Cell Division

Why do we grow? Do our cells get bigger? NO: organisms grow because they produce more cells, not larger ones. A baby’s cells are the same size as an adult’s, there are just less of them. NO: organisms grow because they produce more cells, not larger ones. A baby’s cells are the same size as an adult’s, there are just less of them.

Cell division Before a cell grows too large, it divides into two “daughter cells.” Before it divides, it must copy its genetic material so that both new daughter cells have a complete set of DNA. Before a cell grows too large, it divides into two “daughter cells.” Before it divides, it must copy its genetic material so that both new daughter cells have a complete set of DNA.

Chromosomes: coiled up DNA Located in the nucleus Become visible ONLY during cell division Organisms have different numbers of them: humans have 46. Located in the nucleus Become visible ONLY during cell division Organisms have different numbers of them: humans have 46.

The cell cycle: Interphase: G1 phase: cell growth Cells increase in size, make new proteins & organelles S phase: DNA replication Chromosomes are copied, new DNA molecules made G2 phase: preparation for mitosis Shortest phase, organelles &molecules needed for mitosis are made M phase (MITOSIS): division of the nucleus and cytoplasm into two daughter cells Interphase: G1 phase: cell growth Cells increase in size, make new proteins & organelles S phase: DNA replication Chromosomes are copied, new DNA molecules made G2 phase: preparation for mitosis Shortest phase, organelles &molecules needed for mitosis are made M phase (MITOSIS): division of the nucleus and cytoplasm into two daughter cells

Mitosis phases: PMAT

Prophase First/longest phase (50- 60% of total time to do mitosis) Chromosomes become visible Centrioles separate and position at opposite ends of the cell Spindle fibers form Chromosomes attach to the spindle fibers Nuclear envelope breaks down

Metaphase Lasts only minutes Chromosomes line up in the center of the cell Lasts only minutes Chromosomes line up in the center of the cell

Anaphase Copied chromosomes separate and begin to move toward opposite ends of the cell

Telophase Chromosomes disperse --become a tangle of material rather than distinct chromatids Nuclear envelopes begin to form around each clump of chromosomes Spindles break apart Chromosomes disperse --become a tangle of material rather than distinct chromatids Nuclear envelopes begin to form around each clump of chromosomes Spindles break apart

Cytokinesis (very end of Telophase) Cytoplasm divides In animals the cell membrane pinches in In plants a new cell wall forms Cytoplasm divides In animals the cell membrane pinches in In plants a new cell wall forms

Mitosis Poster Copy figure 10-5 on pages in your book onto a large poster paper Draw each stage//copy what is happening to the cell at each stage Must use color Copy figure 10-5 on pages in your book onto a large poster paper Draw each stage//copy what is happening to the cell at each stage Must use color