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Cell Division

Cell Division. During cell division, DNA in the Eukaryotic cell nucleus coils tightly into structures called chromosomes. Each chromosome is a DNA molecule associated with proteins. DNA wraps tightly around these proteins, which aid the tight packing of the DNA.

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Cell Division

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  1. Cell Division

  2. During cell division, DNA in the Eukaryotic cell nucleus coils tightly into structures called chromosomes. • Each chromosome is a DNA molecule associated with proteins. • DNA wraps tightly around these proteins, which aid the tight packing of the DNA. • Chromosomes consist of 2 identical halves, each is called a chromatid.

  3. Chromatids form as DNA copies itself before cell division. • 2 new cells each receive one of the chromatids. • The centromere holds the two chromatids together until cell division. Centromeres are important for chromosome movement. • Between cell divisions DNA is not as tightly packed, this way it can be read and can direct cell activity. This loosely packed DNA is called chromatin. • Prokaryotic cells usually only have one chromosome.

  4. Each species has a characteristic number of chromosomes. Ex: the Fruit fly has 8 • Some species have the same number of chromosomes i.e. potato, plum, and chimpanzee all have 48 • There are 2 types of chromosomes, autosomes and sex chromosomes. • Sex chromosomes determine what gender an organism is. It may also carry genes for other characteristics. Women have two X chromosomes, while the men have one X and one Y.

  5. All other chromosomes are autosomes. Humans have 44 autosomes and 2 sex chromosomes. This makes 46 total chromosomes in every human body cell.

  6. All cells produced by sexual reproduction have 2 copies of each autosome, they receive one from each parent. • The two copies are called homologous chromosomes. • They are the same size, shape, and carry out the same set of traits. • If one contains the trait for eye color, so does the other one. • Humans have 22 homologous pairs.

  7. Cells with two complete sets of chromosomes are said to be diploid. • Diploid cells have chromosomes for each homologous pair and include sex chromosomes. • All human cells except for the sperm cells and egg cells are diploid. This is abbreviated 2n.

  8. Sperm and egg cells are called haploid. • Haploid cells contain only one complete set of chromosomes, half that of diploid cells, and is abbreviated 1n. • When 1 sperm cell (1n) and 1 egg cell (1n) combine they make a diploid cell (2n) 1 1 = 2 +

  9. Cell Division

  10. In eukaryotic cells, both the cytoplasm and the nucleus divide • 2 types of cell division, Mitosis and Meiosis • Mitosis occurs in the reproduction of unicellular organisms. • Meiosis reduces the number of chromosomes in half in a new cell, which are joined together later in the cell’s life to complete the set of chromosomes during sexual reproduction.

  11. Cell Cycle • The life of a cell is split between the time of cell division, and the time in between, which is called interphase. • Interphase is divided into three phases, and cell division is divided into 2. • Cell division consists of mitosis, where the nucleus divides, and Cytokinesis, where the cytoplasm divides

  12. Interphase 1 • The 3 phases of Interphase are: • G phase where the cell grow to mature size. • S phase where DNA is copied. • And the G phase, where the cell grows big enough and prepares for cell division. • Cells can also enter G phase, where no growth occurs. Many human cells are in this stage. • Ex: Cells of a mature human central nervous system. 2 0

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