Copyright © 2005 Pearson Prentice Hall, Inc. Chapter 8 DNA: The Molecule of Heredity NUCLEIC ACID – your “4 th ” macromolecule! Nucleic Acid – “a polymer consisting of many nucleotide monomers, serves as a blueprint for proteins and, through the action of proteins, for all cellular structures and activities.” Example - DNA (and RNA)

Copyright © 2005 Pearson Prentice Hall, Inc. 8.1 What Are Genes Made of? Figure 8.1 Genetic differences (p. 114)

Copyright © 2005 Pearson Prentice Hall, Inc. Many human traits are inherited, including (a)Viggo Mortensen’s (b)cleft chin and (b) (c)Orlando Bloom’s (d)smoothly rounded (e)chin.

Copyright © 2005 Pearson Prentice Hall, Inc. 8.2 What Is the Structure of DNA? DNA Is Composed of Four Different Subunits, called nitrogenous bases – 8_UN01 Thymine and adenine (p. 114) – 8_UN02 Cytosine and guanine (p. 114)

Copyright © 2005 Pearson Prentice Hall, Inc. sugar phosphate base = cytosine sugar phosphate base = thymine

Copyright © 2005 Pearson Prentice Hall, Inc. sugar phosphate base = guanine sugar phosphate base = adenine

Copyright © 2005 Pearson Prentice Hall, Inc. What is a nucleotide? Phosphate + sugar + nitrogenous base, makes up the “sugar phosphase backbone” Nitrogenous bases (DNA) are A, T, G, C (in RNA they are w/ U, uracil instead of tyamine)

Copyright © 2005 Pearson Prentice Hall, Inc. 8.2 What Is the Structure of DNA? A DNA Molecule Contains Two Nucleotide Strands –Figure 8.2 The Watson-Crick model of DNA structure (p. 115) –Base pairing (complementary) –In spiral (double helix)

Copyright © 2005 Pearson Prentice Hall, Inc. TA CG GC C G T T T A A A C A A T T G CG AT

C G T T T A A A

What to notice Spiral Backbone Base pairing Nitrogenous bases Sugar location

Copyright © 2005 Pearson Prentice Hall, Inc. TA CG GC C A A T T G CG AT

8.3 How Does DNA Encode Information? Figure E8.1 The discovery of DNA (p. 116)

Copyright © 2005 Pearson Prentice Hall, Inc. James Watson and Francis Crick with a model of DNA structure

Copyright © 2005 Pearson Prentice Hall, Inc. Discovery of DNA DNA molecules were know over 100 years ago, chromosomes were known in the 1940’s, but they thought that the 20 amino acids of proteins made up the genes 3 levels of study: Griffith (bacteria, 1928); Hershey and Chase (bacteriophage, 1952) then Watson and Crick (the STRUCTURE…as you’ve seen…)

Copyright © 2005 Pearson Prentice Hall, Inc. Griffith (bacteria, 1928); 2 types of bacteria: harmless, non-pneumonia carrying bacteria, and disease carrying strains. He heated the disease carrying bacteria and denatured the disease and then chopped it up. These (deactivated bacterial parts) were then mixed with the non-diseased bacteria and the diseased strain CAME BACK! He further noted that when these newly infected bacteria reproduced, they passed on the disease (i.e. it was INHERITED!). This is an example of bacterial transformation.

Copyright © 2005 Pearson Prentice Hall, Inc. Hershey and Chase, 1952 DNA was the genetic material of a bacteriophage (T2), a “virus that attacks bacteria.” EXPERIMENT: Using E. coli they labeled protein “phages” with radioactive sulfur (yellow) and DNA “phages” with radioactive phosphorus (green). OVERHEAD 10.1a. These were then each allowed to infect bacteria. Shake mixture to separate loose pieces of phages that had not infected (entered) the E. coli. Centifuge, separates the heavier bacteria into a pellet and leaves the phages in the liquid. Test for radioactivity between the pellet and the liquid.

Copyright © 2005 Pearson Prentice Hall, Inc. Result… They found that: In the PROTEIN (sulfur) containing liquid: The radioactivity remained in the liquid. In the DNA (phosphorus) containing liquid: The radioactivity was in the pellet (bacteria) not the liquid. OVERHEAD 10.1c They then took these bacteria out of the liquid and allowed them to lyse (reproduce) and they reproduced bacteria with radioactive phosphorus inside – it was INHERITED!

