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DNA and RNA Chapter 12 12-1: DNA DNA Structure DNA is made up of monomers called nucleotides each nucleotide is made up of three parts: 1. 5-carbon sugar (deoxyribose) 2. phosphate group 3. nitrogenous base FOUR types of nitrogenous bases adenine (A) & guanine (G) – purines cytosine (C) & thymine (T) – pyrimidines Nitrogenous bases purines (A & G): two rings pyrimidines (C & T): one ring Chargaff’s Rules # of A = # of T # of G = # of C # of purines = # of pyrimidines DNA “double helix” discovered by Watson & Crick two strands are wound around each other like a spiral staircase or twisted ladder DNA “double helix” base pairing explains Chargaff’s Rules A always bonds with T (“points”) – double bond C always bonds with G (“curves”) – triple bond So if you have one side of DNA that has these bases, Cytosine (C) Adenine (A) Thymine (T) Guanine (G) Guanine (G) Thymine (T) --(G) Guanine --(T) Thymine --(A) Adenine --(C) Cytosine --(C) Cytosine --(A) Adenine These bases will make the other side. DNA Origami Two types of FOLDS Step 1 Cut the white border off the top, bottom, and sides of the template. Step 2 Fold all solid lines going lengthwise down the page into “mountain folds”. Step 3 Fold all dashed lines going lengthwise down the page into “valley folds”. Check Yourself Your paper should look like this: Step 4 Bring the two sides of the model together, similar to an “I” beam. Step 5 Look for the words ‘front’ and ‘back’ at the top of your model. Hold the model with the ‘front’ side facing you. Step 6 Fold the two sides of the DNA model so the ‘front’ side is flat. Step 7 Crease each solid, horizontal line into a mountain fold (away from you). Step 8 Flip the model to the ‘back’ side. Crease each solid diagonal line into a mountain fold (away from you). Check Yourself Your model should look like this. Step 9 Fold ALL of the creases together in the directions of the folds made in steps 7 and 8. Your model will fold up like an accordion. While you are folding, pinch the middle of the model to keep it together to make a cylindrical shape. Step 9 Step 10 Release the model. You should be able to see the shape of a double helix. Step 11 Straighten out the sides of the DNA model (the DNA “backbones”) to make them perpendicular to the creases in the middle. You’re DONE! Bell Work 2/22/10 A scientists is researching the effect long-term exposure to sunlight has on cell reproduction. Which scenario extends the current understanding of this relationship? – A) a culture of liver cells exposed to different pH levels over a 10-day period – B) a culture of muscle cells exposed to different nutrients over a 30-day period – C) a culture of skin cells exposed to different temperatures over a 50-day period – D) a culture of brain cells exposed to different electrical impulses over a 75-day period 12-2: Chromosomes and DNA Replication DNA and Chromosomes prokaryotes have a SINGLE, circular chromosome in the cytoplasm containing their DNA DNA and Chromosomes prokaryotes have a SINGLE, circular chromosome in the cytoplasm containing their DNA eukaryotes have MANY chromosomes in the nucleus containing their DNA Chromosome Structure DNA is very tightly packed DNA is wound around histones (proteins) to form nucleosomes nucleosomes wind into coils and supercoils to ultimately form chromosomes tightly wound DNA is called chromatids Flashback! What happens during the S phase of the cell cycle? DNA replicates (copies) itself! DNA Replication DNA Replication to make a copy of itself, DNA “unzips” C—G G---C T-A-G-G-- --A --T --C --C DNA Replication new bases come in to make a new complementary strand C—G G--C G --C T--A T--A A--T A--T G--C G--C G--C G--C Notice these strands are the same. Your turn copy and complete the DNA strand C-G-G-T-A-A-C-G-- Does it look like this? C--G G--C G--C T--A A--T A--T C--G G--C “Unzip” and copy it! C—G G---C G---C T---A A---T A---T C---G G---C Does it look like this? C—G G--C G--C T--A A--T A--T C--G G--C G--C G--C T--A A--T