Hemoglobin Structure and Function

A comprehensive set of vocabulary flashcards covering hemoglobin and myoglobin structure, oxygen transport mechanisms, developmental variants, and related clinical pathologies based on the lecture notes.

Myoglobin

A monomeric protein of red muscle that binds oxygen tightly as a reserve against oxygen deprivation.

Hemoglobin (Hb)

A tetrameric protein that interacts in a cooperative way to offload $O_2$ in peripheral tissues while efficiently binding it in the lungs.

2,3-bisphosphoglycerate (BPG)

A molecule that enhances oxygen delivery by stabilizing the deoxygenated (T-state) of hemoglobin melalui the formation of salt bridges.

Heme

A prosthetic group and member of the porphyrin family consisting of an iron-containing cyclic tetrapyrrole molecule linked by methyne bridges.

HbA

The principal normal adult hemoglobin composed of $\text{α}_2\text{β}_2$ subunits.

HbF

Fetal hemoglobin composed of $\text{α}_2\text{γ}_2$ subunits, characterized by a higher affinity for $O_2$ than adult hemoglobin.

HbS

Sickle cell hemoglobin with the subunit composition $\text{α}_2\text{β}^S_2$, where valine replaces glutamate at position 6 of the $\text{β}$ subunit.

HbA2

A minor adult hemoglobin composed of $\text{α}_2\text{δ}_2$ subunits.

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

The oxidation state of iron residing at the center of the planar tetrapyrrole in active hemoglobin; oxidation to $Fe^{3+}$ destroys biologic activity.

Cooperative binding

A phenomenon where hemoglobin binds an $O_2$ molecule more readily if other $O_2$ molecules are already bound to the tetramer.

$$P_{50}$$

The partial pressure of $O_2$ at which a given hemoglobin reaches half-saturation; for HbA and HbF, these values are $26\text{ mm Hg}$ and $20\text{ mm Hg}$ respectively.

$\text{ξ}_2\text{ε}_2$ tetramer

The initial hemoglobin tetramer synthesized by the human fetus during early development before being replaced by HbF.

T state

The "tense" or deoxygenated conformation of hemoglobin stabilized by salt bridges.

R state

The "relaxed" or oxygenated conformation of hemoglobin triggered by $O_2$ binding, involving the rupture of salt bridges and a $15^\text{o}$ rotation of subunit pairs.

Carbamates

Forms of $CO_2$ (approximately 15% of venous blood $CO_2$) carried by hemoglobin on amino terminals, favoring salt bridge formation.

Bohr effect

The coupling of the interconversion of $CO_2$ and $H_2CO_3$ with the reciprocal binding of protons and $O_2$ by T- and R-state hemoglobin.

Carbonic anhydrase

The enzyme that dehydrates $H_2CO_3$ in the lungs to form $CO_2$ for exhalation.

Hemoglobinopathy

A clinical condition resulting from a mutation in the genes encoding the $\text{α}$ or $\text{β}$ subunits that affects hemoglobin's biologic function.

Methemoglobin

A form of hemoglobin where the heme iron is ferric ($Fe^{3+}$) instead of ferrous ($Fe^{2+}$), rendering it unable to bind or transport $O_2$.

HbM

A hemoglobin variant where histidine F8 is replaced by tyrosine, stabilizing the iron in its $Fe^{3+}$ form.

Polycythemia

An increased concentration of erythrocytes resulting from tissue hypoxia, such as that caused by HbM.

Myoglobinuria

The presence of myoglobin in the urine, typically following massive skeletal muscle injury and subsequent renal damage.

Thalassemias

Genetic defects resulting from the partial or total absence of one or more $\text{α}$ or $\text{β}$ chains of hemoglobin.

Glycation

A non-enzyme-catalyzed process where blood glucose forms a covalent adduct with the $\text{ε}$-amino groups of lysyl residues and N-terminal valines.

HbA1c

Glycated hemoglobin that reflects the mean blood glucose concentration over the preceding 6 to 8 weeks, used in managing diabetes mellitus.