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Lesson Overview Fermentation Lesson Overview 13.1 RNA Lesson Overview Fermentation The Role of RNA How does RNA differ from DNA? (1) sugar in RNA is ribose instead of deoxyribose (2) RNA is generally single-stranded and not doublestranded (3) RNA contains uracil (U) in place of thymine (T) Lesson Overview Fermentation 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 Lesson Overview Fermentation Functions of RNA The three main types of RNA are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA) Lesson Overview Fermentation Messenger RNA The RNA molecules that carry copies of DNA instructions are known as messenger RNA (mRNA) Lesson Overview Fermentation Ribosomal RNA ribosomal RNA (rRNA) makes up the ribosome (where mRNA gets “read”) Lesson Overview Fermentation Transfer RNA transfer RNA (tRNA) – carries (transfers) each amino acid to the ribosome Lesson Overview Fermentation 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) Lesson Overview Fermentation 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 Lesson Overview Fermentation 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 Lesson Overview Fermentation 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 Lesson Overview Ribosomes and Protein Synthesis Lesson Overview 13.2 Ribosomes and Protein Synthesis Lesson Overview Ribosomes and Protein Synthesis 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 Lesson Overview Ribosomes and Protein Synthesis 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. Lesson Overview Ribosomes and Protein Synthesis 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 Lesson Overview Ribosomes and Protein Synthesis 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 Lesson Overview Ribosomes and Protein Synthesis 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 Lesson Overview Ribosomes and Protein Synthesis 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/ani mations.asp http://highered.mcgrawhill.com/sites/0072556781/student_view0/chapter12/animation_quiz_2.html Lesson Overview Ribosomes and Protein Synthesis Steps in Translation 1. ribosome attaches to an mRNA molecule in the cytoplasm Lesson Overview Ribosomes and Protein Synthesis Steps in Translation 2. ribosome reads each codon of mRNA, and directs tRNA to bring the specified amino acid into the ribosome Lesson Overview Ribosomes and Protein Synthesis Steps in Translation 3. the ribosome then attaches each amino acid to the growing chain (attaching them together by PEPTIDE bonds Lesson Overview Ribosomes and Protein Synthesis Steps in Translation 4. The polypeptide chain continues to grow until the ribosome reaches a “stop” codon on the mRNA molecule Lesson Overview Ribosomes and Protein Synthesis 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 Lesson Overview Ribosomes and Protein Synthesis The Molecular Basis of Heredity The central dogma of molecular biology is that information is transferred from DNA to RNA to protein