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A Level Biology: Nucleic acids and protein synthesis MCQs — Biology

23 multiple-choice questions on A Level Biology: Nucleic acids and protein synthesis from Biology, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. Which codon starts translation?

  1. UAA
  2. AUG
  3. UGA
  4. GGG

Answer: B) AUG

Explanation: AUG codes for methionine and is the start codon. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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2. Which bases are purines?

  1. Thymine and uracil
  2. Cytosine and thymine
  3. Uracil and cytosine
  4. Adenine and guanine

Answer: D) Adenine and guanine

Explanation: Purines have a double ring. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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3. A deletion of one base usually has a greater effect than a substitution because

  1. it causes a frameshift changing all following codons
  2. it adds a stop codon at the start
  3. it never changes the protein
  4. it changes only one amino acid

Answer: A) it causes a frameshift changing all following codons

Explanation: All codons after it are altered. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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4. A substitution mutation may have no effect on the protein because

  1. the code is overlapping
  2. tRNA ignores it
  3. mRNA is not translated
  4. the genetic code is degenerate

Answer: D) the genetic code is degenerate

Explanation: The new codon may code for the same amino acid. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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5. In sickle cell anaemia, a substitution changes

  1. all the amino acids in haemoglobin
  2. the haem group
  3. the number of chromosomes
  4. glutamic acid to valine in the β-globin chain

Answer: D) glutamic acid to valine in the β-globin chain

Explanation: One codon change in HBB. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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6. DNA replication is semi-conservative because

  1. each new molecule has one old strand and one new strand
  2. only half the DNA is copied
  3. both strands are new
  4. the original molecule is conserved intact

Answer: A) each new molecule has one old strand and one new strand

Explanation: Definition of semi-conservative. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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7. Translation takes place at

  1. ribosomes
  2. the nucleolus
  3. the Golgi body
  4. the nucleus

Answer: A) ribosomes

Explanation: Ribosomes translate mRNA. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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8. Nucleotides in a strand are joined by

  1. peptide bonds
  2. phosphodiester bonds
  3. hydrogen bonds
  4. glycosidic bonds

Answer: B) phosphodiester bonds

Explanation: Sugar–phosphate backbone. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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9. In which phase of the cell cycle does DNA replication take place?

  1. G1
  2. S phase
  3. Prophase
  4. Cytokinesis

Answer: B) S phase

Explanation: Replication occurs in S phase. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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10. A DNA template strand reads TAC. The mRNA codon is

  1. AUG
  2. TAC
  3. ATG
  4. UAC

Answer: A) AUG

Explanation: Complementary with U for T. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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11. mRNA leaves the nucleus through

  1. the Golgi
  2. nuclear pores
  3. lysosomes
  4. the nucleolus

Answer: B) nuclear pores

Explanation: Pores in the nuclear envelope. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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12. The lagging strand is made discontinuously because

  1. it has no template
  2. it contains uracil
  3. DNA polymerase can only add nucleotides to the 3′ end
  4. helicase works slowly

Answer: C) DNA polymerase can only add nucleotides to the 3′ end

Explanation: Synthesis is only 5′→3′. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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13. Which enzyme joins Okazaki fragments?

  1. RNA polymerase
  2. DNA ligase
  3. Helicase
  4. DNA polymerase

Answer: B) DNA ligase

Explanation: Ligase seals gaps. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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14. During transcription, mRNA is made by

  1. ribosomes
  2. DNA polymerase
  3. RNA polymerase
  4. DNA ligase

Answer: C) RNA polymerase

Explanation: RNA polymerase builds mRNA. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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15. ATP is a phosphorylated nucleotide containing

  1. adenine, glucose and two phosphates
  2. adenine, ribose and three phosphate groups
  3. thymine, ribose and three phosphates
  4. adenine, deoxyribose and one phosphate

Answer: B) adenine, ribose and three phosphate groups

Explanation: ATP = adenosine triphosphate. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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16. Introns are

  1. non-coding sequences removed from pre-mRNA
  2. coding sequences joined together
  3. sections of tRNA
  4. stop codons

Answer: A) non-coding sequences removed from pre-mRNA

Explanation: Splicing removes introns. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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17. DNA helicase

  1. joins nucleotides
  2. seals Okazaki fragments
  3. adds a primer
  4. breaks hydrogen bonds to unwind the helix

Answer: D) breaks hydrogen bonds to unwind the helix

Explanation: Helicase unzips DNA. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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18. The two strands of DNA are antiparallel, meaning

  1. they run in the same direction
  2. they never pair
  3. they are identical
  4. they run in opposite directions (5′→3′ and 3′→5′)

Answer: D) they run in opposite directions (5′→3′ and 3′→5′)

Explanation: Antiparallel strands. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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19. How many hydrogen bonds join cytosine and guanine?

  1. Three
  2. One
  3. Two
  4. Four

Answer: A) Three

Explanation: C–G has three H-bonds; A–T has two. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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20. mRNA differs from DNA because mRNA

  1. is double-stranded
  2. contains uracil and ribose and is single-stranded
  3. contains deoxyribose
  4. contains thymine

Answer: B) contains uracil and ribose and is single-stranded

Explanation: RNA uses U and ribose. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.1 Structure of nucleic acids and replication of DNA

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21. The anticodon is found on

  1. mRNA
  2. tRNA
  3. DNA
  4. rRNA in the nucleolus

Answer: B) tRNA

Explanation: tRNA carries the anticodon. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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22. The non-transcribed strand has the same base sequence as the mRNA except that it has

  1. uracil instead of thymine
  2. thymine instead of uracil
  3. ribose
  4. no adenine

Answer: B) thymine instead of uracil

Explanation: mRNA copies the coding strand with U. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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23. The genetic code is described as degenerate because

  1. codons overlap
  2. some codons have four bases
  3. it is the same in all organisms
  4. most amino acids are coded for by more than one codon

Answer: D) most amino acids are coded for by more than one codon

Explanation: Several codons per amino acid. AS & A Level Biology · Topic 6 Nucleic Acids and Protein Synthesis · 6.2 Protein synthesis

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