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Questions and Answers
What type of transport involves movement between the cytosol and the nucleus?
What type of transport involves movement between the cytosol and the nucleus?
Proteins cannot cross membranes and must be transported in vesicles.
Proteins cannot cross membranes and must be transported in vesicles.
False
What are the two main types of sorting signals that proteins can carry?
What are the two main types of sorting signals that proteins can carry?
Signal Peptides and Signal Patches
The __________ pathway refers to the transport of proteins from the ER to the Golgi and then to the plasma membrane.
The __________ pathway refers to the transport of proteins from the ER to the Golgi and then to the plasma membrane.
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Match the transport type with its example:
Match the transport type with its example:
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What role do sorting receptors play in protein transport?
What role do sorting receptors play in protein transport?
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All proteins maintain their orientation during transport across membranes.
All proteins maintain their orientation during transport across membranes.
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What must proteins do to successfully cross or embed into membranes?
What must proteins do to successfully cross or embed into membranes?
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Proteins lacking appropriate sorting signals remain in their __________ compartment.
Proteins lacking appropriate sorting signals remain in their __________ compartment.
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Which of these correctly defines the function of sorting signals?
Which of these correctly defines the function of sorting signals?
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Which of the following is an example of epigenetic regulation?
Which of the following is an example of epigenetic regulation?
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Transcription factors can regulate their own expression through a positive feedback loop, which is considered epigenetic.
Transcription factors can regulate their own expression through a positive feedback loop, which is considered epigenetic.
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What is the term used for the ability of cells to retain specialized functions across divisions?
What is the term used for the ability of cells to retain specialized functions across divisions?
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The process that involves movement across membranes between the cytosol and organelles is called ______.
The process that involves movement across membranes between the cytosol and organelles is called ______.
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Match the type of cellular transport with its description:
Match the type of cellular transport with its description:
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Which transport mechanism commonly uses protein translocators?
Which transport mechanism commonly uses protein translocators?
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Vesicular transport can only move in one direction between organelles.
Vesicular transport can only move in one direction between organelles.
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What is the main purpose of epigenetic regulation?
What is the main purpose of epigenetic regulation?
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What is maintained during vesicular transport?
What is maintained during vesicular transport?
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Compartments that share the same internal or external membrane orientation are considered to be ______.
Compartments that share the same internal or external membrane orientation are considered to be ______.
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Gene expression is regulated primarily during mitosis.
Gene expression is regulated primarily during mitosis.
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Stable and heritable control of gene expression in epigenetic regulation is characterized by which of the following?
Stable and heritable control of gene expression in epigenetic regulation is characterized by which of the following?
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What are the four mechanisms of epigenetic regulation?
What are the four mechanisms of epigenetic regulation?
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During DNA replication, histone codes are __________ to ensure daughter cells inherit the same gene expression patterns.
During DNA replication, histone codes are __________ to ensure daughter cells inherit the same gene expression patterns.
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Match the following epigenetic signatures with their descriptions:
Match the following epigenetic signatures with their descriptions:
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Which of the following is a consequence of DNA methylation?
Which of the following is a consequence of DNA methylation?
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Stem cells can differentiate into specialized cell types without losing their identity.
Stem cells can differentiate into specialized cell types without losing their identity.
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What role does maintenance methyltransferase play in DNA methylation?
What role does maintenance methyltransferase play in DNA methylation?
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Prion diseases are examples of epigenetic change that are often __________.
Prion diseases are examples of epigenetic change that are often __________.
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What effect do covalent histone modifications have on gene expression?
What effect do covalent histone modifications have on gene expression?
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Study Notes
Gene Expression Patterns
- Gene expression is primarily regulated during interphase
- Most transcription and synthesis processes stop during mitosis
- Some mechanisms maintain stable gene expression, even without changing DNA sequences
Epigenetic Regulation
- Epigenetics modifies gene expression without changing DNA
- Essential for cellular differentiation (e.g., liver cells remain liver cells)
- Stem cells differentiate into diverse cell types.
Four Mechanisms of Epigenetic Regulation
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Positive Feedback Loops
- A protein activates its own transcription
- Maintains its expression even after the initial signal ends
- Ensures stable gene expression until a new signal comes
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Covalent Histone Modifications
- Chemical modifications of histones (e.g., acetylation, methylation) change chromatin accessibility
- Ensures stable gene expression patterns across cell generations
DNA Methylation
- Methyl groups added to CpG sequences silence genes
- Maintenance methyltransferase preserves methylation patterns during DNA replication
- Newly synthesized DNA strands are initially unmethylated and then methylated to match the template strand
Protein Aggregates
- Proteins can fold into different states, some of which are pathological (e.g., prions)
- Pathological protein folding can be a stable epigenetic change, affecting conditions like Alzheimer's and Parkinson's
Epigenetic Regulation and Cellular Differentiation
- Epigenetics allows cells to retain specialized functions across divisions.
- Stable epigenetic changes facilitate tissue and organ function in multicellular organisms.
