Transcription — From DNA to mRNA
Genes stay in DNA, but the instructions for building a protein need a portable copy. Transcription produces mRNA from a DNA template strand so coded information can move on to the next stage of polypeptide synthesis.
Transcription (this lesson) copies a gene into mRNA; translation (next lesson) builds the protein.
Practise this lesson
Four printable worksheets that build from the foundations up to exam-style questions — start at whatever level suits you.
A student says, "If DNA already contains the code, the cell should just send the DNA out to the ribosome whenever it needs a protein. There is no real reason to make mRNA first."
Before reading on, explain why cells use mRNA rather than moving the DNA itself. What advantage does a temporary RNA copy give the cell?
Know
- A gene is a DNA sequence that codes for a product.
- Transcription forms mRNA from a DNA template strand.
Understand
- Why mRNA is needed as a temporary copy rather than moving DNA itself.
- How codons preserve the code in transferable form.
Can Do
- Convert a DNA template sequence into an mRNA sequence correctly.
- Explain transcription using the CFTR gene as a disease-relevant example.
Core Content
Gene concept · the order of bases carries information
The cell does not use the whole genome at once. It reads particular gene sequences when it needs a particular product.
A gene is a section of DNA containing the base sequence information needed to produce a functional product. In the HSC Biology context for this module, the important link is that genes contain the code that will later direct polypeptide synthesis.
The base sequence matters because the order of bases carries information. That information must be copied into a usable form for the next step of protein production.
What to write in your book
- A gene = a section of DNA coding for a functional product (usually a polypeptide).
- The order of bases carries the information.
- The cell reads particular genes when it needs particular products.
- Say a gene "codes for" a product, not "is a trait".
A section of DNA that codes for a functional product (usually a polypeptide) is called a _____.
Transcription steps · complementary pairing with uracil
During transcription, the relevant section of DNA unwinds and one strand acts as the template strand. RNA nucleotides pair with the exposed DNA bases using complementary base pairing rules, except that RNA uses uracil instead of thymine.
If the DNA template strand has adenine, the mRNA formed will contain uracil. If the template has thymine, the mRNA formed will contain adenine. Cytosine still pairs with guanine, and guanine still pairs with cytosine.
Once the RNA sequence is formed, the mRNA separates and carries the coded information away from the DNA.
What to write in your book
- DNA unwinds; one strand = the template strand.
- RNA nucleotides pair complementarily: A→U, T→A, C→G, G→C.
- RNA uses uracil instead of thymine.
- Only ONE DNA strand is used as the template for a given gene.
In RNA, which base replaces thymine and pairs with adenine?
Why mRNA matters · protecting the DNA
In eukaryotic cells, DNA remains in the nucleus. mRNA is important because it acts as a temporary copy of the gene that can be used outside the nucleus in the next stage of polypeptide synthesis.
This protects the original DNA from having to move around the cell each time a protein is needed. It also allows the cell to make multiple RNA copies from the same gene if many copies of a protein are required.
mRNA therefore does not replace DNA. It carries the relevant information from DNA in a form that can be used by the cell.
What to write in your book
- In eukaryotes, DNA stays in the nucleus; mRNA carries the code out.
- mRNA = temporary, portable copy of the gene.
- Protects DNA and allows many copies from one gene.
- mRNA does NOT replace DNA — it carries the message.
After transcription, the mRNA permanently replaces the cell's DNA.
During transcription, RNA polymerase synthesises mRNA using the template (antisense) strand of DNA.
Transcription produces a DNA copy of an RNA template for protein synthesis.
Transferable information · DNA vs mRNA bases
The sequence on mRNA is read in groups of three bases called codons. At this lesson stage, the key idea is that codons hold transferable information copied from DNA. In the next lesson, you will see how those codons are used in translation.
DNA During Transcription
- Stays as the original hereditary material
- One strand acts as the template
- Uses bases A, T, C and G
mRNA During Transcription
- Temporary copy of the coded sequence
- Forms by complementary pairing to the template
- Uses bases A, U, C and G
What to write in your book
- mRNA is read in groups of three bases = codons.
