Bio 5.3 HW

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 endoplasmic reticulum (ER), the answer would be two membranes: one into the ER and another out of the ER.

What does animal cells have that plant cells does not?

Cholesterol

Besides the proteins being processed for distribution, what other components could be expected to be found inside the Golgi apparatus?

Enzymes

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 microtubules are a key part of the mitotic spindle that is used to move chromosomes during cell division.

Organelles compartmentalize various functions in a eukaryotic cell. Which organelle is important in keeping toxic levels of hydrogen peroxide separated from the rest of the cell?

Peroxisome

What are the major differences between prokaryotic cells and eukaryotic cells?

Prokaryotic cells are smaller than eukaryotic cells and lack organelles

How could scientists use radioisotopes to study the function of the Golgi apparatus?

Radiolabeled sugars could be tracked as they are covalently attached to proteins within the Golgi apparatus

Which sequence describes the path of a protein from its synthesis until it is exported out of a cell?

Rough endoplasmic reticulum➔vesicle➔Golgi apparatus➔vesicle➔plasma membrane➔exterior of cell

Which is a difference between the endoplasmic reticulum and the Golgi apparatus?

Steroid synthesis is carried out in the endoplasmic reticulum, but not in the Golgi apparatus

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?

a) For a lysosomal enzyme, the pathway would be ribosome → interior of ER → Golgi apparatus → Golgi vesicles → lysosome. b) For an extracellular protein (animal cell), the pathway would be ribosome → interior of ER → Golgi apparatus → Golgi vesicles → cell membrane → extracellular region

The correct order of movement of proteins through the Golgi apparatus is

cis, medial, trans

A student discussing the role of the Golgi apparatus in cells makes the following three statements: A variety of proteins enter the Golgi from vesicles that pinch off from the rough ER Within the Golgi apparatus, different proteins are modified by the activities of sugar molecules After modification, the proteins move within vesicles to specific locations in the cell Evaluate the accuracy of the student's statements

the first and third statements are accurate; the second statement isn't accurate