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Questions and Answers
What occurs when a signal molecule binds to a receptor tyrosine kinase (RTK)?
What occurs when a signal molecule binds to a receptor tyrosine kinase (RTK)?
- The receptor becomes inactive.
- Intracellular proteins are immediately deactivated.
- The receptor undergoes degradation.
- A dimer forms and activates the tyrosine kinase domain. (correct)
Phosphorylation adds a phosphate group to specific amino acids to regulate gene expression.
Phosphorylation adds a phosphate group to specific amino acids to regulate gene expression.
True (A)
What is the role of phosphorylation cascades in cellular signaling?
What is the role of phosphorylation cascades in cellular signaling?
Signal amplification
Protein _________ is a common post-translational modification in eukaryotes.
Protein _________ is a common post-translational modification in eukaryotes.
Match the following terms with their descriptions:
Match the following terms with their descriptions:
Which statement best describes the function of kinases in signaling pathways?
Which statement best describes the function of kinases in signaling pathways?
Signal amplification can occur through a series of protein phosphorylations.
Signal amplification can occur through a series of protein phosphorylations.
What is a proprotein or zymogen?
What is a proprotein or zymogen?
Name one example of a signaling pathway that uses phosphorylation for signal amplification.
Name one example of a signaling pathway that uses phosphorylation for signal amplification.
Proteolysis is a reversible process that allows proteins to remain in their active state.
Proteolysis is a reversible process that allows proteins to remain in their active state.
What is the name of the active enzyme produced from pepsinogen?
What is the name of the active enzyme produced from pepsinogen?
Factor Xa cleaves prothrombin at Arg-___ and Arg-___ to activate thrombin.
Factor Xa cleaves prothrombin at Arg-___ and Arg-___ to activate thrombin.
Which of the following is true regarding insulin production?
Which of the following is true regarding insulin production?
Match the following terms with their descriptions:
Match the following terms with their descriptions:
Protein phosphorylation is the least abundant post-translational modification in eukaryotes.
Protein phosphorylation is the least abundant post-translational modification in eukaryotes.
What is the function of proteases in protein regulation?
What is the function of proteases in protein regulation?
What is the main purpose of post-translational modifications (PTMs) of proteins?
What is the main purpose of post-translational modifications (PTMs) of proteins?
Post-translational modifications can only activate protein activity.
Post-translational modifications can only activate protein activity.
Name one example of a post-translational modification that can activate protein activity.
Name one example of a post-translational modification that can activate protein activity.
The covalent cleavage of peptide fragments in proteins is primarily driven by __________.
The covalent cleavage of peptide fragments in proteins is primarily driven by __________.
Match the following types of post-translational modifications with their effects:
Match the following types of post-translational modifications with their effects:
Which of the following describes a reversible change in proteins due to post-translational modifications?
Which of the following describes a reversible change in proteins due to post-translational modifications?
Proteins modified by post-translational alterations can only exist in one state: active.
Proteins modified by post-translational alterations can only exist in one state: active.
Identify one broad class of post-translational modifications.
Identify one broad class of post-translational modifications.
What is the primary function of ubiquitin in cellular processes?
What is the primary function of ubiquitin in cellular processes?
Monoubiquitination typically results in the degradation of a protein.
Monoubiquitination typically results in the degradation of a protein.
What are the three key types of enzymes involved in the ubiquitination process?
What are the three key types of enzymes involved in the ubiquitination process?
Polyubiquitination primarily targets proteins for ______ by directing them to the proteasome.
Polyubiquitination primarily targets proteins for ______ by directing them to the proteasome.
Which statement accurately describes ubiquitin's structure?
Which statement accurately describes ubiquitin's structure?
Ubiquitin ligases (E3) are responsible for identifying target proteins and ______ the ubiquitin from E2 to the target protein.
Ubiquitin ligases (E3) are responsible for identifying target proteins and ______ the ubiquitin from E2 to the target protein.
