Amino Acids, Peptides, and Proteins

What are amino acids?

Amino acids are the “building blocks” of proteins. Generally, only the L-form is used to make proteins

What is the structure of amino acids?

Amino acids consist of a tetrahedral carbon. This carbon is connected to an amino group, the characteristic side chain, and a carboxylic group.

Which amino acids have hydrophobic side chains?

Glycine, alanine, valine, leucine, isoleucine, methionine, and proline

Which amino acids contain aromatic side chains?

Tryptophan, tyrosine, and phenylalanine

Which amino acids contain polar, uncharged side chains?

Serine, threonine, cysteine, asparagine, and glutamine

Which amino acids contain positively charged side chains?

Lysine, arginine, and histidine

Which amino acids contain negatively charged side chains?

Aspartate and glutamate

Which amino acids commonly undergo phosphorylation?

Serine, threonine, tyrosine

How is cystine formed?

Cystine is formed when disulfide bonds between cysteine form

At what wavelength do proteins absorb?

Around 280 nm

What are zwitterions?

Molecules that contain both a positive and a negative region

What is an amino acid’s isoelectric point?

The isoelectric point is where the net charge of an amino acid is zero. The isoelectric point can be found halfway between the pKa where the charge is -1 and the pKa where the charge is +1.

What are peptide bonds?

Peptide bonds are planar bonds that link the carboxyl group of one amino acid to the amino group of another

What is the primary structure of a protein?

Primary structures are linear chains of amino acids linked together with peptide bonds

What is the secondary structure of a protein?

Secondary structure is the local spatial arrangement of the backbone.

What are the characteristics of an alpha helix?

Alpha helices are mostly right-handed. They are repeating groups of 3.6 amino acids stabilized by hydrogen bonds.

What are the characteristics of beta sheets?

Beta sheets are extended zig-zag sheets that can either be parallel or anti-parallel with one another. They are stabilized by hydrogen bonds between adjacent peptides within sheets.

What are the characteristics of a beta turn?

Beta turns consist of 4 amino acids, often with glycine and proline present.

What is the tertiary structure of a protein?

The tertiary structure is a folded polypeptide chain. By this point, the protein is fully functional. The protein folding determines its function.

What is the quaternary structure of a protein?

The quaternary structure is multiple tertiary structures coming together.

What are the two types of quaternary structure?

Fibrous proteins and globular proteins

What are the characteristics of fibrous proteins?

Fibrous proteins provide strength and/or flexibility and are insoluble in water.

What are the characteristics of globular proteins?

Globular proteins have a more compact shape than fibrous proteins and have a wide variety of biological functions.

How does a vitamin C deficiency lead to scurvy?

Vitamin C maintains the levels of Fe2+ needed for the enzyme propyl 4-hydroxylase to convert proline to 4-hydroxyproline. 4-hydroxyproline is an important component of collagen. A lack of collagen causes scurvy.