Cell Compartmentalization (College Board AP® Biology): Exam Questions

Prokaryotic cells lack membrane-bound organelles found in eukaryotes. However, prokaryotes must perform many of the same functions as eukaryotes. For three of the organelles identified in part (a), explain how prokaryotic cells carry out the associated functions.

According to the endosymbiotic theory, some organelles are believed to have evolved through a symbiotic relationship between eukaryotic and prokaryotic cells. Describe three observations that support the endosymbiotic theory. 

Cellular organelles are specialized compartments within cells that have a specific structure and function. Organelles are often membrane-bound in eukaryotic cells, allowing for compartmentalization of cellular processes. Figure 1 below shows a cellular organelle.

Identify the organelle in Figure 1, and the cellular process that takes place here.

Explain the benefit of compartmentalizing the process identified within the organelle shown in Figure 1.

The organelle in Figure 1 contains its own DNA and ribosomes. Table 1 below contains some information about the DNA and ribosomes shown, and compares them with equivalent DNA and ribosomes in mitochondria, bacteria and eukaryotic cells

Table 1. DNA and ribosomes in different locations.

Scientists theorise that the organelle in Figure 1 and mitochondria evolved from the ancestors of modern bacteria. Use evidence from Table 1 to support this claim.

Mutations are changes in the DNA sequence of an organism, they can be harmful, neutral or beneficial to the organism.

Predict how a harmful mutation in the DNA labeled in Figure 1 would affect the cell within which the organelle is located.

Compartmentalization and cell specialization are essential for maintaining efficiency and organization in eukaryotic cells. Compartmentalization refers to the division of cellular processes into separate regions within a cell.

(i) Describe how compartmentalization is achieved in eukaryotic cells.

(ii) Specialized cells have a structure that aids their specific function. Explain how compartmentalization can allow cells to specialize.

Scientists measured organelle density, as well as the rate of some cellular processes, in different cell types. Their results are shown in Table 1 below.

Table 1. Organelle density and rate of cellular processes in different cell types.

(i) In order to determine organelle number per cell, scientists obtained multiple images of slices through a cell, counted the number of organelles visible in each image, and then added the image totals together.

Describe how the data gathered using this procedure would need to be processed to determine organelle density.

(ii) State why organelle density has been measured, rather than organelle number.

(i) Identify the organelle that is likely to be the most abundant in muscle cells.

(ii) Use data from Table 1 to justify your answer to (i).

Pancreatitis is a condition that can affect the function of rough endoplasmic reticulum in the pancreas.

(i) Predict the effect of pancreatitis on pancreatic cells.

(ii) A student suggested that disrupted rough ER function would have a more significant effect on pancreatic cells than on other cell types. Use Table 1 above to evaluate this suggestion.

Synthetic biology uses engineering principles to create new biological parts and systems. Researchers studying synthetic cells wanted to determine the effect of protein localization strategy on cellular processes. Localization refers to the deliberate positioning of proteins within specific regions or structures of the cell.

To inform their work on synthetic cells, the researchers studied the effect of different protein localization strategies on enzyme-catalyzed reactions in bacterial cells.

Some of their results are shown in Table 1 below.

Table 1: The effect of enzyme localization strategy on the rate of substrate use and product yield.

Explain the result for condition C.

(i) State a suitable null hypothesis for the study described in part (a).

(ii) Justify the inclusion of condition A as a control in the study.

(iii) Calculate the percentage increase in product yield between condition A and condition C.

Microcompartments in synthetic cells can be generated in several ways. One method involves a process known as coacervation, during which a fluid separates into separate phases. Coacervation can be triggered by introducing solutes with particular properties; an example would be the production of water-in-oil-in-water double emulsions (DEs), shown in Figure 1 below. In this example, the DE has been stabilized by the addition of phospholipids.

(i) Use information in Figure 1 and your knowledge of phospholipids to explain why coacervation has occurred in this instance.

(ii) A student suggested that DE's could be used to simulate membrane-bound organelles inside synthetic cells. Justify this suggestion.

Scientists working in the field of synthetic biology are still a long way from producing synthetic cells that accurately mimic living cells.

