Proteins

Dipeptide = when 2 amino acids join together
Polypeptide = when more than 2 amino acids join together

Amino acids = same general structure
Carboxyl group (COOH) and amino group (-NH2)
attached to carbon atom
Difference = R group

Proteins have Carbon, Oxygen, Hydrogen, Nitrogen,
(some have Sulfur)


Amino acids joined by peptide bonds
Water molecule released during reaction (condensation reaction)
Water molecule added during reaction to break bond (hydrolysis)

Peptide bond = C - N




Levels of protein structure:

Primary - sequence of amino acids in polypeptide chain

Secondary - Polypeptide chain doesn’t remain flat + straight. Hydrogen bonds form
between nearby amino acids in the chain - makes it coil into an alpha helix or fold into a
beta pleated sheet

Tertiary - coiled/folded chain is often coiled/folded further. More bonds form = Forms
3D structure

Quaternary - Some proteins are made of several different polypeptide chains held
together by bonds. Quaternary structure is the way these polypeptide chains are assembled
together. For proteins with more than 1 polypeptide chain, the quaternary structure =
final 3D structure


Bonds in each level:

Primary = peptide bonds between amino acids

Secondary = hydrogen bonds

Tertiary:
1. Ionic bonds - attractions between negatively-charged R and positively-charged
R groups
2. Disulfide = 2 molecules of cysteine come close together. Sulfur atom in 1 cysteine
bonds to another sulfur-contained cysteine