MCAT Content / Amino Acids / Reactions

Reactions

Topic: Amino Acids

There are a few ways for peptides to react and be modified.

Amino acids are the building blocks for the proteins responsible for the biological functions within our body. Amino acids are chemical compounds consisting of a carbon atom bonded to an amine group, a hydrogen atom, a carboxylic group, and a varying side-chain (R group); it is this side chain that distinguishes each amino acid from another. Higher-ordered structures such as peptide chains and proteins are formed when amino acids bond to each other.

 

Sulfur linkage for cysteine
A covalent disulfide bond (sulfur linkage) can form between the sulfur-containing R groups in two cysteine molecules and produce cystine. Disulfide bonds between cysteine residues can affect protein folding and stability.

 

Peptide Linkage: Polypeptides and Proteins
A peptide is a molecule composed of two or more amino acids. The bond that holds together the two amino acids is a peptide bond, or a covalent chemical bond between two compounds (in this case, two amino acids). This can also be referred to as peptide linkage. It occurs when the carboxylic group of one molecule reacts with the amino group of the other molecule, linking the two molecules and releasing a water molecule.

 

Hydrolysis
Long chain polypeptides can be formed by linking many amino acids to each other via peptide bonds. The amide bond can only be broken by amide hydrolysis, where the bonds are cleaved with the addition of a water molecule. The peptide bonds of proteins are metastable and will break spontaneously in a slow process. Living organisms have enzymes that are capable of both forming and breaking peptide bonds.


Practice Questions


Khan Academy

 

MCAT Official Prep (AAMC)

Chemistry Online Flashcards Question 24

 


Key Points

  • Amino acids are the basic building block of proteins; they are composed of a carbon atom attached to a hydrogen, a carbonyl group, an amine group, and an R group.
  • Cysteines can interact with each other to form a disulfide bond known as a cystine.
  • Large proteins are formed by linking amino acids with peptide bonds. This occurs when the carboxylic group of one molecule reacts with the amino group of the other molecule, linking the two molecules and releasing a water molecule.
  • Hydrolysis (the addition of a water molecule) can break a peptide bond.


Key Terms

  • Cysteine: a non-essential sulfur-containing amino acid
  • Cystine: a sulfur-containing amino acid obtained by the oxidation of two cysteine molecules which are then linked via a disulfide bond
  • Disulfide bond (also called an S-S bond, disulfide bridge, or sulfur linkage): a covalent bond derived from two thiol groups
  • Peptide bond (also called peptide linkage): a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water
  • Hydrolysis: the chemical breakdown of a compound due to reaction with water


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