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AQA A Level Chemistry

3.3.13
Amino Acids,
Proteins and DNA

Section 3.3.13 covers amino acids (3.3.13.1): their acidic and basic properties, zwitterions and the ions formed in acid and alkali; proteins and enzymes (3.3.13.2-3.3.13.3): the peptide link, drawing peptides and the amino acids they hydrolyse to, separation by thin-layer chromatography with ninhydrin and Rf values, primary, secondary and tertiary structure held by hydrogen bonds and sulfur–sulfur bonds, and enzymes with stereospecific active sites and inhibitor drugs. DNA and cisplatin (3.3.13.4-3.3.13.5) cover nucleotides, the double helix, complementary base pairs and how cisplatin prevents DNA replication.

Exam Paper
Paper 2
7405/2 (and Paper 3)
Specification Points
3.3.13
5 sub-sections
Sub-topics
3 lessons
Revision notes available
Exam Board
AQA
7405 (2015 onwards)

Revision Notes

3 revision notes, in the order the specification teaches them.

An amino acid with charged groups at each end
1

Amino Acids and Zwitterions

Amino acids: zwitterions, acid and base behaviour, the isoelectric point and chirality.

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A protein chain folding into a helix
2

Peptides and Proteins

Peptides and proteins: the peptide link, dipeptides and tripeptides, hydrolysis, protein structure and enzymes.

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Two arrangements of a square planar complex
3

DNA and Cisplatin

DNA and cisplatin: nucleotides, the sugar-phosphate backbone, complementary base pairs and how cisplatin stops DNA replication.

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Summary Map

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Amino Acids Map

AQA A Level Chemistry · 3.3.13 Amino acids, proteins and DNA

Every reaction on one A4 page: reagents, conditions and reaction type for each arrow, colour coded, with the key tests.

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Illustration of a summary map: compounds joined by reaction arrows
Summary map · PDF

Amino Acids, Proteins and DNA Map

AQA A-level Chemistry · 3.3.13 Amino acids, proteins and DNA

All of 3.3.13 on one A4 page: amino acids, peptides, protein structure, chromatography, enzymes, DNA and cisplatin.

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3.3.13.1

  1. i a

    know that amino acids have acidic properties

    Revise
  2. i b

    know that amino acids have basic properties

    Revise
  3. i c

    know that amino acids form zwitterions

    Revise
  4. ii a

    draw the structures of amino acids as zwitterions

    Revise
  5. ii b

    draw the ions formed by amino acids in acid solution

    Revise
  6. ii c

    draw the ions formed by amino acids in alkaline solution

    Revise

3.3.13.2

  1. i

    know that proteins are sequences of amino acids joined by peptide links

    Revise
  2. ii

    know the importance of hydrogen bonding and sulfur-sulfur bonds in proteins

    Revise
  3. iii a

    know the primary structure of proteins

    Revise
  4. iii b

    know the secondary structure of proteins, including alpha-helix

    Revise
  5. iii c

    know the secondary structure of proteins, including beta-pleated sheets

    Revise
  6. iii d

    know the tertiary structure of proteins

    Revise
  7. iv

    know that hydrolysis of the peptide link produces the constituent amino acids

    Revise
  8. ix

    calculate Rf values from a chromatogram

    Revise
  9. v a

    know that amino acids can be separated and identified by thin-layer chromatography using ninhydrin

    Revise
  10. v b

    know that amino acids can be separated and identified by thin-layer chromatography using ultraviolet light

    Revise
  11. v c

    know that amino acids can be identified by their Rf values

    Revise
  12. vi

    draw the structure of a peptide formed from up to three amino acids

    Revise
  13. vii

    draw the structure of the amino acids formed by hydrolysis of a peptide

    Revise
  14. viii a

    identify primary structures in diagrams

    Revise
  15. viii b

    identify secondary structures in diagrams

    Revise
  16. viii c

    identify tertiary structures in diagrams

    Revise
  17. viii d

    explain how protein structures are maintained by hydrogen bonding

    Revise
  18. viii e

    explain how protein structures are maintained by S-S bonds

    Revise

3.3.13.3

  1. i

    know that enzymes are proteins acting as catalysts with a stereospecific active site that binds to a substrate molecule

    Revise
  2. ii

    know the principle of a drug acting as an enzyme inhibitor by blocking the active site

    Revise
  3. iii

    know that computers can be used to help design enzyme inhibitor drugs

    Revise
  4. iv

    explain why a stereospecific active site can only bond to one enantiomeric form of a substrate or drug

    Revise

3.3.13.4

  1. i a

    know the structure of the phosphate ion

    Revise
  2. i b

    know the structure of 2-deoxyribose

    Revise
  3. i c

    know the structure of adenine

    Revise
  4. i d

    know the structure of cytosine

    Revise
  5. i e

    know the structure of guanine

    Revise
  6. i f

    know the structure of thymine

    Revise
  7. ii

    know that a nucleotide is made up from a phosphate ion bonded to 2-deoxyribose which is in turn bonded to one of the four bases

    Revise
  8. iii a

    know that a single strand of DNA is a polymer of nucleotides

    Revise
  9. iii b

    know that DNA nucleotides are linked by covalent bonds between the phosphate group of one nucleotide and the 2-deoxyribose of another

    Revise
  10. iii c

    know that linked DNA nucleotides form a sugar-phosphate backbone

    Revise
  11. iii d

    know that bases are attached to the sugar-phosphate backbone

    Revise
  12. iv

    know that DNA exists as two complementary strands in the form of a double helix

    Revise
  13. v

    explain how hydrogen bonding between base pairs leads to the two complementary strands of DNA

    Revise

3.3.13.5

  1. i

    know that the Pt(II) complex cisplatin is used as an anticancer drug

    Revise
  2. ii a

    know that cisplatin prevents DNA replication in cancer cells by ligand replacement

    Revise
  3. ii b

    know that cisplatin forms a bond between platinum and a nitrogen atom on guanine

    Revise
  4. iii

    explain why cisplatin prevents DNA replication

    Revise
  5. iv

    explain why anticancer drugs such as cisplatin can have adverse effects

    Revise
  6. v

    appreciate that society needs to assess the balance between the benefits and adverse effects of drugs such as cisplatin

    Revise