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Transcription and translation practice
Transcription makes an RNA sequence from a DNA template. Translation reads mRNA codons to build an amino-acid sequence. Strand identity and direction are essential.
By ExamCat · Original study lesson · Published September 24, 2026
Understand the method
RNA is synthesized in the 5′ to 3′ direction while the template is read 3′ to 5′. A coding DNA strand matches the RNA sequence except that DNA has T where RNA has U. Translation requires a reading frame; an arbitrary fragment is not necessarily a complete gene.
Worked example, step by step
A template fragment is 3′-TAC GGA-5′. Write the complementary mRNA and identify the two codons.
- Read the template in the direction given, 3′ to 5′.
- Pair bases: T with A, A with U, C with G and G with C.
- The RNA is 5′-AUG CCU-3′.
- In the standard genetic code, those codons specify methionine and proline when translated in this frame.
A mistake to watch for
Replacing T with U works for the coding strand written 5′ to 3′, not directly for the template strand. Also do not reverse a sequence without tracking its direction labels.
Try it yourself: three questions
Write an answer before opening the explanation. For calculations, keep your units and intermediate steps; for concepts, state the reason for your choice.
1. Coding DNA is 5′-ATG TTT-3′. What is mRNA?
Show answer and explanation
5′-AUG UUU-3′. The coding strand matches the RNA apart from T/U.
2. Why can a one-base deletion affect many downstream codons?
Show answer and explanation
It can shift the reading frame, changing how subsequent bases are grouped in threes. Location and sequence determine the actual effect.
3. Does every base substitution change an amino acid?
Show answer and explanation
No. Different codons can encode the same amino acid, and substitutions may also occur outside a translated region.
Build your next practice session
Mark the first step where your reasoning differed from the explanation. Turn that step into a question, answer it without looking, then change one condition in the example and explain what would change. A correct guess is a reason to revisit the method.
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Further reading
OpenStax Biology 2e provides textbook background. The worked scenario and practice questions on this page were written independently for ExamCat.
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