1 - STRUCTURE OF AMINO ACIDS AND PROTEINS 2025

Most abundant organic molecule in the HUMAN BODY

Proteins

Enantiomer of amino acids seen in the human body

L-isomer

An imino acid

Proline

AA with the smallest side chain, only achiral amino acid among the 20 AAs

Used in the first step of heme synthesis

Glycine

Accumulated AAs in maple syrup urine disease (MSUD);Valine

Leucine

Isoleucine

AA with the largest side chain

Tryptophan

Known as the 21st AA

Selenocysteine

Known as the 22nd AA, restricted only in some methanogenic archaea and bacteria

Pyrrolysine

Only semi-essential AA

Arginine

Sulfur-containing amino acids

Cysteine

Methionine

AAs with aromatic structures (benzene rings)

Phenylalanine

Tyrosine

Tryptophan

Histidine

Most basic AA

Arginine

Most acidic AA

Aspartic acid

First ever sequenced protein

Insulin

First discovered hormone

Secretin

Most common secondary structure

Alpha-helix

Secondary structure seen in abnormal prion protein (PrP Sc) and Alzheimer disease histopathology

Beta-sheets

AAs that can disrupt the alpha-helix structure

Proline

Glycine

The only structure of proteins not affected by denaturation

Primary structure

Reading of amino acid sequences

Order of amino acid sequence synthesis

From N-terminus (NH3 end) to C-terminus (COOH end)

Amino acid terminus containing targeting signals

N-terminus

Amino acid terminus containing retention signals

C-terminus

Amino acid terminus allowing protein to be inserted into a membrane without having a transmembrane domain

C-terminus

Number of pyrrole rings in a porphyrin

Four

Structure of pyrrole rings

Aromatic structure

Bridge formed between pyrrole rings in a porphyrin

Methenyl or methyne bridges

Maximum absorption spectrum of porphyrins

400 nm (known as the Soret peak)

Heme is a metalloporphyrin containing this metal

Iron

Amino acid serving as the biosynthetic precursor to porphyrins

Glycine

Most common form of hemoglobin after birth

Hemoglobin A1

Location of alpha-globin genes

Chromosome 16; Location of beta-globin genes; Chromosome 11

Defect in sickle cell disease

Glutamate → Valine at the 6th position of the beta-globin

Defect in hemoglobin C disease

Glutamate → Lysine at the 6th position of the β-globin

Hemoglobin Bart composition

4 gamma-globin

Hemoglobin H composition

4 beta-globin

Oxygen dissociation curve of myoglobin

Hyperbolic

Oxygen dissociation curve of hemoglobin

Sigmoidal

Most abundant protein in the body

Collagen

Most common form of collagen in the body

Type I collagen

Type of collagen present in early wound repair

Type III collagen

Type of collagen in late wound repair

Type I collagen

Defective step of collagen synthesis encountered in scurvy

Hydroxylation step

Defective step of collagen synthesis encountered in osteogenesis imperfect

Formation of triple helix

Defective step of collagen synthesis encountered in Menkes disease

Cross-linking step (dysfunction in copper-requiring lysyl oxidase)

Most common form of Ehlers-Danlos syndrome (EDS)

Hypermobility EDS

Most serious form of EDS

Vascular EDS

Most common type of collagen affected in EDS

Type III collagen

Defective type of collagen in dystrophic epidermolysis bullosa (DEB)

Type VII collagen

Defective structure in Marfan syndrome

Fibrillin

Triad of Marfan syndrome

Skeletal changes

Aortic dilatation

Upward and outward dislocation of the lens

(vs downward and inward dislocation of the lens in homocystinuria)

Main cell that synthesizes antibodies or Igs

Plasma cells (derived from B cells)

Fragment of Ig containing the antigen-binding site

Fab

Fragment of Ig containing the complement-binding site and macrophage-binding site

Fc

Responsible for determining the isotype of class of Ig

Heavy chains

Most abundant light chain in humans

Kappa chain

Proteins containing light chains and can be found in the urine of patients with multiple myeloma

Bence-Jones protein

Most abundant Ig in the BODY (which includes mucous membranes)

IgA

Most abundant Ig in SERUM

IgG > IgA > IgM > IgD > IgE

Cleaves Ig into 3 parts

Papain

Cleaves Ig into 2 parts

Pepsin

Refers to the part of the ANTIGEN to which an antibody binds

Epitope

Refers to the part of the ANTIBODY that binds to the epitope of the antigen

Paratope