MCAT Content / Amino Acids Peptides Proteins / Peptides And Proteins Reactions

Peptides and proteins: reactions

Topic: Amino Acids Peptides Proteins

Several ways that peptides within proteins can react and be modified include the formation of covalent disulfide bonds and other weaker interactions between the R groups of amino acids in the peptide backbone.

Each amino acid is attached to its neighboring amino acid by a covalent bond, known as a peptide bond. During the formation of this peptide bond, the carboxyl (-COOH) group of one amino acid and the amino (-NH2) group of the other amino acid combine and release a molecule of water. Therefore, to break a peptide bond, it must be cleaved with the addition of a water, in a process called hydrolysis.

A disulfide bond between two cysteine amino acids (with thiol groups) can be formed in the presence of oyxgen. This oxidized, covalent, disulfide bond is known as a cystine.

Other interactions between the R groups of amino acids in a protein structure include ionic bonds, hydrogen bonds, and hydrophobic interactions. A section of folded protein showing several interactions which can occur within a protein, such as a disulfide bond, is shown here:


Practice Questions


MCAT Official Prep (AAMC)

Section Bank C/P Section Passage 1 Question 6

Section Bank C/P Section Question 97

Practice Exam 3 C/P Section Question 27

Online Flashcards Chemistry Question 24

Online Flashcards Biochemistry Question 24

Online Flashcards Biochemistry Question 25

Practice Exam 2 B/B Section Passage 4 Question 18

Practice Exam 3 B/B Section Passage 2 Question 9


Key Points

• Amino acids are covalently bound by a peptide bond – carboxyl group of one to amino group of the other – which will release water.

• Hydrolysis (addition of water) can break a peptide bond.

• Two cysteines in a polypeptide can interact with each other to form a disulfide bond, known as a cystine.

Key Terms

Cysteine: amino acid with a thiol group (-SH)

Cystine: disulfide bond between two cysteine amino acids

Peptide bond: bond between two amino acids (-COOH group of one to -NH2 group of the other)

Hydrolysis: addition of water (for peptides, will break peptide bond)

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