Chapter 6 Chromosomes & Cell Reproduction I. Chromosomes DNA & histones (organizing proteins) A. Formation of New Cells by Cell Division • 2 Trillion cells/day or 25 million/sec • PURPOSE growth & development, repair & sex cells/gametes* • Cell Genetic Info DNA to make proteins enzymes (cell machinery) metabolism • Each new cell needs a complete set of DNA or genetic info 1. Prokaryotic Cell Reproduction (bacteria) binary fission 1 circular chromosme 2. Eukaryotic Cell Reproduction (rest of organisms) Mitosis & Cytokinesis • gene segment of DNA that codes for a protein/enzyme or RNA molecule • Chromosome long segment of DNA with 1000s of genes (2%) & 98% non-coding DNA • chromatids “condensed” chromosomes for dividing & moving (DNA has been duplicated) • centromere area that holds identical chromatids together until cell division • Fg. 2 p. 119 organization of chromosomes B. How Chromosomes Number & Structure Affect Development • Humans 46 chromosomes (23 prs) • Each chromosome contains 1000s of genes (20,000 -25,000 genes total) 1. Sets of Chromosomes • Homologous chromosomes chromosomes similar in size, location & genetic content • Diploid full set of chromosomes (½ from mother/female & ½ from dad/male) • Haploid half set of chromosomes for SEXUAL REPRODUCTION • Zygote fertilized egg with 2 haploid sets or 1 diploid set 2. Sex Chromosomes • Sex Chromosomes 23rd pair of chromosomes that contain gender determination • Autosomes 1st through 22nd pairs of chromosomes 3. Change in Chromosome Number • Down Syndrome 47 chromosomes/cell (extra 21st chromosome)(Triosomy 21) • Klinefelter’s Syndrome 47 chromosomes/cell (extra sex chromosome) (XXY) • Turner’s Syndrome 45 chromosomes/cell (missing sex chromosome) (XO) • Patua’s Syndrome 47 chromosomes/cell (extra 13th Chromosome) • Edward’s Syndrome 47 chromosomes/cell (extra 18th chromosome) • Triosomy X 47 chromosomes/cell (Extra X chromosome) • 47 XYY (extra sex chromosome) 4. Change in Chromosome Structure a. Deletion Example: Cri-du-chat Partial Deletion of Chromosome 5 b. Duplication Example: Fragile X Extra portion of the X chromosome c. Inversion may or may not cause any harm, but may lead to a chromosome mutation in offspring d. Translocation TWO chromosomes switch parts (may or may not be a problem, but may lead to a chromosome disorder) II. The Cell Cycle A. The Life of a Eukaryotic Cell • Cell division is eukaryotic cells is more complex than prokaryotic (bacteria) cells • nucleus and other organelles must be divide into TWO functioning cells 1. The Cell Cycle repeating sequence of events of cell division a. Interpahse generally 90% of cell’s life i. G1 (First Growth) phase cell growth and functioning ii. S (Synthesis) phase duplication of DNA iii. G2 (Second Growth) phase preparation for cell division b. Mitosis division of the nucleus and the chromosomes (identical number & type) c. Cytokinesis division of the cell’s cytoplasm into 2 cells after mitosis B. Control of a Eukaryotic Cell • ensures normal and appropriate growth • complex systems are in place to control cell growth 1. Three Checkpoints a. G1 (Cell Growth) Checkpoint allows cell to move on to S phase for mitosis b. G2 (DNA Synthesis) Checkpoint “repair” enzymes will check DNA before mitosis c. Mitosis Checkpoint triggers the completion of mitosis and the beginning of cytokinesis 2. When Control Is Lost: Cancer • cancer uncontrolled cell growth & division; no response to checkpoints; error in cell systems allow cells to divide uncontrollably and disrupt metabolism III. Mitosis & Cytokinesis • 2 million RBCs produced every second in bone marrow • Spindles direct movement of chromosomes to opposite sides of the cell • Centrioles (animal cells only) are the destination of the moving chromosomes in cell division A. Chromatid Separation in Mitosis 1. Forming the Spindle • pathway for chromosome movement that begin to be formed in G2 phase of cell cycle 2. Separation of Chromosome by attaching Spindle Fibers • centromeres split to allow chromatids (now chromosomes to move to opposite sides during cell division B. Mitosis & Cytokinesis 1. Mitosis 4 stages (track nucleus membrane, chromosomes, centrioles & spindle) a. Prophase nucleus breaks down & disappears, chromosomes are condensing, centrioles divide into 2 & move to opposite sides of cell, spindle begin to form b. Metaphase nucleus is completely broken down, chromosomes are fully condensed and lined-up at center of cell, centrioles are opposite sides of cell, spindles stretch from centrioles to centromeres of chromosomes c. Anaphase nucleus is still gone, centromere of chromosomes split and chromosomes begin to move to opposite sides of cell, centrioles are directing movement, spindle is the chromosomes pathway d. Telophase 2 nuclei begins to form, chromosomes are opposite sides of the cell and begin to “un-condense”, centrioles are finished directing movement of chromomes and spindle begins to break down and disappear 2. Cytokinesis other cell organelles have duplicated and are divided into the 2 new cells formed by cleavage furrow (animal cells only) or cell plate (plant & fungi cells with cell walls)