Biochemistry of Complex Proteins: Structure, Properties, and Functions

Comprehensive vocabulary flashcards covering the definitions, structures, and classes of complex proteins, as well as specific functional groups, allosteric regulation, and transport mechanisms.

Complex Protein

A biomolecule, also known as a conjugated protein, composed of an amino acid chain (the protein portion) and a non-protein component known as a prosthetic group.

Apoprotein

The protein portion of a complex protein that is typically inactive on its own and requires a prosthetic group for biological functionality.

Prosthetic Group

A non-protein molecule essential for the biological activity of a complex protein, often directly involved in catalysis or ligand binding.

Holoprotein

The complete, biologically active complex protein formed by the combination of an apoprotein with its prosthetic group.

Quaternary Structure

The structural organization defining the number and order of connection of individual polypeptide chains (protomers) in an oligomeric protein.

Protomer

An individual monomeric polypeptide chain that connects with other chains via non-covalent interactions to form an oligomeric protein.

Glycoproteins

A class of complex proteins whose prosthetic group consists of carbohydrate chains (heterooligosaccharides) covalently attached to the polypeptide backbone.

Lipoproteins

Complex lipid-protein particles consisting of a hydrophobic core of cholesterol esters and triglycerides surrounded by a shell of phospholipids, free cholesterol, and apoproteins used for lipid transport.

Metalloproteins

A class of complex proteins that contain metal ions (such as $\text{Fe}$, $\text{Cu}$, or $\text{Zn}$) as their prosthetic group.

Phosphoproteins

Complex proteins containing phosphoric acid residues attached via ester bonds to the hydroxyl groups of amino acids, predominantly serine and threonine.

Chromoproteins

A class of complex proteins containing colored pigment molecules, such as heme or flavins, as their prosthetic group.

Hemoglobin

A tetrameric chromoprotein composed of four globin subunits (two $\frac{1}{2}$ or $\beta$ chains) and four heme groups responsible for oxygen transport in vertebrate blood.

Heme Group

A prosthetic group consisting of a porphyrin ring system complexed with a single ferrous iron ion ($\text{Fe}^{2+}$) that serves as the reversible binding site for oxygen.

2,3-Bisphosphoglycerate (BPG)

A strongly negatively charged regulatory ligand synthesized in red blood cells that binds to hemoglobin's central allosteric cavity, reducing its affinity for $\text{O}_2$ by 26 times.

Methemoglobin (met-Hb)

A blue-brown form of hemoglobin produced when the central iron ion is oxidized from $\text{Fe}^{2+}$ to $\text{Fe}^{3+}$, rendering it incapable of binding $\text{O}_2$ or $\text{CO}$.

Carboxyhemoglobin (HbCO)

A stable complex formed when carbon monoxide binds to hemoglobin, requiring 200 times lower partial pressure than oxygen and causing death when 70% of hemoglobin is bound.

Carbaminohemoglobin

A compound formed by the reversible binding of carbon dioxide to amino groups on the globin chains of hemoglobin.

Bohr Effect

The physiological mechanism where elevated hydrogen ion concentration (lower pH) and higher temperature in tissues decrease hemoglobin's affinity for oxygen, promoting oxygen release.

Flavoproteins

Enzymes that contain flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN) derived from riboflavin (Vitamin $\text{B}_2$) to catalyze metabolic redox reactions.

Succinate Dehydrogenase

A flavoprotein enzyme that catalyzes the oxidation of succinate to fumarate while reducing FAD to $\text{FADH}_2$.

Nucleoproteins

Complexes composed of nucleic acids bound to proteins, classified as deoxyribonucleoproteins (DNP) or ribonucleoproteins (RNP).

Histones

Positively charged eukaryotic nuclear proteins rich in basic amino acids that interact electrostatically with DNA to pack it into chromosomes.

Chromatin

The substance in eukaryotic cell nuclei composed of nuclear DNA, histones, and non-histone chromosomal proteins that condenses to form chromosomes during cell division.