Cell Cycle & Checkpoints Lecture 1

Eukaryotic organisms Heritable information is passed to the next generation via processes that include cell cycle and mitosis or meiosis plus fertilization

Cell Reproduction Cell division (MITOSIS) process that forms new cells from one cell results in two cells that are identical to the original, parent cell.

Importance of Cell Reproduction Growth (increase in size) Repair (replace dead or damaged cells) Asexual reproduction

Cell Cycle Sequence of growth and division of a cell Growth period= Interphase Nuclear Division= mitosis

Interphase Cell grows in size Carries on metabolism Chromosomes duplicate (synthesis of DNA) Preparation for mitosis (actual division into 2 identical cells)

INTERPHASE = G1, S, G2 G2- Gap 2 Grow Produce molecules & organelles needed for cell division MITOSIS G1- Gap 1 Grow by producing proteins & organelles G0- Cell leaves cycle and stops dividing Most body cells in this phase S- Synthesis DNA replication Some can return to cycle with signal (external or internal signals) (Ex; Liver cells respond to injury) Some never divide again (Ex: Mature nerve, muscle cells)

Cyclin-dependent kinases (Cdk’s) are present all the time but inactive unless combined with cyclins Enzymes that work by adding a phosphate group to other molecules Presence of MPF (mitosis promoting factor) triggers passage past G1 & G 2 checkpoints

Cyclin levels change throughout cell cycle Fluctuating levels of different Cyclin-Cdk complexes seem to control all stages of cell cycle

Cyclin & Cyclin Dependent Kinases Conserved through evolution Genes are same across Eukaryotes