The Cell Cycle!

Objectives • The reproduction of cells and organisms accounts for the continuity of life. • The work of a cell is carried out by many structures made up of a variety of molecules. • Understanding the processes and functions of related structures found in unicellular and multicellular organisms. • Illustration and explanation of how traits are passed from parent to offspring.

The Cell Cycle Cell cycle: the regular sequence of growth and division that cells undergo What happens during the cell cycle? a cell grows, prepares for division, and divides into two new cells called “daughter cells”

Three stages of the cell cycle: 1.Interphase 2. Mitosis 3. Cytokinesis

Stage One: Interphase the first stage of the cell cycle the period before cell division While in interphase, the cell grows, makes a copy of its DNA, and prepares for division into two new cells

Interphase cont.. Cell Growth first part of interphase where the cell grows to its maximum size it then produces structures it need for division new ribosomes are made new enzymes are produced copies are made of the mitochondria and chloroplasts

Interphase cont.. Copying the DNA Replication: when the cell makes an exact copy of the DNA in its nucleus After copying the DNA, the parent cell will have 2 identical sets of DNA. This is important because each daughter cell must have a complete set of DNA. If the DNA replication goes wrong, the daughter cells would not survive.

Stage Two: Mitosis What happens during mitosis? the cell’s nucleus divides into two nuclei one copy of the DNA is distributed into each of the two daughter cells There are 4 phases of mitosis: Prophase Metaphase Anaphase Telophase

Phase 1: Prophase Chromatin in the nucleus condenses into chromosomes Chromatin is threadlike and condenses into double-rod shaped chromosomes Each chromosome has two rods. Each rod has an exact copy of DNA as the other. Individual rods of the chromosomes are called chromatids. The two chromatids are held together by a centromere to make the chromosome.

Two pairs of centrioles move to opposite side of the nucleus. Spindle fibers form a bridge between the pairs of centrioles. During prophase, the nuclear envelope breaks down.

PROPHASE

Phase 2: Metaphase chromosomes attach to a spindle fiber (microtubule) at the centromere attached chromosomes line up across the center of the cell

Phase 3: Anaphase Centromeres split The two sister chromatids separate. Once separated, the chromatids move to opposite ends of the cell. The cell stretches outward as the ends are pushed out.

Phase 4: Telophase Chromosomes start to stretch and look more like chromatin again. A new nuclear envelope forms around each set of chromosomes

Stage 3: Cytokinesis Final stage of the cell cycle What happens during cytokinesis? the cytoplasm divides organelles are distributed into each new cell At the end of cytokinesis, two daughter cells have been made and each contain the same number of chromosomes as the parent cell. Each cell then enters interphase and the cycle starts over.

Cell Division Gone Wrong What happens when cell division goes wrong? apoptosis (cell suicide) cancer (uncontrolled cell growth)