Chapter 2 Cell Cycle, Mitosis, Meiosis 2.1-2.2 Flashcards
Diploid (2n)
Contain two copies of each chromosome, autosomal cells.
Haploid (n)
Contain only one copy of each chromosome, germ cells.
The cell cycle
Four stages of the cell cycle: G1, S, G2, M.
Interphase
The first three stages of the cell cycle (g1, s, g2). The longest part of the cell cycle, actively dividing cells spend about 90% of their time in interphase.
Chromatin
Less condensed form of a chromosome. Chromosomes are not visible during interphase because they are in this less condensed form because DNA must be available to RNA polymerase so that genes can be transcribed.
G1 Phase of the cell cycle
Presynthetic gap
Cells increase in size and create organelles such as mitochondria, ribosomes, and endoplasmic reticulum. This is part of the cell interphase cycle.
Side note: passage from g1 to s phase is governed by a restriction point.
S phase of the cell cycle
Synthesis of DNA
The cell replicates its genetic material so that each daughter cell will have identical copies. After replication, each chromosome consist of two identical chromatids that are bound together at a specialized region known as the centromere. Cells entering G2 have twice as much DNA as cells in G1. This is part of the cells interphase cycle.
Side note: the ploidy of the cell does not change even though the number of chromatids doubles.
G2 stage of the cell cycle
Postsynthetic gap
G2 phase is a quality control checkpoint. DNA has already been duplicated, and the cell checks to ensure that there are enough organelles and cytoplasm for two daughter cells. This is part of the cells interphase.
This checkpoint is very important because the cell makes sure that DNA replication has proceeded correctly to avoid passing on an error the daughter cells.
M stage of the cell cycle
Mitosis
Consist of mitosis and cytokinesis. Divided into four phases: prophase, metaphase, anaphase, and telophase.
Molecules responsible for the cell cycle
Cyclins and cyclin dependent kinases (cdk).
Transcription factor
Transcription factors promote transcription of genes for the next stage of the cell cycle. Phosphorylated by CDK – cyclin complex.
The main protein in control of checkpoints of the cell cycle.
P53
p53 is a tumor suppressor protein that regulates cell cycle checkpoints, while cyclins are proteins that control cell cycle progression.
Mitosis
Consist of prophase, metaphase, anaphase, telophase. Creates two identical daughter cells.
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Keywords: centrosome, centriole, spindle fibers.
Prophase
Chromosomes condense, spindles form. The nuclear membrane dissolves during prophase, allowing spindle fibers to contact the chromosomes. The nuclei become less distinct and may disappear completely.
Centrioles
barrel-shaped organelles that help organize microtubules and other cell components in animal cells.
Metaphase
The centriole pairs are now at opposite ends of the cell. Chromosomes align at the metaphase plate (equatorial plate) via kinetocore fibers interacting with the fibers of the spindle apparatus.
Anaphase
The centromeres split so that each chromatid has its own distinct centromere thus allowing the sister chromatids to separate. Chromatids are pulled towards the opposite poles of the cell by the shortening of the kinetochore fibers.
Telophase and cytokinesis
Telophase is essentially the reverse of prophase. The spindle apparatus disappears, a nuclear membrane reform around each set of chromosomes, and the nuclei reappear. The chromosomes uncoil, resuming their interphase form.
Cytokinesis is the separation of the cytoplasm giving rise to two daughter cells with enough materials to survive on their own. Each cell undergoes a finite number of divisions before programmed death. 20-50 cell divisions in humans until apoptosis occurs.
Meiosis
Occurs in gametocytes (germ cells) and results in up to four non-identical sex cells called gametes.
Meiosis I
Generates haploid daughter cells by separating homologous chromosomes. This is known as reductive division.
Crossing over between homologous chromosomes happens in meiosis I (prophase I).
2n to n
Meiosis II
Similar to mitosis, in that it results in the separation of sister chromatids without of change in ploidy. Known as equational division.
Prophase I
Similar to prophase in mitosis up to the point after homologous chromosomes come together. Genetic recombination occurs by crossing over of sister chromatids.
Metaphase I
Homologous pairs (tetrads) form up in a line at the metaphase plate in each pair attaches to a separate spindle fiber by its kinetochore.
Anaphase I
Homologous pairs separate and are pulled to opposite poles of the cell, a process called disjunction.
