Podcast
Questions and Answers
Which of the following is NOT a primary function of the cytoskeleton?
Which of the following is NOT a primary function of the cytoskeleton?
- Intracellular transport
- Spatial organization
- Structure and support
- Energy production (correct)
The cytoskeleton is a static structure within the cell, maintaining a fixed organization.
The cytoskeleton is a static structure within the cell, maintaining a fixed organization.
False (B)
What are the three well-defined filamentous structures that comprise the cytoskeleton?
What are the three well-defined filamentous structures that comprise the cytoskeleton?
- Cellulose, hemicellulose, and pectin fibers
- Actin, myosin, and keratin filaments
- Microtubules, intermediate filaments, and microfilaments (correct)
- Collagen, elastin, and fibronectin fibers
The dynamic behavior of the cytoskeleton can be observed using a technique called live-cell ______.
The dynamic behavior of the cytoskeleton can be observed using a technique called live-cell ______.
Match each cytoskeletal element with its primary protein subunit:
Match each cytoskeletal element with its primary protein subunit:
What is the key function of motor proteins associated with the cytoskeleton?
What is the key function of motor proteins associated with the cytoskeleton?
Prokaryotic cells lack cytoskeletal elements.
Prokaryotic cells lack cytoskeletal elements.
Name two types of motor proteins associated with microtubules.
Name two types of motor proteins associated with microtubules.
Which of the following is a characteristic of microtubules?
Which of the following is a characteristic of microtubules?
The plus end of a microtubule is typically terminated by a row of ______ subunits.
The plus end of a microtubule is typically terminated by a row of ______ subunits.
Which technique involves bleaching a specific area of fluorescently labeled microtubules to study their dynamics?
Which technique involves bleaching a specific area of fluorescently labeled microtubules to study their dynamics?
Microtubules are composed of 15 protofilaments.
Microtubules are composed of 15 protofilaments.
What is the primary function of microtubule-organizing centers (MTOCs)?
What is the primary function of microtubule-organizing centers (MTOCs)?
The process of tubulin dimer assembly requires that a GTP molecule be bound to the ______-tubulin subunit.
The process of tubulin dimer assembly requires that a GTP molecule be bound to the ______-tubulin subunit.
Which of the following is NOT a characteristic of intermediate filaments (IFs)?
Which of the following is NOT a characteristic of intermediate filaments (IFs)?
Intermediate filaments have polarity.
Intermediate filaments have polarity.
Name two functions of the cytoskeleton.
Name two functions of the cytoskeleton.
Which cellular structure is NOT made up of the protein tubulin?
Which cellular structure is NOT made up of the protein tubulin?
The diameter of Microfilaments is approximately ______ nm.
The diameter of Microfilaments is approximately ______ nm.
All motility is dependent on which component?
All motility is dependent on which component?
Unlike microfilaments and microtubules, IFs are a chemically heterogeneous group of structures that, in humans, are encoded by approximately how many different genes?
Unlike microfilaments and microtubules, IFs are a chemically heterogeneous group of structures that, in humans, are encoded by approximately how many different genes?
Motor proteins move along cytoskeletal filaments in a energy independent mechanism
Motor proteins move along cytoskeletal filaments in a energy independent mechanism
What processes are disrupted if a cell lacks the KIF5B gene that is responsible for transporting mitochondria?
What processes are disrupted if a cell lacks the KIF5B gene that is responsible for transporting mitochondria?
The technique ______ involves labeling protein subunits in vitro with a fluorescent dye, then injecting them into a cell to examine the dynamic behavior of cells
The technique ______ involves labeling protein subunits in vitro with a fluorescent dye, then injecting them into a cell to examine the dynamic behavior of cells
GTP hydrolysis is important for what biological mechanism?
GTP hydrolysis is important for what biological mechanism?
Match the following terms:
Match the following terms:
Microtubules are typically found in animal cells only
Microtubules are typically found in animal cells only
What process happens in vitro, slowly, but inside a cell rapidly and in association with a variety of specialized structures
What process happens in vitro, slowly, but inside a cell rapidly and in association with a variety of specialized structures
Which subunit contains a bound GTP that is not hydrolyzed and is nonexchangeable?
Which subunit contains a bound GTP that is not hydrolyzed and is nonexchangeable?
The cytoplasmic microtubules in a cell help determine the ______ of that cell.
The cytoplasmic microtubules in a cell help determine the ______ of that cell.
What provides cells with mechanical strength that are subjected to physical stress?
What provides cells with mechanical strength that are subjected to physical stress?
