IMMS Flashcards
DNA structure
DNA double helix coils around nucleosomes, coils again into supercoils and then condenses further into chromosomes
Stain for chromosomes
Giemsa: G banding for complementary chromosome pair identification
Quinacrine: Q banding for individual light and dark bands on chromosome
Cell cycle
Interphase:
G1 growth phase
Synthesis phase
G2 growth phase
Mitosis
G0
Cells not in cell cycle (e.g. liver cells)
Cells that do not undergo mitosis
Myocyte cells in heart and neurones in the brain
Cells constantly in cell cycle
bone marrow cells
gut cells
What happens during S-phase?
DNA replication and centrosome replication
What occurs during prophase?
chromatin condenses into chromosomes and centrosomes nucleate microtubules which move to opposite poles of the nucleus
What occurs during prometaphase?
Nuclear membrane breaks down, microtubules invade nuclear space and chromatids attach to microtubules.
What occurs during metaphase?
Chromosomes align along equatorial place (metaphase plate)
What occurs during anaphase?
The sister chromatids separate, and chromatids are pulled to opposite poles of the cell
What occurs during telophase?
Nuclear membranes reform, chromosomes unfold into chromatin, and cytokinesis begins
What occurs during cyotkinesis?
2 identical daughter cells are produced
Clinical relevance of mitosis (epithelium)
One of the indicators of precancerous lesions is mitotic figures at multiple levels in a microscope sample. No mitotic figures in areas where it shouldn’t be means that the tumour is benign. The number of mitotic figures helps grade the severity of the malignant tumours.
Mitosis + drugs
Chemotherapeutic agents such as taxol and vinca alkaloids (vinblastine, vincristine) work by preventing the formation of the mitotic spindle.
What is ispinesib?
Monoclonal antibody therapy targeting spindle poles
Colchicine-like drugs:
chemotherapeutic agents which arrest mitosis in anaphase and give rise to abnormal mitotic figures where the chromosomes form a circle.
Process of meiosis summary
- interphase
- prophase 1 (crossing over)
- metaphase 1
- anaphase 1
- telophase 1
- prophase 2
- metaphase 2
- anaphase 2
- telophase 2
- cytokinesis into 4 zygote cells
Crossing over
Independent sorting of genes during prophase 1 of meiosis
Production of sperm
Primordial germ cells undergo a lot of mitosis to produce spermatogonia (precursor stem cells).
Meiotic divisions commence at puberty.
Production of eggs
Primordial germ cells undergo 30 mitoses to produce oogonia, the primitive gametes of women. Oogonia enter prophase of meoisis 1 by 8th month of intrauterine life, at which point the process is suspended. Cells enter ovulation 10-50 years later.
Meiosis 2 is only completed if fertilisation occurs.
Non-disjunction
Failure of chromosome pairs to separate in Meiosis I, or sister chromatids to separate properly in Meiosis II.
Monosomy
only one copy of chromosome
Trisomy
extra copy of chromosome