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DNA and Replication

Discover the fascinating world of DNA and replication, where the genetic information that determines our cells' functions is stored and transmitted. Explore the Hershey-Chase experiment, the structure of DNA, antiparallel strands, and the steps to DNA replication. Learn about telomeres and their role in aging and cancer. Get ready to unravel the secrets of DNA!

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DNA and Replication

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  1. DNA and Replication

  2. If you unwrap all the DNA you have in all your cells, you could reach the moon! 6000 times!!!

  3. DNA… • Deoxyribonucleic Acid (DNA) • Primary Function = • to store and transmit the genetic information that tells cells which proteins to make and when to make them.

  4. The Hershey-Chase Experiment

  5. DNA is... • an ORGANIC compound • made up of repeating subunits called NUCLEOTIDES • composed of TWO long chains of nucleotides

  6. DNANUCLEOTIDE • 3 PARTS: • Sugar Molecule – deoxyribose • Phosphate Group: phosphorous (P) & oxygen (O) • Nitrogen Base: adenine (A), cytosine(C), guanine(G), and thymine(T)

  7. Circle 1 nucleotide...

  8. Nitrogen bases come in two types: 2. Guanine 1. PURINES Purines have tworings. And come in two types 1. Adenine

  9. Nitrogen bases come in two types: 2. PYRIMIDINES Pyrimidines have ONEring And come in two types: 2. Thymine 1. Cytosine

  10. Nucleotides & DNA • Nucleotides can join together in any order, anysequenceof nitrogen basesis possible.

  11. Complimentary Base Pairing Certain bases always pair together 1. Cytosine bonds with Guanine 2. Adenine bonds with Thymine Nitrogen bases form hydrogen bonds

  12. chargaff’s rule Must be an equal number of Cs and Gs As and Ts 3 H bonds 2 H bonds

  13. In 1953, JAMES WATSON & FRANCIS CRICK suggested a model for the structure of DNA. Two nucleotide strands wrap around each other to form a double spiral (spiral staircase) The Double Helix

  14. Contention in Science World Rosalind Franklin used X-ray diffraction to reveal an X-shaped pattern in DNA, suggesting DNA contained 2 strands and was twisted like the coils of a spring.

  15. Image of the Double Helix **Sugar-phosphate backbone is held together by covalent bonds (strong) **Nitrogen bases connect by hydrogen bonds (weak) *

  16. The nitrogen bases form the center rungs of DNA The outside, sugar-phosphate backbone, is made of alternating phosphates and sugars held together by covalent bonds DNA Structure

  17. Antiparallel strands • DNA strands run anti-parallel to each other • One strand runs 3’5’ • One strand runs 5’3’ • This is important for DNA replication

  18. The process of copying DNA. Overall: Two nucleotide chains separate and serve as TEMPLATE for a new nucleotide chain. Recall, when does DNA replication occur? Before what stages? DNA Replication

  19. Steps to DNA Replication 1. DNA is split down the middle (between base pairs) by helicase, breaking the hydrogen bonds. • This forms a replication fork • Similar to a zipper 2. The nitrogen bases on each strand are used as a pattern for a new strand.

  20. Steps to DNA Replication 3. Complementary bases are added to each individual strand by DNA polymerase (enzyme). 4. Each new cell can now get a complete copy of all the DNA. Semi-conservative: • One of the original strand, one new

  21. DNA Replication • Helicase enzymes untwist and unzip the DNA helix. (A replication fork is now formed.) • DNA primase enzyme adds a primer to each side of the open strand. • Primer: piece of RNA that starts replication

  22. DNA Replication • DNA polymerase adds the new nucleotides one at a time. • Lastly, DNA ligase enzyme “glues” nucleotides together on the lagging strand.

  23. Antiparallel strands • Because DNA is antiparallel, we call one strand the leading strand(5’ →3’) and the other the lagging strand (3’→5’). • Leading Strand: copied continuouslyfrom a replication origin by in the same direction that the replication fork moves. • Lagging Strand: copied discontinuouslyfrom a replication origin in the opposite direction that the replication fork moves. The small pieces that are created are referred to as Okazaki fragments.

  24. DNA Replication Animation

  25. ***You are left with 2 exactly identical molecules of DNA double helix.*** New New Original Original strands of DNA Original O N N O Semi-conservative Model

  26. Telomeres • The tipsof chromosomes (the ends of the DNA molecule) • Telomeres are difficultto copyand so they can be losteach time a chromosome is replicated. • Telomerase (enzyme)adds short, repeated DNA sequences to telomeresto slightly lengthen the chromosometo make it less likely that important gene sequences will be lost.

  27. Telomeres • In humans, repeating sequence of TTAGGG • At birth, roughly 11,000 bases long • At old age, less than 4,000 bases long • Declines faster in men than women

  28. Shortened telomeres result in more chromosomal damage • Shortened or damaged telomeres are found in many cancers • Helps to explain increase in cancer prevalence as age increases • Suggested to play role in human aging

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