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 DNARNA Deoxyribose is 5-carbon sugar Ribose is 5-carbon sugar Double strandedSingle stranded Contains bases A, T, G, CContains bases A, U (uracil), G, C **U bonds to A

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

7. Animations http://www.fed.cuhk.edu.hk/~johnson/teachin g/genetics/animations/transcription.htm http://www.fed.cuhk.edu.hk/~johnson/teachin g/genetics/animations/transcription.htm http://www.johnkyrk.com/DNAtranscription.ht ml http://www.johnkyrk.com/DNAtranscription.ht ml

8. 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

9. 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.

10. 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

11. 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

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

13. 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

14. 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

15. 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

16. 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

17. 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