Biochemistry Chapter 1: Amino Acids, Peptides and Proteins Flashcards
What are the 4 groups attached to the alpha-carbon?
R group, carboxylic acid group, amino group & a hydrogen
What is the stereochemistry for all amino acids in eukaryotes?
L
Where are D amino acids found?
They can exist in prokaryotes
Which amino acid does not have an S configuration?
cysteine
All amino acids are chiral except…
glycine (H)
What are the nonpolar, nonaromatic amino acids?
glycine, alanine, valine, leucine, isoleucine, methionine, proline
What are the aromatic amino acids?
tryptophan, phenylalanine, tyrosine
What are the polar amino acids?
serine, threonine, asparagine, glutamine, cysteine
What are the acidic amino acids?
aspartate, glutamate
What are the basic amino acids?
lysine, arginine, histidine
What does amphoteric mean?
They can accept or donate protons
what is the pka?
the pH at which half of the species is deprotonated; (HA) = (A-)
At low pH, the amino acid is…
Fully protonated
At pH near pI, the amino acid is…
a neutral zwitterion
at high pH, the amino acid is…
fully deprotonated
How can the isoelectric point, pI, be calculated?
calculating the average of the two pKa values
How can you tell the pKa from a titration curve? pI?
flat at pka values & nearly vertical at the pI
Amino acids without charged side chains have a pI around…
6
Acidic amino acids have a pI…
Well below 6
Basic amino acids have a pI…
Well above 6
How is a peptide bond formed?
condensation or dehydration; the nucleophilic amino group of one amino acid attacks the electrophilic carbonyl group of another amino acid
Why are amide bonds rigid?
resonance
How do you break a peptide bond?
hydrolysis
What amino acid can interrupt secondary structure of a protein?
Proline because of its rigid cyclic structure
What can lead to protein denaturation?
heat and increasing solute concentration
