Mitosis
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of the stages of the cell cycle and the role of mitosis in growth and repair. You can test your knowledge on these below.
What are the main stages of the cell cycle?
- Interphase
- Mitosis (Prophase, Metaphase, Anaphase, Telophase)
- Cytokinesis
Why is DNA replication important before mitosis?
Ensures each daughter cell receives a genetically identical copy of DNA.
What enzymes are used in DNA replication and what are their roles?
- DNA helicase breaks the hydrogen bonds between complementary base pairs to separate the two strands.
- DNA polymerase joins adjacent nucleotides together by making phosphodiester bonds.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains mitosis or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Mitosis Overview
- Mitosis is a form of cell division producing two genetically identical daughter cells.
- It occurs for growth, repair, and replacement of cells in multicellular organisms.
- It is also used for asexual reproduction in some plants, fungi and a small number of animals.
- Mitosis is preceded by interphase, where DNA is replicated.
- After DNA replication each chromosome will consist of 2 identical sister chromatids held together by a centromere.
The Stages of Mitosis
Prophase
- Chromosomes condense and become visible.
- The nuclear envelope breaks down.
- Centrioles move to opposite poles, forming the spindle apparatus.
Metaphase
- Chromosomes line up along the cell equator.
- Spindle fibres attach to centromeres of the chromosomes.
Anaphase
- Spindle fibres contract, centromeres split and sister chromatids are pulled apart to opposite poles.
Telophase
- Chromosomes decondense so they are no longer visible.
- Nuclear envelopes reform around each set of chromosomes.
- At the end of mitosis (also known as nuclear division) two new nuclei have formed.
Cytokinesis (after mitosis)
- The cytoplasm and the cell membrane divides, forming two genetically identical daughter cells.
- The cells produced will be diploid (2n) as they have homologous pairs of chromosomes.
Key Terms
- Mitosis: A type of cell division that produces two genetically identical daughter cells.
- Chromosome: A structure of coiled DNA and histone proteins found in the nucleus.
- Spindle Fibres: Microtubules made of protein that attach to chromosomes and help separate them.
- Centromere: The region where two sister chromatids are joined together.
- Cytokinesis: The process of dividing the cytoplasm and cell membrane to form two cells.
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Exam Tips
In mitosis-related questions, always describe chromosome movement accurately and specify the stage in which changes occur.
Don't confuse mitosis with meiosis, which produces genetically varied, haploid gametes.
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Maths Tips
The table shows the number of cells in each stage of the cell cycle when a tissue sample was viewed under the microscope.
Use this information to calculate the time spent in metaphase during the cell cycle in minutes.
One complete cell cycle takes 24 hours.
Step 1: calculate the % of cells in metaphase
(12/ 212) x 100 = 5.66%
This equates to 5.66% of the time spent in metaphase.
Step 2: find 5.66% of 24 hours
24 x 60 = 1440 minutes
1440 x 0.0566 = 81.5 minutes
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A scientist observed cells under a microscope and found that 10% of the cells were in anaphase. The complete cell cycle takes 24 hours.
Calculate how long, in minutes, the cells spend in anaphase. (2 marks)
- Step 1: 10% of 24 hours = (10/100) × 24 = 2.4 hours.
- Step 2: Convert to minutes: 2.4 × 60 = 144 minutes.
Final Answer: 144 minutes
In prophase of mitosis, the chromosomes become visible. Describe what happens in metaphase (2 marks)
- The chromosomes line up along the equator of the cell.
- Attached to the spindle fibres via their centromeres.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!