Cell Growth and Division Chapter 10 Chromosomes, Mitosis and Regulation

Why do cells divide? Purpose? Is it a set rate of division? What happens when rate changes?

Limitations to Cell Growth 1. Larger a cell becomes, the more demand on DNA. Why? -The larger a cell becomes, the harder it is for a cell’s DNA to keep up with the entire cell. -Compare it to a growing town… -…….Library has enough books for a small town, when it continues to grow the library can no longer keep up with the demands of the citizens.

Limitations to Cell Growth 2. Exchanging of materials. - water, food, oxygen come in the cell. - wastes leave the cell. - not always at the same rate because water, food, oxygen aren’t always used at the same rate. - Based on the relationship between the cell’s volume and surface area.

Division of the Cell -Cell Division- the process by which a cell divides into 2 daughter cells. -Parent Cell- original cell -Daughter Cells- 2 cells produced after the parent cell divides. -Before a cell divides DNA copies or replicates itself. 1 set of DNA for each daughter cell. -Cell division solves the problem of a cell getting too large

Cell Division 2 stages of Cell Division - Mitosis- Division of the cell nucleus - Cytokinesis- Division of the cell cytoplasm Before cell division can occur, chromosomes need to replicate! - chromosomes aren’t visible in cell until cell division. - at beginning of cell division the chromosomes become visible contract into dense, visible structures.

Chromosome Continued In your notebook draw and label a replicated chromosome! Be sure to label- Chromatids, centromere What relationship do we recognize the chromatids as having?

CELL DIVISION The Cell Cycle – 2 Parts Interphase Mitosis (Mitotic Phase) What parts on the diagram of cell cycle do you think make up interphase? – G1, S, G2

Interphase Period of time between cell divisions. During Interphase the cell will grow, replicate DNA and prepare for mitosis. Longest phase of the cell cycle. The three stages are….. – G1 phase- Growth – S phase- DNA replication – G2 phase- prepares for mitosis

Mitosis (Mitotic Phase) Stages of Mitosis are divided into 4 phases – Prophase – Metaphase – Anaphase – Telophase

TO DO: Cell Cycle What are the 2 phases of the cell cycle? Why do cells need to divide? What are the steps (stages) of the cell cycle?

Prophase First and longest phase of mitosis The chromosomes become visible. Chromatin condense and thicken- now called Chromosomes. The nuclear envelop begins to break down. Centrioles move to opposite “poles” or ends of the nucleus. The centrioles help to begin to form/organize the spindle Prophase PictureProphase Picture

Metaphase The mitotic spindle (organized by centriole) fully develops. The chromosomes line up at the metaphase equator ( middle) Each chromosome is connected to a spindle fiber. Metaphase Picture

Anaphase Sister chromosomes split and begin moving to opposite ends (poles) of the cell. Spindle fibers lengthen and elongate the cell. Each pole contains a full compilation of chromosomes The sister chromatids split into individual chromosomes Anaphase Picture

Telophase Chromatin begin to form at opposite poles. – Chromosomes lose their distinct shapes. The nuclear envelope and nucleolus also reappear. 2 distinct new nuclear envelops develop. Telophase Picture

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Cytokinesis The cytoplasm of the original cell’s are split in half. In plant cells a cell plate forms between the 2 new cells. In animal cells a cleavage furrow is formed.

Cell Division What does it really look like? m_mitosis.html m_mitosis.html

10.3- Regulating the Cell Cycle Not all cells move through the cell cycle at the same rate. – Most muscle and nerve cells don’t divide after creation. – Most skin, bone marrow and digestive cells regulate constantly- go through the cell cycle every 4 hours.

Controls on Cell Division Cells don’t divide when they touch other cells. Proved by scientists- grew cells in a petri dish and they only grew to cover the entire dish. When cells in the middle of the dish were removed, the section grew back so the entire dish was covered. Similar in our bodies- cut on skin, cells closest to it are stimulated and begin to grow- this is when healing begins.

Cell Cycle Regulators Cyclin- protein found in 1980’s that is only found in cells that are dividing. When cyclin is placed in a non-dividing cell the cell instantly begins the process of cell division. Internal and External Cell regulators.

Internal Cell Regulators Proteins that respond to events inside the cell Allow the cell to only proceed when certain checkpoints have been met. – Ex: when ALL chromosomes have been replicated will cell division begin. – Ex: All chromosomes must be attached to a mitotic fiber at the centromere before anaphase can begin.

External Regulators Respond to events outside the cell. Speed up or slow down the cell cycle. Growth factors are the most important cell regulators – Stimulate the growth and division of cells. – Important during embryo growth or healing. – Molecules found on the surface of other cells often stop cells from growing.

Uncontrolled Cell Growth So many cell regulators because of the severe consequences of cell growth. Main way we see uncontrolled cell growth is through Cancer. Cancer- when certain body cells lose the ability to control growth. Cancer cells DO NOT respond to the signals that regulate the growth of most cells. Result of growth cells form tumors and tumor damage surrounding tissue. Severe consequences.

Cancer Causes- – Smoking tobacco – Radiation exposure – Viral Infections An extremely high amount of cancer cells contain a defect in gene p 53. p 53 normally halts cells division until all chromosomes have replicated. Defect in p53 gene does not allow cells to respond to signals that control their growth.

Cancer types See Handout Begin discussion on Cancer photostory. Serious issue, expect it to be taken as such!