Proteins

There are 20 different amino acids with 11 being made in the body (non-essential) and 9 having to be eaten (essential). 

 

The structure of an amino acid is the central carbon with an amino group (NH2), a carboxyl group (COOH), a hydrogen, and a side chain determining the 20 different amino acids. 

 

Nonpolar: glycine, alanine, proline, valine, leucine, isoleucine, methionine

 

Polar (uncharged): serine, threonine, cysteine, aspargine, glutamine

 

Positively charged: lysine, arginine, histidine

 

Negatively charged: aspartate, glutamate

 

Aromatic: phenylalanine, tyrosine, tryptophan

 

The essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. 

 

Protein Structure: 

 

Primary: linear sequence of amino acids

 

Secondary: 

• Alpha-helix: H bonds every 4 amino acids and a right handed helix

• Beta-sheets: Parallel or antiparallel strands connected by H bonds

• Beta-turns: Tight loops with glycine or proline
   

Tertiary: Full 3D shape consisting of secondary structures with H bonds, ionic bonds, hydrophobic, and disulfide bonds. 

 

Quaternary: Multiple tertiary complexes 

 

Protein digestion and amino acids metabolism: 

 

Beginning in the stomach pepsin will break proteins into small peptides. The small intestine utilizes trypsin to further break it down into amino acids. This then results in three fates: 

 

• Protein synthesis: building tissues or enzymes

• Conversion to energy: Deamination removes the amino group which becomes urea and is excreted while the carbon skeleton is converted into energy. 

• Other molecules: neurotransmitters or hormones for example

 

Muscle is primarily made of actin and myosin which are common proteins. Starting with catabolism muscle is broken down and torn into microtears. Then with anabolism protein synthesizes new muscle tissue and hypertrophy (addition of new proteins to existing fibers) results in the muscle growing. Insulin promotes amino acid uptake and leucine is one of the most important amino acids for muscle growth.