Cell Growth and Division How would you describe the process by which a multicellular organism increases its size? Why do cells stay small?

Objectives Explain the problems that growth causes for cells. Describe how cell division solves the problems of cell growth.

Limits to Cell Growth The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and wastes across the cell membrane. Two reasons why cell size is limited: If a cell were to grow without control, DNA overload would occur. Rate of material exchange is dependent on surface area http://www.youtube.com/watch?v=xuG4ZZ1GbzI

Exchanging Materials Food, oxygen and water enter the cell through the cell membrane. Waste products leave the same way. The rate at which this exchange takes place depends on surface area (the total area of its cell membrane)

Ratio of surface area to volume As the length of a cell increases, its volume increases faster than its surface area. The resulting decrease in the cell’s surface-area-to-volume ratio makes it more difficult for the cell to move needed materials in and waste products out.

Cell Division Before a cell becomes too large, it divides into two daughter cells by a process called cell division.

What are Chromosomes? Chromosomes are made up of DNA DNA carries the cell’s genetic code The cells of every organism have a specific number of chromosomes.

Uncoiled DNA

DNA Coils into Chromosomes

The structure of a chromosome Chromatin Chromatid Centromere Chromosomes are not visible in most cells except during cell division. At the beginning of cell division the chromosomes condense into compact, visible structures that can be seen under a light microscope.

The Chromosome Chromosome: “X” shaped cell structure that directs cell activities and passes on traits to new cells. Each identical strand of the chromosome is called a chromatid. The strands are held together by a structure called the centromere. Chromatin: Loosely coiled DNA

Parts of a Chromosome

The Cell Cycle M Phase Interphase Prophase Metaphase Anaphase G1 Phase: Cell Growth S Phase: DNA Replication G2 Phase: Preparation for Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis M Phase

I Promised My Aunt Tina Chocolate The Phases Interphase Prophase Metaphase Anaphase Telophase Cytokinesis I Promised My Aunt Tina Chocolate

Links http://www.cellsalive.com/mitosis.htm http://www.cellsalive.com/cell_cycle.htm

Interphase: G1 Cell Grows Synthesis of proteins and new organelles

S-Phase Chromosomes are duplicated and the synthesis of DNA molecules takes place.

G2 Phase Many of the organelles and molecules required for cell division are produced. The cell is then ready to enter M-Phase to begin the process of Cell division

Prophase The chromatin condense into chromosomes. The centrioles separate and a spindle begins to form. The nuclear membrane breaks down.

Metaphase The chromosomes line up along the middle of the cell. “M”eet in the “M”iddle! Each chromosome is connected to a spindle fiber at its centromere.

Anaphase Anaphase pulled Apart The sister chromatids separate into individual chromosomes and move apart. Anaphase pulled Apart

Telophase Two new Nuclei The chromosomes gather at opposite ends of the cell and lose their distinct shapes. Two new nuclear membranes form Two new Nuclei

Cytokinesis The cell membrane pinches the cytoplasm in half. Each daughter cell has an identical set of duplicate chromosomes.

Plant Cells Plant cells have a cell plate that forms between the two cells. The cell wall is too rigid to be pinched apart.

Length of the Cell Cycle of a Human Liver Cell Interphase: 21 hours Growth : 9 hours DNA Replication: 10 hours Preparation for Division: 2 hours Mitosis: 1 hour Prophase Metaphase Anaphase Telophase

Uncontrolled Cell Growth Cancer- a disorder in which some of the body’s own cells lose the ability to control growth. Disease of the cell cycle

Summary Video