Mitosis - Cell Reproduction Adapted from: Schutzer’s BIO 102, Portland Community College, Rock Creek Campus 1

From One to Two Mitosis is the process of cell reproduction. Cell reproduction involves the physical division of a parent cell into two daughter cells. Parent cells must provide their daughter cells with hereditary information (DNA) and enough cytoplasmic machinery to start up their own operation. Mitosis is the basis for growth and tissue repair. 2

Mitosis 3

Mitosis and the Cell Cycle Cells undergo a “regular” cycle. The cycle begins at the cells “birth” and ends after division. Mitosis is only a small portion of the cycle. A large portion of the cell cycle is devoted to normal cell function as well as DNA duplication (preparation for mitosis). 4

Mitosis and the Cell Cycle G1 Cell growth prior to DNA replication S DNA duplication interphase Mitosis G2 After DNA duplication Cell prepares for division 5

Interphase Interphase involves the cells increase in size and doubling of cytoplasmic components and chromosomes.

Mitosis and Chromosomes A single chromosome is a single molecule of DNA and its associated proteins. DNA PROTEIN a single DNA molecule Chromosome: DNA + PROTEIN 8

Mitosis and Chromosomes During the cell cycle, in preparation for mitosis, chromosomes duplicate. a single duplicated chromosome

Mitosis and Chromosomes Since chromosomes are largely made of DNA, chromosomal replication involves DNA replication. The duplicated chromosome is made up of 2 sister chromatids. Each chromatid contains one DNA molecule (a double helix). Therefore, a duplicated chromosome contains 2 double helix DNA molecules. a single duplicated chromosome one chromatid its sister chromatid 10

Mitosis and Chromosomes 11

Mitosis and Chromosomes The two chromatids are joined together in a region called the centromere. This is an area which has attachment sites for microtubules. Microtubules are involved in chromosome movement. centromere 12

Mitosis and Chromosomes The number of chromosomes is species specific. humans = 46 pea plants = 14 gorillas = 48 Half of an individuals chromosomes come from the mother, the other half from the father. Genes for traits are located on chromosomes, therefore each individual has at least 2 genes for each trait. 13

Mitosis and Chromosomes Recall, a single chromosome contains a single DNA molecule (which is a double helix). Each strand of DNA, contains many different genes. Consider each chromosome as a book. You received 23 “books” (chromosomes) from your mother and 23 “books” (chromosomes) from your father. However, the maternal chromosomes (or books) may be edited differently from the paternal. 14

Mitosis and Chromosomes That is to say, both maternal and paternal chromosomes contain information for eye color, hair color, etc. However, one may say blue eyes while the other says brown. Or, one may say straight hair and the other says curly. We will examine these interactions later. 15

Mitosis and Chromosomes The “chromosome number” (n) refers to the number of types of chromosomes. Thus, humans have 46 chromosomes, but the chromosome number (n) is 23. Likewise, pea plants have 14 chromosomes, but the chromosome number (n) is 7.

Mitosis and Chromosomes Any type of cell containing both sets are called diploid (2n). Most cells in the body are diploid, or 2n. Cells that only contain the individual complement are called haploid, or n. 17

Mitosis and Chromosomes Therefore, a human diploid cell contains 46 chromosomes (or 23 pairs). While a human haploid cell contains 23 chromosomes. What kind of cell in the human body would be haploid? a sex cell (like egg and sperm).

Mitosis and Chromosomes A diploid cell that undergoes mitosis always produces two diploid cells. A diploid cell that undergoes meiosis produces haploid cells. 19

The Process of Mitosis Interphase occurs prior to mitosis. During interphase (between, among), chromosomes duplicate There are 4 stages of mitosis Prophase - earlier than, prior too Metaphase - later, or more highly organized Anaphase - of each an equal quantity Telophase - end Cytokinesis - cytoplasm division - occurs immediately after mitosis. 20

Prophase EARLIER THAN, PRIOR TO. Recall, DNA and therefore chromosomal duplication has already occurred. Thus, each chromosome consists of two sister chromatids. Chromosomes condense. Kinetochore forms at the centromere. The kinetochore is a disk-shaped structure It serves as the attachment site for the microtubules of the spindle centrioles kinetochore one chromatid 21

Prophase Spindle begins to form. Microtubules, cytoplasmic proteins, disassociate from the cytoskeleton, and reallocate as spindle fibers. The microtubules will be the “workers” of mitosis. Microtubules begin to segregate the centrioles to opposite poles of the cell. centrioles kinetochore one chromatid 22

Prophase

Transition to Metaphase AKA - PROMETAPHASE Nuclear envelope breaks down. Microtubules invade the nuclear space and interact with both kinetochores and microtubules from the opposite pole. As kinetochore attachments are occurring, the chromosomes are moved about the cell 24

LATER, OR MORE HIGHLY ORGANIZED Metaphase LATER, OR MORE HIGHLY ORGANIZED Central alignment of chromosomes along an axis that is referred to as the “equator”, as compared to the “poles” where the centrioles are located. 26

Metaphase

OF EACH AN EQUAL QUANTITY. Anaphase OF EACH AN EQUAL QUANTITY. Separation of sister chromatids of each chromosome. Once each sister chromatid is separated from its sister, it is known as an unduplicated chromosome, no longer as a chromatid. Therefore, each chromosome present in the parent cell has a daughter chromosome present at both spindle poles. 28

Anaphase

Movement of Chromosomes The microtubules are responsible for physically moving the chromosomes toward their respective poles. Microtubules are also responsible for stretching the cell. There are two mechanisms involved Kinetochore microtubules attached to the kinetochores shorten, thereby pulling chromosomes toward microtubule poles. Nonkinetochore microtubule fibers attach to one another centrally and ratchet past each other, thereby elongating and stretching the entire cell.

Movement of Chromosomes These kinetochore microtubules shorten... ...and pull the chromosomes toward each pole

Stretching the Cell These nonkinetochore microtubules ratchet against each other... ...thereby stretching the cell

Telophase END Telophase begins as the daughter chromosomes arrive at opposite spindle poles. Microtubules disassociate from the centromeres of the chromosomes. Chromosomes uncondense. Nuclear membrane reforms. 32

Cell Division and Cytoplasm A critical portion of cell division is the segregation of the cytoplasm. Cytoplasmic division is called cytokinesis. Cytokinesis occurs throughout anaphase and telophase. The process involves cleavage of the cell. Centrally located microfilaments contract the cell, causing a pinching off and eventually a complete separation. 33

Telophase & Cytokinesis

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Summary Mitosis is the process of cell division (repro.) - from one cell comes two. Mitosis divides cell hereditary information (DNA) and functional machinery (cytoplasm) into two. Mitosis is the basis for growth and tissue repair. Single chromosomes contain a single strand of DNA and assoc. proteins. Each strand of DNA has many genes coding for many traits. The cell cycle starts with the formation of a new cell and ends with that cell concluding mitosis. Part of the cell cycle, interphase involves the cells increase in size and doubling of cytoplasmic components and chromosomes. Mitosis is made up of 4 phases Prophase - condensation of chromosomes, microtubule organization Metaphase - microtubule attachment and chromosomal organization Anaphase - separation of chromosomes Telophase - chromosomal decondensation and cell separation