Tubulin dimers are organized in a nonlinear array along the length of each protofilament.
Tubulin dimers are organized in a nonlinear array along the length of each protofilament.
Which of the following is NOT considered a super family of motor proteins?
Which of the following is NOT considered a super family of motor proteins?
The monomers found in actin are considered ______ subunits
The monomers found in actin are considered ______ subunits
What cellular events are known to depend on microfilaments?
What cellular events are known to depend on microfilaments?
Which is the correct order from smallest to largest?
Which is the correct order from smallest to largest?
All Cells have each component of the cytoskeleton
All Cells have each component of the cytoskeleton
Besides cell motility what are two other functions of the cytoskeleton
Besides cell motility what are two other functions of the cytoskeleton
When ATP associates with an actin monomer it then becomes ______
When ATP associates with an actin monomer it then becomes ______
How many classes are the polypeptide subunits of Ifs divided into?
How many classes are the polypeptide subunits of Ifs divided into?
Flashcards
What is the cytoskeleton?
What is the cytoskeleton?
A network of filamentous structures within cells, including microtubules, microfilaments, and intermediate filaments.
What are microtubules?
What are microtubules?
Long, hollow, unbranched tubes made of tubulin protein subunits.
What are microfilaments?
What are microfilaments?
Solid, thinner structures often organized into branching networks and composed of actin.
What are intermediate filaments?
What are intermediate filaments?
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What are the 3 types of cytoskeletal filaments?
What are the 3 types of cytoskeletal filaments?
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What is live-cell fluorescence imaging?
What is live-cell fluorescence imaging?
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What is FRAP?
What is FRAP?
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What are motor proteins?
What are motor proteins?
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Which filaments do Kinesins, Dyneins, and Myosins move along?
Which filaments do Kinesins, Dyneins, and Myosins move along?
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What is the plus end?
What is the plus end?
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What is the minus end?
What is the minus end?
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What are MTOCs?
What are MTOCs?
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Is GTP hydrolysis required for the incorporation of the dimer?
Is GTP hydrolysis required for the incorporation of the dimer?
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What is the function of intermediate filaments?
What is the function of intermediate filaments?
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What is the basic building block of IF assembly?
What is the basic building block of IF assembly?
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What is the function of microfilaments?
What is the function of microfilaments?
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Study Notes
- Chapter focuses on the cytoskeleton and cell motility.
Overview of the Major Functions of the Cytoskeleton
- Skeleton of a vertebrate:
- Consists of hardened elements
- Supports body tissues
- Mediates bodily movements
- Eukaryotic cells possesses a cytoskeleton, which is a skeletal system with analogous functions
- Cytoskeleton consists of filamentous structures:
- Microtubules
- Microfilaments
- Intermediate filaments
- These structures form an elaborate interactive network
The Cytoskeleton Components
-
Microtubules:
- Long
- Hollow
- Unbranched tubes
- They are comprised of tubulin protein subunits
-
Microfilaments:
- Also called actin filaments
- Solid
- Thinner structures
- Organized into branching networks
- Composed of actin protein
-
Intermediate Filaments:
- Rope-like fibers
- Composed of various related proteins
- They are tough
-
Cytoskeletal components appear stationary in micrographs but are dynamic structures capable of dramatic reorganization
-
Prokaryotes contain tubulin- and actin-like proteins to polymerize cytoplasmic filaments for cytoskeletal activities
-
Proteins distantly related to intermediate filaments have been discovered in prokaryotes
Functions of the Cytoskeleton
- Dynamic scaffold providing structural support
- Determines cell shape
- Resists deforming forces
- Framework for positioning organelles
- Evident in polarized epithelial cells
- Organelles arranged in order from apical to basal end
- Network of tracks for directing movement of materials and organelles within cells
- Delivers mRNA to specific parts of cell
- Transports neurotransmitters
- Transports vesicles
- Force-generating apparatus for cell movement
- Single-celled organisms crawl or propel themselves
- Multicellular animals uses:
- Sperm
- White blood cells
- Fibroblasts
- Essential for cell division
- Separates chromosomes during mitosis/meiosis
- Splits parent cell into daughter cells during cytokinesis
Studying the Cytoskeleton
- Live-Cell Fluorescence Imaging:
- Eukaryotic cells contain cytoskeletal network
- Electron microscope produces static images
- Fluorescence microscopy allows observation of molecular processes in living cells
- Fluorescently labelled subunits are microinjected into a living cell
- Behavior of structure is followed over time
- In Vitro and In Vivo Single-Molecule Assays
- Detects activity of individual protein molecules acting as motor
- Visualizes movement of individual kinesins inside living cells
- Cells are genetically engineered to synthesize fluorescently labeled microtubule polymers and fluorescently labeled kinesin molecules.
