DORSAL VENTRAL PATTERNING IN DROSOPHILA
03:10

DORSAL VENTRAL PATTERNING IN DROSOPHILA

#DROSOPHILA #AXIS_FORMATION #DORSAL_VENTRAL_AXIS Generating the Dorsal-Ventral Axis (Dorsal-ventral patterning in the oocyte) • In this video we are going to learn about how dorsal-ventral patterning occurs in drosophila oocytes. • As oocyte volume increases, the Oocyte nucleus travels to the anterior dorsal side of the oocyte where it localizes gurken mRNA responsible for establishing the anterior-posterior axis. • This gurken mRNA also initiates the formation of the dorsal-ventral axis. • The gurken signal is received by the Torpedo proteins made by somatic follicle cells. • Due to the short diffusibility of the signal, only the follicle cells closest to the oocyte nucleus (i.e., the dorsal follicle cells) receive the Gurken signal, which causes the follicle cells to differentiate into a dorsal morphology and inhibit the synthesis of pipe protein. • This establishes the dorsal-ventral polarity in the follicle cell layer that surrounds the growing oocyte. • Hence, now the pipe protein is made only by the ventral follicle cells. • Maternal deficiencies of either gurken or torpedo gene cause ventralization of the embryo. • Pipe signal sulfates the ventral vitelline proteins and hence modifies the vitelline envelope. • Now, this sulfated vitelline membrane protein recruits Gastrulation defective (GD) which in turn cleaves Snake to its active form and forms a complex with Snake and then cleave Easter proteins into its active protease form. • Easter then cleaves the Spätzle protein and activated Spätzle binds to Toll receptor protein. • This Toll protein is a maternal product that is evenly distributed throughout the cell membrane of the egg but gets activated only after binding with Spätzle protein. • Toll activation activates Tube protein and a protein kinase called Pelle, which phosphorylate the Cactus protein bound to dorsal protein. • After phosphorylation, Cactus is degraded, releasing it from Dorsal. • Now this dorsal protein get free and enters the nucleus and thereafter ventralizes the cell by activating those genes responsible for specifying ventral cell types. • Hence, the dorsal protein is responsible for distinguishing the dorsum from ventrum in the fly embryo. • The Dorsal protein signals the first morphogenetic event of Drosophila gastrulation. • In the 16 ventral most cells of the embryo—those cells containing the highest amount of Dorsal in their nuclei—invaginate into the body and form the mesoderm and those cells present at more lateral become neurogenic ectoderm.
Attenuation in trp Operon || Gene regulation in Prokaryotes
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Attenuation in trp Operon || Gene regulation in Prokaryotes

#attenuation #trp_operon #gene_regulation Attenuation is a regulatory mechanism used in bacterial operons to ensure proper transcription and translation. In bacteria, transcription and translation are capable of proceeding simultaneously. The need to prevent unregulated and unnecessary gene expression can be prevented by attenuation, which is characterized as a regulatory mechanism. The process of attenuation involves the presence of a stop signal that indicates premature termination. The stop signal, referred to as the attenuator, prevents the proper function of the ribosomal complex, stopping the process. The attenuator is transcribed from the appropriate DNA sequence and its effects are dependent on the metabolic environment. In times of need, the attenuator within the mRNA sequence will be bypassed by the ribosome and proper translation will occur. However, if there is not a need for a mRNA molecule to be translated but the process was simultaneously initiated, the attenuator will prevent further transcription and cause a premature termination. Hence, attenuators can function in either transcription-attenuation or translation-attenuation. Transcription-attenuation is characterized by the presence of 5′-cis acting regulatory regions that fold into alternative RNA structures which can terminate transcription. These RNA structures dictate whether transcription will proceed successfully or be terminated early, specifically, by causing transcription-attenuation. The result is a misfolded RNA structure where the Rho-independent terminator disrupts transcription and produced a non-functional RNA product. This characterizes the mechanisms of transcription-attenuation. The other RNA structure produced will be an anti-terminator that allows transcription to proceed. Translation-attenuation is characterized by the sequestration of the Shine-Dalgarno sequence, which is a bacterial specific sequence that indicates the site for ribosomal binding to allow for proper translation to occur. However, in translation-attenuation, the attenuation mechanism results in the Shine-Dalgarno sequence forming as a hairpin-loop structure. The formation of this hairpin-loop structure results in the inability of the ribosomal complexes to form and proceed with proper translation. Hence, this specific process is referred to as translation-attenuation.
Lac Operon Animation (Advanced) || Lac Operon mutations || Gene regulation in Prokaryotes
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Lac Operon Animation (Advanced) || Lac Operon mutations || Gene regulation in Prokaryotes

