Untitled Quiz

Study Notes

The essential covalent structural feature of proteins is the peptide bond linking amino acids.
Natural proteins typically consist of 100-1000 amino acid residues, but can have fewer or more.
Proteins are mainly built from 18 common protein L-amino acids.
Proline is an L-imino acid, and glycine is also incorporated into proteins.
Rare exceptions include L-selenocysteine.
D-amino acids aren't typically incorporated biosynthetically.
Nonnatural amino acids can be incorporated into proteins chemically.
Protein amino acid structure follows IUPAC-IUB conventions.

Proteins are linear chains of L-amino acids connected by peptide bonds.
L-amino acids have unique features contributing to protein structure and function.
Many post-translational modifications of amino acids occur during synthesis and degradation.

Each residue is listed with three- and one-letter codes along with their respective structures.

Protein chemical methods are essential for confirming protein structure and post-translational modifications.
Mass spectrometric methods are increasingly crucial.

The initial step of protein biosynthesis in bacteria involves the formation of a peptide bond between N-formyl-L-methionyl-tRNA and the second aminoacyl tRNA.
N-terminal methionyl residues are often removed rapidly, and their removal is influenced by the identity of the adjacent residues.
Proteins are further modified by acetylation or alkylation of the amino-terminal residue.

The N-acetyl group is a common constituent of proteins.
N-acetylation is a cotranslational event (occurring when the nascent peptide chain is about 40 residues long).
Some mature proteins are acetylated post-translationally.

Amino-terminal glycine residues on many proteins are often fatty acylated (most commonly myristoyl).
This modification influences protein-membrane association and protein-protein interactions.
Other variants of fatty acylation involving C14:1, C14:2, and C12:0 are also common.

Pyroglutamyl is formed by cyclization of N-terminal glutamine residues, potentially with or without enzymatic catalysis.

Other acyl modifications like N-formyl glycine are found, though less frequently, in proteins, primarily in prokaryotic systems and are frequently associated with specific metabolic enzymes.

Glycosylation, the addition of carbohydrate chains to proteins, is common in extracellular proteins, particularly membrane-bound and secreted proteins.
It's a crucial post-translational modification, often involving a branching glycan moiety, involving multiple steps leading to complex modifications.

Methylation of amino acid residues, particularly arginine, histidine, and lysine, is a post-translational modification observed in diverse proteins. Methylation modification affects protein structure and function in important ways.

Hydroxylation: A modification of specific amino acids like proline (in collagen) that affects protein structure and function, particularly in extracellular matrix proteins. Specific sequences and types of hydroxylation are also significant.
Cross-linking of amino acid residues to form stable bonds affects protein stability, interactions, and overall structure, important in structural proteins.
Oxidation: The formation of disulfide bonds affects protein structure by linking cysteine residues, crucial for the stability and function of proteins, especially extracellular ones.
Hydrolysis and Isomerization: Proteins are subject to hydrolysis, affecting certain amino acid residues like asparagine by deamidation or isomerization.
Oligoglutamylation: A modification of glutamic acid residues where multiples, often varying in length or structure, are present.