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Lesson Overview

Lesson Overview. 13.1 RNA. The Role of RNA. How does RNA differ from DNA? sugar in RNA is ribose instead of deoxyribose (2) RNA is generally single-stranded and not double- stranded (3) RNA contains uracil (U) in place of thymine (T). Comparing RNA and DNA.

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Lesson Overview

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  1. Lesson Overview 13.1 RNA

  2. The Role of RNA How does RNA differ from DNA? • sugar in RNA is ribose instead of deoxyribose (2) RNA is generally single-stranded and not double- stranded (3) RNA contains uracil (U) in place of thymine (T)

  3. Comparing RNA and DNA • RNA copies info from DNA and can take that info OUTSIDE of the nucleus safely • Job of RNA is to assemble amino acids into proteins

  4. Functions of RNA • The three main types of RNA are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA)

  5. Messenger RNA • The RNA molecules that carry copies of DNA instructions are known as messenger RNA (mRNA)

  6. Ribosomal RNA • ribosomal RNA (rRNA) - makes up the ribosome (where mRNA gets “read”)

  7. Transfer RNA • transfer RNA (tRNA) – carries (transfers) each amino acid to the ribosome

  8. Transcription • Using template from DNA to make RNA • Takes place in nucleus • Makes single strand of RNA • Uracil (U) is paired up with adenine (A)

  9. Transcription • THREE MAJOR STEPS: • 1. INITIATION – RNA polymerase attaches to promoter region and unwinds DNA • 2. ELONGATION – RNA polymerase adds bases (A, U, C, G) to make transcript • 3. TERMINATION – transcript reaches termination site and is released

  10. Transcription • Transcription requires an enzyme, known as RNA polymerase, that is similar to DNA polymerase/helicase • - unwinds DNA strands and pairs up bases • http://www.wwnorton.com/college/biology/discoverbio3/core/content/index/animations.asp

  11. RNA Editing • Sometimes RNA needs to be modified (edited) • INTRONS – portions of RNA that are cut out and discarded • EXONS - The remaining pieces thjat are put back together

  12. Lesson Overview 13.2 Ribosomes and Protein Synthesis

  13. The Genetic Code • The first step in decoding genetic messages is to transcribe a nucleotide base sequence from DNA to RNA • The transcript contains a code for making proteins

  14. The Genetic Code • Proteins are made by joining amino acids together into long chains, called polypeptides. • As many as 20 different amino acids are commonly found in polypeptides.

  15. The Genetic Code • Each three-letter “word” in mRNA = codon • A codon consists of three consecutive bases that specify a single amino acid to be added to the polypeptide chain

  16. How to Read Codons • Because there are four different bases in RNA, there are 64 possible three-base codons (4 × 4 × 4 = 64) in the genetic code

  17. Start and Stop Codons • The codon AUG serves as the START codon for protein synthesis. • After AUG, mRNA is read until it reaches one of three different “stop” codons

  18. Translation • The decoding of an mRNA message into a protein is a process known as translation • Happens at the ribosome (in cytosol/cytoplasm) • http://www.wwnorton.com/college/biology/discoverbio3/core/content/index/animations.asp • http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter12/animation_quiz_2.html

  19. Steps in Translation • 1. ribosome attaches to an mRNA molecule in the cytoplasm

  20. Steps in Translation • 2. ribosome reads each codon of mRNA, and directs tRNA to bring the specified amino acid into the ribosome

  21. Steps in Translation • 3. the ribosome then attaches each amino acid to the growing chain (attaching them together by PEPTIDE bonds

  22. Steps in Translation • 4. The polypeptide chain continues to grow until the ribosome reaches a “stop” codon on the mRNA molecule

  23. Steps in Translation • Each tRNA molecule carries just one kind of amino acid • In addition, each tRNA molecule has three unpaired bases, collectively called the anticodon—which is complementary to one mRNA codon

  24. The Molecular Basis of Heredity • The central dogma of molecular biology is that information is transferred from DNA to RNA to protein

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