Institut d’Optique Graduate School – 2ème année
Examen Optique et Biologie
N. Westbrook – Karen Perronet
14 mai 2013
Durée : 2h
No document authorized – Answers can be given in english
Questions about the lectures (independent questions – write the n° of the question):
1) Give the definition of the following processes: replication, transcription, translation.
2) What is the main role of ATP (adenosine triphosphate) in the cell? In which compartment of the cell
is it produced?
3) Where are located the epithelial cells in a tissue? Where is collagen?
4) What is a metastasis?
5) We have 2 microscope objectives with the following characteristics: 60x/1,40 oil and 100x/1,25oil.
Which one can give the best resolution? Give the corresponding resolution limit in the visible
(0,5µm). Is there a condition on the camera used for the observation so that we will really be limited
by diffraction?
6) What is the advantage of trapping a dielectric bead attached to the biological system rather than trap
directly the biological object itself? Give at least one argument in the case of a whole cell, and one in
the case of a DNA strand.
7) Give 2 main advantages of non-linear two-photon fluorescence compared to classical (linear)
confocal microscopy.
8) Which optical signal can be used to detect cerebral activity, either with diffuse optical tomography or
photo-acoustic tomography?
9) What is a restriction enzyme? Give one example of application of these molecules.
10) How can you easily amplify a DNA strand?
11) Cite one method to separate proteins according to their size. Explain briefly its principle.
12) Give in a few lines the principle of atomic force microscopy (AFM).
13) Comment on the following cytogramme, obtained when studying a population of white blood cells
using flow cytometry. Specify in particular the kind of information obtained from these
measurements.
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Vertical axis : intensity
scattered at small angles
Horizontal axis : intensity
scattered at large angles
Questions about the 3 articles:
On « Fluorescence Lifetime Imaging… » :
1) What is the cellular process under study in this article?
2) Which fluorescence microscopy configuration is used here: wide field, confocal or total internal
reflection? Is the image obtained with or without scanning?
3) In figure 2(a), red areas are visible. What do they correspond to? Why do they not appear in figure
2(b)?
4) Why is the lifetime of the blue peak in figure 3Top longer than that of the blue peak in figure 1?
On « The Fragile X retardation protein… » :
1) Explain what the colors in the different images in figure 3B correspond to, in particular the
« Merge » image. What information can be extracted from it?
2) What kind of labeling has been used in figure 8? What is its advantage compared to the labeling used
in figure 3?
3) In the case of figure 8, how are the markers introduced in the cell?
On « Following translation by single ribosomes… » :
1) Why can messenger RNA (mRNA) form a secondary structure (hairpin) ? Is it possible also for
DNA?
2) Describe and explain the positions of the trapped bead and of the trapping laser beam during the
experiment shown in figure 2a.
3) How is the strand of mRNA attached to the two beads?
4) Does translation occur in a particular direction along mRNA? If so, which one and why is it
important?
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