Question

13. (9 pts) (a) Draw out the general cis and trans elements of the yeast Gall locus in the absence of Galactose (Gall OFF, - Galactose). (b) What is one conceptual aspect of this regulation that is distinct from how prokaryotes tend to regulate gene expression? (c) In class, we talked about the activator bypass experiments. Draw out one experiment and the conclusion from this series of experiments.

Answer 1

DATELL Oleerviene genes of the yeart Galactose utilization UASG -UPSE UAS UAS S UASA र O GA17 GALI chromosome GAL2 Chrono le Vergeladtocab alectalets . Phosphate 4-lbimee hele tidylstand -serade Permeate Galacto linase Talanes Extracellular galectate intracellular galectole Gabetose phosphate UDP galeatose UDP _ glucose Galactose tlusese / pholphate

Gal80p GalBop Gal80p Gal4p Gal4p Gal4p Gal4p Transceptional machinery Galap +Galactose +ATP Gal3p Gai 3 Gal80p Gal3p Gal 30p Cytoplasm Cytoplasm Nucleus Nucleus Gal80p Galop Gal4o Gal4p Gal4p Gal4p +Galactose Transsctional machinery Sama terapie se

a.Above given are the diagrams

b.

To understand how gene expression is regulated, we must first understand how a gene codes for a functional protein in a cell. The process occurs in both prokaryotic and eukaryotic cells, just in slightly different manners.

Prokaryotic organisms are single-celled organisms that lack a cell nucleus, and their DNA therefore floats freely in the cell cytoplasm. To synthesize a protein, the processes of transcription and translation occur almost simultaneously. When the resulting protein is no longer needed, transcription stops. As a result, the primary method to control what type of protein and how much of each protein is expressed in a prokaryotic cell is the regulation of DNA transcription. All of the subsequent steps occur automatically. When more protein is required, more transcription occurs. Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.

Eukaryotic cells, in contrast, have intracellular organelles that add to their complexity. In eukaryotic cells, the DNA is contained inside the cell’s nucleus and there it is transcribed into RNA. The newly synthesized RNA is then transported out of the nucleus into the cytoplasm, where ribosomes translate the RNA into protein. The processes of transcription and translation are physically separated by the nuclear membrane; transcription occurs only within the nucleus, and translation occurs only outside the nucleus in the cytoplasm. The regulation of gene expression can occur at all stages of the process . Regulation may occur when the DNA is uncoiled and loosened from nucleosomes to bind transcription factors (epigenetic level), when the RNA is transcribed (transcriptional level), when the RNA is processed and exported to the cytoplasm after it is transcribed (post-transcriptional level), when the RNA is translated into protein (translational level), or after the protein has been made (post-translational level).

c.activator bypass performed in yeast and bacteria, have played an important role in formulating the idea that many transcriptional activators work by recruiting the transcriptional machinery to the promoter.

Experimental support: "Activator bypass" My A sequence-specific DNA-binding domain is experimentally fused directly to a component of the mediator # The hybrid protein lacks an activation domain It strongly stimulates transcription initiation when the DNA sequence to which it binds is placed in proximity to a promoter (B) Dr.2 asim 80 Lyesh Figure 7-43 part 2 of 2. Molecular Biology of the Cell, 4th Edition.