Protein Regulation - GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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How do Bax and Bak promote cell death?
How do Bax and Bak promote cell death?
Bax and Bak dimerize to form a pore in the mitochondria outer membrane, which allows cytochrome c to escape into the cytosol. When cytochrome c is found in the cytosol, procaspase becomes activated and is cleaved into caspase. Once the caspase cascade begins the cell is destined for death.
Bax and Bak have nothing to do with the apoptosome and, while Bcl2 does block Bax and Bak from dimerizing, Bax and Bak do not prevent the action of Bcl2.
Bax and Bak dimerize to form a pore in the mitochondria outer membrane, which allows cytochrome c to escape into the cytosol. When cytochrome c is found in the cytosol, procaspase becomes activated and is cleaved into caspase. Once the caspase cascade begins the cell is destined for death.
Bax and Bak have nothing to do with the apoptosome and, while Bcl2 does block Bax and Bak from dimerizing, Bax and Bak do not prevent the action of Bcl2.
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One commonly studied outcome of G protein-coupled receptor (GPCR) activation is the activation of phospholipase C (PLC). What two important second messengers are formed when PLC cleaves phosphoinositide-4,5-bisphosphate 
?
One commonly studied outcome of G protein-coupled receptor (GPCR) activation is the activation of phospholipase C (PLC). What two important second messengers are formed when PLC cleaves phosphoinositide-4,5-bisphosphate
Interactions between 
, 
, 
, and PKC do indeed occur downstream of activation of PLC to contribute to numerous downstream cascades primarily initiated by protein kinase C (PKC). However, it is important to understand that the second messengers are 
and 
, which are specifically formed by the cleavage of 
, and each of the other molecules is considered an effector of those second messengers in this context.
Interactions between
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What is the key functional difference between GEFs (guanine nucleotide exchange factors) and GAPs (GTPase activating proteins)?
What is the key functional difference between GEFs (guanine nucleotide exchange factors) and GAPs (GTPase activating proteins)?
A GEF activates a small GTPase by exchanging a bound GDP (which confers an inactive state) for a GTP (which is higher energy, and activates the protein). A GAP performs the opposite; GAPs enhance the intrinsic GTPase activity of the small GTPase, which causes hydrolysis of the GTP on the active protein, thus converting it back to GDP and an inactive state.
A GEF activates a small GTPase by exchanging a bound GDP (which confers an inactive state) for a GTP (which is higher energy, and activates the protein). A GAP performs the opposite; GAPs enhance the intrinsic GTPase activity of the small GTPase, which causes hydrolysis of the GTP on the active protein, thus converting it back to GDP and an inactive state.
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What provides the necessary information to specify the three dimensional shape of proteins?
What provides the necessary information to specify the three dimensional shape of proteins?
Proteins have different level of protein structure, termed primary, secondary, and tertiary (quarternary is also a type in certain proteins). The 3D shape of proteins is largely due to the tertiary structure of a protein. This level is dictated by the specific amino acid sequence of the protein.
Proteins have different level of protein structure, termed primary, secondary, and tertiary (quarternary is also a type in certain proteins). The 3D shape of proteins is largely due to the tertiary structure of a protein. This level is dictated by the specific amino acid sequence of the protein.
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Which of the following are means of controlling protein concentrations?
Which of the following are means of controlling protein concentrations?
All of the given answers are ways that a cell may regulate protein concentrations. Polyubiquination is a signal for the protein to be degraded by a proteasome. Gene silencing will prevent transcription, which will lower the amount of mRNA template that can be translated into a protein. RNAi will degrade specific mRNAs or prevent the translation of specific mRNAs into proteins.
All of the given answers are ways that a cell may regulate protein concentrations. Polyubiquination is a signal for the protein to be degraded by a proteasome. Gene silencing will prevent transcription, which will lower the amount of mRNA template that can be translated into a protein. RNAi will degrade specific mRNAs or prevent the translation of specific mRNAs into proteins.
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Proteins are brought to a __________ for degradation after they undergo __________.
Proteins are brought to a __________ for degradation after they undergo __________.
Polyubiquination is a modification results from the binding of small ubiquitin residues to a protein. Polyubiquination of a protein signals damage or problems with functionality, and triggers the mechanisms that result in protein degradation. The polyubiquinated protein is then brought to a proteasome (a complex of proteins) that will degrade the protein.
