Salam Academy
Sign inCreate account
LearnYBI11WBI12 · Unit 2: Cells, Development, Biodiversity and ConservationCell structure, reproduction and developmentGene expression and stem cells
Cell structure, reproduction and development · Subtopic 3 of 5

Gene Expression and Stem Cells

Every cell has the same genes, but different cells express different ones. Stem cells are undifferentiated: totipotent (any cell, including placenta; early embryo), pluripotent (any body cell; embryonic stem cells), multipotent (a range, e.g. bone marrow → blood cells), unipotent (one type). Induced pluripotent stem (iPS) cells are made by adding transcription factor genes to adult cells. Transcription factors bind promoters to start or stop transcription; oestrogen enters cells and binds a receptor, releasing a transcription factor. RNA interference (siRNA) destroys specific mRNA, blocking translation. In prokaryotes the lac operon switches on lactose-digesting genes only when lactose is present. Epigenetics: heritable changes without changing base sequence: DNA methylation (silences genes) and histone acetylation (opens chromatin, activates). Cancer: mutated oncogenes (overactive) or tumour suppressor genes (inactive), sometimes by abnormal methylation.

Edexcel YBI11 WBI12Edexcel YBI11 WBI15AQA 7402 Paper 2≈ 50 minRevision 1 · updated 2026-11-02
Section 1 of 14

Learning objectives

  • Describe types and uses of stem cells.
  • Explain transcription factors and RNAi.
  • Describe the lac operon.
  • Explain epigenetics and its role in cancer.
Pause and think

A liver cell and a nerve cell contain the same DNA. Why are they so different?

Section 2 of 14

Core idea

Start hereSame genes, different cells

Your skin cells and brain cells carry identical DNA. What differs is which genes are switched on.

The big idea

Gene expression is controlled by transcription factors, RNA interference and epigenetic marks; losing that control can cause cancer.

Levels of control

Before, during and after transcription.

Worked exampleStem cell potency

Classify: early embryo cell; embryonic stem cell; bone marrow stem cell.

Goal
Potency.
Strategy
Range of cell types.
  1. early embryo: totipotent\text{early embryo: totipotent}
    Any cell, including placenta.
  2. ESC: pluripotent; bone marrow: multipotent\text{ESC: pluripotent; bone marrow: multipotent}
    Fewer options.
AnswerTotipotent, pluripotent, multipotent.
✓ CheckPotency decreases with development ✓.

Summary

  • Stem cell types.
  • Transcription factors; RNAi.
  • Epigenetics; cancer.
Key words
Transcription factor
Protein controlling transcription of a gene.
Epigenetics
Heritable changes in gene expression without base sequence change.
HistoryYamanaka factors. In 2006 Shinya Yamanaka turned mouse skin cells into pluripotent stem cells with just four transcription factors, winning the 2012 Nobel Prize.
Fun factDutch hunger winter. Children of mothers starved during the 1944 Dutch famine showed health effects decades later, linked to epigenetic changes.
Keep reading for free

Create a free account to read the rest of this lesson: key formulae, worked examples, explore the graph, common mistakes, exam tip, guided practice and more. Your answers are checked and your progress is saved.

Create free accountSign in