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Unit – Cell Reproduction
Mitosis & The Cell Cycle Unit – Cell Reproduction Biology
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How many cells do you think your body has?
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Each of us began as a single cell,
so one important question is: How did that single cell develop into a body with more than a trillion cells?
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Thus, cell division is needed for growth.
The production of such a large number of body cells is accomplished by many, many repeats of a cycle of cell division in which one cell gives rise to two cells, each of which in turn gives rise to two cells, etc. Thus, cell division is needed for growth.
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Even in a fully grown adult, cells still undergo cell division.
Why is this useful? Think about your skin, for example.
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Cell Division The two cells that come from the division of one cell are called daughter cells. Each of the daughter cells needs to have a complete set of chromosomes.
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What are chromosomes? Chromosomes are compact spools of DNA
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Chromosomes Each half is called a chromatid
The chromosome (left in the picture) was isolated from a dividing cell. Notice that the chromosome consists of two identical halves Each half is called a chromatid
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Chromosomes The point where the two chromatids touch and are held together is called a centromere
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Review chromosome structure
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Let’s make some chromosomes
Obtain 2 white pipe cleaners and 2 of another color. Cut white pipe cleaners into 2: 4 inch long pieces 3 inch long 2 inch long 1½ inch long
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Let’s make some chromosomes
Pick two different colored beads. You will need 8 of each color Put one of the colored beads on each of the white pipe cleaners and move them to the center of the pip cleaners. Repeat by putting one of the other colored beads on each of the colored pipe cleaners
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Each species has a certain number of chromosomes in each cell.
Chromosome Numbers Each species has a certain number of chromosomes in each cell. 46 78 52 18
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Sex chromosomes Chromosomes that determine the sex of the organism In humans, sex chromosomes are either X or Y XY XX
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Autosomes All the other chromosomes in an organism
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Unsorted Human Chromosomes
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Karyotype Photomicrograph of the chromosomes in a dividing cell found in a human What is the sex of the person whose chromosomes are shown here?
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Question What percent of your genes come from your mom?
What percent of your genes come from your dad?
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Where did my chromosomes come from?
We inherit one member of each chromosome pair from each parent.
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Where did my chromosomes come from?
The 46 chromosomes in our somatic cells are actually two sets of 23 chromosomes—a maternal set (from our mother) and a paternal set (from our father.)
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Homologous chromosomes
The two copies of each chromosome They are the same size and shape and carry genes for the same traits
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Diploid Cells 46 Cells having two sets of chromosomes
All normal human cells are diploid cells (except reproductive cells – egg and sperm cells) Commonly abbreviated as 2n In humans the diploid number is 46
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Haploid Cells Human sperm cells and egg cells
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Haploid Cells Contain only 1 set of chromosomes
Haploid cells have only 1 chromosome of each homologous pair and only 1 sex chromosome Abbreviated as 1n When a sperm (1n) and egg cell (1n) combine, the new cell will be diploid (2n)
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A comparison Diploid Haploid
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Cell Division How do you think each daughter cell gets a complete set of chromosomes? In each cycle of cell division, the cell first makes a copy of all of the DNA in each of the chromosomes.
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Cell Division After the DNA in each chromosome has been copied, the cell undergoes a type of cell division called mitosis, which carefully separates the two copies of each chromosome to opposite ends of the dividing cell, so each daughter cell ends up with a complete set of chromosomes.
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What is the cell cycle? The repeating set of events that make up the life of a cell Cell division is one phase of the cell cycle
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What is the cell cycle? Interphase G1, S, G2 phase Mitosis (M phase)
Prophase Metaphase Anaphase Telophase Cytokinesis
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Interphase The time between cell divisions
Divided into 3 phases (G1, S, G2 phases)
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G1 phase Offspring cells grow to mature size
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S phase Cell’s DNA is copied
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S phase Cell’s DNA is copied
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The time to prepare for cell division
G2 phase The time to prepare for cell division
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G2 phase Centrosomes – two pairs of dark spots; it is the microtubule organizing center Centrioles - structures in the cytoplasm from which the spindle fibers form
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G0 phase Cells can exit the cell cycle and enter a state called the G0 phase Cells do not copy DNA and do not prepare for cell division
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Division of the nucleus
Mitosis Division of the nucleus
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Prophase DNA tightens and coils into chromosomes
Nuclear membrane breaks down and disappears
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Metaphase Chromosomes line up in the center of the cell
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Anaphase The chromatids of each chromosome separate at the centromere
chromatids move to opposite poles of cell
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Telophase Chromosomes return to chromatin state
A nuclear membrane forms around each set of chromosomes
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Cytokinesis The cytoplasm of the cell divides
The area of the cell membrane that pinches in and eventually separates the dividing cell into two cells is called the cleavage furrow.
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Cytokinesis
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Cytokinesis Vesicles formed by the Golgi apparatus fuse at the midline of the dividing cell, forming a membrane-bound cell wall called the cell plate.
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Plant cells in various stages of mitosis
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Cell Cycle
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Cancer cells
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Cancer cells
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Cancer cells
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Cancer cells
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