M4 peptides and peptide bonds

What reaction forms a peptide bond?

Condensation rxn (eliminates water)

What catalyzes peptide bond formation

Ribosomes, with tRNA delivering amino acids

What is the portion of the amino acid left in a peptide chain called?

An amino acid residue

Which terminal are new amino acids added to during translation?

The C terminal

Why is the peptide C–N bond shorter than a typical amine C–N bond?

Resonance gives it partial double bond character (~40%)

Are peptide bonds planar or flexib

Planar (coplanar due to resonance)

Why is the trans configuration more common than cis?

Trans avoids steric hindrance between side chains

Which amino acid is often found in the cis configuration?

Proline

What are the three main torsion angles of a polypeptide backbone?

Phi (φ)

Psi (ψ)

Omega (ω)

What is the typical value of ω in trans and cis peptide bonds?

Trans = 180°

Cis = 0°

What is the difference between a polypeptide and a protein?

A polypeptide is an amino acid chain

protein is a properly folded, sometimes modified, polypeptide.

What is the average molecular weight of an amino acid residue in a protein?

~110 Da

How do you estimate the number of residues in a protein?

Divide protein molecular weight by 110

What determines the folding and function of a protein?

The sequence of amino acids and their side chain properties.

What stabilizes the final conformation of a protein?

Interactions among side chains (hydrophobic, ionic, hydrogen bonding, disulfide bonds)

Peptide sequence formula

Number of sequence = (number of possible AA’s) (peptide leng

Leucine is the ____ occurring protein

Highest

Tryptophan is the ___ occurring protein

Lowest

In aqueous solution, formation of a peptide bond is ___ favored thermodynamically

Not

For every amino acid made ___ water molecule is removed

1