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 .