Orgo II Proteins (Ch 24)

Amino acids in a peptide

<50

Amino acids in a protein

>50

How are amino acids joined

peptide bonds

What orientation do most amino acids take?

L, related to L-(-)-glyceraldehyde

Acidicty of amino acids

Less acidic than carboxylic acids, less basic than amines

Acidic amino acids

isoelectric pH ~3, deprotonated (anionic) at neutral pH

Basic amino acid

ioselectric pH ~9, protonated (cationic) @ neutral pH

Neutral amino acids

isoelectric pH ~5/6,

pKb of acidic, deprotonated OH in amino acid

12

pKa of basic, protonated amine in amino acid

10

Alpha-helix

carbonyl O hydrogen bonds with an N-H hydrogen on next coil turn

Pleated Beta-sheet

Carbonyl O hydrogen bonds with an N-H hydrogen on adjacent peptide chain

Tertiary structures

segments of alpha-helix with segments of random coil where helix is folded, imparts function

Quaternary structures

aggregated structures of protein with other proteins

Glycine

Alanine

Valine

Leucine

Isoleucine

phenylalanine

proline

serine

Threonine

Asparagine

Cysteine

Tyrosine

Carbamate

t-BOC

How is t-BOC removed?

TFA acid

TFA acid

cBz

How is cBz removed

mild acid or hydrogenolysis

Hydrogenolysis

H2 / Pd-C

FMOC

How is FMOC removed

Piperidine

Piperidine

Protecting groups

t-BOC, cBz, FMOC

carbodiimide

DCC (dicyclohexylarbodiimide)

urea

isocyanate

DCU

How to cleave polypeptide from solid support

HF