A--T C--G G--C DNA Replication the main enzyme involved in DNA replication is DNA polymerase RESULTS in two identical DNA molecules! Bellwork 2/23/10 When designing a scientific investigation, which of the following should be identified first? – A) lab equipment needed – B) appropriate sample size – C) useful analysis software – D) a testable hypothesis 12-3: RNA and Protein Synthesis RNA vs DNA structure RNA sugar: ribose DNA sugar: deoxyribose single-stranded double-stranded uracil (U) base thymine base 3 Types of RNA RNA is mainly involved in PROTEIN SYNTHESIS messenger RNA (mRNA) ribosomal RNA (rRNA) transfer RNA (tRNA) Protein Synthesis 1. Transcription 2. RNA Editing 3. Translation Overview Transcription DNA is “transcribed” into a RNA strand with the help of RNA polymerase Transcription how does RNA polymerase “know” where to start and stop making the RNA copy of DNA? the promoter region of the DNA is the light switch ON then the middle part is the coding region, or the TV show you watch the RNA polymerase stops at the termination sequence, the light switch OFF RNA Editing like a writer’s 1st draft introns (intervening sequences) are removed exons (expressed sequences) are left to make up the mRNA Translation mRNA “translated” into amino acids (which form proteins!) occurs in the RIBOSOME How does the ribosome “read” the mRNA? using the GENETIC CODE! this “code” only uses 4 letters: A, U, C, G these 4 letters represent 20 different amino acids the code is read 3 letters at a time (in triplicate) – these are called codons example: RNA sequence UCGCACGGU would be read UCG CAC GGU The Genetic Code each codon represents an amino acid there are 64 codons that code for 20 amino acids 1 start: AUG 3 stops: UAA UAG UGA Translation before translation starts, mRNA is transcribed in the NUCLEUS Translation then, in the cytoplasm, an mRNA molecule attaches to a RIBOSOME translation starts at AUG, and the transfer RNAs come in! (AUG = methionine) Translation it’s a polypeptide “assembly line” of amino acids … Translation … until a stop codon is reached Protein Synthesis Bell Work 2/26/10 In 1928 Alexander Fleming observed the mold Penicilium notatum growing in a Petri dish. Also in the dish was the bacteria Staphylococcus aureus. Fleming observed that no bacteria colonies were found growing in the area where the Penicillium notatum was. Which conclusion is BEST defended by Fleming’s discovery? – – – – A) P. notatum destroys all colonies of S. aureus B) P. notatum prevents the growth of all bacteria C) P. notatum inhibits the growth of S. aureus D) P. notatum promotes the growth of certain bacteria colonies Bell Work 3/1/10 A pesticide manufacturer claims that a new product will decrease the pest population 15% more than the current pesticide for a 10week period. A population of 50 beetles of the same species is exposed to the new pesticide for a 10-week period. A separate population of the same species of beetle is exposed to the same amount of the current pesticide for a 10-week period. The data collected is sent to an independent research company to verify the results. Which statement BEST explains how an independent research company verifies data to ensure unbiased results. A) The company compares the data given to similar investigations B) The company performs the same investigation and compares results C) The company sends out the data to another researcher to investigate D) The company tests many types of pesticides and draws its own conclusion 12-4: Mutations What is a mutation? any change in the DNA sequence two types: 1. gene mutations (changes in a single gene) 2. chromosomal mutations (changes in whole chromosomes) Gene Mutations POINT mutations - mutations that affect ONE nucleotide - mainly substituting one nucleotide for another FRAMESHIFT mutations - mutations that affect MULTIPLE nucleotides and shift the “reading frame” - adding/deleting a nucleotide Gene Mutations Gene Mutations Chromosomal Mutations 4 types: deletion duplication inversion translocation MUTATIONS