1 / 12

Science Section III: Molecular Genetics Pages 54-64

Science Section III: Molecular Genetics Pages 54-64. Wendy Nguyen Sept. 3, 2013. Objectives:. The Identification of DNA as the Genetic Material The Cracking of the Genetic Code Franklin’s Contribution Watson and Crick The Organization of DNA The Genetic Code

gallia
Download Presentation

Science Section III: Molecular Genetics Pages 54-64

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. Science Section III:Molecular GeneticsPages 54-64 Wendy Nguyen Sept. 3, 2013

  2. Objectives: • The Identification of DNA as the Genetic Material • The Cracking of the Genetic Code • Franklin’s Contribution • Watson and Crick • The Organization of DNA • The Genetic Code • The Basic Rules of DNA Replication • Semi-Conservative DNA Replication • Mutation

  3. The Identification of DNA as the Genetic Material • When the flu pandemic had subsided, millions of people died, primarily from bacterial infections, as their bodies’ defense systems became weak from fighting the influenza virus. • Streptococcus pneumoniae was the bacterium responsible for most of the deaths. • Through clinical research of the bacterium, it led the discovery of DNA as the genetic material. • Per Oswald Avery, DNA was a “transforming substance” enriched with nucleic acids • Per Frederick Griffin, there were 2 different strains of bacterium that led him to believe that DNA is the “transforming principle” • Per Hershey and Chase, bacteriophage occurs when a virus infects a bacteria thus changing the genetic makeup of DNA

  4. The Cracking of the Genetic Code - Franklin’s Contribution • Rosalind Franklin isolated the DNA crystal to produce a 3-D, double-stranded twisted-ladder image of the DNA molecule. • X-ray crystallography – a technique using x-ray to produce a shadow image of a molecule, which provides information regarding the size, shape, and spatial relationship of certain key components • The image suggested that sugar and phosphate form the backbone of the two DNA strands and the nitrogenous bases are locate near the center of the two strands • Franklin’s contribution provided the foundation that later constructed the DNA model.

  5. The Cracking of the Genetic Code - Watson and Crick • James Watson and Francis Crick introduced the famous double helix model of DNA • Deoxyribose and phosphate form the two backbones (strands) with the complementary bases (A pairs with T; C pairs with G) held together by hydrogen bonds

  6. The Organization of DNA • Eukaryotic DNA is highly diverse in structure and organization. It consists of a nucleus with multiple linear chromosomes located within. • Majority of eukaryotes have two copies of each chromosomes from each parent through sexual reproduction. • The human genome has an estimate of 3.1 billion nucleotides; however, about 22,000 genes we have are not coded from our genome. • For a typical gene, there are intervening events of introns with exons. • Introns – noncoding regions • Exons– coding regions; are part of the mRNA used to make a specific functional protein

  7. The Organization of DNA -The Genetic Code • A language of nucleotides where information is stored in the DNA molecule • Composed of 4 letters: A, T, G, and C • These 4 letters are arranged as triplets – each set is defined as a codon in the mRNA • i.e.: AUG, CCA, GGG • Maximum number of 64 codons • Only 20 codons are used for protein synthesis, where each amino acid is coded for by more than one codon (except UGG, which only codes for tryptophan). • Stop codons– UAA, UAG, and UGA do not code for any amino acids where they signal the cell to terminate translation • Start codon– AUG signals the start of protein synthesis or translation, and it also codes for the amino acid methionine

  8. The Basic Rules of DNA Replication –Semi-Conservative DNA Replication • Semi-conservative DNA Replication: the double-stranded DNA helix is replicated, each new double-stranded DNA is composed of one strand from the original helix and one newly synthesized strand of DNA • DNA replication consists of a highly coordinated and regulated process involving more than a dozen enzymes and other proteins that adjust the on/off switch regulating DNA function. • Replication in eukaryotes take place simultaneously at multiple sites. • Some of the following enzymes: • 1. Helicase (“unzipper”) – unzips a portion of the DNA double helix at the starting point to create a replication fork and then a replication bubble; the unzipped DNA strand is protected by proteins to prevent the strands from reconnecting into the double helix.

  9. The Basic Rules of DNA Replication –Semi-Conservative DNA Replication • Some of the following enzymes: • 2. Primase– creates and attaches RNA primers to the replicating strands; the RNA primer is a short segment of RNA that initiates the process of DNA replication • 3. DNA polymerases (“builders” and “proofreaders”) – are multiple enzymes complexes that continuously add complementary nucleotides to the leading stand of one daughter DNA strand in the right direction; other (lagging) daughter strand is added piece by piece • 4. Nucleases (“editors”) – detects incorrect nucleotides and removes them • 5. DNA ligase (“zipper”) – adds phosphate in the remaining gap of the backbone; joins the new DNA fragment to the parent DNA template

  10. Mutation • A mutation is defined when an organism’s DNA is damaged, resulting in the possibility that genes can become altered. • It can be lethal in terms of a rare cancer gene, or considered as the “junk” gene portion where it is tolerable. • Mutation can also be a source of evolution thus the formation of new species. • Can occur randomly during DNA replication. Metabolic and/or environmental products can also increase the risk for mutation.

  11. Mutation • Mutations are classified based on the alterations of the amino acid sequence: • Missense – when the amino acid being coded for is changed by a nucleotide substitution • Nonsense – when a substitution causes a stop condon • e.g., ACC  becomes ATC  which codes for UAG = a stop codon • Frameshift– when one nucleotide is added or deleted, causing a shift in the triplet to all downstream codons; causes dramatic changes in the amino acid sequence

  12. END OF PRESENTATION

More Related