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AP Biology Tests back today Curve was 12 points Grades on test haven’t had 12 points added (they are correct in ps) Study guide changes rip out page 7 (that is a different chapter) Test is December 20 History of DNA Thomas Morgan 1900 Frederick Griffith 1928 Oswald Avery 1940 Hershey and Chase 1952 Erwin Chargaff 1950 Rosalind Franklin 1950 Watson and Crick 1953 Griffith Conclusion: Phage Hershey/Chase Hershey/Chase Hershey/Chase Conclusion: Franklin Franklin Watson/Crick AP Biology Review from last class Continue DNA talk Replication today Watson/Crick DNA Replication Semiconservative: when a double helix replicates, each of the daughter molecules has one old strand and one new Replication Vocab on Replication Origin of replication- special sites where replication begins Replication fork- a “bubble” where parental strands are unwound Helicase- unzips parent strand Single-stranded binding protein- binds to unpaired DNA to stabilize them Topoisomerase- relieves strain from twisting Replication Vocab contd. Primer- initial nucleotide is a short stretch of RNA Primase- an enzyme that synthesizes the primer DNA polymerase- catalyzes the synthesis of new DNA by adding nucleotides to a preexisting chain DNA 3’ vs 5’ The 5’ 3’ runs in the opposite direction as the: 3’ 5’ Antiparallel- the two strands of DNA are oriented in opposite directions to each other. DNA DNA can ONLY add nucleotides from the 3’ side on parent Strand DNA daughters are “built” from 5’ 3’ DNA Leading strand- the continuous strand Lagging strand- the strand that is copied away from the fork Lagging strands called- Okazaki fragments. DNA Chapter 17 Gene Test expression and protein synthesis next Thursday Proteins Proteins are link between genotype and phenotype Gene expression- process by which DNA directs protein synthesis, includes two stages called transcription and translation DNA DNA RNA Protein Protein Review Amino acids - building blocks of protein Polymer bonded - many building blocks covalently Peptide bonds- covalent bond between amino acids 20 total amino acids DNA/RNA DNA RNA Double helix Single strand A,T,C,G A,U,C,G Deoxyribose sugar Ribose sugar mRNA rRNA tRNA Protein Synthesis Codons How be if: many nucleotides could there 1. Each kind of nucleotide base were translated into an amino acid? 2. If a two-letter sequence was in place? 3. If there were triplet bases? Codons Codons – the mRNA nucleotide triplets, written normally in the 5’ 3’ direction CCU AUG AGC AGG Transcription Vocabulary: RNA polymerase- separates DNA and joins RNA nucleotides together, nucleotide bases assemble in a 5’ 3’ direction (no primer required) Promoter- When RNA polymerase initiates transcription sequence Terminator- when RNA polymerase signals the end of transcription Transcription Steps of Transcription 1. 2. 3. Initiation- RNA synthesis begins Elongation- the RNA strand gets bigger Termination- the RNA transcript is released Transcription RNA Processing Pre-mRNA must be altered before it travels outside of the nucleus Alternation of mRNA ends 1. 5’ cap – a modified guanine added to the 5’ end 2. Poly-A tail- 50-250 adenine nucleotides are added to the 3’ side RNA Processing Pre-mRNA must be altered before it travels outside of the nucleus RNA splicing- removal of large portions of the RNA molecule (cut-and-paste) This means that there are long noncoding portions of DNA are not coding for anything. Introns - noncoding regions Exons – coding regions Translation Vocabulary: Anticodon- attached to tRNA molecules, a nucleotide triplet. Complementary to the mRNA codon Wobble – the flexible base pairing at the third nucleotide position. Translation Translation Translation Translation Translation Steps of Translation 1. 2. 3. Initiation- brings together mRNA and tRNA to begin synthesizing proteins Elongation – Amino acids are added Termination – A stop codon reaches A site, and the amino acids (polypeptide) is released Translation