Glycosylation involves the attachment of a carbohydrate complex to a protein. The identity of the carbohydrate is essential for determining the functional outcome of glycosylation, but generally results in signaling and transport labels for the protein. Glycosylation is not by itself a signal to be brought to either a proteasome or a lysosome.
Polyubiquination is a modification results from the binding of small ubiquitin residues to a protein. Polyubiquination of a protein signals damage or problems with functionality, and triggers the mechanisms that result in protein degradation. The polyubiquinated protein is then brought to a proteasome (a complex of proteins) that will degrade the protein.
Glycosylation involves the attachment of a carbohydrate complex to a protein. The identity of the carbohydrate is essential for determining the functional outcome of glycosylation, but generally results in signaling and transport labels for the protein. Glycosylation is not by itself a signal to be brought to either a proteasome or a lysosome.
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Which of the following answers best describes the sequence of events carried out by enzymes E1, E2, and E3 in the ubiquitin-proteasome pathway?
Which of the following answers best describes the sequence of events carried out by enzymes E1, E2, and E3 in the ubiquitin-proteasome pathway?
E1, E2, and E3 all have unique activities that progress step-wise to activate ubiquitin and then attach those ubiquitins to mark a protein for degradation. Their functions are not redundant, nor do they activate acids, autophagosomes or ATP complexes over the course of their pathways.
E1, E2, and E3 all have unique activities that progress step-wise to activate ubiquitin and then attach those ubiquitins to mark a protein for degradation. Their functions are not redundant, nor do they activate acids, autophagosomes or ATP complexes over the course of their pathways.
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Ubiquitination of a protein is one way to mediate protein degradation, however, ubiquitination is only a signal. What is ultimately responsible for ubiquitin-mediated degradation of a protein?
Ubiquitination of a protein is one way to mediate protein degradation, however, ubiquitination is only a signal. What is ultimately responsible for ubiquitin-mediated degradation of a protein?
The correct answer is proteasome. Ubiquitination of a protein signals for the proteasome to degrade it and recycle the ubiquitin. Alternatively, the lysosome does degrade proteins, however, this process is independent of ubiquitin. The peroxisome is responsible for the degradation of fatty acids, certain amino acids, and reactive oxygen species. Hydrolysis simply refers to a chemical mechanism that splits apart a compound by the addition of water, it does not however, describe an organelle or cellular compartment that is reponsible for protein degradation.
The correct answer is proteasome. Ubiquitination of a protein signals for the proteasome to degrade it and recycle the ubiquitin. Alternatively, the lysosome does degrade proteins, however, this process is independent of ubiquitin. The peroxisome is responsible for the degradation of fatty acids, certain amino acids, and reactive oxygen species. Hydrolysis simply refers to a chemical mechanism that splits apart a compound by the addition of water, it does not however, describe an organelle or cellular compartment that is reponsible for protein degradation.
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The ubiquitin-mediated protein degradation process targets proteins to which cellular structure for degradation?
The ubiquitin-mediated protein degradation process targets proteins to which cellular structure for degradation?
The correct answer is proteasome. There are two general protein degradation processes: the first involving the lysosome and the second involving the proteasome. Lysosomal protein degradation is non-selective and occurs during cell starvation. Degradation through the proteasome is dependent on ubiquitination of the target protein, and as such, ensures protein-specific degradation.
The correct answer is proteasome. There are two general protein degradation processes: the first involving the lysosome and the second involving the proteasome. Lysosomal protein degradation is non-selective and occurs during cell starvation. Degradation through the proteasome is dependent on ubiquitination of the target protein, and as such, ensures protein-specific degradation.
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How does ubiquitination of a protein facilitate its degradation?
How does ubiquitination of a protein facilitate its degradation?
The correct answer is recognition of ubiquitin by the proteasome. Ubiquitin-mediated protein degradation by the proteasome is a well characterized method of specific protein degradation. The protein targeted for degradation is phosphorylated, then ubiquitinated. The proteasome recognizes these distinct ubiquitin chains and degrades the protein. Protein degradation can also occur through the lysosome, but this is independent of ubiquitination and is less specific. The golgi complex is involved in protein folding and modification of recently translated amino acid chains.
