Cell Cycle, Mitosis, Meiosis and Cancer Flashcards
Cell Division
Occurs by mitosis (somatic or body cells) and meiosis (germ or sex cells)
Eukaryotes
Any cell or organism that has a nucleus. The cell has a nuclear membrane that surrounds the nucleus, where the chromosomes are located.
Prokaryotes
Organisms whose cells lack a nucleus and other organelles
G1 phase (Gap 1)
Growth, cellular metabolism
S phase (Synthesis)
DNA replication (chromosome duplication)
G2 phase (Gap 2)
Preparation for mitosis
M phase (mitosis)
Chromosomal separation and cytokinesis
Interphase
Time between successive mitoses (G1 + S + G2)
The Human Karyotype
Ploidy
The number of complete sets of chromosomes in a cell is known as its ploidy.
Haploid (n)
A cell with one complete set of chromosomes
E.g. Sperm cell or an egg cell
Diploid (2n)
A cell with two complete sets of chromosomes: one from the mother & one from the father
E.g. A somatic cell, leaf cell, skin cell
Prophase
1st stage of Mitosis
Chromosomes condense.
Centrosomes radiate microtubules and migrate to opposite poles
Prometaphase
2nd stage of Mitosis
Microtubules of the mitotic spindle attach to chromosomes
Metaphase
3rd stage of Mitosis
Chromosomes align in center of cell.
Anaphase
4th stage of Mitosis
Sister chromatids (which become individual chromosomes when the centromere splits) separate and travel to opposite poles
Telophase
5th stage of Mitosis
Nuclear envelope re-forms and chromosomes decondense
Cell Cycle Checkpoints
Cells have many cell-cycle checkpoints, where they can pause the cell cycle if something is not right, before progressing to the next stage
DNA damage checkpoint
Checks for damaged DNA before the cell enters S phase
DNA replication checkpoint
Checks for any unreplicated DNA at the end of G2 before the cell enters mitosis
Spindle assembly checkpoint
Checks for all chromosomes being attached to the spindle before the cell progresses with mitosis
Cancer
Develops when the normal controls on cell division break down
Oncogene
Cancer-causing gene
Proto-oncogene
Normal genes are important for promoting cell division that have the potential to become cancerous if mutated
Tumor suppressors
Genes that encode proteins whose normal activities inhibit cell division (e.g. p53)
Prophase I
1st stage of Meiosis I
Starting cell is diploid (2n=4)
Homologous chromosomes pair up and exchange fragments (crossing over)
Metaphase I
2nd stage of Meiosis I
Homologous pairs line up in the center of the cell, with bivalents oriented randomly with respect to each other
Anaphase I
3rd stage of Meiosis I
Homologues separate to opposite ends of the cells, and sister chromatids stay together
Telophase I
4th stage of Meiosis I
Newly forming cells are haploid (n=2)
Meiosis II
Cells move from meiosis I to meiosis II without copying their DNA. Mitosis for haploid cells.
Prophase II
The nuclear envelope breaks down and the chromosomes condense.
Metaphase II
Chromosomes align in the center of the cell
Anaphase II
The sister chromatids separate and are pulled toward opposite poles of the cell
Telophase II and cytokinesis
The nuclear envelope reforms and the cytoplasm divides
Prometaphase II
Spindles attach to kinetochores on chromosomes
Prometaphase I
Spindles attach to kinetochores on chromosomes
Cancer development steps
Normal, Benign, Malignant, Metastatic cancer
Mitosis
- Body’s somatic cells
- Results in two diploid daughter cells
- Each daughter cell is genetically identical
