Ch.16-The Cytoskeleton Flashcards
- What are the differences between microtubules, intermediate filaments and actin filaments?
A) Microtubules:
= Hollow tubes that can grow and shrink very rapidly; they are the largest.
B) Intermediate filaments:
= The strongest; composed of a variety of different proteins that are expressed in different types of cells
C) Actin:
= Linear polymers of globular actin subunits; only one type; smallest
2A. What are microtubule filaments made of/composed?
= are made up of tubulin heterodimers»_space; alpha and beta tubulin
2B. What are Intermediate filaments made of/composed?
= are composed of a variety of proteins; made up of subunits that wrap around each other and then stack together; tetramers twisted in a ropelike filament
2C. What are actin filaments made of/composed?
= are made up of actin subunits
3A. What is the function of microtubule filaments?
= act as highways for transport of vesicles, organelles, and chromosomes
3B. What is the function of Intermediate filaments?
= provide mechanical support for the plasma membrane where it comes into contact with other cells or with the extracellular matrix
3C. What is the function of actin filaments?
= Provide structure and shape to a cell
4A. Where in the cell would you find microtubule filaments?
Most, not all, originate from the centrosome
4B. Where in the cell would you find Intermediate filaments?
Extensive network found in the cytoplasm
4C. Where in the cell would you find actin filaments?
Cytoskeleton
5A. Polymerization of Actin
- Actin filament binds to ATP, hydrolyzes it to ADP.
- ARP complex controls where actin filaments grow
- Some proteins (like Thymosin) control actin subunit availability.
5B. Polymerization of Microtubules
- Gamma-tubulin ring starts growth of microtubules and is found in centrosomes;
- minus end of microtubule attaches to gamma-tubulin ring while the plus end grows and shrinks
- What is the difference between the plus and the minus end of actin and microtubules?
- Microtubules:
= The “plus end” ends with a beta tubulin and the “minus end” ends with an alpha tubulin; - Prefers to grow on the “plus end” while it grows and shrinks slowly on the “minus end.”
- Actin:
= The ARP complex binds to the “minus end” and can start nucleation; - The “plus end” is what grows and shrinks
- What are GTP caps? What types of filaments have these caps?
= is a specially altered nucleotide that controls growth and shrinkage on a microtubule.
- If the GTP cap is lost, the microtubule shrinks.
- If the GTP cap is regained, growth restarts
- Compare the mechanical properties of actin, microtubules and intermediate filaments.
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- Name an intermediate filament.
= Keratin
- How can a mutation in a keratin gene lead to blistering?
Mutation causes basal cells to rupture between the nucleus and the hemi-desmosomes»_space; inflammation response»_space; blistering of the skin
- How are microtubules nucleated? Name the protein involved.
They are nucleated by gamma-tubulin rings
12A. Name the protein involved when actin filaments are nucleated.
ARP complex
12B. How are actin filaments nucleated?
ARP complex binds to the minus end of actin filaments and start nucleation
- What is a centrosome?
= The organizing center of animal cells, abundant with gamma-tubulin rings
14A. How does profilin affect actin polymerization rates?
- Many actin subunits bound to profilin and make it more likely to be added to actin filament;
- profilin promotes growth of actin filaments
14B. How does thymosin affect actin polymerization rates
- Controls actin subunit availability by binding to actin subunits;
- actin subunits not available for growth
- How does stathmin affect the polymerization rate of microtubules?
- Sequesters free tubulin and makes it unavailable to microtubule;
- addition of subunits is stopped and microtubule shrinks
- How does capping of filaments affect their polymerization rates?
- Capping stabilizes filaments;
- actin subunits ready to be added onto filament but cannot because of the cap
17A. How do cross-linking proteins organize different assemblies of actin filaments?
Cross-linking proteins organize actin filaments differently by linking them in different ways
17B. What impact would spectrin have on the properties of actin bundles?
= forms pentagonal or hexagonal arrangements meant to maintain plasma membrane and structure; long filaments
17C. What impact would fimbrin have on the properties of actin bundles?
= parallel bundles of actin filaments; short and tight packing
- Why are there fimbrin crosslinking proteins in microvilli?
= To prevent things that are not wanted from entering the cell.
- Describe the cytoskeleton rearrangements that occur in a blood platelet when it is activated.
- Actin filaments capped by capping protein in inactivated blood plate
- Signal mediated Ca++ influx activates gelsolin
- Severed actin filaments capped by gelsolin
- Signal mediated slow rise in PIP2
- Gelsolin and capping protein removed and rapid actin filament growth from man short fragments
- What does gelsolin do?
= Severs (cuts) actin filaments
- Why sever actin filaments during platelet activation?
- Allows new actin filaments to grow
»_space;(because cut segments won’t have caps on them)« - This accelerates assembly of new actin filaments.
22A. What are myosins?
= ATP-dependent motor proteins best known for their role in muscle contraction
22B. What filament are they associated with?
= they move along actin filaments
- In what part of the myosin protein is the motor activity located?
= The motor head
- How are organelles moved around a cell?
Motor proteins pull organelles along microtubules
25A. What is a skeletal muscle cell?
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25B. How is a skeletal muscle cell formed?
= form by the fusion of many muscle cell precursors called myoblasts
26A. What is a myofibril?
= Basic rod like unit of muscle cell, consists of thin and thick filaments; Repeated subunits called sarcomeres and Z-discs.
26B. Describe the structure of myofibrils in detail.
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27A. What is a Z-disc?
= are narrow plate-shaped regions that separate neighboring sarcomeres
27B. What is a sarcomere?
= composed of long, fibrous proteins as filaments that slide past each other during muscle contraction.
- basic unit of striated muscle tissue (appear as repeating dark and light bands)
- How do your muscles move?
- Sliding of thin and thick filaments, using myosin motor heads
- Describe how a muscle cell receives a signal for contraction in detail.
- Action potential goes down the axon
- Eventually, a voltage-gated Calcium channel opens up and calcium rushes into cell
- Acetylcholine vesicle opens and acetylcholine is released into the synaptic cleft
- Acetylcholine opens Ca++ ligand channel
- Voltage sensitive protein changes shape
- Ca++ goes out of sarcoplasmic reticulum
- Ca++ relieves tropomyosin blockage and exposes myosin binding site
30A. What are transverse tubules?
= They are deep invaginations of sarcolemma
30B. Why are transverse tubules necessary?
= allow depolarization of membrane to quickly penetrate interior of the cell
- Describe in detail how Ca2+ causes myofibrils to contract.
It relieves tropomyosin blockage and exposes myosin binding site so actin can attach and the muscle can shorten
- What is tropomyosin?
- It can cover up myosin binding sites on actin
- Troponin complex can shift tropomyosin off myosin binding sites.
