Transcript chromosome
Between cell divisions DNA is not tightly coiled into chromosomes-called chromatin Regions uncoil to be read to direct cell’s activities Prokaryotes have only 1 chromosome attached to the inside of the cell membrane, still compact to fit in cell but in a loop When a eukaryotic cell prepares to divide, the DNA and the proteins associated with the DNA coil into a structure called a chromosome Histones-aid in tight packing of DNA and help maintain the shape of the chromosome Nonhistone proteins are involved in controlling the activity of specific regions of the DNA The 2 exact copies of DNA that make up each chromosome are called chromatids The 2 chromatids of a chromosome are attached at the centromere The chromatids separate during cell division and are placed into each new cell Each new cell will have the same genetic information as the original cell Each species has a characteristic number of chromosomes Sex chromosomes determine the sex of an individual –XY Autosomes are all other chromosomes Chromosomes come in pairs – one member from each parent Chromosome pairs carry genes for the same traits Chromosome number (n) tells how many of each type of chromosome is present in a cell; 2n is diploid Sperm and egg cells are haploid (1n)-have only ½ the number of chromosomes of diploid cellswhy? Karyotype-a picture of the condensed chromosomes of an individual Cell Division Three reasons why cells reproduce by asexual reproduction: 1. Growth 2. Repair 3. Replacement You make about 2 trillion new cells per day! • Mitosis-eukaryotic nuclear divisionleads to the equal distribution of DNA to 2 new nuclei of daughter cells • Prokaryotic cells reproduce asexually (only 1 parent) by an entirely different mechanism called binary fission G1 (Growth 1) –cell carries out routine functions S (Synthesis) - DNA copied, each chromosome is 2 chromatids attached at the centromere G2 (Growth 2) - cell prepares for division, microtubules rearranged Mitosis – nucleus divided into 2 nuclei Cytokinesis – cytoplasm divides G0 phase-cell does not copy DNA or prepare to divide Interphase Prophase Metaphase Anaphase Telophase & Cytokinesis • • Chromosome # doubles Chromosomes appear as threadlike coils (chromatin) Animal Cell Plant Cell Mitosis (cell begins to divide)DNA tightens into chromosomes, nuclear membrane breaks down and disappears • Centrosomes-dark spots that appear next to the nucleus and begin to move to opposite end of the cell-if an animal-then has a pair of centrioles • Spindle fibers made of microtubules, form between the poles-mitotic spindle-to equally divide the chromatids • Kinetochore fibers-attach to centromeres-extend to the centrosomes Polar fibers-extend across cell from pole to pole, do not attach to chromosomes Animal Cell Plant Cell Kinetochore fibers move chromosomes to the center of the cell Animal Cell Plant Cell Chromatids separate and begin to move to opposite ends of the cell. Animal Cell Plant Cell Two new nuclei form • Chromosomes appear as chromatin (threads rather than rods) • Mitosis ends • Animal Cell Plant Cell Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes Interphase Prophase Metaphase Anaphase Telophase Interphase Interphase Prophase Metaphase Anaphase Telophase Interphase