3.7 Cell Cycle Flashcards
What is mitosis?
- A eukaryotic cell divides to produce 2 daughter cells that have the same number of chromosomes as the parent cell and each other (identical copies of DNA produced by the parent cell during DNA replication)
What happens during interphase?
DNA replication
What are the 4 stages of mitosis in order?
Prophase
Metaphase
Anaphase
Telophase and cytokinesis
What happens during prophase?
- Chromosomes become visible
- Centrioles move to opposite poles of the cell and spindle fibres develop from each of the centrioles which span the cell from pole to pole
- Nucleolus disappears and nuclear envelope breaks down –> chromosomes free in the cytoplasm of the cell
What happens during metaphase?
- Spindle fibres attach to centromere and align the chromosomes along the equator of the cell
Chromosomes made up of 2 chromatids (each an identical copy of DNA from parent cell)
- Chromatids joined by centromere
What happens during anaphase?
- Centromeres divide into 2
- Spindle fibres pull the individual sister chromatids apart
- Chromatids move to opposite poles (now referred to as chromosomes) by the spindle fibres
Paired chromatids separate at the centromeres and move to opposite poles of the cell
What happens during telophase?
- Chromosomes reach their respective poles and become longer and thinner and disappear, leaving chromatin
- Spindle fibres disintegrate
- Nuclear envelope and nucleolus re-form
- Cytoplasm divides via cytokinesis
What are the main features to recognise when identifying the stages of mitosis?
Prophase
- Chromosomes are visible
The nuclear envelope is breaking down
Metaphase
- Chromosomes are lined up along the middle of the cell
Anaphase
- Chromosomes are moving away from the middle of the cell, towards opposite poles
Telophase
- Chromosomes have arrived at opposite poles of the cell
- Chromosomes begin to decondense
- The nuclear envelope is reforming
Describe the process of binary fission (protoctists)
- Circular DNA molecules replicates and both copies attach to the cell membrane
- Plasmids also replicate
- Cell membrane begins to grow between the two DNA molecules and begin to pinch inwards, dividing the cytoplasm into two
- New cell wall forms between the 2 DNA dividing the cell into 2 identical daughter cells
- Each have single copy of the circular DNA and variable number of copies of the plasmids
How do viruses replicate?
- Attach to their host cell via proteins on their surface
- Inject nucleic acid into the host cell
- Genetic information on the injected viral nucleic acid provide ‘instructions’ for the host cell’s metabolic processes to start producing the viral components, nucleic acid, enzymes and structural proteins
- Assembled into new viruses
What is mitosis important for?
Growth
Repair
Asexual reproduction
Explain why mitosis is important for growth
- The two daughter cells are genetically and have the same number of chromosomes as the parent cell
- Enables unicellular zygotes (as the zygote divides by mitosis) to grow into multicellular organisms
(When 2 haploid cells fuse to form a diploid, has all the genetic information needed to form the new organism)
Explain why mitosis is important for repair
Damaged tissues can be repaired by mitosis followed by cell division
As cells are constantly dying they need to be continually replaced by genetically identical cells
Explain why mitosis is important for asexual reproduction
Single-celled organisms divide by mitosis to give two new organisms both genetically identical to the parent organism
What are the 3 stages of the cell cycle?
Interphase
Nuclear division
Division of the cytoplasm
