Nate ofthe Iucroscopc Nam: ofthe parts ofthe microscope and their functions_ Know calculate the final magnification Using "Pcili objective lens Know what kind ...

The bacterium 3. Mycobacterium tuberculosis, the cause of tuberculosis, can invade the lungs and persist in a latent state for years. During this time, the bacteria reside in granulomas nodular scars containing bacteria and host-cell debris in the center and surrounded by immune cells. The granulomas are lipid-rich, oxygen-poor environments. How these bacteria manage to persist is something of a mystery. The results of recent research suggest that the glyoxylate cycle is required for the persistence. The following data show the amount of bacteria [presented as colony-forming units (cfu)] in mice lungs in the weeks after an infection. In graph $A$, the black circles represent the results for wild-type bacteria and the red circles represent the results for bacteria from which the gene for isocitrate lyase was deleted. (a) What is the effect of the absence of isocitrate lyase? The techniques described in Chapter 5 were used to reinsert the gene encoding isocitrate lyase into bacteria from which it had previously been deleted. In graph $\mathrm{B},$ black circles represent bacteria into which the gene was reinserted and red circles represent bacteria in which the gene was still missing. (b) Do these results support those obtained in part $a$ ? (c) What is the purpose of the experiment in part $b$ ? (d) Why do these bacteria perish in the absence of the glyoxylate cycle? (GRAPH CAN'T COPY)

Let us complete the following statement. The purpose of gram staining is blank. Let's discuss gram staining. Gram staining, also called grimm's method, is a method of staining used to distinguish and classify bacterial species into two large groups gram positive bacteria and grab negative bacteria. Let us revisit our sentence again and completed. The purpose of gram staining is to infer the structure of a bacterial cell wall and the bacterial response to antibiotics. Mhm.

Uh huh. Let us complete the following sentence. The process of gram staining is used to what? So now let us go back and reread our statement and fill in the blank. The process of gram staining is used to in for the structure of the cell wall of bacteria and their response to antibiotics.

Those question explains a simple procedure. An experiment. Um, and they were just looking at the fraction of cells and my toes is over time and were given a graph for this. So promotion, eh? It asks what all cells be accepted are expected to contain the radioactive DNA. Um, after they are labeled in the experiment and on lee the cells that are in the S phase of their cell cycle, Um, and the ass phasing that cells are making DNA. Um, during the 30 minute labeling period may contain any radioactive unite number. Question be it asks. Initially, there are no my tonic cells that contain radioactive DNA. We want to know why. This is, um so initially might have excels contained no radioactive Dina, because these cells, um, we're not engaged And, uh, Deena synthesis during living period. It takes about two hours for the 1st 8 will make hot Excel with here. Next, we went to explain the rise and fall, and then the rise again of this curve that we see and just for reference, the curve looks something like this. Besides, what? This question is your friend. So the initial rise of the curve corresponds to cells that were just finishing DNA replication. When the radioactive diamond in was added, a curve rises, more is more labelled. Cells entered my toe, sis, and the peak corresponds to those cells. I just started the s phase in the radioactive gravity was added. So this first arise is, um so starting ass fades. Whether that was they were just finishing it when this, I mean, it was at or they were just starting it when it was added, the labelled cells, then exit for my toes is replaced by unable. Night hot excels which were not in the s phase during the labeling period. So cells then exit my closest and that's the fall and last after 20 hours occur. So it's rising again because it labeled toes. Enter second, my cases and lastly, want to estimate the length of the S phase from this graph. So the initial two hour lag before any label might have excels appear corresponds to the G T phase. Um, which is the time between the end of the S phase and beginning of my toe sis. The first labelled cells seen in my toes is where those just finishing s phase when they radioactive gabardine was added. So in summary, the, um again, the first table cells were those that were just finishing the s phase eso The initial two hour lag corresponds to the G two phase.

Eso chemical stands are gonna be required for visualizing cells and tissues with the basic light microscope because most cellular material does not absorb visible light and therefore cells are essentially invisible and a bright field of ah, light microscope. So say, for example, this is the field of your maker scope that you're seeing and without a die, the cells in here just gonna be washed out. There's gonna be no contrast. It's gonna be too bright, and you won't be able to see them without die. So say, for example, we stay in ourselves with a blue dye with a blue chemical dye. Then there's gonna be more contrast than you're going to see the cells in a blue color under the light microscope. Or so the chemicals dyes air using visible light, which limits the resolution obtained from the sample. So fluorescent microscopy is not faced with this limitation, since it can use whatever light excites the floor force. So fluorescence microscopy can. You can be used in conjunction with other types of light microscopy, and this is another advantage that it has over chemical um, stands. And so, due to the fact that it creates images from reflect reflected light reflected light rather than the directly that chemical stands used. It can be used with other microscopy techniques. And this includes the con focal scanning microscopy which facilitates optical sectioning of thick segments as opposed to physical sectioning, which can be pretty difficult in the lab and D convolution, microscopy, AIDS and clearer resolutions. So there you have it.