BIOL 302 Lecture 6 Outline of Last Lecture I. DNA duplicationa. Semiconservative replicationb. Replication forkc. DNA polymerased. Lagging strand, leading strandII. DNA synthesisa. Telomeresb. Sickle cell anemiaIII. DNA mismatch repaira. Depurinationb. Deaminationc. MutationsIV. Basic DNA repairOutline of Current Lecture I. Synthesis of Proteina. Genetic infob. Intramolecular base pairsII. TranscriptionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. RNA polymerase in eukaryotesIII. Prokaryote vs eukaryote RNA transcriptsIV. TranslationV. UPPCurrent LectureCh. 7 From DNA to Protein: How Cells Read the GenomeGenetic info directs the synthesis of protein- This flow of genetic info in cells from DNA to RNA to protein is so fundamental that it hasbeen termed the central dogma of molecular biology- The central dogma of molecular biology was first articulated in 1958 by Francis Crick, who discovered DNA structure with James Watson- Transcription: copy the nucleotide sequence of DNA into RNA- Translation: use the info in RNA to make proteinGenes can be expressed with different efficiencies- Gene A is transcribed and translated much more efficiently than gene B- This allows the amount of protein A in the cell to be much higher than that of protein BThe chemical structure of RNA differs slightly from that of DNA- RNA contains the sugar ribose, which differs from deoxyribose, the sugar used in DNA, by the presence of an additional –OH group.- RNA contains the bases adenine, guanine, cytosine, and uracil, which differs from thymine, the equivalent base in DNA, by the absence of a –CH3 group- The chemical linkage b/w nucleotides in RNA is the same as that in DNAUracil forms a base pair with adenine- Despite the absence of a methyl group, uracil has the same base pairing properties as thymine- Thus, U-A base pairs closely resemble T-A base pairsRNA molecules can form intramolecular base pairs and fold into specific structures- RNA is single stranded, but it often contains short stretches of nucleotides that can basepair with complementary sequences found elsewhere on the same molecule- The conventional (Watson –Crick) base pair interaction and “nonconventional” base interaction pair, allow a RNA molecule to fold into a three dimensional structure that is determined by its sequence of nucleotides.Transcription produces a RNA complementary to one strand of DNA- The nontemplate strand of the DNA is sometimes called the coding strand because its sequence is equivalent to the RNA product.- The RNA chain produced by the transcription is called the transcript and has nucleotide sequence exactly complementary to the template strandDNA is transcribed by the enzyme RNA polymerase- The RNA polymerases catalyze the formation of the phosphodiester bonds that link the nucleotides together and form the sugar-phosphate backbone of the RNA chain- The RNA polymerase moves along the DNA, unwinding the DNA helix in front of it.- Using an exposed DNA strand as a template, the polymerase adds nucleotides one by one to the RNA chain at the polymerization site.- As it moves along the DNA template, the polymerase displaces the newly formed RNA, allowing the two strands of DNA behind the polymerase to rewind- A short region of hybrid DNA/RNA helix (about nine nucleotides in length) therefore forms only transiently, causing a window of DNA/RNA helix to move along the DNA with the polymeraseTranscription can be visualized in the electron microscope- The micrograph shows many molecules of RNA polymerase simultaneously transcribing two adjacent genes- Molecules of RNA polymerase are visible as series of dots along the DNA with transcripts(fine threads)attached to them- rRNAs transcribed from genes are used directly as components of ribosomes, the machines on which translation takes place- the particles at the 5’ end (free end) of each rRNA transcript are believed to be ribosomal proteins that have assembled on the rRNASignals in the sequence of a gene determine where bacterial RNA polymerase starts and stops transcription- Bacterial RNA polymerase contains a subunit called the sigma factor that recognizes the promoter on the DNA- Once transcription has begun, the sigma factor is released and the polymerase continuessynthesizing the RNA without it- Chain elongation continues until the polymerase encounters a termination signal (terminator or stop site) in the DNA- There the enzyme halts and releases both the DNA template and the newly made mRNA- The polymerase then reassociates with a free sigma factor and searches for another promoter to begin the process againBacterial promoters and terminators have specific nucleotide sequences that are recognized by RNA polymerase- The first nucleotide transcribed is designated as: +1 (start site)- The asymmetry of the promoter with the conserved -35 sequence located upstream of the -10 sequence, orients the RNA polymerase and determines the direction of transcription- Terminator is the stop signal for transcriptionSome genes are transcribed using one DNA strand as a template, whereas others are transcribed using the other DNA strand- The direction of transcription is determined by the orientation of the promoter at the beginning of each gene- The genes transcribed form left to right use the bottom DNA strand as the template, whereas those transcribed from right to left use the top strand as the templateThe three RNA polymerase in eukaryotic cells- While bacteria contain a single type of RNA polymerase, eukaryotic cells have three (RNA polymerase I, II, and III)- The bacterial RNA polymerase (along with its sigma subunit) is able to initiate transcription on its own, whereas eukaryotic RNA polymerases require the assistance of a large set of accessory proteins. Principle among these are the general transcription factors, which must assemble at each promoter along with the polymerase before the polymerase can begin transcription- The mechanisms that control transcription initiation in eukaryotes are much more elaborate than those in prokaryotes- Eukaryotic transcription initiation must take into account the packing of DNA into nucleosome and more compact forms of chromatin structureEukaryotic RNA polymerase II requires general transcription factors for transcription initiation -