- Interaction of proteins occur within cell's cytoplasm under physiological conditions
- TIRF microscopy is used to follow movement of individual kinesin molecules
- Fluorescence Recovery After Photobleaching (FRAP)
- Powerful technique to monitor the dynamics of the cytoskeleton
- Cell injected with fluorescent tubulin or expresses GFP-tubulin
- Laser bleaches small region
- Analyze specimen over time
- Measure recovery of fluorescent signal
Microtubules
-
Hollow, rigid, tubular structures in eukaryotic cells
-
Components of mitotic spindle and core of cilia/flagella
-
Outer diameter of 25 nm and 4 nm thick wall
-
Walls consist of globular proteins arranged in longitudinal rows called protofilaments
-
Cross sections reveals 13 protofilaments in a circular pattern
-
Noncovalent interactions between protofilaments maintain structure
-
Protofilament made of α-tubulin and β-tubulin subunits
-
Tubulin dimers are organized in a linear array
-
Protofilament is asymmetric, with α-tubulin at one end and β-tubulin at the other end.
-
Polymers contain polarity
-
One end plus end because it contains B-tubulin
-
Opposite end the minus end
-
Video microscopy:
- Vesicles move along microtubules of axon, toward or away from cell body
- Movement is mediated by microtubules
- Motor proteins generate forces in cell
Motor Proteins
- Motor proteins convert chemical energy (ATP) into mechanical energy
- This generates force or moves cellular cargo
- Types of transported cargo:
- Ribonucleoprotein particles
- Vesicles
- Mitochondria
- Lysosomes
- Chromosomes
- Cytoskeletal filaments
- Cells contain hundreds of different motor proteins
- Motor Proteins
- Kinesins, dyneins, and myosins move along microtubules,
- Kinesins and dyneins move along microtubules
- Myosins move along microfilaments (aka actin filament)
- Microtubules in:
- Flagella
- Cilia
- Centrioles
Microtubule Organizers
- Studied in vitro
- Assembly from αβ-tubulin dimers have
- Nucleation, for slow microtubule formation
- Elongation, a rapid growth phase
- Nucleation occurs inside cell, in association with specialized structures called microtubule-organizing centers (MTOCs)
- The Centrosome is the best studied MTOC
Bases of Microtubule Dynamics
- GTP is required for microtubule assembly
- GTP molecule bound to β-tubulin subunit
- β-tubulin is an enzyme GTPase
- GTP hydrolysis isn't required for dimer incorporation
- GTP hydrolyzes to GDP after dimer incorporates
- GDP remains bound to assembled polymer
- After release from microtubule during disassembly and enters pool
- GDP replaced by GTP for reuse
Intermediate Filaments
- Diameter of 10–12 nm
- Identified in animal cells only
- Ropelike fibers that provide mechanical strength
- Humans have ~70 genes that encode IFs
- Polypeptide subunits divided into five classes based on cell type
Intermediate Filament Organization
- IF polypeptides share structural organization for similar shape
- Polypeptides contain central, rod-shaped, α-helical domain
- Fibrous domain differs from globular tubulin and actin subunits
- Intermediate filaments are insoluble
Intermediate Filament Assemble
- It is thought that building blocks is four long tetramers
- Tetramers that become aligned side by side in staggered fashion
- No + or - end
- Recent studies suggest 8 tetramers associate
- Side by side - (lateral) arrangement
- Subsequent growth of polymer length-wise is a side-by-side - (lateral) arrangement
- Growth of polymer by units associating end to end
- Building blocks are nonpolar like assembled
- Assembly requires ATP or GTP
Microfilaments
- Cells contain motility
- Neural crest forms products
- White blood cells patrol tissues
- Epithelial cells pull sheets Cells survey surfaces
- All share microfilaments
- Plant cells rely primarily on microfilaments
Microfilament Overview
- ~8 nm in diameter
- Composed of globular actin subunits
- Most abundant protein
- ATP forms flexible helical filament.
- Essentially two-stranded with two helical grooves
- Actin = polar, so is the subunit.
- Filaments have polarity, therefore different dynamics
Microfilament Assemble
- Before incorporation, action binds to an ATP molecule.
- Actin contains an ATPase
- Assembly similar to GTPase.
- ATP Hydrolyzed to ADF
- Bulk consists of ADF/Acting
- Contained in vitro
- As microtubules initially assemble then slow
- Filaments grow more quickly
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