Proteins are linear chains built from amino acid monomers.
Types of Amino Acids
There are 20 different base amino acids used in protein synthesis.
Some amino acids can be modified (e.g., proline to hydroxyproline), resulting in more than 20 variations.
Amino Acid Structure
Amino acids have an asymmetric carbon atom.
Asymmetric carbon: bonded to four different groups.
Bonds:
Amine group ()$-NH_2)
Carboxyl group ()$-COOH)
Hydrogen ()$-H$$)
R group
The R group is what varies between different amino acids and gives each its unique characteristics.
R Groups
R groups determine the characteristics of each amino acid.
L and D Forms (Enantiomers)
Amino acids can exist in two forms: L and D, which are mirror reflections (enantiomers) of each other.
L form is used to build proteins.
D form is found in nature but not used for protein synthesis; it gets destroyed in cells.
Characteristics of Amino Acids Based on R Groups
The elements in the R group dictate the characteristics of the amino acid.
Fewer oxygen or nitrogen atoms: More hydrophobic (water-repelling).
More oxygen or nitrogen atoms: More hydrophilic (water-attracting).
Protein Folding and Amino Acid Location
Hydrophobic amino acids tend to be located in the center of a protein, away from water.
Hydrophilic amino acids tend to be located on the outside of a protein, in contact with water.
Proteins with long stretches of hydrophobic amino acids can be embedded in membranes, with the hydrophobic regions interacting with the lipids in the membrane.
Condensation Reaction
(This is the last topic mentioned, setting up the next discussion point.)