Match the following types of ubiquitination with their effects:
Match the following types of ubiquitination with their effects:
Ubiquitination is a reversible process.
Ubiquitination is a reversible process.
What is the primary role of glycosylation in cell surface receptors?
What is the primary role of glycosylation in cell surface receptors?
Disorders of glycosylation can lead to health issues such as cancer and immune disorders.
Disorders of glycosylation can lead to health issues such as cancer and immune disorders.
What do glycosyltransferases do?
What do glycosyltransferases do?
The process of adding sugar molecules to proteins is known as ___.
The process of adding sugar molecules to proteins is known as ___.
Which of the following is NOT a benefit of post-translational modifications?
Which of the following is NOT a benefit of post-translational modifications?
Match the following types of modifications with their function:
Match the following types of modifications with their function:
Post-translational modifications do not contribute to the diversity of the proteome.
Post-translational modifications do not contribute to the diversity of the proteome.
Name a potential consequence of abnormalities in glycosylation processes.
Name a potential consequence of abnormalities in glycosylation processes.
Study Notes
Post-Translational Modifications (PTMs)
- PTMs are essential for regulating protein activity and gene expression.
- Critical for protein function, stability, and localization within cells.
Types of Post-Translational Modifications
- Two main classes:
- Enzyme-assisted covalent modifications (addition or elimination of chemical groups).
- Covalent cleavage of protein fragments, typically by proteases.
Reversible vs. Irreversible Modifications
- Many PTMs (e.g., phosphorylation) are reversible, allowing proteins to toggle between active and inactive states.
- Cleavage of peptide fragments by proteases is typically irreversible.
Activation and Repression of Protein Activity
- PTMs can increase protein activity, such as phosphorylation activating certain enzymes.
- PTMs can also inhibit activity, reprogramming proteins to become inactive.
- Some modifications lead to protein degradation.
Role of Proteases
- Proteins often synthesized as inactive forms (proproteins or zymogens).
- Proteolytic cleavage by proteases activates these forms without needing energy.
- Example: Pepsinogen is converted into active pepsin through cleavage.
Thrombin Activation in Blood Clotting
- Prothrombin is converted to thrombin through specific cleavages by Factor Xa, crucial for preventing excessive blood clotting.
Insulin Activation
- Synthesized as a pre-pro-protein that is cleaved in pancreatic beta cells to produce active insulin.
- Removal of the signal sequence and the C peptide chain leads to insulin activation.
Phosphorylation
- Most common PTM in eukaryotes, playing a key role in regulating protein activity in signaling pathways.
- Activated by receptor tyrosine kinases (RTKs) through a cascade effect, amplifying signals in cells.
- Important for processes like cellular responses and gene expression regulation.
Ubiquitination
- Involves the addition of ubiquitin (76 amino acids, 8kD protein) to lysines on target proteins.
- Can be monoubiquitination (single addition) or polyubiquitination (chain formation).
- Polyubiquitination typically signals degradation of proteins via the proteasome.
- Monoubiquitination often directs proteins to new cellular locations.
Ubiquitination Mechanism
- Ubiquitin activating enzyme (E1) transfers ubiquitin to ubiquitin conjugation enzyme (E2).
- Ubiquitin ligases (E3) help transfer ubiquitin to target proteins.
- Polyubiquitination leads to proteasomal degradation of unwanted proteins.
Role in Cell Division Regulation
- Cyclins, regulated by ubiquitination, control progression through the cell cycle, initiating transitions between phases.
- Glycosylation of proteins is vital for their structural integrity and activity, particularly in surface receptors.
Importance of PTMs
- PTMs are crucial for the regulation of gene product activity and increasing the diversity of the proteome.
- Dysregulation or disorders in PTMs, such as glycosylation, can lead to diseases including cancer and immune disorders.
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Description
Explore the mechanisms of post-translational modification (PTM) and its critical role in regulating gene expression. This quiz will help you understand the various PTMs and their impact on protein activity. Gain insights from Professor Guy Tear's expertise in this essential topic of molecular biology.
