1 / 21

DNA: The Double Helix

DNA: The Double Helix. Deoxyribonucleic Acid. DNA Structure. DNA Structure. DNA has a basic structure called a “double helix” DNA has two strands that form the spiral shape These strands are made of repeating subunits called nucleotides. Nucleotides. Nucleotides. Composed of three parts:

brian-russo
Download Presentation

DNA: The Double Helix

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. DNA: The Double Helix Deoxyribonucleic Acid

  2. DNA Structure

  3. DNA Structure • DNA has a basic structure called a “double helix” • DNA has two strands that form the spiral shape • These strands are made of repeating subunits called nucleotides

  4. Nucleotides

  5. Nucleotides • Composed of three parts: • Sugar (Deoxyribose) • Phosphate Group • Nitrogenous Base (A, T, C, G)

  6. Bonds. Many Bonds.

  7. Bonds. Many Bonds. • DNA’s double helix is held together with bonds – think spiral staircase! • Covalent Bonds • Found between the sugar of one nucleotide and the phosphate of another • Form the railings of the staircase • Hydrogen bonds • Found between the bases • Form the steps of the staircase • Each full turn has 10 nucleotide pairs

  8. Nitrogenous Bases

  9. Nitrogenous Bases • There are four types of bases. • Adenine (A) • Thymine (T) • Guanine (G) • Cytosine (C) • Grouped by rings • Pyrimidines: One ring • C and T • Purines: Two rings • A and G

  10. Base-Pairing Rules • American biochemist Erwin Chargaff discovered that the bases always pair off together! • A and T • C and G • This is called “complementary base pairing”

  11. DNA and Chromosomes Nucleotides  DNA  Genes  Chromosomes

  12. DNA and Chromosomes • The number of chromosomes varies by species from one to many • Eukaryotes have two sets and are diploid • One from mother, one from father • Prokaryotes and sex cells have one set and are are haploid • Matching pairs of maternal and paternal chromosomes are called homologous chromosomes

  13. Human Chromosomes

  14. Human Chromosomes • Humans have 46 chromosomes • Humans have 23 sets of chromosomes • 22 are homologous pairs • 1 is a set of sex chromosomes • Other living things? • Fruit flies have 4 pairs of chromosomes • Rice plants have 12 pairs of chromosomes • Dogs have 39 pairs of chromosomes

  15. DNA Replication • Before a cell divides, the DNA inside must copy itself • This is done through DNA Replication DNA Replication Animation

  16. DNA Replication • Step 1: Unwinding • DNA helicase binds to the DNA • Helicase is an enzyme • Helicase begins to move along the DNA and breaks the hydrogen bonds • The best area for this is one where there are a lot of A-T bonds because there are only 2 bonds to break

  17. DNA Replication • Step 2: Replication Fork • Helicase causes the replication fork to form where the strands separate • RNA Primase attaches a starter of RNA nucleotides at the initiation point • DNA Polymerase attach to strands to start adding nucleotides • Polymerase is an enzyme

  18. DNA Replication • Step 3: Strand Growth Begins • Polymerase adds complementary nucleotides, found floating in the nucleus • Leading Strand (Blue) adds bases continuously • Lagging Strand (Red) adds bases in fragments • Called Okazaki fragments • RNA Primase inserts RNA primer into the gaps to hold everything in place

  19. DNA Replication • Step 4: Strand Growth Continues • Strands continue to add more bases • Notice that the leading strand follows the motion of replication fork • The lagging strand adds in the opposite direction

  20. DNA Replication • Step 5: Ligase Joins Pieces • Exonuclease strips away the RNA primer and DNA polymerase fills in the gaps • Enzyme called DNA Ligase joins the fragments of DNA together

  21. DNA Replication • Step 6: Strands Are Completed • Four single strands of DNA are created, resulting in two new double helixes • Each helix has one new strand and one old strand • Semi-conservative replication

More Related