assignment 10

1,3,4

Speculate about why enhancers are not part of transcription of bacterial genes. Select the three correct answers. 1. There is little to no intergenic space on bacterial chromosomes, which makes long-range-acting enhancer sequences unnecessary. 2. The high level of mutation in bacterial genomes would likely alter these conservative sequences rendering them nonfunctional. 3. Bacterial operons make coordinate regulation of protein synthesis by enhancers unnecessary. 4. Enhancers often provide a mechanism for cell-specific transcription of genes, and most bacteria lack differentiated cell types. 5. Bacteria mostly regulate gene expression at the level of translation, making transcription enhancers unnecessary.

2,3,4

What is the role of enhancer sequences in transcription of eukaryotic genes? Select the three correct answers. 1. Enhancers act as alternative promoter sequences that increase the rate of transcription. 2. Enhancers increase the level of transcription of genes in a position independent manner. 3. Enhancers bind transcription factors that stimulate transcription of one or more genes. 4. Enhancers increase the level of transcription of genes in an orientation independent manner.

a. same sequence as RNA transcript (except for having T instead of U) b. produces stem-loop structure RNA transcripts c. recognized by subunit of RNA polymerase d. complementary to RNA transcript e. leads to an unstable RNA-DNA duplex ( Bacterial transcription is a four-stage process. 1. Promoter recognition: RNA polymerase is a holoenzyme composed of a five-subunit core enzyme and a sigma (σσ) subunit. Different types of σσ subunits aid in the recognition of different forms of bacterial promoters. The bacterial promoter is located immediately upstream of the starting point of transcription (identified as the +1 nucleotide of the gene). The promoter includes two short sequences, the -10 and -35 consensus sequences, which are recognized by the σσ subunit. 2. Chain initiation: The RNA polymerase holoenzyme first binds loosely to the promoter sequence and then binds tightly to it to form the closed promoter complex. An open promoter complex is formed once approximately 18 bp of DNA around the -10 consensus sequence are unwound. The holoenzyme then initiates RNA synthesis at the +1 nucleotide of the template strand. 3. Chain elongation: The RNA-coding region is the portion of the gene that is transcribed into RNA. RNA polymerase synthesizes RNA in the 5′ → 3′ direction as it moves along the template strand of DNA. The nucleotide sequence of the RNA transcript is complementary to that of the template strand and the same as that of the coding (nontemplate) strand, except that the transcript contains U instead of T. 4. Chain termination: Most bacterial genes have a pair of inverted repeats and a polyadenine sequence located downstream of the RNA-coding region. Transcription of the inverted repeats produces an RNA transcript that folds into a stem-loop structure. Transcription of the polyadenine sequence produces a poly-U sequence in the RNA transcript, which facilitates release of the transcript from the DNA.)

label Drag the labels to their appropriate locations in the diagram to describe the function or characteristics of each part of the gene. Not all labels will be used.