Quest 1:
(a) At the 5-minute point: the location of these proteins indicated that protein X and
protein Y were synthesized at the free ribosome and the ER, respectively.
At the 20-30 minute point: protein X was entirely transported to the cytosol while
protein Y was being transported through the Golgi apparatus to the plasma
membrane (not entirely nor directly to the plasma membrane).
(b) Protein Z is located in the mitochondrion. It was initially synthesized at the free
ribosome and was released into the cytosol, then eventually transported to the
mitochondrion to perform its function.
(c) (I) False. At the 10-minute point, all protein Z had already been in the cytosol while a
quarter of protein X was still in the free ribosome.
(II) False. The total quantity of all four proteins remained unchanged at the 30-minute
point, so the degrading rate can not be determined.
(III) False. Similar to (II).
(IV) True. Similar to (I). It took protein X 30 minutes to be entirely transported to the
cytosol while protein Y took only 10 minutes.
Quest 2:
- Gibberellic acid treatment: produce long, thin shoots
- Ethylene treatment: produce short, fat shoots.
- Explanation: Cells elongate perpendicular to the orientation of the cellulose
microfibrils. Gibberellic acid promotes the cortical microtubule array perpendicular to
the long axis of the cell -> cells elongate parallel to its long axis. The opposite for
ethylene -> cells elongate perpendicular to its long axis.
Quest 3:
(2) Only external portions of the proteins are cleaved by the protease (it is too large to
penetrate the vesicle membrane)
(3) External and lumen portions of the proteins are cleaved by the protease (since it went
under permeabilisation treatment to penetrate the membrane)
The small fragments are cleaved protein parts while the big fragments are uncleaved protein
parts.
A. False. The bigger fragments are the uncleaved transmission portions of the protein
located in the internal of the phospholipid bilayer. They must be hydrophobic.
B. True. They are external portions that are cleaved into small fragments by protease.
C. False. Domain a should be rich in lysine since it binds to phosphate areas of the
phospholipid membrane.
D. False. Lane 2 showed two big fragments, indicating that there are two domains located
internal to the membrane -> b, c protrude into the lumen while a, d, and e protrude outside
the membrane.
Protease is too large to penetrate the membrane of vesicles. Those parts of the membrane's
proteins that are situated on the external side of the lipid bilayer are subjected to digestion
by protease, but those parts within the bilayer or lumen face of the membrane are not
affected. Under the condition of treatment with permeabilisation and protease, the
membrane no longer acts as a barrier to the penetration of the protease, so that the lumen
portions of the protein are also subjected to digestion. Under this condition (Lane 3), there
were 4 bigger fragments, indicating that domains a, b, c and d were cleaved by protease.
Under the condition of treating with protease only, protease could not enter the lumen, and
only 2 bigger fragments were, therefore, observed on the gel. This means that it was domain
