3.2.2 - All cells arise from other cells Flashcards
Topic 2
Summarise the stages of the cell cycle in eukaryotic cells
- Stage 1
Interphase
> DNA replicates semi-conservatively (S phase)
○ Leading to 2 chromatids (identical copies) joined at a centromere
> Number of organelles & volume of cytoplasm increases, protein synthesis (G1 / G2) - Stage 2
Mitosis
> Nucleus divides
> To produce 2 nuclei with identical copies of DNA produced by parent cell - Stage 3
Cytokinesis
> Cytoplasm and cell membrane (normally) divide
> To form 2 new genetically identical daughter cells
What are the stages of mitosis?
Stage 1: prophase
Stage 2: metaphase
Stage 3: ananphase
Stage 4: telophase
Describe the behaviour of chromosomes & the role of spindle fibres in stage 1: prophase of mitosis
- Chromosomes condense, becoming shorter / thicker so visible
> Appear as 2 sister chromatids joined by a centromere - Nuclear envelope breaks down
- Centrioles move to opposite poles of cell forming spindle network
- Spindle fibres start to attach to chromosomes by their centromeres
Describe the behaviour of chromosomes & the role of spindle fibres in stage 2: metaphase
- Spindle fibres attach to chromosomes by their centromeres
- Chromosomes align along equator
Describe the behaviour of chromosomes & the role of spindle fibres in stage 3: anaphase
- Spindle fibres shorten / contract
- Centromere divides
- Pulling chromatids (from each pair) to opposite poles of cell
Describe the behaviour of chromosomes & the role of spindle fibres in stage 4: telophase
- Chromosomes uncoil, becoming longer / thinner
- Nuclear envelopes reform = 2 nuclei
- Spindle fibres / centrioles break down
Why do some eukaryotic cells not undergo the cell cycle?
- Within multicellular organisms, not all cells retain the ability to divide (eg. neurons)
- Only cells that do retain this ability go through a cell cycle
Explain the importance of mitosis in the life of an organism - Parent cell divides to produce 2 genetically identical daughter cells for…
● Growth of multicellular organisms by increasing cell number
● Replacing cells to repair damaged tissues
● Asexual reproduction
Describe how tumours and cancers form
- Mitosis is a controlled process so:
- Mutations in DNA / genes controlling mitosis can lead to uncontrolled cell division
- Tumour formed if this results in the growth of a mass of abnormal cells
○ Malignant tumour = cancerous, can spread (metastasis)
○ Benign tumour = non-cancerous
Suggest how cancer treatments control rate of cell division
● Some disrupt spindle fibre activity / formation
○ So chromosomes can’t attach to spindle by their centromere
○ So chromatids can’t be separated to opposite poles (no anaphase)
○ So prevents / slows mitosis
● Some prevent DNA replication during interphase
○ So can’t make 2 copies of each chromosome (chromatids)
○ So prevents / slows mitosis
Which cells are cancer treatments most effective on?
They are more effective
against cancer cells due
to uncontrolled cell
division, but also disrupts
cell cycle of rapidly
dividing healthy cells
How do prokaryotic cells replicate
Binary fission
Describe the process of binary fission (prokaryotic cell replication)
- Replication of circular DNA
- Replication of plasmids
- Division of cytoplasm to produce 2 daughter cells
○ Single copy of circular DNA
○ Variable number of copies of plasmids
Describe how viruses replicate
- Being non-living, viruses do not undergo cell division, there replication is as follows:
- Attachment proteins attach to complementary receptors on host cell
- Inject viral nucleic acid (DNA/RNA) into host cell
- Infected host cell replicates virus particles:
a. Nucleic acid replicated
b. Cell produces viral protein / capsid / enzymes
c. Virus assembled then released.
The scientists measured the percentage change in tumour volume.
Suggest why they recorded both percentage change and tumour volume.
Percentage change:
- To allow comparison as tumours may differ in volume/size (at the start of the investigation)
Tumour volume:
- (As) tumours may differ in length/width/shape
OR
- (As) volume is (best) indication of the number of cells in tumour
