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recap5 (5.3 recap (The movements of newly synthesized proteins can be…
recap5
5.3 recap
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Through how many membranes would a molecule have to pass in moving (a) from the interior (stroma) of a chloroplast to the interior (matrix) of a mitochondrion? (b) From the interior of a lysosome to the outside of a cell? (c) From one ribosome to another?
(a) Four membranes: two in the chloroplast and two in the mitochondrion. (b) Two membranes: the lysosomal membrane and the cell membrane (via vesicle; the molecules do not themselves cross any membranes). (c) No membranes: ribosomes do not have membranes. However, if the ribosomes were associated with the endo-plasmic reticulum (ER), the answer would be two membranes: one into the ER and another out of the ER.
The drug vincristine is used to treat many cancers. It appears to work by causing microtubules to depolymerize. Vincristine use has many side effects, including loss of dividing cells and nerve problems. Explain why this might be so.
Microtubules line the long axons of nerve cells, where they act as tracks for vesicles that carry substances down the neuron. Without microtubules, the contents of these vesicles cannot be delivered to their destination, which can result in nerve problems. Depolymerization of microtubules can interfere with cell divisions because microtu-bules are a key part of the mitotic spindle that is used to move chromosomes during cell division.
The movements of newly synthesized proteins can be followed through cells using a “pulse-chase” experiment. During synthesis, proteins are tagged with a radioactive isotope (the “pulse”), then the cells are allowed to process the proteins for varying periods of time. The locations of the radioactive proteins are then determined by isolating cell organelles and quantifying their levels of radioactivity. What would be the expected pathway for (a) a lysosomal enzyme and (b) a protein that is released from the cell?
For a lysosomal enzyme, the pathway would be ribosome → interior of ER → Golgi apparatus → Golgi vesicles → lysosome.
For an extracellular protein (animal cell), the pathway would be ribosome ? interior of ER → Golgi apparatus → Golgi vesicles → cell membrane → extracellular region.
5.4 recap
When a cancer spreads from the initial site to another location in the body, initial events are the detachment of the cancer cells from its surrounding extra cellular matrix and digestion of the matrix as the cell migrates. How might these events occur?
Initially, there is a digestion of molecules that attach the cell membrane to the extracellular matrix. Then enzymes are produced and secreted from the cell that digests the macromolecules of the extracellular matrix. The cell migrates by microfilaments.
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How could a biologist use chemical analysis to differentiate between a plant cell and an animal cell?
Chemical analysis could identify a plant cell by the presence of cellulose in the extracellular matrix and an animal cell by the presence of collagen in the extracellular matrix. These two compounds are distinct to the two different types of cells.
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5.2 recap
What are the structure and function of the following specialized prokaryotic cell features: cell wall, capsule, and flagellum?
The cell wall is composed of a large complex of polysaccharides and peptides. It supports the cell and gives it shape. The capsule is a slimy polysaccharide layer that encloses the cell walls of some prokaryotes and keep cells from drying out. It may be used to attach to other cells. The flagellum is composed of strands of a large protein called flagellin and is attached to the cell wall and membrane by a motor complex. It is used for cell movement.
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5.5 recap
How could membrane infolding in a prokaryotic cell lead to the formation of the endomembrane system?
The cell membrane could fold inward and then pinch off, forming vesicles for the Golgi apparatus and flat sheets for the ER.
When they are removed from a cell, organelles such as mitochondria no longer function as they did inside the cell. What aspect of endosymbiotic theory explains this observation?
The endosymbiotic theory states that one cell engulfed another cell. Over time the engulfed cell lost some DNA and the ability to perform independently of the host cell. Thus the engulfed cell became dependent on the host cell for its survival.