Globular Proteins and Hemoglobin Practice Flashcards

Comprehensive practice flashcards covering protein classification, hemoglobin/myoglobin structure and function, and clinical conditions related to oxygen transport as discussed in Lecture 6.

Fibrous Proteins

Long, thin protein molecules that lie side by side to form fibers and are insoluble in water.

Globular Proteins

Proteins that fold into a spherical 3-D shape, are soluble in water, and play metabolic roles.

Keratin

A fibrous protein found in hair and fingernails providing structural support.

Collagen

A fibrous protein that provides structural support in skin, bone, and cartilage.

Globin fold

The shared overall folding pattern for globin monomers in myoglobin and hemoglobin.

Myoglobin

A globular protein monomer in muscle tissue mostly composed of \text{\alpha-helix} and devoid of \text{\beta-sheet} , used for oxygen storage.

Hemoglobin A (HbA)

The primary hemoglobin tetramer in adults, consisting of a pair of identical \text{\alpha\beta} dimers ( \text{\alpha_2\beta_2} ).

Ferrous state ($Fe^{2+}$)

The oxidation state of the central iron in the heme group that is capable of reversibly binding oxygen.

Ferric state ($Fe^{3+}$)

The oxidized version of iron found in methemoglobin that is unable to bind oxygen.

Porphyrin ring

The part of the heme group consisting of four nitrogen molecules that bind to a central iron atom.

Proximal F8 Histidine

The specific amino acid residue that binds directly to the central iron ($Fe^{2+}$) in the heme group.

Distal E7 Histidine

The amino acid residue that stabilizes the iron atom once oxygen has bound.

Methemoglobin

A hemoglobin derivative containing iron in the ferric state ($Fe^{3+}$), often resulting from the release of superoxide ($O_2^{-1}$).

T-state (Tense state)

The deoxyhemoglobin conformation characterized by a lower affinity for oxygen.

R-state (Relaxed state)

The oxyhemoglobin conformation characterized by a higher affinity for oxygen.

0.4 Å

The distance the ferrous iron moves into the plane of the heme ring when it becomes oxygenated.

Bicarbonate ($HCO_3^-$)

The primary form (70%) in which CO2 is transported from tissues to the lungs.

Carbaminohemoglobin ($\text{HbCO}_2$)

The form of CO2 transport (21–25%) where carbon dioxide binds to the amino terminal ends of hemoglobin.

Haldane effect

The phenomenon where oxygenation of Hb in the lungs promotes the dissociation of H+ and facilitates the release of CO2.

Bohr effect

The decrease in hemoglobin's oxygen affinity caused by binding protons ($H^+$) and CO2 at the tissue level, facilitating O2 release.

Oxygen Dissociation Curve

A graphical representation of the relationship between the partial pressure of oxygen and the oxygen saturation of Hb.

Sigmoidal curve

The shape of the hemoglobin oxygen dissociation curve due to cooperative ligand binding.

Hyperbolic curve

The shape of the myoglobin oxygen dissociation curve, reflecting lack of cooperativity.

Cooperative ligand binding

A mechanism where the binding of one O2 molecule increases the affinity of the remaining subunits for oxygen.

2,3-DPG (2,3-BPG)

A glycolytic intermediate in RBCs that acts as a negative allosteric effector to decrease Hb's affinity for oxygen.

Hexokinase deficiency

A glycolytic defect leading to reduced 2,3-BPG levels, an increased O2 affinity, and a left shift on the dissociation curve.

Pyruvate kinase deficiency

A glycolytic defect leading to elevated 2,3-BPG levels, a decreased O2 affinity, and a right shift on the dissociation curve.

High altitude adaptation

A condition that increases 2,3-BPG synthesis, causing a right shift of the oxygen dissociation curve to aid O2 unloading.

Methemoglobinemia

A blood disorder characterized by high methemoglobin levels, resulting in tissue hypoxia and chocolate-colored blood.

NADH methemoglobin reductase

The enzyme whose deficiency leads to congenital methemoglobinemia.

Methylene blue

An intravenous treatment used for methemoglobinemia to help reduce ferric iron back to ferrous iron.

Carbon monoxide (CO)

A colorless, odorless gas that binds to Hb with 220 times more affinity than oxygen.

CarboxyHb

The compound formed when carbon monoxide binds to the iron in heme proteins.

Hyperbaric oxygen

The treatment for CO poisoning involving 100% oxygen delivered under elevated pressure.

Cyanide (CN)

A toxin that binds to the central $Fe^{3+}$ in methemoglobin and other iron-containing proteins.

Sodium thiosulfate

An antidote for cyanide poisoning that converts cyanide to thiocyanide, which is excreted in urine.

Fetal Hemoglobin (HbF)

The main hemoglobin in the fetus ( \text{\alpha_2\gamma_2} ) with a higher affinity for O2 than adult HbA.

Gamma subunit

The polypeptide chain in HbF that contains serine residues instead of histidine, preventing it from binding 2,3-BPG.

HbA1c

A glycated form of hemoglobin used to monitor long-term blood glucose levels (previous three months).

Glycation

A non-enzymatic, spontaneous reaction where glucose binds to hemoglobin, such as at the N-terminal valine.

Almond breath

A characteristic clinical symptom associated with cyanide poisoning.

Chocolate-colored blood

The classic physical presentation of the blood in patients with methemoglobinemia.

Cherry red skin

A physical sign associated specifically with carbon monoxide poisoning.

p50

The partial pressure of oxygen at which a globin protein is 50% saturated with oxygen.

Anemia (chronic blood loss)

A condition resulting in decreased Hb concentration and O2 content, but normal O2 saturation and normal partial pressure.

Polycythemia

A condition characterized by an increase in both hemoglobin concentration and oxygen content in the blood.

Salt bridges

Ionic interactions facilitated by protonated histidine side chains (like His146) that stabilize the deoxy form of Hb.

Valine

The specific N-terminal amino acid that is usually glycated in the formation of HbA1c.

Serine residues

The residues in the HbF gamma chain that replace the charged histidines found in the adult beta chain.

Coordination bonds

The six bonds formed by $Fe^{2+}$: four to porphyrin nitrogens, one to globin, and one to oxygen.

Relaxed form

The high-affinity conformation of hemoglobin induced by carbon monoxide binding that prevents O2 release in tissues.

Negative allosteric effector

A substance like 2,3-BPG that binds to a site other than the active site and decreases the protein's affinity for its ligand.

Thiocyanide

The less toxic compound formed when sodium thiosulfate combines with cyanide, which is then excreted.

Hydroxyurea

A medication noted in the context of synthesis and replacement of fetal hemoglobin.

Nitrites

Oxidizers used in cyanide poisoning to induce MetHb formation, which sequesters cyanide from mitochondria.

Alveolus

The site in the lungs where gas exchange occurs and where partial pressure of O2 is high.

Quaternary structure

The organization of multiple polypeptide subunits, present in hemoglobin (tetramer) but absent in myoglobin (monomer).

Strenuous exercise

An activity that increases tissue CO2 and decreases pH, causing a right shift in the oxygen dissociation curve.

Benzocaine

One of the common substances known to cause acquired methemoglobinemia.

Left-shift

A movement of the oxygen dissociation curve indicating increased affinity for O2, caused by decreased temp, pCO2, or [H+].