All cells arise from other cells Flashcards
State what the cell cycle is and outline its stages.
cycle of division with intermediate growth periods
- interphase
- mitosis or meiosis (nuclear division)
- cytokinesis (cytoplasmic division)
Explain why the cell cycle does not occur in some
cells.
After differentiation, some types of cell in multicellular organisms (e.g. neurons) 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 & refers only to nuclear division.
Outline what happens during interphase.
G1: cell synthesises proteins for replication & cell size doubles
S: DNA replicates = chromosomes consist of 2 sister chromatids joined at a centromere
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
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 (proportion of cells undergoing mitosis).
Explain how to prepare a temporary root tip mount.
- Place root in hydrochloric acid to halt cell division & hydrolyse middle lamella.
- Stain root tip with a dye that binds to chromosomes.
- Macerate tissue in water using mounted needle.
- Use mounted needle at 45° to press down coverslip & 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 (programmed cell death) / slow cell cycle (e.g. p53 acts between G1 & S in interphase so damaged DNA cannot replicate).
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 & 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 the cell cycle:
● prevent DNA replication
● disrupt spindle formation = inhibit metaphase/ anaphase
NB: can also damage healthy cells
How do prokaryotic cells replicate?
Binary fission:
- DNA loop replicates. Both copies stay attached to cell membrane. Plasmids replicate in cytoplasm.
- Cell elongates, separating the 2 DNA loops.
- Cell membrane contracts & septum forms.
- Cell splits into 2 identical progeny cells, each with 1 copy of the DNA loop but a variable number of plasmids.
