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UNIT 6: DNA BIG IDEA: DNA contains the genetic information to produce proteins but must first be converted to RNA to do so http://evolution.berkeley.edu/evolibr ary/article/mutations_02 Why do cells need DNA? • DNA contains the information cells need to function and live. • Two main roles for DNA are 1. Storing genetic info and to 2. “Read” and translated to make proteins DNA Replication “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material” ~Watson and Crick Why do cells need to replicate (copy) their DNA? • To make new cells and make sure all new cells have a complete set of the genetic info How do cells replicate their DNA? 1. The DNA double helix is unwound by an enzyme. 2. Another enzyme moves down the 2 original DNA strands and adds complementary nucleotides. 3. Two separate DNA molecules are formed, each with one new strand and one old strand. Replication Stats • 6 billion base pairs per cell. • All are replicated in a few hours. • Mistake happens one per billion nucleotides. Mistakes = Mutations • Mutations are changes in the base sequence of the DNA molecules. • This can have serious affects on genes and the functions of cells. • Cancer is caused by mutations in DNA. Mutagens • Physical or chemical factor that increases the frequency of mutations. • Examples: UV rays, X-rays, smoking 3 Types of Mutations • Insertion • Deletion • Substitution MUTATIONS DO NOW: • What words do you think of when you hear the term mutations? Three Types 1. Substitute: one nitrogen base is substituted for another in the DNA strand • Normal DNA: TAGCGCTA ATCGCGAT Mutated DNA: TAGCGCTA ATCTCGAT Three Types • Insertion: One nitrogen base is inserted or added to a DNA strand • Normal DNA: TAGCGCTA ATCGCGAT • Mutated DNA: TAGCGCTA ATTCGCGAT Three Types 3. Deletion: one nitrogen base is deleted from the DNA strand • Normal DNA: TAGCGCTA ATCGCGAT Mutated DNA: TAGCGCTA ATCGCAT Substitution Examples Normal DNA: AAA ATG CTT DNA with Mutation: AAA ATG TTT mRNA: UUU UAC GAA mRNA: UUU UAC AAA Amino Acid: Phe-Tyr-Glu Amino Acid: Phe-Tyr-Lys Create: 1. DNA strand with one base inserted 2. DNA strand with one base deleted How does this effect amino acid sequence? Chromosomal Mutations • Deletion: loss of a piece of chromosome Mutation Type 2 & 3 • Inversion: chromosomal segment breaks off, flips around backward, and reattaches • Translocation: piece of one chromosome breaks off and reattaches to a nonhomologous chromosome Mutation Type #4 • Nondisjunction- chromosome fails to separate from it homologue Protein Synthesis Transcription DNA • Double stranded • Deoxyribose sugar • Thymine • Nucleus vs. RNA • Single stranded • Ribose sugar • Uracil • Anywhere 3 Types of RNA • Messenger RNA (mRNA): Carries information from DNA to ribosome for________________. protein synthesis • Transfer RNA (tRNA): Transport _________________. amino acids • Ribosomal RNA (rRNA): makes up the _____________. ribosomes Part 1:Steps of Transcription 1. An enzyme _________ attaches to a section of DNA, separating the two strands. 2. The enzyme moves down the DNA, building a strand of RNA that is complementary to the DNA. __________________ STOP code 3. The enzyme reads a ________ and the new strand of RNA is completed and moves into the cytoplasm _______________. Protein Synthesis Translation The genetic code • The base sequence is read in groups of ____________________________. three adjacent nucleotides • Each 3-nucleotide sequence is codon called a _________. • Each codon encodes for a specific stop amino acid a ______or start ______signal. ____________or Amino Acid Anti-codon Steps of Translation ribosome 1. mRNA attaches to a ____________. Amino acids floating in the cytoplasm are transported to tRNA the ribosome by _______. 2. The first tRNA binds to the start codon: AUG. ______ 3. Another tRNA binds to the next codon and carries the appropriate peptide bond forms amino acid. A __________________ between the two amino acids. 4. The first tRNA leaves and the ribsome moves across the next codon __________. 5. Another tRNA binds to the codon and attaches the corresponding polypeptide amino acid. The __________________ chain continues to grow. 6. Finally, the ribosome reads the ___________________, and the STOP codon polypeptide falls off the ribosome. http://www.wellesley.edu/Chemistry/chem227/nucleicfunction/translation/prtsynth.mov Amino acid polypeptide tRNA ribosome mRNA The final step of protein synthesis: The polypeptide made at the end of translation, folds into the proper shape ________, becoming a protein functional ________. The central dogma of biology DNA RNA protein