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Chromosome structure


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Chromosome structure

  1. 1. Chromosome Structure Miss Pollack Please take out your classwork notebook.
  2. 2. Where is DNA found in the eukaryotic cell? • Nucleus – In the nucleus, DNA is coiled into very compact structures called chromosomes • Chromosomes are rod-shaped structures made of DNA and proteins – Each chromosome is a gigantic single DNA molecule wrapped around proteins called histones • Histones help to keep the shape of the chromosome and allow tight packing of DNA
  3. 3. A Single Chromosome • A chromosome has 2 identical halves – Each half is called a chromatid – Chromatids form as the DNA makes a copy of itself before cell division ; when the cell divides each of the 2 new cells gets one chromatid from each chromosome • 2 chromatids of 1 chromosome are attached at the centromere • When DNA is not dividing, DNA is not tightly coiled into chromosomes – Loosely packed and uncoiled as chromatin; not condensed
  4. 4. Centromere
  5. 5. Chromatin, Chromatid & Chromosome
  6. 6. We just discussed the eukaryotic chromosome… • Humans, dogs, plants, whales, worms, flowers • But, what about for prokaryotic organisms: – Prokaryote single celled organism; no nucleus; no membrane bound organelles • Have single, circular piece of DNA as their chromosome –Examples: bacteria, cyanobacteria, archaebacteria
  7. 7. Questions for Understanding • Together: Draw a chromosome – Label: • Chromatid • Centromere What is the difference between chromatin and chromatid?