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I. Cell Growth and Division A. Cell Cycle: 1. Sequence of events that occurs in a cell from mitosis to mitosis. 2. 5 parts: a) G1 phase – cell growth occurs (make new proteins + organelles). b) S phase – DNA is copied in preparation for mitosis. c) G2 phase – Organelles needed for nuclear division are made. d) Mitosis – nuclear division. e) Cytokinesis – cytoplasm divides. 3. Interphase – G1 + S + G2 phases. 1 4. Figure 10-4 page 245 2 B. Mitosis 1. Chromosome structure: 3 2. Done to produce more cells (growth and replacement). 3. Occurs in somatic cells (body cells) not sex cells (gametes) 4. 4 steps: a)Prophase: 1)Nuclear membrane + nucleolus disappear. 2)Chromosomes condense + become visible. 3)Centrioles form + move to poles. 4)Spindle fibers first appear. 4 b)Metaphase: 1)Spindle fibers attach to centromere (center of chromosome). 2)Chromosomes line up at the equator. c)Anaphase: 1)Sister chromatids spilt. 2)Chromosomes (now w/ only 1 chromatid) move to opposite poles. d)Telophase: 1)Nuclear membrane + nucleolus reappear. 2)Chromosomes spread out + become invisible. 3)Spindle fibers disappear. 5 5. Figure 10-5 page 246-47 6 C. Cytokinesis – division of the cytoplasm. 1. After mitosis, one cell with two nuclei. 2. Animals – cytoplasm pinches in (cleavage furrow) 3. Plants – cell plate forms in the center and works towards the cell wall. a)Figure 10-6 page 248 7 D. Uncontrolled cell growth 1. Cancer – uncontrolled cell growth (tumor). 2. Causes: a)Smoking/chewing tobacco b)Radiation exposure (X-rays, tanning beds, etc.) c)Viruses d)Other (chemicals, defective genes, etc.) 8 II. Production of Sex Cells A. Meiosis 1. Nuclear division that reduces the number of chromosomes by half. 2. Production of gametes (sex cells: sperm + eggs) 3. Homologous chromosomes – pairs of the same chromosomes a) Humans – 46 chromosomes (23 pairs) b) Diploid – both homologs are present (2N) c) Haploid – only 1 chromosome of each homolog pair is present. (1N) 9 4. 2 parts: a)Meiosis I b)Meiosis II B. Meiosis I 1. Prophase I: 2N a)Chromosomes become visible. b)Nuclear membrane + nucleolus disappear. c)Spindle fibers appear. d)Synapsis (pairing of homologs) occurs. 1)Forms a tetrad (4 chromatids = 2 chromosomes). e)DNA may be exchanged between tetrad (crossing over) = genetic variety 10 2. Metaphase I: 2N a)Tetrads move to equator by the spindle fibers. 3. Anaphase I: 2N -> 1N a)Tetrad splits, however each chromosome still has two chromatids. 4. Telophase I: 1N a)Cytoplasm divides. b)Nuclear membrane + nucleolus reappear. c)Spindle fibers disappear. d)Now have two cells. 11 C. Meiosis II (1N) 1. Prophase II: a)New spindle fibers form. b)Nuclear membrane + nucleolus disappear. 2. Metaphase II: a)Chromosomes move to equator by spindle fibers. 3. Anaphase II: a)Sister chromatids are split with each chromatid moving to opposite poles. 4. Telophase II: a)Same as Telophase I. b)Have 4 cells now. 12 Figure 11-15 page 276 – 77 Meiosis I 13 • Meiosis II 14 Summary:15 Mitosis: Meiosis: Start 1 cell, 2N 1 cell, 2N End 2 cells, 2N 4 cells, 1N D. Human gamete Production 1. Males = 4 (1N) sperm cells from Meiosis. a)Starts at puberty 2. Females = 1 egg (1N) + 3 polar bodies (garbage). a)Starts in the womb but not completed until ovulation. 15 Figure 11-7, page 278 16 III. Deoxyribonucleic acid, DNA – double helix molecule that carries hereditary information for genes. A. Structure: 1. Composed of 3 parts: a) Deoxyribose (sugar) b) Phosphate group c) Nitrogen base 2. Double helix shape a) Discovered by James Watson and Francis Crick. b) Twisted ladder shape. 17 c)Figure 12-7 page 294 3. Four Nitrogen Bases a)Adenine (A) Purine b)Guanine (G) “ c)Thymine (T) Pyrimidine d)Cytosine (C) “ 18 4. Bonding patterns: a) G ≡ C (3 bonds) b) A = T (2 bonds) B. Replication – process of copying a DNA molecule. 1. Needed for mitosis (S phase) IV. Ribonucleic acid, RNA – single strand nucleic acid used for protein synthesis. A. Different from DNA: 1. Single stranded 2. Ribose not Deoxyribose 3. Uracil instead of Thymine (A = U) 19 B. Types: 1. Messenger RNA (mRNA) – carries message from DNA to make proteins. 2. Transfer RNA (tRNA) – brings amino acids to ribosome to make proteins. 3. Ribosomal RNA (rRNA) – makes up the ribosomes. 4. Figure 12-12 page 300 20 C. Transcription – process of making RNA from DNA. 1. DNA all types of RNA 2. Ex: 21 V. Protein synthesis – formation of proteins using genetic code from DNA and carried out by RNA. A. Translation – process of forming proteins from mRNA. 1. mRNA leaves nucleus (nuclear pores) and goes to ribosomes. 2. mRNA is grouped into 3 consecutive bases called codons. a) Each codon corresponds with a certain amino acid. 22 b)Figure 12-17 page 303 23 3. DNA – transcription – mRNA – translation – proteins 4. tRNA has a compliment (opposite) base sequence to the codon called anticodon. a)The amino acid that corresponds with the codon is attached to the tRNA. 24 5. Figure 12-18 page 304 25 VI. Mutations – spontaneous changes in a gene or chromosome. A. Many types 1. Single Base switch: a) Ex: Normal Mutation DNA: ATG CGA GTG CGA RNA: UAC GCU CAC GCU AA : Tyrosine Histidine - Arginine - Arginine 26 2. Single Base a)Ex: Normal DNA: ATG CGA T RNA: UAC GCU A AA : Tyrosine - Arginine Deletion: Mutation AGC GAT UCG CUA Serine - Leucine 3. Environmental factors may cause, but not always. 4. Not passed to offspring unless occurs in gametes (sex cells) 27