Lecture Notes: Amino Acids, Proteins, and DNA

Introduction

• Presented by Chris Harris from Alley Chemistry.
• Focus is on AQA specification for A-Level Chemistry.
• Contains revision videos and whiteboard tutorials, including exam paper walkthroughs.
• Videos are available for free on the Alley Chemistry YouTube channel.

Amino Acids

• Structure: Contains an amino group (NH2) and a carboxyl group (COOH).
  • Basic (NH2) and acidic (COOH) properties.
  • Amino acids are amphoteric (can act as both acids and bases).
  • Contains an organic side chain (R group), except glycine (R = H).
• Chirality: Most amino acids (except glycine) are chiral and can rotate plane polarized light.
• Naming: Amino acids have common and IUPAC names.
  • Example: Glycine vs. 2-amino propanoic acid.
• Zwitterions:
  • Molecules with both positive and negative charges.
  • Exist at the isoelectric point (pH where the charge is zero).
• Reactions:
  • In acidic solutions, carboxyl group becomes COOH.
  • In basic solutions, amino group loses a hydrogen.

Protein Structure

• Polymerization:

  • Proteins are polymers made from amino acid monomers.
  • Formed by condensation polymerization, creating peptide links.
  • Can be broken by hydrolysis under severe conditions.

• Levels of Structure:

  • Primary: Sequence of amino acids.
  • Secondary: Alpha helices and beta-pleated sheets formed by hydrogen bonding.
  • Tertiary: Overall 3D shape held by disulfide and hydrogen bonds.

Enzymes

• Function: Biological catalysts that speed up reactions.
• Structure:
  • Proteins with 3D active sites.
  • Active sites are stereo-specific and may contain chiral centers.
• Inhibition:
  • Enzymes can be inhibited by molecules of similar shape to the substrate.
  • Inhibitors can slow reaction rates.
• Drug Design:
  • Computer modeling used to design drugs as enzyme inhibitors.

DNA

• Structure:
  • Polymer made of nucleotide monomers.
  • Nucleotides consist of a phosphate group, a pentose sugar, and a nitrogenous base.
  • Four bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
• Double Helix:
  • Two strands with a sugar-phosphate backbone and bases that pair (A with T, C with G).
  • Held together by hydrogen bonds.

Anti-Cancer Drugs: Cisplatin

• Structure: Square planar complex with platinum and ligands.
• Function:
  • Binds to DNA in cancer cells, preventing cell replication and causing cell death.
  • Inhibits DNA replication, hindering cancer cell growth.
• Side Effects:
  • Can affect healthy cells, leading to side effects like immune suppression and hair loss.
  • Usage involves balancing benefits against potential side effects.

Conclusion

• Comprehensive coverage of amino acids, proteins, enzymes, and DNA.
• Importance of understanding protein structures and enzyme specificity in biochemical processes.
• Relevance of cisplatin as a treatment for cancer, despite its side effects.