Hemoglobin, Collagen, and Elastin – Vocabulary Flashcards

A vocabulary-style set covering heme groups and hemeproteins, Hb/Mb structure and function, allosteric regulation and disease, plus collagen and elastin biology and related disorders.

Heme group

The iron-containing prosthetic group of hemeproteins (Fe2+ bound to protoporphyrin IX) that binds O2.

Hemeproteins

Proteins that contain a heme prosthetic group; include hemoglobin and myoglobin; they are metalloproteins due to the central iron.

Metalloproteins

Proteins that require a metal ion (such as iron) for activity; many contain heme groups.

Heme (Fe-Protoporphyrin IX)

The planar tetrapyrrole ring coordinating an Fe2+ ion; central site for O2 binding.

Proximal histidine

Histidine residue that coordinates the heme iron from the globin on the proximal side.

Fe2+ binds O2

Ferrous iron at the center of the heme that binds molecular oxygen.

Hemoglobin (Hb)

Tetrameric protein in red blood cells (two α and two β chains) that binds O2 in the lungs and transports it to tissues.

Myoglobin (Mb)

Monomeric heme protein in muscle that stores and buffers O2; not allosterically regulated like Hb.

Heme color

Heme proteins are strongly colored (reddish-brown) due to the heme moiety.

Heme iron Fe2+

Ferrous iron at the center of heme that binds O2.

Deoxyhemoglobin (T state)

Taut form of Hb without bound O2; stronger inter-dimer interactions; low O2 affinity.

Oxyhemoglobin (R state)

Relaxed form of Hb with bound O2; higher O2 affinity; Fe moves into the plane.

T to R transition

Oxygenation triggers structural changes that transition Hb from T to R state, increasing affinity.

Oxygen dissociation curve

Plot of O2 saturation versus pO2; Hb is sigmoidal (cooperativity); Mb is hyperbolic.

P50

Partial pressure of O2 at 50% saturation; Mb ≈ 1 mmHg; Hb ≈ 26 mmHg.

Cooperativity

Oxygen binding to one Hb subunit increases affinity at the other subunits.

Bohr effect

Lower pH or higher CO2 promotes O2 release from Hb; shifts curve to the right.

Allosteric effectors of Hb

pO2, pH, pCO2, and 2,3-BPG that modulate Hb O2 binding.

2,3-BPG

Anionic glycolytic intermediate in RBCs that binds deoxy Hb in the central cavity, reducing O2 affinity.

HbA1c

Glycated Hb used to monitor long-term glucose control in diabetes; reflects average glucose over ~3 months.

Fetal hemoglobin HbF

Hb with α2γ2 composition; higher O2 affinity and reduced 2,3-BPG binding; gradually replaced by HbA.

HbGower 1

Embryonic Hb in yolk sac: 2 zeta chains and 2 epsilon chains.

HbS (sickle cell Hb)

Glutamate 6 to valine 6 mutation in β-globin; deoxygenated HbS polymerizes, causing RBC sickling.

HbC

Glutamate 6 to lysine 6 mutation in β-globin; HbC disease with mild hemolytic anemia.

Thalassemias

Hereditary disorders with imbalanced synthesis of α- or β-globin chains leading to anemia.

Sickle cell disease (summary)

Glu6Val mutation causes polymerization of deoxygenated Hb and rigid, sickled RBCs.

Scurvy

Vitamin C deficiency that impairs proline/lysine hydroxylation in collagen, destabilizing the triple helix.

Ehlers-Danlos syndrome

Hereditary connective tissue disorders due to defective collagen processing; hyperflexible joints.

Osteogenesis imperfecta

Brittle bone disease from mutations in type I collagen; glycine substitutions disrupt the triple helix.

Dentinogenesis imperfecta

Tooth development disorder associated with OI; discolored, fragile teeth.

Alport syndrome

Inherited type IV collagen mutations causing defective basement membranes in kidney, ear, and eye.

Collagen

Fibrous ECM protein providing structural support; most abundant protein in the body; forms triple helices.

Collagen triple helix

Three α-chains form a right-handed triple helix stabilized by hydroxyproline/hydroxylysine.

Gly-X-Y pattern

Repeating collagen sequence with glycine every third residue (X often Pro, Y often hydroxyproline).

Prolyl hydroxylase

Enzyme that hydroxylates proline residues to hydroxyproline in collagen; requires O2 and Fe2+.

Hydroxyproline/hydroxylysine

Modified amino acids in collagen that promote hydrogen bonding and cross-linking.

Procollagen processing

Secreted procollagen is cleaved to tropocollagen, which assembles into fibrils with cross-links.

Lysyl oxidase

Enzyme that cross-links collagen by converting lysine/hydroxylysine to reactive aldehydes.

Collagen cross-links

Covalent bonds that stabilize mature collagen fibers via lysyl/hydroxylysyl residues.

Collagen synthesis site

Produced by fibroblasts, osteoblasts, and chondrocytes; processed in the ER and Golgi before secretion.

Elastin

Elastic ECM protein that allows tissues to resume shape after stretching; secreted as tropoelastin.

Tropoelastin

Soluble precursor to elastin; secreted into the ECM for assembly into elastic fibers.

Desmosine crosslinks

Cross-links in elastin formed from lysine residues, stabilizing the elastic network.

Marfan syndrome

Genetic disorder of connective tissue due to fibrillin-1 mutations; tall stature, long limbs, aortic risk.

Fibrillin

Glycoprotein scaffold for elastin; forms microfibrils that organize elastic fibers.

Alpha-1 antitrypsin deficiency

Mutations produce misfolded AAT; inadequate inhibition of elastase leading to emphysema; treated with AAT therapy.

Methemoglobinemia

Elevated methemoglobin (Fe3+) in blood reducing O2 delivery; can be acquired or congenital.