THE CELL CYCLE: CELL DIVISION BY MITOSIS CH 12 In order for life to continue, cells must reproduce mx8itzrdV7I

I. Overview of cell division In unicellular organisms cell division produces new organism In multicelled organisms cell division produces new cells for growth, repair, and development from fertilized egg Most cell divisions produce identical cells Only meiosis produces egg and sperm (ch 13)

II. Organization of Cellular Genetic Material

Genome: the cell’s DNA DNA molecules are organized into chromosomes Prokaryotic genomes: single circular DNA Most eukaryotic genomes: many linear DNA strands with associated histone proteins Eukaryotic chromosomes are called chromatin that coil to fit in the nucleus

III. The Cell Cycle Consists of 2 phases: o Interphase: G1, S, G2 o Mitotic phase: mitosis and cytokinesis

A. Interphase

G1: cell grows to critical size S: DNA is replicated forming identical sister chromatids held at centromere. Centromere has a kinetochore where spindle proteins attach G2: cell prepares to divide

B. Mitotic Phase Consists of Mitosis (nuclear division) Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis (division of cytoplasm)

C. Mitotic Spindles and Mitosis

Made of microtubule protein, centrosomes(in animal cells), and aster Centrosome is microtubule organizing center and is where microtubules form Centrosome replicates and both move to opposite sides of cell Spindle microtubules from both centrosomes eventually attach to kinetochore to help move and separate chromatids

D. Role of spindles in mitosis

During prometaphase, spindle microtubules attach to kinetochore and begin to move chromosomes During metaphase, the spindle microtubules align chromosomes in center of cell During anaphase, spindle microtubules depolymerize and shorten, separating sisters During telophase genetically identical nuclei form and mitotic spindle breaks down

Cytokinesis is the division of the cytoplasm and begins during anaphase/telophase

In animal cell cleavage furrow forms pinching cell in two In plant cells cell plate forms in center building cell wall and membrane to separate cells

IV. Bacterial Cell Division Chromosome replicates and two chromosomes move apart Cell divides

IV. Control of the Cell Cycle A.Cell cycle checkpoints 1. cells will only divide when new cells are needed: contact inhibition

Uncrowded cells release growth factors that stimulate cell division crowded cells don’t divide. No growth factors produced Cancer cells don’t follow contact inhibition Always produce growth factors Overexpress growth factor receptors Have mutations that allow them to grow without growth factors

2. Cell division will proceed if identical cells will be produced – DNA must be replicated correctly – There must be enuf telomeres at the ends of the DNA – The spindles are attached to kinetochores correctly

3. There are 3 checkpoints:

4. Cyclin and cyclin dependent kinases regulate the cell cycle

Cyclin levels fluctuate during cell cycle In order for mitosis to proceed, cyclin dependent kinases must bind cyclins forming mitosis promoting factor