Fe2+ atom, preventing the formation of reactive oxygen species.
- Iron in heme forms six coordination bonds, with Fe2+ binding O2 reversibly, while Fe3+ does not.
- The globin family of proteins, including myoglobin, hemoglobin, neuroglobin, and cytoglobin, have a highly conserved tertiary structure and different functions in O2 transport or storage.
- Myoglobin has a single binding site for oxygen, with the majority of its amino acid residues found in the eight α helices typical of the globin fold.
- The reversible binding of a protein to a ligand can be quantitatively described using an equilibrium expression and association constant (ka) to measure ligand affinity.
- The dissociation constant (kd) is the equilibrium constant for the release of ligand, with lower Kd indicating higher affinity.
- Protein structure affects how ligands bind, with carbon monoxide (CO) binding free heme much better than O2, but the difference in relative affinity is mediated by the globin structure.
- Oxygen binds to heme with the O2 axis at an angle, readily accommodated by myoglobin, while carbon monoxide binds to free heme with the CO axis perpendicular to the porphyrin ring.
- Differences in the orbital structures of CO and O2 affect their binding geometries, highlighting the importance of protein structure in ligand binding.
Hemoglobin: Structure, Function, and Regulation
- Myoglobin's distal His enhances heme's O2 affinity via hydrogen bonding, stabilizing the Fe-O2 complex 20,000-fold stronger than free heme for CO compared to O2
- This selective O2 affinity enhancement in globins prevents CO poisoning from metabolism and industrial sources
- Hemoglobin is formed from hemocytoblasts, loses organelles in maturation, and survives for about 120 days in humans
- Erythrocytes transport O2, carrying high concentrations of hemoglobin; arterial blood is ~96% saturated with O2, releasing about one-third of oxygen per 100 mL passing through tissue
- Hemoglobin has two globin types (α and β chains), undergoes conformational changes for O2 binding and release
- Strong interactions between unlike subunits, hydrophobic effects, hydrogen bonds, and ion pairs stabilize hemoglobin's quaternary structure
- Hemoglobin has R and T states, with T state stabilized by ion pairs at the α1β2 interface
- O2 binding to hemoglobin triggers a conformational change from T to R state, affecting ion pairs and conformation near heme
- Hemoglobin binds O2 cooperatively, with a hybrid sigmoid binding curve, influenced by pO2 levels in lungs and tissues
- Hemoglobin is an allosteric protein, binding O2 and modulating its conformation
- Hemoglobin transports H+ and CO2, influenced by pH and CO2 concentration, and carries them to the lungs and kidneys for excretion
- Carbonic anhydrase in RBCs catalyzes the hydration of CO2 to bicarbonate, influencing oxygen binding and release in the blood
Test your knowledge of protein function and reversible interactions with this quiz. Explore topics such as protein-ligand binding, myoglobin and hemoglobin, heme structure, ligand affinity, and the influence of protein structure on ligand binding.
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