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Chapter 8: DNA and RNA

Chapter 8: DNA and RNA. Section 8-3: RNA. Introductory Question. How is the genetic code decoded? What does it say?. RNA. RNA = ribonucleic acid Molecule used to decode the genetic information found in DNA Carries out the instruction coded in DNA. RNA vs DNA. Transcription.

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Chapter 8: DNA and RNA

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  1. Chapter 8:DNA and RNA Section 8-3: RNA

  2. Introductory Question • How is the genetic code decoded? • What does it say?

  3. RNA • RNA = ribonucleic acid • Molecule used to decode the genetic information found in DNA • Carries out the instruction coded in DNA

  4. RNA vs DNA

  5. Transcription • Process of making RNA from DNA template • Part of DNA sequence is transcribed (copied) into RNA • RNA polymerase carries out transcription by binding directly to DNA and matching nucleotides one at a time AACTGT on DNA UUGACA on RNA

  6. Animations • http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animations/transcription.htm • http://www.johnkyrk.com/DNAtranscription.html

  7. Transcription • Transcription begins at a special “start” sequence on the DNA (promoter) and ends at a “stop” sequence • Usually, one gene is transcribed at a time

  8. Why go through the trouble? • By using RNA as an intermediary, the cell is able to copy the same DNA sequence over and over if needed, allowing the DNA to stay intact.

  9. Forms of RNA • Messenger RNA (mRNA) • Carries copies of the instructions to make a protein • Acts as “messenger” between DNA and the rest of the cell

  10. Forms of RNA • Ribosomal RNA (rRNA) • Remember that proteins are assembled at ribosomes • Ribosomes are composed of several dozen proteins and a unit of rRNA

  11. Forms of RNA • Transfer RNA (tRNA) • Used to transfer one amino acid after another to the ribosome when proteins are assembled

  12. The Genetic Code • There are 20 different amino acids that make up all proteins • The genetic code = the language of instructions in DNA and RNA • Nucleotides in mRNA are read in groups of three

  13. Codons • A group of 3 nucleotides in mRNA is called a codon and specifies a particular amino acid • Example: mRNA AAACACGGU read as AAA – CAC – GGU Lysine – Histidine – Glycine

  14. Codons • More than one codon for each amino acid • Example: UUU and UUC = phenylalanine • AUG is called the start or initiation codon (codes for methionine, which is usually the first amino acid in a protein) • The three stop or termination codons are UAA, UAG, and UGA

  15. Translation • Process in which nucleotide sequence in mRNA is decoded into a series of amino acids to make a protein (all forms of RNA) • mRNA decoded at ribosome, where tRNA brings amino acids needed (tRNA = anticodon) • P. 185 – mRNA gets “read” at ribosome and “translated” into an amino acid sequence

  16. Genes and Proteins • A gene is a section of DNA the directs the synthesis of a protein • DNA transcribed into mRNA • mRNA translated into an amino acid sequence to form a protein at a ribosome • Proteins control traits

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