#lacoperon #operon #generegulation Bacteria adapt to changes in their surroundings by using regulatory proteins to turn groups of genes on and off in response to various environmental signals. Francois Jacob and Jacques Monod received the Nobel Prize for their experiments which increased our basic understanding of how the lactose metabolizing genes are regulated in E. coli. There are three structural (protein-coding) genes involved in lactose metabolism in E. coli. These 3 lac genes are organized into the lac operon. An operon is a cluster of genes along with an adjacent promoter and operator that control the transcription of those genes. When the structural genes in an operon are transcribed, a single mRNA is produced. This mRNA is said to be polycistronic, because it carries the information for more than one type of protein. lacz+ encodes beta galactosidase which breaks down lactose into glucose and galactose. lacY+ encodes lactose permease which transports lactose into the cell. lacA+ encodes transacetylase whose function is not fully understood. The operator (laco+) is a short region of DNA that lies partially within the promoter and that interacts with a regulatory protein that controls the transcription of the operon. The regulatory gene lacI+ produces an mRNA from which is synthesized a repressor protein, that can bind to the operator of the lac operon. The general term for the product of a regulatory gene is a regulatory protein. The lac regulatory protein is called a repressor because it keeps RNA polymerase from transcribing the structural genes. In the absence of lactose, the lac repressor binds to the operator and keeps RNA polymerase from transcribing the lac genes. When lactose is present, small amounts of it are converted to an isomer called allolactose which acts as an inducer to turn on the lac genes. The lac genes are expressed because allolactose binds to the lac repressor protein, changing its shape so that it cannot bind to the lac operator. RNA polymerase can then bind to the promoter and transcribe the lac genes. Jacob and Monod produced mutations in the lac operon to show how they may affect the regulation of gene expression. They produced a mutation in the lacI gene (lacI-) such that mutant, inactive repressor proteins were synthesized. These proteins cannot bind to the operator. The result is that the structural genes are expressed constitutively, that is, in the presence or absence of lactose. Mutations in the operator are called constitutive (lacOc). DNA base-pair alterations in the operator region make this sequence unrecognizable to the repressor protein. Since the lac repressor cannot bind, the structural genes are constitutively (always) expressed in the absence or presence of lactose. Another mutation in the lacI gene called lacls (superrepressor) showed no synthesis of the lac enzymes in the presence or absence of lactose. This mutant repressor protein binds to the operator but is unable to recognize allolactose. Therefore, the lac repressor binds to the operator even in the presence of allolactose, and transcription does not occur. The lac operon is one example of how bacteria can turn on or turn off genes in response to environmental conditions. The presence of lactose induces the synthesis of enzymes necessary to convert lactose into glucose. Mutations in this operon demonstrate how the different regions are controlled. Music: Royalty Free Music from Bensound
Lac Operon (Basic) Animation || Gene regulation in Prokaryotes
03:01

Lac Operon (Basic) Animation || Gene regulation in Prokaryotes

#lacoperon #operon #generegulation The promoter is the binding site for RNA polymerase, the enzyme that performs transcription. The operator is a negative regulatory site bound by the lac repressor protein. The operator overlaps with the promoter, and when the lac repressor is bound, RNA polymerase cannot bind to the promoter and start transcription. The CAP binding site is a positive regulatory site that is bound by catabolite activator protein (CAP). When CAP is bound to this site, it promotes transcription by helping RNA polymerase bind to the promoter. Let's take a closer look at the lac repressor and CAP and their roles in regulation of the lac operon. The lac repressor The lac repressor is a protein that represses (inhibits) transcription of the lac operon. It does this by binding to the operator, which partially overlaps with the promoter. When bound, the lac repressor gets in RNA polymerase's way and keeps it from transcribing the operon. [Where does the lac repressor come from?] When lactose is not available, the lac repressor binds tightly to the operator, preventing transcription by RNA polymerase. However, when lactose is present, the lac repressor loses its ability to bind DNA. It floats off the operator, clearing the way for RNA polymerase to transcribe the operon. The promoter is the binding site for RNA polymerase, the enzyme that performs transcription. The operator is a negative regulatory site bound by the lac repressor protein. The operator overlaps with the promoter, and when the lac repressor is bound, RNA polymerase cannot bind to the promoter and start transcription. The CAP binding site is a positive regulatory site that is bound by catabolite activator protein (CAP). When CAP is bound to this site, it promotes transcription by helping RNA polymerase bind to the promoter. Let's take a closer look at the lac repressor and CAP and their roles in regulation of the lac operon. The lac repressor The lac repressor is a protein that represses (inhibits) transcription of the lac operon. It does this by binding to the operator, which partially overlaps with the promoter. When bound, the lac repressor gets in RNA polymerase's way and keeps it from transcribing the operon. [Where does the lac repressor come from?] When lactose is not available, the lac repressor binds tightly to the operator, preventing transcription by RNA polymerase. However, when lactose is present, the lac repressor loses its ability to bind DNA. It floats off the operator, clearing the way for RNA polymerase to transcribe the operon. This change in the lac repressor is caused by the small molecule allolactose, an isomer (rearranged version) of lactose. When lactose is available, some molecules will be converted to allolactose inside the cell. Allolactose binds to the lac repressor and makes it change shape so it can no longer bind DNA. Allolactose is an example of an inducer, a small molecule that triggers expression of a gene or operon. The lac operon is considered an inducible operon because it is usually turned off (repressed), but can be turned on in the presence of the inducer allolactose. Music: Royalty Free Music from Bensound