Cell Cycle: Interphase & Cell Division Stages

Interphase

G₀ — the cell performs normal metabolism, and it stays in this phase until it receives the right signals that stimulate it to re-enter and go through the cell cycle

G₁ — the cell continues to grow and perform normal metabolic functions, while some organelles are replicated

S — “Synthesis”, or DNA replication in the cell’s nucleus occurs; DNA is doubled (sister chromatids are produced)

G₂ — the cell undergoes its final growth and makes final preparations for mitosis or meiosis, such as duplicating the last necessary organelles

Mitosis

Prophase — Chromatin coils down into chromosomes; nuclear membrane disintegrates; spindle fibers form and attach to chromosomes at their centromeres

Metaphase — spindle fibers push and pull the chromosomes until they are lined up at the equator of the cell

Anaphase — the spindle fibers shorten, pulling apart the sister chromatids to opposite sides of the cell

Telophase — the sister chromatids start to uncoil, and a new nuclear envelope forms around them, and the cell prepares for cytokinesis

Mitosis: Cytokinesis

In animal cells, the cell membrane pinches in to create two new cells in something called a cleavage furrow is formed and extended, which completely separates the two cells

In plant cells, vesicles containing cellulose from the Golgi apparatus continuously fuse in the middle of the “two cells” in what is called a cell plate until they eventually become a part of the cell wall and the two cells separate

Meiosis I & II

Prophase I — chromatin coils down into chromosomes, and synapsis occurs where each chromosome pairs up to form a homologous pair to form a tetrad (four chromatids); the chromosomes undergo crossing over (segments of alleles are exchanged between the homologous pairs); spindle fibers form and attach to the homologous chromosomes at their centromeres

Metaphase I — the homologous chromosomes are pushed or pulled by the spindle fibers so they line up randomly at the middle of the cell

Anaphase I — the spindle fibers separate the homologous chromosomes in each tetrad to opposite poles of the cell

Telophase I — the cell now has one chromosome from each homologous pair at its opposite poles; spindle fibers disappear; nuclear membrane reforms around the chromosomes; cytokinesis occurs

Meiosis II is the same thing, it is just that crossing over and synapsis do not occur, and instead sister chromatids are pulled apart to opposite poles instead of a whole chromosome

Prophase II —

Metaphase II —

Anaphase II —

Telophase II —