1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 3 Cell Structures and Their Functions Dividing Cells

2. Information Transfer from DNA to RNA DNA triplets are transcribed into mRNA codons by RNA polymerase mRNA Codons base pair with tRNA anticodons at the ribosomes Amino acids are peptide bonded at the ribosomes to form polypeptide chains Start and stop codons are used in initiating and ending translation

3. Cell Division: The Cell’s Life Cycle

4. 2 Types of Cell Division Mitosis produces new cells for growth and tissue repair Meiosis produces gametes (sex cells) –Sperm cells in males –Oocytes (egg cells) in females

5. Cell Division: DNA Chromosomes –Somatic cells have a diploid # of chromosomes –Gametes have a haploid # –In humans, diploid #: 46 (23 pairs) and haploid #: 23 22 pairs of autosomal chromosomes 1 pair of sex chromosomes –Females XX –Males XY DNA replicates during interphase, the time between cell division

6. Replication of DNA 1.strands of DNA separate from each other 2.Each old strand (dark purple) functions as a template on which a new, complementary strand (light purple) is formed. Base-pairing relationship between n’tides determines sequence of n’tides in newly formed strands 3.2 identical DNA molecules are produced Fig. 3.26

7. Replication of a Chromosome 1.DNA of a chromosome is dispersed as chromatin 2.DNA unwinds and each strand of molecule is replicated 3.During mitosis, chromatin from each replicated DNA strand condenses to form a chromatid. Chromatids are joined at centromere to form a single chromosome 4.Chromatids separate to form 2 new, identical chromosomes. They’ll unwind to form chromatin in the nuclei of the 2 daughter cells Fig. 3.26

12. Mitosis and Cytokinesis Fig. 3.28

13. Interphase Fig. 3.28 1.Interphase = time between cell divisions. DNA is thin threads of chromatin (in nucleus). DNA replication occurs. Organelles, other than the nucleus, duplicate during interphase

14. Prophase Fig. 3.28 2.In prophase, chromatin condenses into chromosomes. Centrioles move to opposite ends of cell, and nucleolus and nuclear envelope disappear. Microtubules form near centrioles and project in all directions. Spindle fibers project toward an invisible line called the equator and overlap with fibers from opposite centrioles.

15. Metaphase Fig. 3.28 3.In metaphase, chromosomes align in center of cell in association with spindle fibers. Some spindle fibers are attached to kinetochores in centromere of each chromosome

16. Anaphase Fig. 3.28 4.In anaphase, chromatids separate, and each chromatid is then referred to as a chromosome. Thus, chromosome number is double, and there are 2 identical sets of chromosomes. The chromosomes, assisted by spindle fibers, move toward centrioles at each end of cell. Separation of chromatids signals beginning of anaphase, and, by the time anaphase has ended, chromosomes have reached the poles

17. Telophase and Cytokinesis Fig. 3.28 5.In telophase, migration of each set of chromosomes is complete. Chromosomes unravel to become less distinct chromatin threads. The nuclear envelope forms from endoplasmic reticulum. Nucleoli form, and cytokinesis continues to form 2 cells

18. Mitosis Fig. 3.28 6.Mitosis is complete, a new interphase begins. The chromosomes have unraveled to become chromatin. Cell division has produced 2 daughter cells, each with DNA that is identical to DNA of parent cell

19. Mitosis and Cytokinesis Fig. 3.28 1.Interphase is the time between cell divisions. DNA is found as thin threads of chromatin in the nucleus. DNA replication occurs during interphase. Organelles, other than the nucleus, duplicate during interphase 2.In prophase, the chromatin condenses into chromosomes. The centrioles move to the opposite ends of the cell, and the nucleolus and the nuclear envelope disappear. Microtubules form near the centrioles and project in all directions. Spindle fibers, project toward an invisible line called the equator and overlap with fibers from opposite centrioles. 3.In metaphase, the chromosomes align in the center of the cell in association with the spindle fibers. Some spindle fibers are attached to kinetochores in the centromere of each chromosome 4.In anaphase, the chromatids separate, and each chromatid is then referred to as a chromosome. Thus, the chromosome number is double, and there are two identical sets of chromosomes. The chromosomes, assisted by the spindle fibers, move toward the centrioles at each end of the cell. Separation of the chromatids signals the beginning of anaphase, and, by the time anaphase has ended, the chromosomes have reached the poles 5.In telophase, migration of each set of chromosomes is complete. The chromosomes unravel to become less distinct chromatin threads. The nuclear envelope forms from the endoplasmic reticulum. The nucleoli form, and cytokinesis continues to form two cells 6.Mitosis is complete, and a new interphase begins. The chromosomes have unraveled to become chromatin. Cell division has produced two daughter cells, each with DNA that is identical to the DNA of the parent cell

21. Lastly...Cell Differentiation Process by which cells develop specialized structures and functions All cells in an individual’s body contain same amount and type of DNA because they resulted from mitosis Differentiation results from selective activation and inactivation of segments of DNA in each different cell type