Cellular Transport and Topological Compartments
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Cytoplasmic to Nuclear Transport
- Molecules enter and exit the nucleus
- Transport occurs between topologically similar areas
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Transmembrane Transport
- Movement across membranes between cytosol and organelles (e.g. ER, mitochondria)
-
Vesicular Transport
- Transport between organelles
- Involves vesicles that carry cargo while maintaining the topology of the membrane
Gated Transport: Nuclear-Cytosol Exchange
- Nucleus and cytosol are topologically similar due to the continuity of the nuclear envelope and ER membrane.
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Nuclear Pore Complex (NPC)
- Acts as a selective gateway between the nucleus and cytosol.
- Small molecules can diffuse freely through the NPC while larger ones require active transport.
- Specific signal sequences are needed for import and export, recognized by nuclear transport receptors
Transmembrane Transport: Crossing Membranes
- Proteins cross the lipid bilayer using translocators.
- Proteins are often unfolded to pass through translocators and then refolded.
Vesicular Transport: Between Topologically Equivalent Compartments
- Vesicular transport is the movement of proteins between compartments that share the same topological orientation.
- Protein orientation is preserved during transport.
- Vesicles are created to move cargo.
Shared Features of Transport Mechanisms
- Involve protein recognition and sorting for delivery to correct destinations
- Signal sequences (e.g., NLS, NES) specify location
Nuclear Transport and Ran-GTP Gradient
- Crucial for moving proteins and other macromolecules between the nucleus and cytosol.
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Ran-GTP Gradient creates directional transport.
- High Ran-GTP concentration is in the nucleus
- High Ran-GDP concentration is in the cytosol
- Ensures that proteins move in one direction
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Mechanisms of Nuclear Transport:
- Import
- Cargo with NLS binds to import receptors
- Complex moves through NPCs
- Ran-GTP causes cargo release.
- Release receptor & Ran-GTP returns to the cytosol
- Export
- Cargo with NES binds export receptors, & Ran-GTP.
- Complex moves into cytosol
- Ran-GTP hydrolysis releases cargo.
- Releasing export receptor to return.
- Import
Integration of Concepts
- Connecting signal sequences (NLS, NES) & Ran Gradient;
- Coordinate between components (NPC, Ran) for efficient, unidirectional transport
- Using energy from ATP hydrolysis
Mitochondrial Protein Import and Transport Mechanisms
- Mitochondria evolved from endosymbiotic organisms
- Many mitochondrial proteins are synthesized in the cytosol and imported into the mitochondria.
- Proteins utilize import signals (amphipathic alpha-helices) when moving through the mitochondrial membranes, altering orientation to enter different compartments (e.g., outer membrane, intermembrane space matrix)
- Import Machinery (Tom and Tim complexes) help in bringing the proteins into mitochondria
- Chaperone Proteins assists during import and ensure proteins fold correctly in the mitochondria
Vesicular Transport Models and Membrane Trafficking
- Vesicles move proteins and other materials between compartments
- Compartments sometimes change over time (e.g., Golgi cisternae maturation)
- Both models (vesicles as independent "elevators" & compartmental change) work together in the cell
- Retrograde transport plays a role in Golgi and ER functions
Exocytosis and Membrane Protein Transport
- Vesicles fuse with the plasma membrane to release materials
- Rabs and SNAREs mediate vesicle docking and fusion.
- Regulated secretion involves specific signals (e.g., hormonal), while constitutive secretion happens automatically.
Coated Vesicles and Coat Proteins
- Proteins help form vesicles
- COPI, COPII, and clathrin are involved in various transport processes.
- Each has a particular function (e.g. COPI is involved in retrograde transport from the Golgi
- COPII from ER to Golgi)
- Ensures materials in vesicles are transported to the right location
Dynamin in Vesicle Budding
- Dynamin is a GTP-binding protein involved in vesicle severing from the parent membrane.
Lysosomal Targeting and Retrograde Transport
- Cargo destined for degradation (e.g., proteins) is transported to lysosomes using signals
- Mannose-6-phosphate (M6P) and recognition are important components
- Transport towards lysosomes via anterograde direction.
- Receptors are part of the retrograde transport pathway (back to Golgi) to recycle.
ATP and GTP in Vesicular Transport
- GTP plays a role in vesicle assembly, docking, and budding, and ATP is used in processes involving membrane fusion
- Energy required in vesicle trafficking and proteins.
Additional Key Points
- Targeting signals: Critical for correct delivery of cargo
- Signal sequences: guide proteins to their destinations
- Different types of transport: (Gated, transmembrane, and vesicular) each having particular function & mechanism
- Membrane topology: important to ensure correct orientations of proteins and materials inside membranes
- Energy sources: ATP & GTP gradients drive many of these processes
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Description
Explore the intricate world of gene expression regulation and epigenetic modifications. This quiz covers the mechanisms of gene expression during interphase, the role of epigenetics in cellular differentiation, and key regulatory processes such as histone modifications and DNA methylation. Test your understanding of how genes can be expressed without altering the DNA sequence.
