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 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 * * * 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? • http://www.hybridmedicalanimation.com/ani 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!