- Codons hold transferable information copied from DNA.
- DNA bases: A, T, C, G. mRNA bases: A, U, C, G.
- tRNA/ribosomes/peptide bonds = next lesson (translation).
A three-base unit on mRNA that carries coded information is called a:
Model · the CFTR gene as a real example
The CFTR gene is one real example where the DNA sequence matters biologically. Before any CFTR protein can be produced, the gene must first be transcribed into mRNA.
Transcription uses one DNA template strand to build a complementary mRNA sequence.
What to write in your book
- Step 1: the relevant DNA region unwinds and exposes the template strand.
- Step 2: RNA nucleotides pair with exposed DNA bases (A-U, C-G).
- Step 3: the mRNA sequence separates as a temporary copy of the gene.
- Step 4: the mRNA carries codons into translation (next lesson).
Activities
Sequence and Annotate
For the DNA template strand T A C C G A A T T, write the complementary mRNA sequence in codons. Then label which sequence is DNA and which is mRNA.
CFTR Transcription Reasoning
Explain why a change in the DNA sequence of the CFTR gene could change the mRNA produced during transcription, even before translation happens.
Core idea
- Transcription copies the information in a gene from DNA into mRNA.
Mechanism / process
- One DNA template strand guides complementary pairing of RNA nucleotides to form mRNA, which carries codons.
Common mistake
- Do not say the cell moves DNA to the ribosome or that both DNA strands are copied into one mRNA.
Exam sentence starter
- "mRNA is important in transcription because it acts as..."
A fresh set drawn from this lesson's question bank — feedback shown immediately. +5 XP per correct · +25 XP all correct
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UnderstandBand 3(3 marks) 1. Define transcription and outline the role of the DNA template strand.
AnalyseBand 4(4 marks) 2. Explain why mRNA is required as a temporary copy of a gene in eukaryotic cells.
EvaluateBand 5–6(5 marks) 3. Evaluate the statement: "A change in the CFTR DNA sequence can affect the cell even before translation, because transcription depends on the DNA base order."
Show all answers
Multiple choice
MC answers and full explanations are shown inline as you complete each question. Use the retry button to attempt a fresh set from the lesson bank.
Activity 1 — Sequence and Annotate
DNA template strand: T A C C G A A T T
mRNA formed: A U G G C U U A A
Activity 2 — CFTR Transcription Reasoning
If the DNA sequence of the CFTR gene changes, the complementary mRNA sequence produced during transcription can also change. That means the codons carried by the mRNA may differ before translation even begins.
Short Answer Model Responses
Q1 (3 marks): Transcription is the process of producing an mRNA copy from a DNA template strand [1]. The DNA unwinds and one strand acts as the template [1]. Complementary RNA nucleotides pair with that template to form the mRNA sequence [1].
Q2 (4 marks): mRNA is required because DNA remains in the nucleus in eukaryotic cells [1]. The cell therefore needs a temporary copy of the gene that can carry the coded information away from the DNA [1]. mRNA performs this role by holding the copied sequence in transferable form [1]. This protects the original DNA and allows the code to be used in the next stage of polypeptide synthesis [1].
Q3 (5 marks): The statement is valid because transcription depends directly on the DNA base order [1]. During transcription, RNA nucleotides pair complementarily with the DNA template strand [1]. If the CFTR DNA sequence changes, the mRNA sequence produced can also change [1]. That means the codons carried by the mRNA may differ before translation begins [1]. Therefore a DNA sequence change can affect cell function at the transcription stage by altering the copied message [1].
Gene
A DNA sequence containing coded information for a product.
Transcription
Formation of mRNA from one DNA template strand.
mRNA
A temporary, portable copy of the code.
Exam trap
mRNA carries codons, but translation is the next lesson.
Rapid-fire questions on genes, the DNA template strand, mRNA, uracil and codons. Beat the boss to bank a tier — gold (perfect + fast), silver (80%+), or bronze (cleared).
You should now be able to reject the idea that DNA is simply sent to ribosomes. In eukaryotic cells, transcription creates mRNA as the transferable copy of the code, preserving the original DNA in the nucleus.