2.2 Mitosis and the cell cycle Flashcards
State what the cell cycle is
A cycle of division with intermediate growth periods
Outline the stages of the cell cycle
- Interphase
- Mitosis or meiosis
- Cytokinesis
Explain why the cell cycle does not occur in some cells
After differentiation, some types of cell in multicellular organisms no longer have the ability to divide
What is the difference between the cell cycle and mitosis?
Cell cycle includes growth period between divisions ; mitosis is only 10% of the cycle and refers only to nuclear division
Outline what happens during interphase
G1: cell synthesises proteins for replication
S: DNA replicates
G2: organelles divide
State the purpose of mitosis
produces 2 genetically identical daughter cells for:
- Growth
- Cell replacement / tissue repair
- Asexual reproduction
Name the stages of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
Outline what happens during prophase
- Chromosomes condense, becoming visible
- Centrioles move to opposite poles of cell and mitotic spindle fibres form
- Nuclear envelope and nucleolus break down = chromosomes free in cytoplasm
Outline what happens during metaphase
Sister chromatids line up at cell equator, attached to the mitotic spindle by their centromeres
Outline what happens during anaphase
requires energy from ATP hydrolysis
1. Spindle fibres contract = centromeres divide
2. Sister chromatids separate into 2 distinct chromosomes and are pulled to opposite poles of cell
3. Spindle fibres break down
Outline what happens during telophase
- Chromosomes decondense, becoming invisible again
- New nuclear envelopes form around each set of chromosomes = 2 new nuclei, each with one copy of each chromosome
Explain the procedure for a root tip squash experiment
- Prepare a temporary mount of root tissue
- Focus an optical microscope on the slide. Count total number of cells in the field of view and number of cells in a stage of mitosis
- Calculate mitotic index
Outline how to prepare a temporary root tip mount
- Place root in hydrochloric acid to halt cell division and hydrolyse middle lamella
- Stain root tip with a dye that binds to chromosomes
- Macerate tissue in water using mounted needle
- Use mounted needle to press down coverslip and obtain a single layer of cells. Avoid trapping air bubbles
Name 2 dyes that bind to chromosomes
- Toluidine blue (blue)
- Acetic orcein (purple-red)
Why is only the root tip used when calculating a mitotic index?
- Meristematic cells at root tip are actively undergoing mitosis
- Cells further from root tip are elongating rather than dividing
What are tumour suppressor genes?
Genes that code for proteins to trigger apoptosis / slow cell cycle
What are proto-oncogenes?
Genes that code for proteins to stimulate cell cycle to progress from one stage to the next
How can mutation to tumour suppressor genes and proto-oncogenes cause cancer?
- Tumour suppressor: no production of a protein needed to slow the cell cycle
- Proto-oncogenes: form permanently-activated oncogenes
- Disruption to cell cycle –> uncontrolled cell division –> tumour
Suggest how cancer treatments control the rate of cell division
Disrupt cell cycle:
- Prevent DNA replication
- Disrupt spindle formation = inhibit metaphase / anaphase
How do prokaryotic cells replicate?
Binary fission:
1. DNA loop replicates. Both copies attached to cell membrane. Plasmids replicate in cytoplasm
2. Cell elongates, separating the 2 DNA loops
3. Cell membrane contracts and septum forms
4. Cell splits into 2 identical progeny cells, each with 1 copy of the DNA loop but a variable number of plasmids
Estimate the exponential growth of bacteria within 8 hours. Assume binary fission occurs once every 20 minutes and there is 1 bacterium at the start
8 x 60 = 480 mins
480 / 20 = 24 divisions
2^24
Why are viruses classified as non-living?
They are acellular: no cytoplasm, no metabolism and cannot self-replicate
Outline how viruses replicate
- Attachment proteins attach to receptors on host cell membrane
- Enveloped viruses fuse with cell membrane or move in via endocytosis and release DNA/RNA into cytoplasm or viruses inject DNA/RNA
- Host cell uses viral genetic information to synthesise new viral proteins / nucleic acid
- Components of new viral particle assemble
How do new viral particles leave the host cell?
- Bud off and use cell membrane to form envelope
- Causes lysis of host cell
