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DNA

DNA. DNA: The Genetic Material. Genes – instructions for inherited traits Genes are made of small segments of DNA DNA – primary material that causes recognizable, inheritable characteristics in related groups of organisms. DNA. DNA – D eoxyribo n ucleic A cid

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DNA

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  1. DNA

  2. DNA: The Genetic Material • Genes – instructions for inherited traits • Genes are made of small segments of DNA • DNA – primary material that causes recognizable, inheritable characteristics in related groups of organisms

  3. DNA • DNA – Deoxyribonucleic Acid • DNA is a monomer = nucleotide

  4. DNA History • Griffith – Experimented on mice and observed some harmless strains of bacteria could change into harmful strains. He called this transformation. • Avery – Discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation to the next.

  5. More DNA History • Hershey-Chase – Concluded that the genetic material in bacteria was DNA not proteins • Watson & Crick – created the double helix model for DNA.

  6. DNA History

  7. DNA History • In your notebooks, write down at least two facts about each scientist that is discussed in the video. • Title: DNA structure Video Notes

  8. Understanding DNA

  9. Structure of DNA • DNA is a long molecule made up of units called nucleotides.

  10. Structure of DNA • Each nucleotide is made up of three parts: a 5-carbon sugar called dioxyribose, a phosphate group, and a nitorgenous base (Nitrogen Containing).

  11. Structure of DNA • The backbone of DNA is formed by sugar and phosphate groups of the nucleotide. • The nitrogenous base stick out from the sides and can be joined together in any order, meaning that any sequence of bases is possible.

  12. Nitrogenous Bases • There are four kinds of nitrogenous bases. • They are divided into two classes: purines and pyrmidines • Purines – Adenine and Guanine • Two Rings • Pyrmidines – Cytosine and Thymine • One Ring

  13. Chargaff’s Rules • Chargaff discovered how the nitrogenous bases bond together. • He discovered that Adenine always bonds with Thymine and that Cytosine always bonds with Guanine.

  14. Nitrogenous Base Bonds • Number of hydrogen bonds that connect the based: • A-T = 2 bonds • C-G = 3 bonds

  15. The Importance of DNA

  16. The Genetic Code

  17. DNA Length • E. Coli have about 4,639,221 base pairs. It is about 1.6mm in length. This sounds small until you realize the bacteria is only 1.6µm in diameter. • Thus DNA must be wrapped tightly to fit into cells. Imagine fitting 900 yards (300m) of rope into a backpack.

  18. DNA Replication • During DNA replication, the DNA molecule separates into two strands, then produces two new complimentary strands following the rules of base pairing (Chargaff Rules). Each strand of double helix of DNA serves as a template, or model, for the new strand.

  19. How It Occurs • DNA replication is carried out by a series of enzymes. • The enzymes unzip the DNA molecule creating two strands that serve as templates. • Complimentary bases are added to the strands, for example a strand of DNA with the bases ATTCGAG would have a complimentary strand of TAAGCTC.

  20. Replication Continued • Each new DNA molecule has one new stand and one strand from the original molecule. • The enzyme DNA polymerase, the principal enzyme, “proofreads” the new DNA strands, helping to maximize the odds that each molecule is a perfect copy of the original.

  21. Replication of DNA

  22. Key Ideas • How does DNA replicate, or make a copy of itself? • What are the roles of proteins in DNA replication? • How is DNA replication different in prokaryotes and eukaryotes?

  23. DNA Replication • Because DNA is made of two strands of complementary base pairs, if the strands are separated then each strand can serve as a pattern to make a new complementary strand. • The process of making a copy of DNA is called DNA replication. • In DNA replication, the DNA molecule unwinds, and the two sides split. Then, new bases are added to each side until two identical sequences result.

  24. DNA Replication • As the double helix unwinds, the two complementary strands of DNA separate from each other and form Y shapes. These Y-shaped areas are called replication forks. • At the replication fork, new nucleotides are added to each side and new base pairs are formed according to the base-pairing rules. • Each double-stranded DNA helix is made of one new strand of DNA and one original strand of DNA.

  25. DNA Replication Click to animate the image.

  26. Replication Proteins • The replication of DNA involves many proteins that form a machinelike complex of moving parts. Each protein has a specific function. • Proteins called DNA helicases unwind the DNA double helix during DNA replication. These proteins wedge themselves between the two strands of the double helix and break the hydrogen bonds between the base pairs. • Proteins called DNA polymerases catalyze the formation of the DNA molecule by moving along each strand and adding nucleotides that pair with each base.

  27. Replication Proteins • DNA polymerases also have a “proofreading” function. • During DNA replication, errors sometime occur and the wrong nucleotide is added to the new strand. • If a mismatch occurs, the DNA polymerase can backtrack, remove the incorrect nucleotide, and replace it with the correct one.

  28. Prokaryotic Replication • replication starts at a single site • have a single chromosome which is a closed loop attached to the inner cell membrane. • begins at one place along the loop. This site is called the origin of replication. • Replication occurs in opposite directions until the forks meet on the opposite side of the loop.

  29. Prokaryotic and Eukaryotic Replication • In eukaryotic cells, replication starts at many sites along the chromosome. • Eukaryotic cells often have several chromosomes which are linear and contain both DNA and protein. • Replication starts at many sites along the chromosome. This process allows eukaryotic cells to replicate their DNA faster than prokaryotes. • Two distinct replication forks form at each start site, and replication occurs in opposite directions. • This process forms replication “bubbles” along the DNA molecule. • Replication bubbles continue to get larger as more of the DNA is copied.

  30. Prokaryotic and Eukaryotic Replication Click to animate the image. C A E B G F D

  31. Summary • In DNA replication, the DNA molecule unwinds, and the two sides split. Then, new bases are added to each side until two identical sequences result. • The replication of DNA involves many proteins that form a machinelike complex of moving parts. • In prokaryotic cells, replication starts at a single site. In eukaryotic cells, replication starts at many sites along the chromosome.

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