Lecture 10.10 Notes + Section 5 Study Guide Answers
Lecture 10.10 Notes + Section 5 Study Guide Answers MICRB 201
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This 3 page Class Notes was uploaded by Julianna Sickafus on Monday October 10, 2016. The Class Notes belongs to MICRB 201 at Pennsylvania State University taught by Dr. Steven Keating in Spring 2016. Since its upload, it has received 5 views. For similar materials see Introductory Microbiology in Microbiology at Pennsylvania State University.
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Date Created: 10/10/16
Microbiology 201 10/10 Lecture Notes Section 5 Study Guide Answers Mechanisms of DNA Replication -termination at terminus followed by unlinking of replicated chromosomes -replication is much faster in prokaryotes than eukaryotes -about 10x faster Gene Structure and Transcription Genes and terminology: -polynucleotide sequences (DNA or RNA in some viruses) that are transcribed -ie: converted into RNA -genes also known as cistrons -may encode mRNA, tRNA, rRNA, etc -final product of gene expression are not always proteins -genes start at the 3’ end of the template strand or 5’ of the non- template strand -orientation of genes described with respect to RNA product -since 5’ terminus is made first, genes begin at 5’ end and terminate at 3’ end -+1 signifies start site of transcription -upstream of translation site -translation start site is downstream of +1 -leader sequence of mRNA: -between +1 and translation start site -usually not translated -contains ribosome binding site (RBS) -sequence at 5’ region of mRNA that interacts with 3’ end of 16S rRNA to define translation start site -coding region/open reading frame (ORF) -in mRNA codes for polypeptide chain -on mRNA templates starts with 5’AUG3’ -on template strand of DNA, ORF starts with 3’TAC5’ -coding region on mRNA ends at stop codons -UGA, UAG, UAA -trailer: -untranslated region at 3’ end of gene -translation proceeds beyond stop codons and ends at terminator -mRNA in bacteria may be monocistronic or polycistronic -in eukaryotes -always monocistronic tRNA and rRNA Genes -generally, polycistronic in both prokaryotes and eukaryotes -individual rRNAs and tRNAs subsequently generated by post transcriptional cleavages Gene Structure and Transcription 1. A cistron is another word for a gene. A monocistronic transcript would encode only one gene whereas a polycistronic transcript would encode more than one. 2. This statement is a true statement if the strand being described is the template strand. Genes could also be described as starting at the 5’ end if the non-template strand was the one being described instead. 3. The +1 site signifies the start site of transcription and it is upstream of the translation start site. 4. The ribosome binding site is significant because it allows for a place for a ribosome to bind ahead of the gene that needs to be transcribed so that none of the sequence is lost. 5. a) monocistronic or polycistronic b) monocistronic c) polycistronic 6. A terminator sequence is where the transcription process stops. A terminus sequence describes a region of a bacterial chromosome where replication ends. These terms describe the end sequence of two different processes. 7. Prokaryotic cells contain one kind of RNA polymerase while eukaryotic cells contain three kinds of RNA polymerase. 8. Since prokaryotes do not have a 5’ cap like eukaryotes, RNA polymerase needs some sort of initiation factor to know where to start transcription. In prokaryotic cells, these are sigma factors. 9. The steps of mRNA maturation are splicing, capping, polyadenylation, and export to the cytoplasm. Introns are spliced out and exons are spliced together during splicing. To leave the nucleus, the mRNA strand requires a 5’ cap (capping) and a poly-A tail (polyadenylation). After these steps, the mRNA can leave the nucleus to be translated.
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