(i) Identify a component of membrane structure, that has not been addressed in the production of microcompartments, that scientists will need to seek to replicate in synthetic cells that accurately mimic living cells.

(ii) Scientists hope to use synthetic organelles to deliver regulatory proteins to living cells.

Predict how the introduction of new regulatory proteins might affect these living cells.

The Golgi apparatus is an intracellular compartment that plays a critical role in modifying, packaging and sorting proteins destined for various cellular locations, including the lysosomes. Recent research has suggested that defects in Golgi structure and function may contribute to lysosomal dysfunction, resulting in lysosomal storage diseases (LSDs) and neurodegenerative disorders.

Defects in Golgi structure can arise due to depletion of Golgi Reassembly and Stacking Proteins (GRASPs). Figure 1 illustrates the role of GRASP proteins (left) and shows how GRASP depletion affects cells (right).

(i) Use Figure 1 to determine how the Golgi apparatus modifies the lysosome enzyme precursor molecules.

(ii) Describe the effect of Golgi fragmentation on functional lysosomal enzymes.

(iii) Predict the effect of GRASP depletion on cellular processes.

Scientists conducted an experiment to investigate the impact of GRASP depletion on lysosomal enzymes. They measured the activity of a key lysosomal hydrolase, β-hexosaminidase A (HexA), in cells with normal GRASP and in cells with GRASP55 or GRASP65 dysfunction. Table 1 shows their results.

Table 1. The effect of Golgi integrity on HexA activity. The ± values represent standard deviation.

(i) Calculate the percentage decrease between mean HexA activity in control cells and in GRASP65 knockout cells.

(ii) State what can be concluded about the effect of knocking out GRASP55 in comparison to knocking out GRASP65.

(iii) Justify your conclusion in (ii).

A student looked at Figure 1 and hypothesized that the extracellular activity of HexA would increase in the area surrounding GRASP-deficient cells.

(i) Explain why the student may have proposed this hypothesis.

(ii) Evaluate the student's hypothesis using information in Figure 1.

Research has shown that GRASP depletion can influence the export of other molecules. One such group of molecules is the glycosaminoglycans (GAGs), polysaccharides that may be found on the surface of cells, where they interact with extracellular proteins.

Predict a possible effect of a reduction in cell surface GAGs.

Cells compartmentalize metabolic reactions to optimize biochemical pathways and regulate competition for shared coenzymes, such as NAD. Cells of the yeast Schizosaccharomyces japonicus contain organelles known as peroxisomes; the production and regulation of these cellular compartments is controlled by a series of proteins known as peroxins, or PEX proteins.

Explain how compartmentalization can optimize biochemical pathways and regulate competition for shared coenzymes.

Researchers studied the impact of mutations in the genes that code for PEX proteins on the development of peroxisomes in S. japonicus cells. Some of their results are shown in table 1 below.

Table 1. The impact of Pex5 and Pex11 knockout mutations on peroxisome development in yeast. The ± values represent standard deviation.

(i) Identify the control group in Table 1.

(ii) Use the formula provided to calculate the radius of a Pex11 knockout peroxisome

(iii) A researcher claimed that PEX11 protein plays an important role in the division of peroxisomes. Use data from Table 1 to support this claim.

Peroxisomes house Lys3 and His2 enzymes that are essential for the final steps of lysine and histidine biosynthesis.

(i) A researcher claimed that lysine and histidine are both required for yeast growth. Use data in Table 1 to evaluate this claim.

(ii) Pex5 protein is a receptor found on the surface of yeast cells. It binds to proteins in the cytoplasm that contain a peroxisomal targeting signal and facilitates their transport into the peroxisomal matrix. Use this information to give a possible explanation for the effect of the Pex5 knockout mutation on yeast growth.

Another group of researchers investigated human Pex proteins. They wanted to determine whether mutations in the the Pex1 and Pex6 genes could be linked to the inherited disorder, Zellweger syndrome.

(i) State a possible null hypothesis for the research described.

(ii) Pex1 and Pex6 proteins belong to a family of proteins known as AAA ATPases.

Predict a possible effect of a mutation that results in non-functional Pex1 and Pex6 proteins on a cell.