Cell Biology

Take Home Essay Questions - Set 1             Name:_Laayla Muhammad

Download this MS-Word document.  Fill in your name at the top and type your answers below.  Save the questions and your answers as an MS Word document with the .doc file extension (not .docx).  This assignment is due in the D2L Dropbox on Sunday, 02-28-10 at 11:59pm.

A.  For 5 points, correctly answer only one of the questions below (use as much space as needed):

Pts

1. Consider the reaction 7 of glycolysis:

                                                                                DG₀

1,3diPG     3PG                                 -4.5 Kcal/mole

Below are the steady state concentrations of 1,3 diphosphoglyceric acid (1,3diPG) and 3-phosphoglyceric acid (3PG) assayed in the tissues of a hospital patient. 

[1,3diPG]  = 6.5 X 10^-6 M

      [3PG]  = 8 X 10^-4 M

2.5      a)  Determine the DG’ for this reaction as it occurs in the cell. Show all

                calculations.

2.5       b) What tissue was biopsied for these assays?  What can we say about the patient?

      2.   A ribosomal cell fraction was centrifuged on a sucrose density gradient and the gradient was then separated into test tube fractions.  Graph below shows the distribution of polysomes in fraction tubes. 

 5.0      Explain the graph.

       The distribution of polysomes in fraction tubes is represented by this graph. Polysomal content is measured in absorbencies, which in this graph is the absorbance at 280nm. The graph shows that the bottom of the tube, there is more content of the polysomes, therefore, its absorbance at 280nm being higher. Therefore, on the top, after being centrifuged, less content remains and therefore, the absorbency of the sucrose density gradient has is lower than the bottom. In the middle though, as the content is the highest, shows that during the centrifuge, the polysomes are denser in the middle, meaning more concentrated and therefore, the absorbency is the highest.
B.  For 5 points, correctly answer only one of the questions below (use as much space as needed):

1.   You are trying to isolate a Golgi vesicle fraction from cultured pancreatic “Islet of Langerhans” cells by differential centrifugation.  As you perform the steps of the fractionation, you monitor the cell fractions by electron microscopy.  A sample electron micrograph is seen at the right.  In addition to this electron microscope image, what more would you do to prove that this fraction contains pancreatic cell Golgi vesicles?  Be brief but be precise and specific.

  Something we can do to prove that this particular fraction contains pancreatic cell Golgi vesicles is by first noticing that these vesicles look intact like they should be. We should also realize that RERs exist in these vesicles because the proteins synthesized and packaged in them usually travel down to these vesicles for “further processing before reaching their final destination” (VOP: Cell Tour Pt 1). In order to confirm that these are Golgi vesicles, we can “destroy the membranes and then release these proteins” (VOP: Cell Tour Pt 2). This disruption will show the packaged proteins such as secretory or peroxisomal ones. We can also methods such as “cytochemistry (staining parts with chemicals), immunocytochemistry (staining with “tagged” antibodies), and autoradiology (radioactive detection)” (VOP Cell Tour Pt 2) which will darken and reveal the packaged proteins just to confirm the earlier statements about the existence of RERs packaged proteins in the Golgi vesicles for processing.

2.   Overall, eukaryotes and prokaryotes share the same central pathways for getting energy out of nutrients (fermentation, respiration, fatty acid oxidation.  When there is no carbohydrate available, bacteria can survive on amino acids or fatty acids as a sole source of carbon for growth.  In contrast, humans deprived of carbohydrates can survive on amino acids, but they cannot live on fatty acids as a sole carbon source.  What do the bacteria have that we don’t?