Answer: if a regulatory protein in its active state turns off the expression of the operon, the operon is said to be negatively regulated by the regulatory protein. if the regulatory protein in its active state truns on the operon, the operon is positively regulated by the regulatory protein. an operon regulated by a repressor is therefore negatively regulated, because the presence of the active repressor prevents transcription of that operon. in contrast, an operon regulated by an activator is positively regulated, because in its active state the activator protein turns on transcription of the operon under its control.the lac operon of E. coli repressor(lac repressor) is synthesized through the activity of the gene lac I, known as regulator gene. the active form of the lac repressor, is a tetramer that contains four copies of the gene I product. in the absence of the inducer, the repressor binds to the lac operator sequence, preventing RNA polymerase from binding to the promoter and transcribing the structural genes. thus the lac operon is negatively regulatedassociated with the lac operon, there is another site, 16 base pairs upstream of the promoter, which is used for a positive control of the gene expression. this site is called catabolic activator protein site or cyclic AMP(cAMP) protein site or catabolite gene activator(cga) site, because it is utilized for binding of CAP or cga to stimulate gene expression. CAP can bind to this site only when it is bound with cAMP. by binding to it, the CAP-cAMP complex exerts a positive control over the transcription process. it has an effect exactly opposite to that of repressor binding to an operator. yhe effector molecule cAMP determines the effect of CAP on lac operon transcription. presence of glucose inhibits the formation of cAMP and prevents it to bind to CAP
Answer: Both of these organisms initially produce organic acid ends products during the early incubation period. The low acid PH( 4 ) is stabilized and maintained by E. coli at the end of incubation. So, the methyl red indicator in the PH rage of 4 will turn red, which is indicative of a positive test. During the incubation period, E. aerogenes enzymatically converts these organic acids to non acid ends products such as 2-3 butanediol and acetoin, resulting the PH elevating up of 6. So, at a PH 6, it still indicating the presence of acid, but with a lower hydrogen ion concentration. Therefore, the indicator turns yellow and is a negative test.
Answer: 135 gram flannel sheets contain 135 grams of cotton (4.76198 ounces) per square meter of fabric. 190 gram flannel sheets contain 190 grams ( 6.70205 ounces) of cotton per meter of fabric. The more grams per square meter, the heavier ( and usually softer) the sheets will be.
Answer: Bacteria are gram positive or gram negative. Serratia happens to be a gram negative bacteria. They appear pink on a gram stain. Gram positive bacteria stain to a purple color on a gram stain. We can classify and ID bacteria using their gram stain and shape. Some antibiotics only work on gram negative bacteria and some only work on gram positive bacteria. It helps a doctor know which antibiotic to use.
Answer: Typical gram-positive bacteria are those staphylococci that produce boils; typical gram-negative bacteria are the bacilli that cause whooping cough; typical gram-variable bacteria are the bacilli that cause tuberculosis.
Answer: Bacteria are gram positive and gram negative (which means if you apply Gram stain to them, they either pick up the color (positive) or they do not (negative). Entamoeba Hystolytica is not a bacteria, it is a protozoa (one celled organism) that usually causes diarrhea and can be diagnosed from a stool sample and treated with drugs.
Answer: Most acid-fast microorganisms belong to the genus Mycobacterium because organisms of this species have a unique property where they have a lipid rich mycolic acid exterior that prevents ordinary dyes from penetrating.
When decolorized and counterstained, they maintain the red of the carbolfushin, thus they are acid fast.
E. coli is affected by the decolorization by the acid achohol and counterstain by the methylene blue dye because they lack the mycolic acid layer, thus they are non-acid fast.