Cell Division pp.154-159

Chromosomal DNA molecules Figure 12.5-3 Chromosomal DNA molecules Chromosomes 1 Centromere Chromosome arm Chromosome duplication (including DNA replication) and condensation 2 Sister chromatids Figure 12.5 Chromosome duplication and distribution during cell division. Separation of sister chromatids into two chromosomes 3

Purpose Process in which cells produce more offspring (cells) Cell division occurs to replace cells or for growth of an organism

Prokaryotic Cell Division Prokaryotes only have one circular piece of DNA attached the to the inner part of the cell membrane DNA is copied and the cell grows until almost twice its size The cell membrane pushes in and the cell wall forms

Eukaryotic Cell Division Growth, development, repair, asexual reproduction Sexual reproduction to make sex cells

Cell Cycle Repeating set of events divided into three major phases Interphase: time between cell divisions - G1 phase: cell growth - S phase: copying of DNA - G1 phase: more growth and preparation for cell division

M phase (mitosis): division of the nucleus

Cytokinesis: division of the cytoplasm Animal cells: the cytoplasm pinches and forms a cleavage furrow Plant cells: cell plate forms between the cells and becomes the cell wall

Control of Cell Division Proteins at three checkpoints control the cell cycle G1 checkpoint: only passes the checkpoint if the cell has grown to the correct size - Some cells cells stop here (EX. Brain cells) G2 checkpoint: DNA synthesis and accuracy checkpoint M (mitosis) Checkpoint: cells can stop here if errors occur in the nucleus