DNA Structure, Replication, and Genetic Code

00:00 8 marks

2. *Caenorhabditis elegans* is a species of nematode worm widely used in biological research. Its genome is fully sequenced.

(a) State **two** features of DNA structure that allow it to store genetic information. \[2]
(b) Outline the process of DNA replication in eukaryotes, including the roles of **three** named enzymes specific to the HL syllabus. \[4]
(c) Explain how the universality of the genetic code allows genes from one organism, like *C. elegans*, to be expressed in another. \[2]

Part a

3 minutes 2 marks

Question

State **two** features of DNA structure that allow it to store genetic information. \[2]

Hint Hint

Hint

Consider the sequence of bases and the overall structure, including how information is reliably copied.

Answer Answer
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Complete Answer

Any two of: Sequence of bases; large capacity due to length; complementary base pairing.

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Part b

6 minutes 4 marks

Question

Outline the process of DNA replication in eukaryotes, including the roles of **three** named enzymes specific to the HL syllabus. \[4]

Hint Hint

Hint

Describe the unwinding, synthesis (leading/lagging), priming, and joining steps, naming key enzymes like helicase, DNA polymerase III, ligase, etc.

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Helicase unwinds the DNA double helix. DNA polymerase III synthesizes new strands using parent strands as templates in the 5′ to 3′ direction (leading strand continuous, lagging strand discontinuous via Okazaki fragments). RNA primase creates RNA primers. DNA polymerase I removes primers and replaces them with DNA. DNA ligase joins Okazaki fragments.

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Part c

3 minutes 2 marks

Question

Explain how the universality of the genetic code allows genes from one organism, like *C. elegans*, to be expressed in another. \[2]

Hint Hint

Hint

Focus on how the same codons specify the same amino acids across different species during translation.

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Explanation Explanation

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Complete Answer

The genetic code (the correspondence between mRNA codons and amino acids) is nearly identical in all organisms. This means that the translation machinery (ribosomes and tRNA) of a host organism can read the mRNA transcribed from a foreign gene (like one from *C. elegans*) and correctly synthesize the corresponding protein.

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