BIO 105 1st Edition Lecture 11 DNA Synthesis Protein Synthesis RNA Lecture Outline I II III Know the four enzymes in replications and be able to match them with their duty Know the three classes of RNAs and be able to match them with their duty Know about the codons Four Enzymes in Replication 1 Helicase enzyme that unwinds the two strands unzips the DNA in pieces 2 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 RNA o Occurs in the nucleus o 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 rRNA o Major component of ribosomes Transfer RNA tRNA o Delivers amino acids to ribosomes Summary 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 promoter KNOW 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 acid Summary 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 embryo