2.2 All cells arise from other cells

What is the first stage of the cell cycle and what happens during it?

• Interphase.

• DNA replicates semi-conservatively, leading to 2 identical sister chromatids joined by a centromere.

• Number of organelles and volume of cytoplasm increases, with protein synthesis occurring.

What is the second stage of the cell cycle?

• Mitosis, where the nucleus divides to produce 2 nuclei with identical copies of DNA from the parent cell.
  

What is the third stage of the cell cycle?

• Cytokinesis, where the cytoplasm and cell membrane divide to form 2 new genetically identical daughter cells.

What happens to chromosomes during prophase?

• Chromosomes condense, becoming shorter and thicker so they are visible.

• They appear as 2 identical sister chromatids joined by a centromere.

What happens to the nuclear envelope and spindle during prophase?

• Nuclear envelope breaks down.

• Centrioles move to opposite poles forming a spindle network.

• Spindle fibres start to attach to chromosomes by their centromeres.

What happens during metaphase?

• Spindle fibres attach to chromosomes by their centromeres.

• Chromosomes align along the equator.

What happens during anaphase?

• Spindle fibres shorten and contract.

• Centromere divides.

• Chromatids from each pair are separated and pulled to opposite poles of the cell.

What happens during telophase?

• Chromosomes uncoil, becoming longer and thinner.

• Nuclear envelopes reform around sets of chromosomes at each pole, creating 2 nuclei.

• Spindle fibres and centrioles break down.

Why do some eukaryotic cells not undergo the cell cycle?

• Within multicellular organisms, not all cells retain the ability to divide, for example neurons.

• Only cells that do retain this ability go through a cell cycle.

How does mitosis contribute to the growth of multicellular organisms?

• Parent cell divides to produce 2 new genetically identical daughter cells, increasing cell number.

How does mitosis contribute to repairing damaged tissues?

• Parent cell divides to produce 2 new genetically identical daughter cells, replacing faulty cells to repair damaged tissues.

How does mitosis contribute to asexual reproduction?

• Parent cell divides to produce 2 genetically identical daughter cells.

What leads to uncontrolled cell division in tumour formation?

• Mutations in DNA or genes controlling mitosis can lead to uncontrolled cell division.

What forms if uncontrolled cell division results in a mass of abnormal cells?

• A tumour forms.

What is the difference between malignant and benign tumours?

• Malignant tumours are cancerous and can spread through metastasis.

• Benign tumours are non-cancerous and do not spread through metastasis.

How do some cancer treatments disrupt spindle fibre activity?

• Spindle fibres cannot attach to the chromosome by their centromere.

• Chromatids are not pulled from each pair to opposite poles of the cell, preventing anaphase.

• This prevents or slows mitosis.

How do some cancer treatments prevent DNA replication?

• They prevent DNA replication during interphase.

• Cells cannot make 2 identical copies of each chromatid.

• This prevents or slows mitosis.

Why do cancer treatments also affect healthy cells?

• They are more effective against cancer cells due to uncontrolled cell division, but also disrupt the cell cycle of rapidly dividing healthy cells.

What is the first step of binary fission in prokaryotic cells?

• Replication of circular DNA.

What is the second step of binary fission?

• Replication of plasmids.

What is the third step of binary fission?

• New membrane forms and cytoplasm divides to produce 2 daughter cells.

• Each daughter cell receives a single copy of circular DNA and a variable number of copies of plasmids.

What is the first step in viral replication?

• Attachment proteins attach or bind to complementary receptors on the host cell.

What is the second step in viral replication?

• Inject viral nucleic acid into the host cell.

What is the first part of the third step in viral replication?

• Nucleic acid is replicated.

What is the second part of the third step in viral replication?

• The host cell produces new viral proteins, including capsid and enzymes.

What is the third part of the third step in viral replication?

• Virus particles are assembled and released from the cell via budding.

Do viruses undergo cell division? Why?

• No, viruses are non-living, have no metabolism, and do not undergo cell division.