DNA: The Genetic Material - Nucleotides and Replication PDF

DNA: THE GENETIC MATERIAL  DNA The Genetic Code  DNA codes for or instructs the production of all protein in a cell. The blueprints of the protein.  The code is hidden in the order of the nitrogen bases of the DNA molecule  Griffith proved Transformation of DNA (mouse...

DNA: THE GENETIC MATERIAL  DNA The Genetic Code  DNA codes for or instructs the production of all protein in a cell. The blueprints of the protein.  The code is hidden in the order of the nitrogen bases of the DNA molecule  Griffith proved Transformation of DNA (mouse experiment)  Oswald Avery and a group of scientists proved DNA is the genetic code (enzyme & extract experiment)  Hershey & Chase confirmed DNA was the genetic code. (blender & radioactive bacteriophage experiment)  Griffith’s Experiment Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing Harmless bacteria Heat-killed, disease- Control Harmless bacteria bacteria (smooth (rough colonies) causing bacteria (no growth) (rough colonies) colonies) (smooth colonies) Dies of pneumonia Lives Lives Dies of pneumonia Live, disease-causing bacteria (smooth colonies)  Griffith’s Experiment Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing Harmless bacteria Heat-killed, disease- Control Harmless bacteria bacteria (smooth (rough colonies) causing bacteria (no growth) (rough colonies) colonies) (smooth colonies) Dies of pneumonia Lives Lives Dies of pneumonia Live, disease-causing bacteria (smooth colonies)  Hershey-Chase Experiment Bacteriophage with Phage infects Radioactivity inside phosphorus-32 in bacterium bacterium DNA Bacteriophage with Phage infects No radioactivity inside sulfur-35 in protein bacterium bacterium coat  Hershey-Chase Experiment Bacteriophage with Phage infects Radioactivity inside phosphorus-32 in bacterium bacterium DNA Bacteriophage with Phage infects No radioactivity inside sulfur-35 in protein bacterium bacterium coat  Hershey-Chase Experiment Bacteriophage with Phage infects Radioactivity inside phosphorus-32 in bacterium bacterium DNA Bacteriophage with Phage infects No radioactivity inside sulfur-35 in protein bacterium bacterium coat Chargaff’s Observations In 1949, Erwin Chargaff observed that for each organism he studied, the amount of adenine always equaled the amount of thymine (A=T). Likewise, the amount of guanine always equaled the amount of cytosine (G=C). However, the amount of adenine and thymine and of guanine and cytosine varied between different organisms. Weak hydrogen bonds hold the bases together.(A-T have 2, while C-G have 3 bonds) Called base pairing.  Pairing Between Bases  Purines on one strand of DNA always pair with pyrimidines on the other strand. A  T C  G Structure of DNA Nucleotide Hydrogen bonds Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)  Wilkins & Franklin’s Photographs  Used X-ray diffraction to study the structures of molecules  X-ray diffraction of DNA suggested that the DNA molecule was a tightly coiled helix composed of 2 or 3 chains of nucleotides. In 1953 Crick and Watson proposed structure for DNA based on x-ray evidence by Rosalind Franklin and Maurice Wilkins What we now know about DNA: DNA is a double helix (2 strands twisted around each other) Each strand is composed of linked nucleotides Nucleotides are composed of three parts: phosphate group five-carbon sugar (deoxyribose) nitrogen – containing base  DNA Nucleotides Purines Pyrimidines Adenine Guanine Cytosine Thymine Phosphate Deoxyribose group DNA is a polymer of subunits called nucleotides. 5 carbon sugar called deoxyribose, a phosphate group, & a nitrogenous base  Structure of DNA Nucleotides have 2 groups Purines & Pyrimidines – Purines: Adenine & Guanine and have 2 rings – Pyrimidines: Cytosine & Thymine and have 1 ring The Sugars & phosphates form the backbone of the chain and the nitrogenous bases stick out from the chain The sugar phosphate backbone is in the 5’-3’ position. This is determined by the carbon phosphate bonding position Figure 12–7 Structure of DNA Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)  WRAPPED UP! Watson and Crick were looking for a vaccination for pneumonia…. What they found…. They took the ideas of Chargaff about base pairs, “stole” Rosalind Franklins images and quickly started putting the ideas together…. And you have…… DNA IS THE HEREDITARY MATERIAL They figured this all out by noticing that during their studies for the pneumonia vaccination mice were being killed and macromolecules were TRANSFORMING! DNA and Chromosomes  Prokaryotes’ DNA is a circular loop in the cytoplasm  Eukaryotes have up to 1000 times the DNA and keep it in chromosomes.  DNA must be folded and coiled to fit in the cell. Human DNA is over 3 meters long.  Chromosomes are made of super-coiled chromatin.  Chromatin is DNA coiled around the protein Histone.  Figure 12-10 Chromosome Structure of Eukaryotes Chromosome Nucleosome DNA double helix Coils Supercoils Histones  Replication of DNA  Before a cell divides it must replicate (copy) its DNA  Enzymes often work in hundreds of places at a time to replicate the DNA.  An enzyme unzips the DNA (helicase)  An enzyme adds in base pairs to the new strands (DNA Polymerase III) going from the 3’ to 5’ on the template DNA strand. (3’ is sugar and 5’ is phosphate)  Another enzyme proofreads the bases to make sure the bases match (DNA Polymerase I)  The top strand is copied continuously.  The bottom strand is copied in fragments and an enzyme glues the fragments together (DNA Ligase)  DNA gyrase closes the strands.  Figure 12–11 DNA Replication Original New strand strand DNA polymerase Growth DNA polymerase Growth Replication Replication Nitrogenous fork fork bases New strand Original strand