The Cell Cycle and Mitosis

What is Mitosis? Mitosis is the process by which eukaryotic cells divide. Prokaryotes divide through a simpler process called binary fission.

What is the purpose of Mitosis? When single celled organisms go through mitosis, they are reproducing: there are now two new organisms (asexual reproduction). Multicellular organisms go through mitosis to produce new cells to grow or to replace dying or damaged cells (growth and repair).

Human Development Sperm Motility Cleavage and Implantation Development of a fetus

Key terms Chromosome- structure made of highly coiled or condensed DNA. Chromatin – the uncoiled form of DNA. Sister chromatids – two identical sections (copies) of DNA joined together at the centromere. Pictures on next slide

Often confused terms 1. Single strand of chromatin (DNA’s normal structure in the nucleus) 2. Two sister chromatids joined at centromere (After replication) 3. Replicated or double stranded chromosome after condensation. Each half is still considered a sister chromatid (During the cell cycle) Gap1 SynthesisProphase 123

What is the cell cycle? All cells pass through a series of events called the cell cycle. Some cells cycle continually, other cell types only a limited number of times before they die.

Cell Cycle Only one hour out of 22 is spent in active division (Mitosis) Depending upon the type of cell undergoing the cycle.

Relationship of Stages Interphase consists of: Gap 1 (G1) Synthesis (S) Gap 2 (G2) Total time : 21 Hours Mitosis consists of: Prophase Metaphase Anaphase Telophase Total time : 1 Hour

Interphase Typical Cell spends 95% of its time in interphase Centrioles replicate during Gap 1 DNA copies itself during Synthesis Growth occurs during all three phases.

What’s the DNA doing? Chromatin in Gap 1 Replicates in Synthesis Condenses into chromosome during early mitosis (prophase).

Prophase Chromatin starts to coil into chromosomes Nucleus, Nucleolus and Nuclear membrane (N guys) start to dissolve Centrioles moving to opposite ends of cell By end, chromosomes fully formed, N guys gone, and centrioles at opposite ends of cell.

Metaphase All chromosomes line up on equator of cell Spindle fibers attach to each chromosome

Anaphase Spindle fibers contract and pull sister chromatids apart Full set of DNA eventually pulled to opposite ends of cell.

Telophase Chromosomes begin to uncoil Nuclear membrane begins to reform In plants, cell plate forms to divide cytoplasm In animals, cleavage furrow forms to divide cytoplasm