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Chromosomes and DNA Replication

Chromosomes and DNA Replication. Eukaryotic vs. Prokaryotic DNA. Eukaryotic DNA DNA is located in the nucleus in the form of a number of chromosomes. . Eukaryotic vs. Prokaryotic DNA. Prokaryotic DNA Lack nucleus and many of the organelles found in eukaryotes.

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Chromosomes and DNA Replication

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  1. Chromosomes and DNA Replication

  2. Eukaryotic vs. Prokaryotic DNA • Eukaryotic DNA • DNA is located in the nucleus in the form of a number of chromosomes.

  3. Eukaryotic vs. Prokaryotic DNA • Prokaryotic DNA • Lack nucleus and many of the organelles found in eukaryotes. • DNA is located in the cytoplasm. • Have a single circular DNA molecule (usually referred to as the cell's chromosome).

  4. Some Terms • Chromosome - Very long, continuous piece of DNA (a single DNA molecule), which contains many genes. • ONLY VISIBLE DURING CELL DIVISION! • Genes - Sequence of DNA that codes for a protein and thus determines a trait.

  5. Chromosome Structure • DNA molecules are surprisingly long. • The chromosome of the prokaryote E. coli, which can live in the human colon, contains 4,639,221 base pairs! • Analogy: Imagine trying to pack a 300-meter length of rope into your school backpack! • DNA must be dramatically folded and tightly packed to fit within the cell. Do not need to write this part!

  6. More Terms • Chromatin - Granular material visible within the nucleus; consists of DNA tightly coiled around proteins • The cell’s DNA exists as chromatin when it is not dividing.

  7. DNA Replication • Before a cell divides, it duplicates its DNA in a copying process called DNA Replication. • Ensures that each resulting cell will have a complete set of DNA molecules. • Result: Two identical DNA molecules (each DNA molecule has one original strand and one new strand)

  8. How DNA Replication Occurs Step 1: • Enzymes “unzip” or separate the DNA molecule into two strands. • Hydrogen bonds between the base pairs are broken and the two strands unwind.

  9. How DNA Replication Occurs Step 2: Produces two new complementary strands. • As each new strand forms, new bases are added following the rules of base pairing. • Each strand of DNA serves as a template, or model, for the new strand. • DNA Polymerase – Enzyme that joins individual nucleotides to produce a DNA molecule and also “proofreads” each new DNA strand

  10. What Varies in Our DNA • Mutations occur by changing the sequence of the nitrogen bases or the order of nucleotides. • Differences between organisms occur because the sequence of the nitrogen bases or the order of nucleotides are different.

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