Why do Cells Divide? • For repair of cells in case of an injury • Growth and development • Produce Reproductivecells
Chromosome & DNA Chromosomes are wrapped up DNA
Structure of a chromosome Chromatids Centromere Gene – segment of DNA that codes for a specific Protein Chromosomes– Wrapped up DNA Chromatids – two exact copies of DNA Centromere- Center point of the chromosome attaching the two chromatids.
Karyotypes Two Types of Chromosomes • Autosomal Chromosomes • Rest of the cells that do not determine the sex • Sex Chromosomes • Determines male or female • XX = female • XY = male
Karyotype Video • Click Here! Karyotype Project
Cell Cycle • Basically represent the “life of a Eukaryotic cell”
Cell Cycle Includes… • Interphase (“inter-” between) • G1 - First Growth Phase (46 strands of DNA) • Carries out normal functions • Becomes less efficient as it gets bigger • S - DNA Synthesis Phase (92 strands of DNA) • DNA is copied to make an exact duplicate • G2 - Second Growth Phase (92 strands of DNA • Continual Cell Growth • Mitosis (Occurs in every cell except sex cells) • Stages where a cell divides • Cytokinesis • Splitting of the Cytoplasm & Cell Membrane
Cell Cycle Animation Click Here!
Cell Cycle “Check Points” • “Check Points” – make a decision on whether conditions are favorable to move on to the next stage.
Problems with Checkpoints can lead to cancer. Cancer is uncontrolled growth of abnormal cells.
Helpful Terminology Diploid (2N) • Both DNA strands from mom and dad Haploid (1N) • Half the DNA strands of a normal cell • Mixture of mom and dad’s DNA
Mitosis Meiosis • Occurs in normal cells • Produces genetically identical cells • Starts with a Diploid cell and producesDiploid cells • Starts with one cell and produces two cells • Occurs in Sex Cells (or reproductive) • Produces genetically different cells called gametes (Sperm or Eggs) • Starts with a Diploid cell and producesHaploid cells • Starts with one cell and produces four cells Mitosis v. Meiosis
Meiosis (Not Mitosis) • We all started our life out as a zygote (2N) • After that we developed by undergoing mitotic divisions
MitosisHow a cell divides Biology Mr. Gorby
IPMATIIPee Monday And Thursday IPee Monday And Thursday Interphasebetween replicationphase(“Inter-” means between) Phases of Mitosis • Prophase • Metaphase • Anaphase • Telophase
ProphaseWhat Happens? • DNA coils & condenses into chromosomes • Centromeres show up • Nuclear Membrane Disappears • Microtubles, called spindle fibers, (Little fingers) extend out from the centrioles and attach to centromeres Why does the nuclear envelope have to disappear?
MetaphaseWhat happens? • Microtubles push the chromosome to the center to line the chromosomes up at the metaphase plate (in the center) Why does this happen? Click on Picture for Animation
Anaphase & TelophaseWhat happens? Anaphase • Centromeres split and chromatids are each pulled to either side of the cell Telophase • Microtublesdissappear • Nuclear envelope reappears • Centromeresdissappear • DNA uncoils
CytokenesisWhat happens? • Cell splits into two daughter cells • Each cell Begins Interphase over again What does the term “daughter cells” mean?
Remembering Where Mitosis Takes Place “My-toe-sis” • Mitosis occurs in all cells except “sex cells” • Purpose = growth and repair • A cell division called meiosis occurs in Sex Cells • Purpose = Reproduction of organism