AQA A Level Chemistry

Topic Questions

7.7 Amino acids, Proteins & DNA (A Level only)

11 mark

Which of the following is not true about amino acids?

  • They act as buffers

  • They exist as zwitterions in solution

  • They are crystalline solids

  • At high pH the -NH3+ group is formed

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21 mark

Proteins are made of chains of amino acids. One arrangement of proteins is in the shape of a helix.

Which interaction is responsible for holding the protein chain in the shape of a helix?

  • Covalent bonds

  • Ionic bonds

  • Hydrogen bonds

  • Sulfur-sulfur bridges

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31 mark

What two bases pair up together when two separate strands of DNA form a double helix?

  • Cytosine and guanine

  • Cytosine and adenine

  • Guanine and adenine

  • Thymine and guanine

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41 mark

Which of the following is true about enzymes?

  • Enzymes work on a variety of biological molecules

  • Enzymes are globular proteins

  • Enzymes can work on enantiomer substrate pairs

  • Enzymes work best at low pH

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51 mark

Which of these statements is true about the anti-cancer drug cisplatin, Pt(NH3)2Cl2?

  • Cisplatin has a tetrahedral shape

  • Cisplatin prevents DNA replicating

  • Cisplatin destroys cancer cells

  • The platinum in cisplatin is in oxidation state +4

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11 mark

The structures of four ∝-amino acids are shown below. Due to different R-groups, ∝-amino acids can be acidic, basic or neutral.

 7-7-h--q1-aqa-al-chemistry

Which is the correct set of descriptions for these ∝-amino acids?

 

 

Tyr

Asp

Lys

Asn

A

Acidic

Neutral

Neutral

Neutral

B

Neutral

Acidic

Basic

Neutral

C

Neutral

Acidic

Basic

Basic

D

Acidic

Neutral

Neutral

Basic

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21 mark

The structure of the amino acid cysteine is shown below:

7-7-h--q2-aqa-al-chemistry

Cysteines are important ∝-amino acids present in the formation of insulin from two protein chains, containing ‘R’ side groups that can interact with each other.

 

If these interactions do not occur correctly, which of the following will not be affected?

  • The number of ∝-helices that can be formed

  • The way that the insulin hormone forms bonds within the receptor site

  • The way the ∝-helices and ?-pleated sheets are arranged in the protein

  • The number of unfolded sections of the protein chains

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31 mark

A tripeptide was hydrolysed and analysed using thin-layer chromatography. A diagram of the TLC plate is shown below:7-7-h--q3-aqa-al-chemistry

 

Amino acid

Glycine

Threonine

Leucine

Aspartic acid

Alanine

Tryptophan

Rf value

0.26

0.34

0.73

0.24

0.38

0.65

 

Using this information, which of the following amino acids were present in the tripeptide?

  • Glycine, threonine and leucine 

  • Aspartic acid, alanine and tryptophan

  • Aspartic acid, threonine and tryptophan

  • Glycine, alanine and leucine 

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41 mark

Drugs are developed from existing drugs to improve action or reduce side effects. Three anti-inflammatory drugs that act as COX-1 and COX-2 inhibitors are shown below:

7-7-h--q4-aqa-al-chemistry

Which of the following statements is not correct?

  • All of these drugs have an enantiomer that must be absent from the final product

  • Ionic bonds formed within the receptor site are likely to be essential to the drug action

  • A large planar section of the drug molecules is likely to be necessary

  • Forming hydrogen bonds to a hydroxyl group within the receptor site is likely to occur

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51 mark

Adenine and thymine are two of the base pairs involved in the formation of DNA. The structures of these bases are shown on your data sheet.

 

Which statement is not correct about the hydrogen bonding between adenine and thymine?

  • Hydrogen bonds form between the two N-H groups of the two bases

  • Only one of the carbonyl (C=O) groups in thymine forms hydrogen bonds

  • The hydrogen bonds formed are on the inside of the DNA double helix

  • Two hydrogen bonds form between the bases

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11 mark

The structure of the amino acid lysine is shown below:

7-7-m--q1-aqa-al-chemistry

The species present in a solution at low pH would be:

7-7e-q1a-aqa-al-chemistry

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21 mark

A dipeptide molecule is shown below:

7-7-m--q2-aqa-al-chemistry

When the dipeptide is hydrolysed the two molecules formed are

  • H2NCH2CONH2 and H2NCH(CH3)COOH

  • H2NCH2COOH  and H2NCH(CH3)COOH 

  • H2NCH2COOH  and H2NCOCH2COOH

  • H2NCOOH  and H2NCH(CH3)CONH2

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31 mark

Which ways can amino acids in a protein chain bond together?

 

Hydrogen bonding

Ionic attractions

Sulfur-sulfur bonds

A

B

C

D

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41 mark

Which statement is not true about amino acids and DNA?

  • Hydrogen bonding holds together the double helix in DNA

  • Nucleotides are the monomers which make up DNA

  • DNA is made from twenty naturally occurring amino acids

  • Condensation polymerisation occurs when DNA monomers come together

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51 mark

Which statement correctly describes the action of the anti-cancer drug cis-platin?

  • It breaks the hydrogen bonds between sections of DNA

  • It bonds to DNA preventing replication of cells

  • It bonds only to DNA in cancer cells and prevents them growing

  • It breaks the covalent bonds in the DNA chain of cancer cells

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