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

Information Transfer from DNA to RNA DNA triplets transcribed into mRNA codons by RNA polymerase mRNA Codons base pair with tRNA anticodons at ribosomes Amino acids are peptide bonded at ribosomes to form polypeptide chains Start and stop codons initiate and end translation

Cell Division: The Cell’s Life Cycle

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

Cell Division: DNA Chromosomes Somatic cells: diploid # of chromosomes Gametes: haploid # Humans: diploid #: 46 (23 pairs),haploid #: 23 22 pairs autosomal chromosomes 1 pair sex chromosomes Females XX Males XY DNA replicates during interphase (time between cell division)

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

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

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Mitosis and Cytokinesis Fig. 3.28

Interphase Interphase = time between cell divisions. DNA is thin threads of chromatin (in nucleus). DNA replication occurs. Organelles duplicate. Fig. 3.28

Prophase Prophase: chromatin condenses into chromosomes. Centrioles move to opposite ends of cell, nucleolus and nuclear envelope disappear. Microtubules (spindle fibers) form near centrioles, project in all directions toward equator and overlap with fibers from opposite centrioles. Fig. 3.28

Metaphase 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 Fig. 3.28

Anaphase Anaphase: chromatids separate, each chromatid is then referred to as a chromosome. Chromo # is double, 2 identical sets of chromos. Chromos (b/c microtubules) move toward centrioles at each end of cell. Separation of chromatids is @ beginning of anaphase; @ end, chromos @ poles. Fig. 3.28

Telophase and Cytokinesis Telophase: each set of chromos @ ends. Unravel to become chromatin. nuclear envelope forms from endoplasmic reticulum. Nucleoli form, and cytokinesis forms 2 cells Fig. 3.28

Mitosis Mitosis is complete, new interphase begins. The chromosomes are chromatin. 2 daughter cells, each with DNA identical to DNA of parent cell Fig. 3.28

Mitosis and Cytokinesis 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 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. 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 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 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 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 Fig. 3.28

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