The correct answer is recognition of ubiquitin by the proteasome. Ubiquitin-mediated protein degradation by the proteasome is a well characterized method of specific protein degradation. The protein targeted for degradation is phosphorylated, then ubiquitinated. The proteasome recognizes these distinct ubiquitin chains and degrades the protein. Protein degradation can also occur through the lysosome, but this is independent of ubiquitination and is less specific. The golgi complex is involved in protein folding and modification of recently translated amino acid chains.
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What is the difference between proteolysis and ubiquitin-mediated protein degradation?
What is the difference between proteolysis and ubiquitin-mediated protein degradation?
The correct answer is that proteolysis occurs in the lysosome but ubiquitin-mediated protein degradation is in the proteasome. Proteolysis-lysosomal degradation is non-selective and is activated upon cellular starvation. ubiquitin-mediated protein degradation is highly specific and functions to promote a wide range of cellular processes.
The correct answer is that proteolysis occurs in the lysosome but ubiquitin-mediated protein degradation is in the proteasome. Proteolysis-lysosomal degradation is non-selective and is activated upon cellular starvation. ubiquitin-mediated protein degradation is highly specific and functions to promote a wide range of cellular processes.
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Which of the following additions to a protein will signal the cell to degrade it?
Which of the following additions to a protein will signal the cell to degrade it?
Older proteins in our bodies need to be degraded once they become damaged or no longer necessary. One way that the cell tags these proteins is by adding a ubiquitin tag, which can then be recognized by a proteasome, leading to the proteins' deconstruction.
Older proteins in our bodies need to be degraded once they become damaged or no longer necessary. One way that the cell tags these proteins is by adding a ubiquitin tag, which can then be recognized by a proteasome, leading to the proteins' deconstruction.
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Which of the following is a common post-translational modification used to target proteins to the lysosome?
Which of the following is a common post-translational modification used to target proteins to the lysosome?
Mannose-6-phosphate is a post-translational modification found on proteins important to the functionality of the lysosome (such as acid hydrolases). Ubiquination is a signal for proteins to be brought to the proteosome and degraded. Myristoylation involves the addition of a fatty acid chain, and is often seen in proteins targeted to the plasma membrane. Acetylation is a common modification found on histones that can help make genes transcriptionally active.
Mannose-6-phosphate is a post-translational modification found on proteins important to the functionality of the lysosome (such as acid hydrolases). Ubiquination is a signal for proteins to be brought to the proteosome and degraded. Myristoylation involves the addition of a fatty acid chain, and is often seen in proteins targeted to the plasma membrane. Acetylation is a common modification found on histones that can help make genes transcriptionally active.
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An isomerase __________.
An isomerase __________.
An isomerase is an enzyme that catalyzes the rearrangement of bonds in a single molecule. For example glucose-6-phosphate isomerase catalyzes the conversion of glucose-6-phosphate into fructose-6-phosphate during glycolysis.
A hydrolase catalyzes a hydrolytic cleavage reaction, a kinase catalyzes the addition of a phosphate group, and a polymerase catalyzes polymerization reactions.
An isomerase is an enzyme that catalyzes the rearrangement of bonds in a single molecule. For example glucose-6-phosphate isomerase catalyzes the conversion of glucose-6-phosphate into fructose-6-phosphate during glycolysis.
A hydrolase catalyzes a hydrolytic cleavage reaction, a kinase catalyzes the addition of a phosphate group, and a polymerase catalyzes polymerization reactions.
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Which of the following is a protein modification that can initiate the degradation of the modified protein?
Which of the following is a protein modification that can initiate the degradation of the modified protein?
The correct answer is ubiquitination. Ubiquitin is added to the substrate protein to target the protein for degradation by the proteasome, serving as an efficient mechansim to control cellular protein levels. Myristoylation, palmitoylation, isoprenylation, and glycosylation are all post-translational protein modifications that involve the addition of a 14-carbon saturated acid, a 16-carbon saturated acid, an isoprenoid group, and a glycosyl group, respectively. These modifications have diverse functions, however, do not initiate the degradation of the protein.
The correct answer is ubiquitination. Ubiquitin is added to the substrate protein to target the protein for degradation by the proteasome, serving as an efficient mechansim to control cellular protein levels. Myristoylation, palmitoylation, isoprenylation, and glycosylation are all post-translational protein modifications that involve the addition of a 14-carbon saturated acid, a 16-carbon saturated acid, an isoprenoid group, and a glycosyl group, respectively. These modifications have diverse functions, however, do not initiate the degradation of the protein.
