GRE Subject Test: Biology : Understanding Lysosomes and Peroxisomes
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Example Questions
Example Question #1 : Understanding Lysosomes And Peroxisomes
Which of the following is not true of lysosomes?
Lysosomes have an approximate pH of 5
Lysosomes are membrane-bound
Lysosomes contain acid hydrolases
Lysosomes are found in both prokaryotes and eukaryotes
Lysosomes are found in both prokaryotes and eukaryotes
Lysosomes have the function of digesting foreign materials and large structures, such as organelles. They do this by maintaining an acidic pH of approximately 5 and utilizing special proteins called acid hydrolyases, which are specifically designed to function at low pH levels. In order to maintain this low pH, lysosomes must be membrane-bound and have a highly regulated flow of protons.
Prokaryotes do not have membrane-bound organelles, including lysosomes.
Example Question #23 : Cell Membrane And Organelles
If a cell is incapable of catabolizing very long fatty acid chains, it most likely has a problem with which of the following organelles?
Peroxisomes
Mitochondria
Smooth endoplasmic reticulum
Golgi apparatus
Peroxisomes
Peroxisomes are primarily responsible for the breakdown of very long chain fatty acids and D-amino acids, as well as the synthesis of special types of phospholipids known as plasmalogens. If the cell cannot catabolize very long chain fatty acids, the issue is most likely within the peroxisomes.
The Golgi apparatus is very important for protein packaging. Mitochondria are crucial to generating energy for the cell. The smooth endoplasmic reticulum has various functions, including lipid and carbohydrate metabolism.
Example Question #24 : Cell Membrane And Organelles
Which organelle is used for the degradation of macromolecules in the cell?
Mitochondria
Lysosome
Golgi apparatus
Smooth endoplasmic reticulum
Lysosome
The function of breaking down cellular contents is done by the lysosome. Lysosomes have an acidic interior, which is useful for breaking down macromolecules that are no longer being used in the cell.
The smooth endoplasmic reticulum, in contrast, helps to break down foreign material, such as toxins. Mitochondria primarily serve to produce ATP for cellular energy. The Golgi apparatus works in tandem with the rough endoplasmic reticulum and helps to group and package proteins for vesicular transport.
Example Question #2 : Understanding Lysosomes And Peroxisomes
Lysosomes are organelles that contain acid hydrolase enzymes, such that materials that are taken up by lysosomes can be degraded into their basic components, and these components can be reused by the cell. Due to the presence of these enzymes, interior of the lysosome is very acidic, with a pH around 4.7 or 4.8. The cell cytoplasm has pH typically around 7.2, making it slightly basic. What type of membrane component is likely responsible for maintaining the acidic environment within the lysosome?
Histone
G protein-coupled receptor
Calcium channel
Cholesterol
Proton pump
Proton pump
Proton pumps use ATP to continuously pump hydrogen ions into the interior of the lysosome, thus maintaining an acidic environment in which the enzymes are most optimally efficient at breaking down the debris/macromolecules. The membrane of the lysosome is selectively permeable due to these types of transporters, and protects the rest of the cell from the very acidic environment. Recent journal articles suggest that the lysosome's membrane will be deliberately disrupted, releasing the acid and the hydrolases into the cytosol during apoptosis.
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