AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
During development, totipotent cells translate only part of their DNA,…
Full specification wording
Most of a cell’s DNA is not translated (A-level only): During development, totipotent cells translate only part of their DNA, resulting in cell specialisation.
A totipotent cell, such as a zygote, can divide and differentiate into any cell type.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 2 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A totipotent cell, such as a zygote, can divide and differentiate into any cell type. It contains the full genome, but during development, it translates only part of its DNA. Specialisation arises because different genes are switched on or off, so only some genes are transcribed. Transcription factors bind to a gene's promoter region, enabling RNA polymerase to transcribe that gene into mRNA. Only this mRNA is translated at ribosomes, producing a specific subset of proteins. These proteins determine cell structure and function, e.g. haemoglobin in erythrocytes. As development proceeds, potency decreases because more genes become silenced. Unexpressed genes are not lost; they remain present but switched off, for example by methylation.
What earns the marks
- Totipotent cells can divide and differentiate into any cell type; they contain the full genome but translate only part of their DNA.
- Transcription factors bind to promoter regions, allowing transcription of only some genes into mRNA.
- Translation of this specific mRNA produces only certain proteins, which determine the structure and function of the specialised cell.
- Unexpressed genes are not lost or destroyed; they remain present but are switched off, for example by epigenetic methylation of the promoter region.
- As development proceeds, cell potency decreases because more genes become silenced.
Common mistakes and how to put them right
Stating that unused DNA is removed or destroyed during specialisation, rather than being switched off.
Put it right: The genes remain present but are not expressed.
Confusing transcription with translation, such as describing mRNA being made at the ribosome.
Put it right: Transcription makes mRNA in the nucleus; translation makes protein at the ribosome.
Claiming the cell 'chooses' which genes to use, omitting the mechanistic role of transcription factors and promoter regions.
Put it right: Transcription factors binding to promoters control which genes are transcribed.
Exam tips
- Detail the full pathway: gene, transcription, mRNA, translation, protein, cell structure and function.
- When explaining why two cells from the same organism differ, always state first that they contain the exact same genes.
Try the lesson
The start of the Most of a cell’s DNA is not translated (A-level only): During development, totipotent cells translate only part of their DNA, resulting in cell specialisation. lesson, made from checked teaching notes for this specification point.
Have a go first
During development, totipotent cells transcribe and translate only part of their DNA. What is the direct result of this process?
Listen
A totipotent cell, such as a zygote, can divide and differentiate into any cell type. It contains the full genome, but during development, it translates only part of its DNA. Specialisation arises because different genes are switched on or off, so only some genes are transcribed. Transcription factors bind to a gene's promoter region, enabling RNA polymerase to transcribe that gene into mRNA. Only this mRNA is translated at ribosomes, producing a specific subset of proteins. These proteins determine cell structure and function, e.g. haemoglobin in erythrocytes. As development proceeds, potency decreases because more genes become silenced. Unexpressed genes are not lost; they remain present but switched off, for example by methylation. A strong answer earns marks for these points. Totipotent cells can divide and differentiate into any cell type; they contain the full genome but translate only part of their DNA. Transcription factors bind to promoter regions, allowing transcription of only some genes into mRNA. Translation of this specific mRNA produces only certain proteins, which determine the structure and function of the specialised cell. Unexpressed genes are not lost or destroyed; they remain present but are switched off, for example by epigenetic methylation of the promoter region. A common slip: Stating that unused DNA is removed or destroyed during specialisation, rather than being switched off. Instead, the genes remain present but are not expressed. Exam tip: Detail the full pathway: gene, transcription, mRNA, translation, protein, cell structure and function.
Key words
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cell specialisation
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transcription factors
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promoter region
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totipotent cells
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See every definition
- cell specialisation
- Arises because different genes are switched on or off, so only some genes are transcribed.
- transcription factors
- Bind to a gene's promoter region, enabling RNA polymerase to transcribe that gene into mRNA.
- promoter region
- The part of a gene that transcription factors bind to, enabling RNA polymerase to transcribe that gene into mRNA.
- totipotent cells
- Can divide and differentiate into any cell type; they contain the full genome but translate only part of their DNA.
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