NOTES: 10.1 – 10.2 Cell Growth and Division

centriole spindle prophase metaphase anaphase telophase cytokinesis  How big do you think the largest cell is? • Yolk of ostrich egg ~8 cm in diameter • Average cell size range from 2-200µm in diameter  Why aren’t there more large cells like the ostrich’s?  On average, the cells of an adult animal are the same size as those of a young animal  So what’s the difference between a young animal and adult animal? • The difference is that there are a lot MORE cells in an adult animal!  Diffusion  DNA  Surface Area-to- Volume Ratio

Why do you think these factors would influence cell size?  Remember…the cell membrane allows for nutrients and gases to diffuse into and out of cell  Diffusion is fast and efficient but only over short distances • As distance increases, diffusion becomes slow and inefficient As a cell grows in size, more demands are placed on the cell’s DNA

● It takes time to make proteins that play a critical role in cell function

● Ex: a small town library has enough books for people to borrow but if a lot of people move into the town, some people may have to wait for popular books; DNA is like a “genetic library”  As a cell increases in size, volume increases much faster than S.A.  In other words….if a cell size were to double in size, there would be 8 times more waste to get rid of!

 A cell can’t get rid of wastes that quickly…it would poison itself!

 The lower the SA:Volume ratio, the harder it is to get materials into/out of the cell

1. Interphase: longest stage; includes preparation for cell division 2. Mitosis: nucleus divides into 2 nuclei, each with the same # and kind of chromosomes (DNA) as the parent cell 3. Cytokinesis: cytoplasm divides forming 2 distinct cells  Interphase: quite long… • most of the cell’s time spent here  Cell Division: occurs quickly  G1 phase— cells GROW, make organelles and proteins; perform their JOB(S)!...basically, they have a life!  S phase — DNA is copied (S stands for SYNTHESIS!)  G2 phase — more organelles are produced than are needed in preparation for cell division  MITOSIS = division of the NUCLEUS  it stores the DNA (information of life)  all new cells need this information!  Genetic information is passed on from one generation to the next through chromosomes  Every organism has a specific number of chromosomes ex #1: carrots = 18 chromosomes; ex #2: humans = 46  23 came from MOM & 23 came from DAD  Chromosomes are not visible in most cells except in cell division  During interphase, the DNA and protein molecules that make up chromosomes is spread throughout the nucleus being used to direct cell activities / protein synthesis (a.k.a. CHROMATIN)  At the beginning of cell division, the chromosomes condense into compact visible structures (CHROMOSOMES) • Before cell division (in the S phase of interphase), each chromosome is replicated (copied) • Each chromosome is made up of 2 identical “sister” chromatids held together by a centromere CHROMOSOME

centromere

chromatin

DNA

 During a cell’s life, its DNA is being used/ giving instructions to make proteins;

 Cell gets too big so the cell prepares to divide;

 DNA replicates;

 DNA condenses into visible structures (chromosomes);

 Chromosomes are now ready for division! 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

 chromatin condenses & chromosomes become visible

 centrioles separate and move to opposite sides of the nucleus; Centrioles:  spindle fibers (from centrioles) connect to chromosomes at their centromeres;

 nuclear envelope breaks down and the nucleolus disappears EARLY PROPHASE LATE PROPHASE  **chromosomes line up in the center of the cell;

**fibers connect from the poles (end) of the spindle to the centromere of each chromosome

 centromeres split, causing the sister chromatids to separate, becoming individual chromosomes

 individual chromosomes are pulled apart to opposite ends of the cell

 chromosomes uncoil into chromatin;

 new nuclear envelope forms around the chromatin

 spindle breaks apart

 nucleolus reappears in each new nucleus

**Often, telophase overlaps with cytokinesis.  CYTOKINESIS = division of the cytoplasm  in animal cells: cell membrane pinches in & divides  in plant cells: a cell plate (new cell wall) forms