AQA A-Level› Organic Chemistry› 3.3.13 Amino Acids, Proteins & DNA› Flashcards
3.3.13

Flashcards

Interactive study deck for amino acids, proteins, DNA structure, and cisplatin.

Amino Acids, Proteins & DNA: read all 18 questions and answers
  1. Draw the general structure of a zwitterion of an α-amino acid.
    H₃N⁺-CHR-COO⁻ (having a protonated amino group and a deprotonated carboxyl group).
  2. What is the isoelectric point of an amino acid?
    The specific pH at which the amino acid exists predominantly as a zwitterion, with no net electrical charge.
  3. Show the structure of alanine (R = −CH₃) in strongly acidic solution (pH 1).
    H₃N⁺-CH(CH₃)-COOH (the carboxylate group accepts a proton, forming a net positively charged cation).
  4. Show the structure of alanine (R = −CH₃) in strongly alkaline solution (pH 14).
    H₂N-CH(CH₃)-COO⁻ (the ammonium group loses a proton, forming a net negatively charged anion).
  5. What type of bond holds together the primary structure of a protein?
    Strong covalent peptide bonds (−CONH−), formed by condensation polymerisation.
  6. Describe the bonding that stabilizes the secondary structure of a protein.
    Hydrogen bonds between the N-H of one peptide linkage and the C=O of another, forming an α-helix or β-pleated sheet.
  7. List four types of interactions that stabilize the tertiary structure of a protein.
    Hydrogen bonds, ionic bonds (between oppositely charged R groups), disulfide bridges (covalent S-S bonds between cysteine residues), and Van der Waals forces.
  8. Under what conditions can a protein be completely hydrolysed to its constituent amino acids?
    Heating under reflux with 6 mol dm⁻³ hydrochloric acid (HCl).
  9. How are amino acids made visible on a thin-layer chromatography (TLC) plate?
    By spraying the plate with ninhydrin (which turns purple upon reacting with amino acids) or by viewing the plate under ultraviolet (UV) light.
  10. State the formula for calculating \(R_f\) value in chromatography.
    \(R_f = \frac{\text{distance moved by amino acid spot}}{\text{distance moved by solvent front}}\)
  11. What are the three components of a DNA nucleotide?
    A phosphate group, a 2-deoxyribose sugar, and a nitrogenous base (A, T, C, or G).
  12. How is the sugar-phosphate backbone of a DNA strand formed?
    By condensation reactions between the phosphate group of one nucleotide and the deoxyribose sugar of another, forming covalent phosphodiester bonds.
  13. Which bases are complementary in DNA, and how many hydrogen bonds form between them?
    Adenine pairs with Thymine (2 hydrogen bonds); Cytosine pairs with Guanine (3 hydrogen bonds).
  14. What is the chemical name and molecular formula of cisplatin?
    cis-diamminedichloroplatinum(II), [Pt(NH₃)₂Cl₂].
  15. What is the geometry and bond angle around the platinum atom in cisplatin?
    Square planar geometry, with 90° bond angles.
  16. Describe the mechanism by which cisplatin acts as an anticancer drug.
    Cisplatin undergoes a ligand substitution reaction replacing its chloride ions with water. The platinum then binds to nitrogen atoms on two adjacent guanine bases in DNA, distorting the double helix and preventing replication.
  17. Why does cisplatin have side effects like hair loss?
    It also binds to the DNA of healthy cells that divide rapidly (such as hair follicle cells), stopping their replication and division.
  18. How are the side effects of cisplatin minimised in clinical treatment?
    By administering the drug in small doses, and targeting it directly at the tumor site when possible.
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