Where can I find the full H2 Biology Notes series?

Start at the H2 Biology Notes hub, then follow Core Ideas 1-4 and the Extension Topics.

Is this topic tested in Paper 4 (practical)?

Molecular biology itself is rarely tested as a standalone practical. However, techniques such as gel electrophoresis and PCR - both of which rely on DNA replication and base-pairing principles - may appear as data-handling or planning questions in Paper 4.

Do I need to memorise every enzyme in the replication fork?

Yes. SEAB expects you to name helicase, primase, DNA polymerase III, DNA polymerase I, DNA ligase, and SSB proteins, and to state each enzyme's specific role. Simply writing "DNA polymerase" without specifying III or I is insufficient for full marks. [1]

What is the difference between the template strand and the coding strand?

The template strand (antisense strand) is the strand read by RNA polymerase during transcription (read 3' to 5'). The coding strand (sense strand) has the same base sequence as the mRNA (with T instead of U) and is not directly read during transcription.

How do prokaryotic and eukaryotic gene regulation differ?

Prokaryotes primarily use operons (clusters of genes under one promoter, regulated by repressors and inducers). Eukaryotes regulate gene expression at multiple levels including chromatin remodelling, transcription factor binding to enhancers/silencers, mRNA splicing, and epigenetic modifications such as DNA methylation and histone acetylation. [1] ---

Study guide23 Mar 2026, 00:00 Z

H2 Biology: DNA Replication, Transcription & Translation - Notes (2026)

In one line

Replication copies DNA, transcription makes RNA from DNA, and translation uses mRNA codons to build a polypeptide.

Key points

Most exam marks come from directionality, enzyme roles, and how sequence changes affect protein structure.

Download printable cheat-sheet (CC-BY 4.0)

Reviewed by

Ezekiel Tan·Academic Advisor (Biology)

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Read in layers

1 second

Read the summary above.

10 seconds

Scan the first few sections below.

100 seconds

Jump into the section that matches your decision.

Quick central-dogma map
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1 DNA Structure Review
2 DNA Replication

Q: What does H2 Biology: DNA Replication, Transcription & Translation cover?
A: H2 Biology molecular biology notes covering DNA replication, transcription, translation, gene expression regulation, and exam-style worked examples for 9477.

TL;DR
Replication copies DNA, transcription makes RNA from DNA, and translation uses mRNA codons to build a polypeptide.
Most exam marks come from directionality, enzyme roles, and how sequence changes affect protein structure.

Quick central-dogma map

Read depth	What to take away
1 second	DNA -> RNA -> protein.
10 seconds	DNA polymerase and RNA polymerase both read templates, but they make different products.
100 seconds	Track template direction, new strand direction, base pairing, and the final amino acid sequence in every answer.

Concrete example: During transcription, RNA polymerase reads the DNA template strand 3' to 5' and makes mRNA 5' to 3'. During translation, each mRNA codon is matched to a tRNA anticodon, adding one amino acid to the chain.

Molecular biology sits at the heart of Core Idea 3 (Genetics) in the H2 Biology syllabus. DNA replication, transcription, and translation form a tightly connected sequence - the central dogma - that examiners revisit in almost every sitting. Students who can name every enzyme, explain directionality, and link mutations to protein consequences tend to pick up full marks on structured questions.

Use this page alongside the broader H2 Biology notes hub. For the genetics of cell division, see Cell Division - Mitosis & Meiosis. For disease-related genetics, see Genetic Basis of Disease.

Status: SEAB's current H2 Biology (9477) syllabus PDF is labelled for 2026 and identifies 2026 as the first year of examination. This page aligns with Core Idea 3 - Genetics and the Molecular Basis of Inheritance. [1]

Enzyme / Protein	Role
Helicase	Unwinds the double helix by breaking hydrogen bonds between complementary base pairs
Single-strand binding (SSB) proteins	Stabilise the separated single strands and prevent them from re-annealing
Primase	Synthesises a short RNA primer complementary to the template strand, providing the free 3'-OH group that DNA polymerase III requires
DNA polymerase III	Adds deoxyribonucleotides to the 3' end of the growing strand (5' to 3' synthesis); also has 3' to 5' proofreading exonuclease activity
DNA polymerase I	Removes RNA primers and replaces them with DNA
DNA ligase	Seals the nicks (phosphodiester bond gaps) between Okazaki fragments on the lagging strand

Type	What happens	Effect on protein
Silent	Changed codon still codes for the same amino acid (degeneracy of the genetic code)	No change in protein
Missense	Changed codon codes for a different amino acid	May alter protein folding and function (e.g. sickle cell anaemia: GAG to GUG in the haemoglobin gene)
Nonsense	Changed codon becomes a premature stop codon	Truncated, usually non-functional protein

Feature	DNA Replication	Transcription	Translation
Template	Both DNA strands	One DNA strand (template / antisense strand)	mRNA
Product	Two identical DNA molecules	Pre-mRNA (then mature mRNA after processing)	Polypeptide
Key enzyme	DNA polymerase III	RNA polymerase	Ribosome (with peptidyl transferase activity)
Direction of synthesis	5' to 3'	5' to 3'	N-terminus to C-terminus (mRNA read 5' to 3')
Primer required?	Yes (RNA primer by primase)	No	No (initiator tRNA binds start codon)
Nucleotides used	dATP, dTTP, dGTP, dCTP	ATP, UTP, GTP, CTP	Amino acids (carried by tRNA)
Location (eukaryotes)	Nucleus	Nucleus	Cytoplasm (ribosomes)
Base pairing rule	A-T, G-C	A-U (template to mRNA), G-C	Codon-anticodon (mRNA to tRNA)

H2 Biology: DNA Replication, Transcription & Translation - Notes (2026)

Quick central-dogma map

Quick revision box

1 DNA Structure Review

2 DNA Replication

2.1 Overview

2.2 Evidence - the Meselson-Stahl experiment

2.3 Key enzymes and proteins

2.4 Leading strand vs lagging strand

2.5 Proofreading and error correction

3 Transcription

3.1 Initiation

3.2 Elongation

3.3 Termination

3.4 Post-transcriptional modification (eukaryotes only)

4 Translation

4.1 Ribosome structure

4.2 tRNA structure

4.3 Initiation

4.4 Elongation

4.5 Termination

5 Gene Expression Regulation

5.1 Prokaryotic regulation - operons

5.2 Eukaryotic regulation

6 Mutations

6.1 Point mutations (single nucleotide changes)

6.2 Frameshift mutations

6.3 Consequences for protein function

7 Comparison Table: Replication vs Transcription vs Translation

8 How Molecular Biology Appears in Exams

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