Name: - Bio A.P. DNA Replication & Protein Synthesis

Transcription

1 Name: - Bio A.P. DNA Replication & Protein Synthesis 1

2 ESSENTIAL KNOWLEDGE Big Idea 3: Living Systems store, retrieve, transmit and respond to information critical to living systems Enduring Understanding: The information language of DNA is encoded in its structure Heritable information provides for continuity of life. Genetic information flows from a sequence of nucleotides in a gene to a sequence of amino acids in a protein Essential Knowledge: DNA, and in some cases RNA, is the primary source of heritable information. The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. Biological Systems have multiple processes that increase genetic variation Timing and coordination of specific events are necessary for the normal development of an organism, and these events are regulated by a variety of mechanisms. 2

3 I. Nature of the Gene QUESTION: Which of the four classes of organic molecules holds the key for inheritance? Recall Organic Molecule Building Block Carbohydrate Monosaccharide Lipid 3 FA & Glycerol Protein Amino Acid (20) Nucleic Acid Nucleotide (4) A. History 1. Griffith (1928)-was studying the bacterium that causes pneumonia Vocabulary: In vivo-in living organisms/cells In vitro-outside of living organisms/cells (in a test tube) Pathogen-disease causing Virulent-disease causing Non-virulent-not disease causing Experiment Two strains of bacteria S bacteria-virulent form causing pneumonia R bacteria-non-virulent form 3

4 Conclusion Some heritable material of the S bacteria was picked up by the R bacteria causing a genetic change or transformation of the R bacteria into a S bacteria Transformation-picking up of external DNA by a cell resulting in a genetic change 2. Avery, Macleod, & McCarty (1944) Question: What is the genetic component that caused the transformation? Experiment In vitro Isolated and purified the components of the heat killed S bacterium Injected each purified component into R bacteria Tested for transformation DNA was the only component which caused transformation Conclusion: DNA is the transforming component and therefore the molecule of heredity. 3. Hershey & Chase (1952) Question: Is the genetic material DNA or protein? Experiment: Worked with a bacteriophage (virus which infects bacteria) Virus Structure: Protein coat Nucleic acid core Viruses use the host cell to make copies of its nucleic acid and protein (reproduction). Genetic material must be injected into the host cell. Tagged DNA of the virus with P-32 Tagged the Protein with S-35 4

5 Conclusion Nucleic Acid is the genetic material NOT protein 4. Chargaff (1947) Amount of purine (A, G) bases=amount of pyrimidine (T, C, U) bases in any given organism Chargaff s Rule: A=T and G=C 5. Watson & Crick (1953)-Discovery of the DNA Double Helix Other researchers: Levene (1920) Nucleotide structure: Pauling: Worked with helix structure of proteins Wilkins & Franklin: Studied the X ray diffraction of DNA 5

6 Watson & Crick realized a double Helix-structure for DNA fit the X-ray patterns Width=2nm Full Turn=3.4 nm Distance between stacked bases in each strand=.34nm B. DNA Structure 1. Single Stranded DNA Ribose Sugar P C 5 C 1-1' N.Base C 3-3' OH C 5-5 Phosphate O C 4 C 1 N-Base C 3 C 2 OH Growing DNA strand 5' New nucleotide enters as a triphosphate Nucleotide bonds to the 3 OH Bond is formed by condensation reaction Link is phosphodiester bond IMPORTANT Bond is between the 3 OH and the 5 P Strand grows in the 5' 3' direction 3 6

7 2. Double Stranded DNA Recall Hydrogen Bonds form between hydrogen and the elements F, O, N H-bond formation Adenine forms two H-bonds with thymine Guanine forms three H-bonds with cytosine In order for the H-bonds to form between the N-bases, the two DNA strands must be upside down DNA Double helix is 1. Complementary A=T G C 2. Antiparallel Summary REMEMBER Antiparallel Complementary Chain growth 5 3 Phosphodiester bond 3 OH to 5 P 7

8 C. DNA Replication 1. Meselson & Stahl (1958) Hypothesis: Three possible modes of replication: NOTE: Template is a pattern to be copied Conservative Parent strand does not separate and entire strand serves as a template Semiconservative Parent strand separates and each strand serves as a template Dispersive Parent strand breaks into fragments. Fragments serve as a template Experiment Culture bacteria in N-15 (heavy nitrogen). DNA of parent cell contains N 15 Transfer the bacteria to a culture containing N-14 (light nitrogen). Any NEWLY synthesized DNA will contain N 14 Centrifuge the DNA and examine the density bands N 14 Band N 14 / N 15 Band N 15 Band 8

9 Results Conclusion: DNA replication is SEMICONSERVATIVE 2. The Chemical Process of Replication Overview Each parent strand serves as a template H-bonds break, separating the parent strands New nucleotides are incorporated Each daughter DNA has one original parent strand and one newly made strand 9

10 Background Addition of new bases Replication must 1) Unwind DNA 2) Unzip DNA 3) Insert new DNA bases 5 3 direction Complementary Antiparallel 4) Correct mistakes Replication Fork Leading Strand-Newly made DNA strand formed continuously Lagging Strand-Newly made DNA strand formed by backstitching Okazaki fragments 10

11 In Detail Facts: 1. DNA replication can occur in both directions 2. There can be more than one origin of replication (eukaryotes) 3. Replication Fork-place where new DNA is being formed Enzymes of Replication: 1. DNA B-recognizes the origin of replication 2. Helicases-untwists the DNA and unzips DNA (breaks the H-bonds between the parent strands) 3. s.s.b. (single strand binding protein)- Binds to the single parent template strands to keep them from reannealing (coming back together) 4. Topoisomerase-relieves the stress placed on the rest of the DNA ahead of the replication fork 5. Primase-brings in RNA nucleotides (10 bp) complementary to the DNA parent (template) strand. Works in the 5' 3' direction 6. Primer-RNA base pair sequence which begins the replication of the new strand at the 5 end 7. DNA polymerase (III)-brings in DNA nucleotides complementary to the parent strand. Bonds the DNA nucleotides to the Primer. Works in the 5' 3' direction NOTE: DNA polymerase cannot initiate replication; it must attach nucleotide bases to an existing 3 OH 8. DNA polymerase (I)-removes primer and replaces RNA bases with DNA bases 9. DNA Ligase-joins gaps to form continuous DNA strand 11

12 Let s look at the Leading strand first! After the primer is made DNA pol III synthesizes the leading strand The leading strand is made continuously in the 5 to 3 direction 12

13 Now let s look at the Lagging Strand Primase makes the primer After the primer is made DNA pol III adds DNA bases forming an Okazaki fragment Once DNA pol III reaches the next primer it detaches Primase primes fragment 2. DNA pol III forms an Okazaki fragment for section 2 DNA pol I replaces the primer strand of the first segment and replaces the RNA bases with DNA bases DNA ligase joins the Okazaki fragments 1 and 2 13

14 SUMMARY Leading Strand ssb Helicase Lagging Strand How are mistakes corrected? Excision Repair-Corrects mistakes in the replication process and repairs damaged DNA Nuclease enzymes cuts out damaged section DNA polymerase replaced the correct nucleotides Ligase seals nicks 14

15 How are the ends of DNA replicated? Telomeres (Eukaryotes) Sequence of nucleotide bases at the end of a DNA molecule Telomere is shortened in each replication because DNA polymerase cannot begin replication Telomerase-enzyme which lengthens telomere regions Most cells DO NOT contain telomerase When telomeres become too short, the cell may stop replicating REMEMBER: DNA replication occurs during the S phase of the cell cycle DNA replication produces identical sister chromatids 15

16 NOTES 16