Amino acids, proteins and DNA (A-level only) Revision Notes

Revision Note: Amino Acids, Proteins, and DNA

Amino Acids

• Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid contains both an amine group (-NH2) and a carboxylic acid group (-COOH).
• In solution, amino acids can exist as zwitterions, where the amine group is protonated and the carboxylic acid group is deprotonated, resulting in a molecule that has both a positive and a negative charge.

Peptide Bonds

• Peptide bonds are formed through a condensation reaction between the carboxyl group of one amino acid and the amine group of another, releasing a molecule of water.
• This bond links amino acids together to form polypeptides and proteins.

Hydrolysis of Proteins

• Proteins can be broken down into their constituent amino acids through hydrolysis, a reaction that involves the addition of water to break peptide bonds.

DNA Structure

• DNA nucleotides consist of three components: a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, or guanine).
• The sugar-phosphate backbone of DNA is formed through condensation reactions between the phosphate group of one nucleotide and the sugar of another.

Base Pairing

• Complementary base pairing occurs between adenine and thymine (A-T) and between cytosine and guanine (C-G), stabilized by hydrogen bonds.
• This pairing is crucial for the double helix structure of DNA and for accurate replication and information storage.