Transcribe DNA to mRNA and translate to amino acid chains. Includes codon table lookup, mutation analysis, and step-by-step solutions. Perfect for GCSE and A-Level Biology.
Transcribe DNA to mRNA using base-pairing rules
Only A, T, C, G allowed. Spaces and numbers are ignored.
Quick Examples
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Protein synthesis is the process by which cells build proteins from the instructions encoded in DNA. It is one of the most fundamental processes in all living organisms and follows the central dogma of molecular biology: DNA → RNA → Protein.
The process occurs in two main stages: transcription (DNA to mRNA in the nucleus) and translation (mRNA to protein at the ribosome in the cytoplasm). This was first described by Francis Crick in 1958.
Deoxyribonucleic acid — the double-stranded molecule that carries the genetic instructions for all living organisms
Messenger RNA — a single-stranded copy of a gene that carries the code from DNA to the ribosome
Transfer RNA — carries amino acids to the ribosome. Each tRNA has an anticodon that matches an mRNA codon
The cellular machine where translation occurs. It reads mRNA codons and assembles the amino acid chain
A sequence of three mRNA bases that codes for one amino acid (or a stop signal). There are 64 codons in total
A sequence of three tRNA bases complementary to an mRNA codon. It ensures the correct amino acid is added
The building blocks of proteins. There are 20 standard amino acids, each with different chemical properties
A chain of amino acids linked by peptide bonds. Proteins are one or more polypeptide chains folded into 3D shapes
Practice with these GCSE and A-Level style molecular biology problems:
Q: Transcribe the coding strand ATGCGA to mRNA.
A: Since this is the coding strand, replace T with U: ATGCGA → AUGCGA. The mRNA is AUGCGA.
Key point: Coding strand → mRNA: just replace T with U.
Q: Translate the mRNA sequence AUG GCG UAA.
A: AUG = Met (start), GCG = Ala, UAA = Stop. The protein is Met-Ala (2 amino acids).
Key point: Start at AUG, read triplets, stop at UAA/UAG/UGA.
Q: A gene has the coding strand ATGTTCGTCAAC. Determine the protein produced.
A: Step 1 (Transcription): ATGTTCGTCAAC → AUGUUCGUCAAC. Step 2 (Translation): AUG = Met, UUC = Phe, GUC = Val, AAC = Asn. Protein: Met-Phe-Val-Asn (no stop codon in this segment).
Key point: Always transcribe first, then translate starting from AUG.
Q: The normal haemoglobin gene has GAG at codon 6 (coding strand). In sickle cell, it becomes GTG. What is the effect?
A: Normal: GAG → mRNA GAG → Glu (glutamic acid). Mutated: GTG → mRNA GUG → Val (valine). Glu is negatively charged (hydrophilic), Val is nonpolar (hydrophobic). This single amino acid change causes haemoglobin molecules to stick together, forming stiff fibres that distort red blood cells into a sickle shape.
Key point: A single missense mutation can have devastating effects depending on the amino acid properties.
Q: The coding strand is ATGAAAGCTTGA. What happens if a C is inserted after position 4?
A: Original mRNA: AUGAAAGCUUGA → AUG-AAA-GCU-UGA → Met-Lys-Ala-Stop. After insertion: ATGACAAAGCTTGA → mRNA AUGACAAAGCUUGA → AUG-ACA-AAG-CUU-GA... → Met-Thr-Lys-Leu-... The reading frame is completely shifted after the insertion point.
Key point: Frameshift mutations change every codon downstream — usually catastrophic for protein function.
Always check: the coding strand (5'→3') has the same sequence as mRNA with T. The template strand (3'→5') is what RNA polymerase reads.
RNA uses uracil (U) instead of thymine (T). If your mRNA has a T in it, you have made an error.
Translation always starts at the first AUG codon, not at the beginning of the mRNA. Scan from 5' to 3' to find it.
Replication copies the entire DNA molecule (DNA → DNA). Transcription copies one gene into mRNA (DNA → mRNA). Different enzymes and different products.
The reading frame is set by AUG. AUGCGA is read as AUG-CGA, not AU-GCG-A. One base shift changes every amino acid downstream.
The anticodon on tRNA is complementary to the mRNA codon AND read in the antiparallel direction (3'→5'). Codon AUG has anticodon UAC (read 3'→5').
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