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Lipidation is a post-translational modification to a protein that often targets that protein to the plasma membrane. Knowing that lipidation involves covalent bonding of a fatty acid group to a protein, which of the following molecules would be most likely to be attached to a protein for anchorage to a membrane?
Lipidation is a post-translational modification to a protein that often targets that protein to the plasma membrane. Knowing that lipidation involves covalent bonding of a fatty acid group to a protein, which of the following molecules would be most likely to be attached to a protein for anchorage to a membrane?
While each of these molecules could potentially be bound to a protein as a post-translational modification, the only one listed that is a fatty acid is palmitate. Thus, this is the correct answer.
While each of these molecules could potentially be bound to a protein as a post-translational modification, the only one listed that is a fatty acid is palmitate. Thus, this is the correct answer.
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In order for kinases to modify their substrates, what small molecule is needed for this reversible post-translational modification?
In order for kinases to modify their substrates, what small molecule is needed for this reversible post-translational modification?
The correct answer is adenosine triphosphate (ATP). In order to phosphorylate a substrate, kinases catalyze the hydrolysis of ATP to adenosine diphosphate (ADP) and inorganic phosphate. This released phosphate by the hydrolysis reaction is covalently added to an amino acid residue on the substrate. Nicotinamide adenine dinucleotide phosphate, flavin adenine dinucleotide, and nicotinamide adenine dinucleotide are proton carriers. Guanine nucleotide exchange factor aids in exchanging guanine diphosphate for guanine triphosphate in a substrate.
The correct answer is adenosine triphosphate (ATP). In order to phosphorylate a substrate, kinases catalyze the hydrolysis of ATP to adenosine diphosphate (ADP) and inorganic phosphate. This released phosphate by the hydrolysis reaction is covalently added to an amino acid residue on the substrate. Nicotinamide adenine dinucleotide phosphate, flavin adenine dinucleotide, and nicotinamide adenine dinucleotide are proton carriers. Guanine nucleotide exchange factor aids in exchanging guanine diphosphate for guanine triphosphate in a substrate.
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Ubiquitination of proteins is a form of post-translational modification on proteins. Which of the following cellular processes is protein ubiquitination not part of?
Ubiquitination of proteins is a form of post-translational modification on proteins. Which of the following cellular processes is protein ubiquitination not part of?
The correct answer is all of the answers are cellular processes in which ubiquitination is involved. Post-translational ubiquitination of proteins initiates many cellular processes by altering protein activity and the proteins that interact with the ubiquitinated protein.
The correct answer is all of the answers are cellular processes in which ubiquitination is involved. Post-translational ubiquitination of proteins initiates many cellular processes by altering protein activity and the proteins that interact with the ubiquitinated protein.
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What type of enzyme adds a phosphate group to a protein?
What type of enzyme adds a phosphate group to a protein?
A kinase is an enzyme that adds a phosphate group. Do not get this confused with a phosphatase. A phosphatase is an enzyme that removes a phosphate group. The other enzymes listed do not deal with the addition or removal of a phosphate group from a protein.
A kinase is an enzyme that adds a phosphate group. Do not get this confused with a phosphatase. A phosphatase is an enzyme that removes a phosphate group. The other enzymes listed do not deal with the addition or removal of a phosphate group from a protein.
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Which of the following does not require a post-translational modification of a protein to be properly targeted to its destination?
I. Nuclear localization
II. Targeting proteins to the lysosome
III. Targeting proteins to the proteasome
IV. Nuclear export
Which of the following does not require a post-translational modification of a protein to be properly targeted to its destination?
I. Nuclear localization
II. Targeting proteins to the lysosome
III. Targeting proteins to the proteasome
IV. Nuclear export
Nuclear import and export do not require post-translational modifications. The nuclear localization sequence or the nuclear export sequence is contained within the amino acid sequence itself (primary structure), and does not require and special modification.
For targeting to the proteasome, proteins must be ubiquinated. To target a protein to the lysosome the addition of a mannose-6-phosphate is commonly made.
Nuclear import and export do not require post-translational modifications. The nuclear localization sequence or the nuclear export sequence is contained within the amino acid sequence itself (primary structure), and does not require and special modification.
For targeting to the proteasome, proteins must be ubiquinated. To target a protein to the lysosome the addition of a mannose-6-phosphate is commonly made.
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