Copyright © 2005 Pearson Prentice Hall, Inc. Now…back to DNA 5 nitrogenous bases Adenine, Thymine (DNA only), Cytosine, Guanine and Uracil (RNA only). AUGC in RNA (Ribonucleic acid). Sugar = ribose. {{RNA is the genome of most viruses and functions mainly in humans for protein synthesis. Usually single stranded.}} ATGC in DNA (Deoxyribonucleic acid). Sugar = deoxyribose. A and G = Purines, T and C = Pyrimidines (In DNA) Now…to replication…

Copyright © 2005 Pearson Prentice Hall, Inc. 8.4 How Is DNA Copied? Why Does DNA Need to Be Copied? DNA Is Copied Before Cell Division DNA Replication Produces Two DNA Double Helixes, Each with One Original Strand and One New Strand

Copyright © 2005 Pearson Prentice Hall, Inc. free nucleotides

Copyright © 2005 Pearson Prentice Hall, Inc. One DNA double helix. DNA replication Two identical DNA double helixes, each with one parental strand (blue) and one new strand (pink).

Copyright © 2005 Pearson Prentice Hall, Inc. Replication summary Base pairing is needed Complimentary strands (like in a photograph – the negative image would serve as a template for the replicated molecule). Process: (1) Strands separate, (2) Become templates for new base pairing to occur, (3) Nucleotides come in to line up, 1 by 1, along the strand. (4) Enzymes (DNA polymerase and ligase) link the nucleotides to the strands, (5) New (identical) molecule formed = “Daughter DNA.”

Copyright © 2005 Pearson Prentice Hall, Inc. 8.5 What Are the Mechanisms of DNA Replication? Figure 8.4 Details of DNA replication (p. 119)

Copyright © 2005 Pearson Prentice Hall, Inc. replication bubble DNA helicase replication forks DNA helicase DNA polymerase #1 DNA polymerase #2 DNA polymerase #1 continues along parental DNA strand DNA polymerase #3 DNA polymerase #2 leaves DNA polymerase #4 DNA polymerase #3 leaves DNA ligase joins daughter DNA strands together continuous synthesis discontinuous synthesis continuous synthesis discontinuous synthesis

Copyright © 2005 Pearson Prentice Hall, Inc. replication bubble DNA helicase replication forks DNA helicase

Copyright © 2005 Pearson Prentice Hall, Inc. DNA polymerase #1 DNA polymerase #2 continuous synthesis discontinuous synthesis

Copyright © 2005 Pearson Prentice Hall, Inc. DNA polymerase #1 continues along parental DNA strand DNA polymerase #3 DNA polymerase #2 leaves continuous synthesis discontinuous synthesis

Copyright © 2005 Pearson Prentice Hall, Inc. DNA polymerase #4 DNA polymerase #3 leaves DNA ligase joins daughter DNA strands together

Copyright © 2005 Pearson Prentice Hall, Inc. summary Replication can then occur in either direction along the strand, located by “replication bubbles.” OVERHEAD 10.5a : This speeds the process up and a lot of these can go on, until they all form one (identical) daughter strand. Also, remember, these can run in either direction because the base pairs are complimentary, so the sugar phosphate backbone is opposite on each strand. OVERHEAD 10.5b. One side of the backbone will be 3’ to 5’, while the other will go 5’ to 3’. {3’ = Carbon attached to -OH, 5’ = carbon attached to phosphate}. NUCLEOIDES are only added to the 3’ end (so they “grow” in only 1 direction, the 5’ to 3’ way).

Copyright © 2005 Pearson Prentice Hall, Inc. 8.5 What Are the Mechanisms of DNA Replication? DNA Helicase Separates the Parental DNA Strands DNA Polymerase Synthesizes New DNA Strands DNA Ligase Joins Together Segments of DNA

Copyright © 2005 Pearson Prentice Hall, Inc. enzymes DNA polymerase: link nucleotides to the growing strand. This enzyme is also responsible for “proofreading” and removing any nucleotides that are incorrectly trying to base pair. And repair too. DNA ligase: ties smaller synthesized pieces together to form 1 DNA strand through covalent bonding. And it is also responsible for repair.

Copyright © 2005 Pearson Prentice Hall, Inc. 8.4 How Is DNA Copied? Proofreading Produces Almost Error-Free Replication of DNA Mistakes Do Happen