BIO 105 1st Edition Lecture 11DNA Synthesis & Protein Synthesis/ RNALecture Outline: I. Know the four enzymes in replications and be able to match them with their dutyII. Know the three classes of RNAs and be able to match them with their dutyIII. Know about the codons Four Enzymes in Replication1. Helicase- enzyme that unwinds the two strands- “unzips” the DNA in pieces2. DNA polymerase- attaches new complementary nucleotides (brings new bases to the growing strand) (also correct errors)  matches pairs 3. Primase- RNA primer that starts the “lagging strand”- (thumb tack used to hold down lagging strand)4. DNA Ligase- fills in gaps in lagging strand pieces and “proofreads” DNA copied for errors (cuts out primases)Summary of four enzymes in replication: The Helicase unzips the two strands of DNA like unzipping a jacket. The DNA polymerase then matches pairs, A with T and G with C. The primase acts as a thumb tack to hold down the lagging strand. There always has to be a proofreader, so that is what the DNA Ligase does.  Steps from DNA to Proteins- Same two steps produce all proteins:1. DNA is transcribed to form RNAo Occurs in the nucleuso RNA moves into cytoplasm 2. RNA is translated to form polypeptide chains, which fold to form proteins Three Classes of RNAs- Messenger RNA- mRNA o Carries protein, building instruction- Ribosomal RNA- rRNAo Major component of ribosomes- Transfer RNA- tRNAo Delivers amino acids to ribosomesSummary of the Three Classes of RNAs: The mRNA makes a copy of the gene (recipe) and this happens inside the nucleus (kitchen). The rRNA cuts out all the extra material (or not needed ingredients). The tRNA shops for the amino acids for the genes (or the ingredients for the recipes). Promoter- title of recipe- A base sequence in the DNA that signals the start of a gene- For transcription to occur, RNA polymerase must first bind to a promoterKNOW THE FOLLOWING: 61 to 64 triplets code for 20 amino acids there are 3 stop codons, the codon AUG not only codes for the amino acid methionine but also indicates the start of translation- A tRNA (goffer) molecule consists of a strand of about 80 nucleotides that folds back on itself to form a three- dimensional structure- The P site (“park site”)- holds the tRNA carrying the growing polypeptide chain- The A site (“arrival”) carries the tRNA with the next amino acidSummary of Sites: You PARK at the store ARRIVE inside the store and then EXIT the store- Termination occurs when one of the three stop codons reaches the A site- A release factor binds to the stop codon Key Points/ Differences- Eukaryotes- one mRNA = one protein/ polpeptide- Eukarytoes- DNA forms a stable, compacted complex with histones- Eukaryotic DNA- contains large regions of repetitive DNA, much DOES NOT code for proteins (-98% is non-coding in humans) Most genes are turned off- Cells of a multicelled organism rarely use more than 5-10 percent of their genes at any given time- The remaining genes are selectively expressed- Cell differentiation starts in the