2.2 All Cells Arise from Other Cells Flashcards
what are the three stages of the cell cycle
1- interphase
2- mitosis
3- cytokinesis
describe the interphase stage
-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)
describe the mitosis stage
-nucleus divides
-to produce 2 nuclei with identical copies of DNA produced by parent cell
describe the cytokinesis stage
-cytoplasm and cell membrane (normally) divide
-to form 2 new genetically identical daughter cells
describe the behaviour of chromosomes and role of spindle fibres in the prophase
-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 forming spindle network
-spindle fibres start to attach to chromosomes by their centromeres
describe the behaviour of chromosomes and role of spindle fibres in the metaphase
-spindle fibres attach to chromosomes by their centromeres
-chromosomes align along equator
describe the behaviour of chromosomes and role of spindle fibres in the anaphase
-spindle fibres shorten / contract
-centromere divides
-pulling chromatids (from each pair) to opposite poles of cell
describe the behaviour of chromosomes and role of spindle fibres in the telophase
-chromosomes uncoil, becoming longer / thinner
-nuclear envelopes reform = 2 nuclei
-spindle fibres / centrioles break down
what are the stages of mitosis
-prophase
-metaphase
-anaphase
-telophase
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 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
how do prokaryotic cells replicate
-binary fission
describe binary fission
- 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 so:
1. attachment proteins attach to complementary receptors on host cell
2. inject viral nucleic acid (DNA/RNA) into host cell
3. infected host cell replicates virus particles:
a. nucleic acid replicated
b. cell produces viral protein / capsid / enzymes
c. virus assembled then released
mitotic index calculation
number of cells with visible chromosomes / total number of cells
