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Ratio of Surface Area to Volume As the cell grows, its volume increases much more rapidly than the surface area. The cell might have difficulty supplying nutrients and expelling enough waste products. Transport of Substances Substances move by diffusion or by motor proteins. Diffusion over large distances is slow and inefficient. Small cells maintain more efficient transport systems. The Cell Cycle Cell division prevents the cell from becoming too large. It also is the way the cell reproduces so that you grow and heal certain injuries. Cells reproduce by a cycle of growing and dividing called the cell cycle. The Cell Cycle Interphase - the cell grows, carries out cellular functions, and replicates. Mitosis - the cell’s nucleus and nuclear material divide. Cytokinesis - a cell’s cytoplasm divides. The Cell Cycle • Interphase –G1 (Gap1) –S (DNA Synthesis) –G2 (Gap2) • Mitotic (M) Phase • Cytokinesis The Cell Cycle The Stages of Interphase 1st stage - G1 The cell is growing, carrying out normal cell functions, and preparing to replicate DNA. The Stages of Interphase 2nd Stage – S The cell copies its DNA in preparation for cell division. S phase Genetic material (chromosomes) duplicate) The Stages of Interphase 3rd Stage - G2 Cell prepares for division of nucleus (mitosis). Stages of Mitosis Prison (Prophase) Men (Metaphase) Are (Anaphase) Thin (Telophase) Prophase The cell’s chromatin tightens. Sister chromatids are attached at the centromere. Spindle fibers form in the cytoplasm. The nuclear envelope seems to disappear. Spindle fibers attach to the sister chromatids. Metaphase Sister chromatids line up in the middle of the cell. Anaphase Microtubules of the spindle apparatus begin to shorten. Sister chromatids separate. Chromosomes move toward the poles of the cell. Telophase The chromosomes arrive at the poles and begin to relax. Two new nuclear membranes begin to form and the nucleoli reappear. The spindle apparatus disassembles. Cytokinesis Process by which the cytoplasm of a cell is divided in two; usually follows mitosis and meiosis. Cytokinesis in Animal Cells Microfilaments constrict, or pinch, the cytoplasm to create a cleavage furrow Cytokinesis in Plant Cells Cell wall too rigid for microfilaments to constrict cell. Cell plate created. How Cytokinesis Differs in Plants Quality Control Checkpoints The cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong. Spindle checkpoints also have been identified in mitosis. Cancer A disease caused by severe disruption of the mechanisms that normally control the cell cycle. Causes of Cancer The changes that occur in the regulation of cell growth and division of cancer cells are due to mutations. Various environmental factors can affect the occurrence of cancer cells. Causes of cancer • • • • • • • Food Genetic mutations Hormones Radiation Tobacco Weight & physical activity Workplace environment Types of Tumors Benign: An abnormal mass of essentially normal cells. Malignant: A mass of abnormal cells resulting from uncontrolled cell division. Malignant Tumor A mass of abnormal cells resulting from uncontrolled cell division Metastasis The spread of cancer cells beyond their original site Cancerous cells reproduce at an abnormally fast rate! Cancer Treatment • • • • Surgery Radiation therapy Chemotherapy A mix of the three Abnormal Cell Cycle: Cancer Cancer is the uncontrolled growth and division of cells. Cancer cells can kill an organism by crowding out normal cells, resulting in the loss of tissue function. Stem Cells Unspecialized cells that can develop into specialized cells when under the right conditions Embryonic Stem Cells After fertilization, the resulting mass of cells divides repeatedly until there are about 100–150 cells. These cells have not become specialized. Adult Stem Cells Found in various tissues in the body and might be used to maintain and repair the same kind of tissue Less controversial because the adult stem cells can be obtained with the consent of their donor Producing offspring that are clones of the parent No Diversity with asexual reproduction Next Slide Asexual reproduction Process in which a single cell or set of cells produces offspring that inherit all their genetic material from one parent. Offspring are not diverse. Types of Asexual Reproduction 1. Binary Fission 2. Budding 3. Parthenogenesis 4. Regeneration Binary Fission A type of asexual reproduction in which a prokaryote replicates DNA, and divides in half, producing two identical daughter cells. Budding Offspring grows out of body of parent. Yeast Hydra (Unicellular fungi) (Multicellular cnidarian) Regeneration In this form, if a piece of a parent is detached, it can grow and develop into a completely new individual. Echinoderms exhibit this type of reproduction. Genetic material from two parents combines to produce offspring that are genetically different from the parents Next Slide The egg from a female & the sperm from the male combine through fertilization to form a zygote Egg and sperm are called Gametes (sex cells) Next Slide Two Methods of Reproduction Asexual – Offspring identical to the original cell or organism – Involves inheritance of all genes from one parent Sexual – Offspring similar to parents, but show variations in traits – Involves inheritance of unique sets of genes from two parents Sexual reproduction Process in which genetic material from two parents combines and produces offspring that differ genetically from either parent. Leads to diversity in offspring. Sperm, Eggs, & Fertilization Testes - male organ that produces sperm Ovaries - female organ that produces eggs. Meiosis A type of cell division that produces four cells, each with half the # of chromosomes (haploid #) as the parent cell. 23 Parent Cell 46 chromosomes 23 23 23 In meoisis, the final cells have half the number of chromosomes as the parent cell. Humans have 46 Chromosomes (23 homologous pairs) • 1 chromosome of each pair is from your mother and 1 from your dad. • 22 are alike, whether male or female (autosomes) • The 23rd chromosome is called the Sex Chromosome. It occurs as either X or Y. XY = male XX = female Karyotype A display of the chromosomes of an individual. Male Karyotype Female Karyotype Homologous Chromosomes Two chromosomes in a matching pair. Homologous Chromosomes 1. Each has the same sequence of genes. If one has gene for eye color, the other will too - at the same location. 2. However, the genes might be slightly different versions. Mitosis & Meiosis Difference Meiosis – 4 daughter cells with ½ the number (haploid number) of original chromosomes. Mitosis – 2 daughter cells with the same number of original chromosomes. Comparison of Meiosis & Mitosis Meiosis Mitosis DNA Replication 1 time 1 time Nuclear divisions 2 1 Number of daughter cells 4 2 Daughter cell chromosome number Haploid (n) Diploid (2n) Daughter cells identical to parent No Yes Meiosis increases genetic variation Crossing-over Fertilization In humans, (223)2 different zygotes – over 70.3 trillion! possible If crossover occurs only once, then (423)2 4 octillion possible combinations. (27 0’s)