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Lecture

Murphy summ lec 3.doc

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Department
Biology
Course
Biology 1202B
Professor
Shauna Burke
Semester
Winter

Description
LECTURE 3: TRANSCRIPTION, CHAPTER 14, 15 similarity and differences between transcription in prokaryotes and eukaryotes cell - transcription and transla- tion occurs simultane- ously in prokaryote dsDNA = part of a chromosome, is a double stranded DNA, then it turns into a ssDNA ( DNA TEMPLATE STRAND) followin gin transcription ss- RNA nucleotides complementary to the DNA template, each codon / “triplet” 3 RNA nu- cleo- tifes ( universal code), translation, polypeptide is made - there are 3 stop codons: UAA, UGA, UAG, methyanine - start codon for transcription (AUG) TRANSCRIPTION Initially there is a du- plex a rna and dna hybrid, but then RNA starts to come out near the tail i..e the green one DNA is all wrapped and a single mRNA produced 3 Marks Steps of Tran- scription Initiation: Assembly of the transcription components on the promoters Elongation: Reading the string of nucleotides in a sequence of single stranded DNA and changing this information into a string of nucleotides of single strand- ed pre-mRNA Termination: Releas- ing pre-mRNA. Reassembly of dsDNA *transcription occurs in the nucleus of a eu- karyote cell* -Once an RNA poly- merase has started transcription & has moved out of the way of the pro- moter, another mole- cule of RNA polymerase may start creating an- other pre-RNA - DNA polymerase required an RNA primer however RNA poly- merase doesn’t require a primer, continues without one transcription by RNA polymera- seII. the 5’ cap is added soon after transcription begins, than the RNA transcription, then the RNA coding sequence is transcribed and the 3’ poly a tail is added In nucleus, pre-mRNA is processed into mRNA DNA has a promoter, 5’ TO 3’ UTR + most genes have in- trons and need to get rid of them and splice it together 1. capping, 2. poly a tail 3. splicing of the intron, premature Mrna = need to become mature, ready for translation Transcription by RNA polymerase II. The 5‘cap is added sn after transcription begins, then the RNA, coding sequence is transcribed and the 3’ poly A tail is added. * In prokaryotes & eukaryotes pre-mRNA contain regions that code for mRNA/protein & noncoding regions* 5’Cap guanine nucleotide that is reversed so that its 3’OH group faces the begin- ning rather than the end of the molecule. A capping enzyme adds the 5’cap to the pre-mRNA soon after transcription. Eukaryotic Termination of Trans
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