Explain the role of telomeres
Telomeres protect chromosome-end genes from being lost as DNA is replicated; they act as a buffer at chromosome ends.
AS Level · Cambridge International Biology 9700, 2028–2030. These lessons explain cell-cycle concepts and image interpretation. Written practice is self-checked; it does not demonstrate practical microscopy competence or replace teacher-reviewed assessment.
Before you begin
- Recognise DNA as genetic material and use the terms cell, nucleus and chromosome accurately.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Where does a telomere occur?
What you will learn
- Locate telomeres at chromosome ends
- Outline how telomeres help prevent loss of genes during DNA replication
Chromosome ends need protection
Telomeres are regions at the ends of chromosomes. They consist of repeated DNA sequences associated with proteins and do not usually code for proteins. Their location provides a buffer beyond genes near the chromosome ends.
DNA replication does not copy the very ends of linear chromosomes in the same way as internal regions. As a result, chromosome ends can shorten over repeated cell divisions.
A buffer helps retain genes
Telomere sequences can be lost before coding genes at chromosome ends are lost. This is the syllabus-level role: telomeres help prevent loss of genes from chromosome ends during DNA replication.
Avoid claiming telomeres guarantee that no genetic information is ever lost. Their role is protective and limited; chromosome-end replication and telomere shortening depend on cell type and biological context.
Pause and explain
How can telomeres help protect genes during DNA replication?
Worked example
A chromosome end shortens slightly after repeated rounds of DNA replication. Explain how a telomere can reduce the risk of gene loss.
Show the worked solution
- Telomeres are located at chromosome ends.
- Repeated telomere DNA can be lost before genes close to the end.
Answer A telomere is a protective region at the chromosome end. It provides a buffer of repeated DNA that can shorten during replication before genes at the end of the chromosome are lost.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Outline the role of telomeres during DNA replication.
Give me a hint
State their position and the protective effect of repeated end sequences.
Compare my reasoning
- Telomeres are at chromosome ends.
- They provide a buffer that can be shortened before genes are lost.
Telomeres are protective regions at chromosome ends. Their repeated DNA sequences provide a buffer that can be lost during replication before genes near the ends are lost.
Look for these in your work
- Location included
- Gene-protection mechanism outlined
Why is a telomere better described as a buffer than as a gene?
Give me a hint
Compare repeated protective sequence with coding information.
Compare my reasoning
- Telomeres are repeated end regions with a protective role.
- They reduce the risk of losing genes at chromosome ends.
A telomere is a repeated protective region at a chromosome end, rather than a gene that codes for a protein. It acts as a buffer so that shortening can occur before nearby genes are lost.
Look for these in your work
- Protective region described
- Coding gene distinction made
A student claims telomeres mean chromosome ends never shorten. Evaluate this claim.
Give me a hint
Distinguish reducing gene loss from preventing all shortening.
Compare my reasoning
- Telomeres can themselves shorten over repeated replications.
- Their role is to reduce loss of genes at chromosome ends, not to guarantee no shortening.
The claim is too strong. Telomeres can shorten during repeated DNA replication; they provide a buffer that helps prevent loss of genes at chromosome ends, but do not guarantee that chromosome ends never shorten.
Look for these in your work
- Claim evaluated
- Limit stated
Common mistakes
- Placing telomeres at centromeres
- Saying telomeres are genes that code for proteins
- Claiming telomeres prevent every mutation or all chromosome shortening
What can you explain now?
Where does a telomere occur?
Compare with the explanation
At the end of a chromosome
Telomeres protect chromosome ends.
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Make it stick
Where are telomeres, and how can they protect genes when linear chromosome ends are replicated?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.