Structure Types of RNA Transcription RNA-UNIT 6 CONT. RNA =RiboNucleic Acid STRUCTURE Polymer Single stranded Monomers Nucleotides RNA NUCLEOTIDES Monomers made of 3 parts each: Phosphate Group Ribose Sugar 1 of 4 nitrogen bases C, A, G, and U! U = Uracil No Thymine! URACIL Pyrimidine-why? Pairs with adenine COMPARE RNA TO DNA 3 TYPES OF RNA 1. Messenger RNA (mRNA) “Records” information from the DNA in the nucleus and transports it out of the nucleus to the ribosomes 3 TYPES OF RNA 2. Transfer RNA (tRNA) Delivers amino acids to site of protein synthesis (ribosomes) 3. Ribosomal RNA (rRNA) Helps with ribosome structure; function not entirely understood We will not go into detail on these second 2 until next week! WHY IS MRNA IMPORTANT? DNA is at risk of being damaged if it leaves the nucleus The info in DNA is copied into mRNA mRNA is able to leave nucleus and travel to ribosomes (site of protein synthesis) WHY IS TRNA IMPORTANT? It brings amino acids to ribosomes to form protein strand. HOW DO WE GET MRNA FROM DNA? Transcription 4 Steps (similar to replication) What is different between transcription and DNA replication? STEPS OF TRANSCRIPTION 1. DNA is “unzipped” (HELICASE) 2. Match correct nucleotides according to base pair rules *On only one side of the DNA (RNA POLYMERASE) *U’s not T’s! STEPS OF TRANSCRIPTION 3. Bonding-covalent bonds form between sugar and phosphates *Why don’t the hydrogen bonds remain? 4. Transcription occurs until a “stop sign” is reached and the mRNA strand is complete Transcription Animation GENETIC CODE - TRANSLATION 3 Nitrogen bases represents 1 CODON = 1 AMINO ACID 64 possible codons 3 “stop” codons 61 code for amino acids (20 possibilities) 1 codes to start = AUG = methionine Code is universal – codons represent the same amino acid in all organisms CODON DECODER CODON CHART Use your codon chart to answer the following: 1. How many different codons code for valine? 2. The codon CGU is for which amino acid? 3. What are the codons for the three “stops”? 4. What are the first 3 amino acids for this strand of mRNA?