MCAT Biology : Endoplasmic Reticulum and Golgi Body
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Example Questions
Example Question #11 : Endoplasmic Reticulum And Golgi Body
In eukaryotic cells, what organelle is associated with translation of antibody proteins?
Endoplasmic reticulum
Golgi apparatus
Nucleus
Mitochondria
Endoplasmic reticulum
Antibody proteins are translated by ribosomes attached to the rough endoplasmic reticulum, and subsequently secreted out of the cell in vesicles. While the Golgi apparatus is involved in the secretory pathway of these proteins, it is not specifically involved in the translation.
The nucleus and mitochondria are not associated with antibody protein translation.
Example Question #1261 : Biology
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
A critical function of the Golgi apparatus is to modify proteins, typically by adding moieties and not by changing the actual amino acid sequence. A scientist finds that a large, negatively charged unit is added to a protein in the Golgi. Which of the following enzymes is most likely involved in this process?
Kinase
Phosphatase
Lipase
Amylase
Protease
Kinase
The question notes that a large, negatively charges unit is added to the protein. This information, coupled with the answer options, tells us that the unit in question is a phosphate group. Phosphate groups are relatively large and carry a substantial negative charge. The addition of phosphate groups can help mediate protein activity by either activating or inactivating the molecule.
The question asks us to identify the enzyme responsible for adding the phosphate group to the protein; this function is unique to kinases.
Example Question #61 : Cellular Structures And Organelles
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
In the cisternal maturation hypothesis, a change in which of the following is most likely to change the charge of the carboxyl and amino termini in a protein moving through the Golgi network?
Protein concentration
pH
Interaction with chaperone proteins
Carbohydrate content
Disulfide bond formation
pH
The pH is the most direct condition that changes the charge found on the amino and carboxyl ends of a polypeptide. Protonation of both ends is favored by a low pH, while deprotonation is favored in more basic conditions.
Example Question #1262 : Biology
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
A scientist is studying a set of proteins. She finds that protein A has a span of hydrophobic amino acids. Protein B also has a span of hydrophobic amino acids, but protein B also has carbohydrates added during modification in the Golgi, while protein A does not. If both protein A and protein B are hormone receptors, what role do the carbohydrate moieties most likely play?
Modify receptor specificity
Anchor receptor in membrane
Increase receptor lipid solubility
Covalently bind to ligand
Bind to cytosolic proteins
Modify receptor specificity
The span of hydrophobic amino acids specified in the question suggests that these proteins are both transmembrane. Carbohydrate addition primarily occurs on portions of transmembrane proteins that face the extracellular environment, and serve to increase solubility in aqueous conditions. Out of the given options, only a modification to receptor specificity is an appropriate answer.
Example Question #62 : Cellular Structures And Organelles
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
Which of the following is most likely to take place in the Golgi apparatus?
Endosome formation
Glycosylation
Signal sequence hydrolysis
Protein secretion
Co-translational translocation
Glycosylation
Signal sequence removal and co-translational translocation are key events that occur in association with the endoplasmic reticulum, specifically the rough endoplasmic reticulum. The Golgi, in contrast, is specialized for the modification of polypeptides following their synthesis, such as through glycosylation.
Example Question #61 : Cellular Structures And Organelles
Which of the following proteins would be transcribed at the level of the rough endoplasmic reticulum?
Caspases
Glycolytic enzymes
Actin
Insulin receptor
Insulin receptor
It is important for students to understand that transmembrane proteins, as well as secreted proteins, need to be synthesized at the level of the rough endoplasmic reticulum. All of the other options are examples of proteins that exert their function in the cytosol, and thus are transcribed by free ribosomes in the cytosol.
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