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Questions and Answers
What is the role of chaperones in protein folding?
What is the role of chaperones in protein folding?
Which statement about hydrophobic amino acids in proteins is true?
Which statement about hydrophobic amino acids in proteins is true?
What is the consequence of improperly folded proteins?
What is the consequence of improperly folded proteins?
What is the function of the proteasome?
What is the function of the proteasome?
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How do heat-shock proteins (Hsp) respond to cellular stress?
How do heat-shock proteins (Hsp) respond to cellular stress?
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What effect does the presence of exposed hydrophobic residues have on a protein?
What effect does the presence of exposed hydrophobic residues have on a protein?
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Which of the following statements is false regarding post-translational regulation?
Which of the following statements is false regarding post-translational regulation?
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Which factor is least likely to interfere with protein folding?
Which factor is least likely to interfere with protein folding?
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Which of the following processes is NOT involved in the regulation of the proteome?
Which of the following processes is NOT involved in the regulation of the proteome?
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What role does protein phosphorylation play in cellular regulation?
What role does protein phosphorylation play in cellular regulation?
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What initiates the process of translation in eukaryotes?
What initiates the process of translation in eukaryotes?
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Which mechanism is NOT a form of translational regulation in prokaryotes?
Which mechanism is NOT a form of translational regulation in prokaryotes?
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The role of aconitase in eukaryotic translation is to:
The role of aconitase in eukaryotic translation is to:
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Which of the following components plays a crucial role in the formation of the eukaryotic initiation complex?
Which of the following components plays a crucial role in the formation of the eukaryotic initiation complex?
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How does the phosphorylation of eIF2 impact translation?
How does the phosphorylation of eIF2 impact translation?
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Which of these mechanisms is indicative of post-translational regulation?
Which of these mechanisms is indicative of post-translational regulation?
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What is the main function of molecular chaperons in protein synthesis?
What is the main function of molecular chaperons in protein synthesis?
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Which sequence is specifically mentioned as being important in prokaryotic translational regulation?
Which sequence is specifically mentioned as being important in prokaryotic translational regulation?
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What is the potential consequence of the environmental stress on protein expression?
What is the potential consequence of the environmental stress on protein expression?
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In eukaryotic cells, which process does NOT contribute to gene expression regulation?
In eukaryotic cells, which process does NOT contribute to gene expression regulation?
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What distinguishes regulatory GTP-binding proteins from other proteins?
What distinguishes regulatory GTP-binding proteins from other proteins?
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Study Notes
Genome Expression Regulation
- The proteome reflects the expression of the genome and transcriptome
- Proteome differences between tissues are represented with red (common proteins) and blue (tissue specific proteins)
- The regulation of genome expression involves multiple steps: organization, transcription, RNA splicing, translation, protein sorting, and post-translational modification
Translational Regulation
- Prokaryotes and eukaryotes use translational control mechanisms
- Prokaryotes use a Shine-Dalgarno (SD) sequence upstream of the AUG start codon for translation initiation
- Translational regulation in prokaryotes can involve:
- RNA binding proteins blocking access to the SD sequence
- Temperature-regulated RNA structures (e.g., Listeria monocytogenes)
- Riboswitches (e.g., S-adenosyl methionine)
- Antisense RNA (e.g., iron storage proteins) which base-pairs with mRNA to block the SD sequence
Translational Regulation: Eukaryotes
- Eukaryotes lack Shine-Dalgarno sequences
- Repressor proteins can bind near the initiator AUG to inhibit translation, or interfere with 5' cap and 3' poly-A tail interactions
- Small RNA molecules (microRNAs or miRNAs) regulate eukaryotic translation
- Eukaryotic initiation factors (eIFs) regulate translation:
- eIF2 plays a crucial role in translation initiation, forming a complex with GTP and initiator tRNA
- GTP hydrolysis causes a conformational change in eIF2, leading to its release as an inactive GDP-bound form
- Reactivation of eIF2 requires eIF2B, a guanine nucleotide exchange factor (GEF) that promotes GDP-GTP exchange
- However, phosphorylation of eIF2 can sequester eIF2B, forming an inactive complex and inhibiting translation
Post-Translational Regulation: Proteins
- Proteins undergo post-translational modifications to become functional, including:
- Proper folding into 3-D structure
- Covalent modifications with chemical groups (e.g., sugars, phosphate)
- Interactions with other proteins and small molecules (cofactors)
Post-Translational Regulation: Protein Folding
- Hydrophobic amino acids are buried in the protein interior core
- Folding can begin during translation for some proteins or after synthesis
- Chaperones (e.g., Hsp70 and Hsp60) assist with protein folding:
- Interact with exposed hydrophobic residues of misfolded proteins
- Utilize ATP hydrolysis for proper folding
- Misfolded proteins can aggregate and become toxic
- The proteasome is a protein degrading apparatus that targets misfolded proteins:
- Misfolded proteins display exposed hydrophobic residues, leading to proteasome recognition
- Proteasome degradation competes with chaperone interactions, and the longer a protein takes to fold, the higher the chance of degradation
Review Question
- Treatment with HSP inhibitors should reduce protein degradation
- Treatment with an iron chelator should decrease ferritin transcription
- Treatment with a miRNA complementary to eIF2B should result in an increase in transcription
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