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Warm-Up 10/28

Warm-Up 10/28. What are some major differences between DNA and RNA?. 8.4 Transcription. Central Dogma of Molecular Biology. Information flows in one direction DNA  RNA  protein Replication copies DNA Transcription converts DNA to RNA

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Warm-Up 10/28

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  1. Warm-Up 10/28 • What are some major differences between DNA and RNA?

  2. 8.4 Transcription

  3. Central Dogma of Molecular Biology • Information flows in one direction • DNA  RNA  protein • Replication copies DNA • Transcription converts DNA to RNA • Translation interprets RNA into a string of amino acids (protein)

  4. Where does transcription occur? • Prokaryotes • Replication, transcription and translation all occur in the cytoplasm • Eukaryotes • Replication and transcription happen in the nucleus which stores the DNA • Translation happens in the cytoplasm *we will focus on Eukaryotes from here on

  5. RNA • Ribonucleic acid • Still made of sugar (ribose), phosphate group and nitrogenous base • Consider it to be temporary copy of DNA that is used and destroyed

  6. RNA differs from DNA in 3 ways • The sugar has an extra oxygen- ribose instead of deoxyribose • A nitrogenous base called Uracil (U) replaces Thymine and pairs with Adenine • So in RNA we’ve got G-C and A-U • RNA is single-stranded, not a double helix

  7. Transcription • process of copying DNA to make a complementary strand of RNA • Just as DNA is catalyzed by DNA polymerase, transcription is catalyzed by RNA polymerase

  8. 3 Steps of Transcription • RNA polymerase and other enzymes and proteins assemble at the transcription start site on a segment of DNA (gene) then the strands of the double helix are unwound

  9. 3 Steps of Transcription 2. RNA polymerase, using only ONE strand of DNA as a template, creates the complementary RNA strand which will hang freely as the DNA “zips back up” What is the complementary RNA Strand to this DNA segment? AATCGAATTTAGCCGGGATTGCA

  10. 3 Steps of Transcription 3. Once the gene has been transcribed it detaches itself from the DNA

  11. Transcription Produces 3 types of RNA • Messenger RNA (mRNA) • Intermediate message that is translated by a ribosome to make a protein • Ribosomal RNA (rRNA) • Forms a part of ribosomes • Transfer RNA (tRNA) • Brings amino acids from the cytoplasm to a ribosome to help make the growing protein

  12. Questions • How do DNA and RNA differ? • Explain why transcription occurs in the nucleus of eukaryotes. • Why must the DNA strands unwind and separate before transcription can take place? • What happens to the RNA transcript after it separates from the DNA in step 3?

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