Term
| The intricate netowrk of protein filaments that extends throughout the cytoplasm is called.... |
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Definition
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Term
| T/F The cytoskeleton is similar to the human skeleton in that they are both rigid structures. |
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Definition
FALSE
The cytoskeleton is a highly dynamic structure that is continously reorganized as a cell changes shape, divides, and responds to its environment |
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Term
| What are the three types of protein filaments present in the cytoskeleton? |
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Definition
| Intermediate filaments, microtubules, and actin filaments |
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Term
| What are the subunits of each part of the cytoskeleton? |
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Definition
A family of fibrous proteins form the intermediate filaments,
tubulin is the subunit of microtubules, and actin is the subunit of actin filaments |
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Term
| T/F Intermediate filaments have great tensile strength |
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Definition
TRUE
Their main function is to enable cells to withstand mechanical stress when they are stretched. |
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Term
| Why are intermediate filaments called "intermediate"? |
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Definition
| Because their diameter (~10 nm) is between that of thin actin-filaments and thicker myosin filaments of smooth muscle cells, the cells in which intermediate filaments were first discovered |
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Term
| What is the toughest and most durable of the 3 types of cytoskeletal filaments? |
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Definition
| Intermediate filaments. When cells are treated with conc. salt solutions and nonionic detergents, the intermediate filaments are the only part of the cytoskeleton left. |
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Term
| Where do intermediate filaments anchor on the plasma membrane? What is the purpose of this? |
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Definition
| They anchor at desmosomes, where the external face of the membrane is connected to that of another cell |
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Term
| What is the nuclear lamina? What is it made of? |
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Definition
| A mesh of intermediate filaments, the nuclear lamina, underlies and strengthens the nuclear envelope in all eucaryotic cells. |
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Term
| Describe the structure of intermediate filaments |
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Definition
| Ropes with many long strands twisted together to provide tensile strength. |
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Term
| Describe the subunit of intermediate filaments |
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Definition
| Elongated fibrous proteins, with an N-terminal globular head and a C-terminal globuar tail. The rod domain is an extended alpha-helix which wrap around another to form a dimer (a coiled coil). Two dimers bond noncovalently to form a tetramer, and the tetramers bind to each other end-to-end and side-by-side to form the ropelike structure |
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Term
| Describe the variation of size and amino acid sequence in intermediate filaments, and the reasons for the variation/nonvariation |
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Definition
The central rod domain has IF proteins with similar size and amino acid sequence so they can always form filaments of similar diameter and internal structure.
In contrast, the globular domains vary greatly in size and amino acid sequence to promote interactions with other components in the cytoplasm |
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Term
| What kinds of cells possess a LOT of intermediate filaments, and why? |
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Definition
| Nerve cell axons, muscle cells, eipthelial cells...these cells are subject to high mechanical stress |
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Term
| What are the 4 classes of intermediate filaments? |
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Definition
1.) Keratin filaments (epithelial cells)
2.) Vimentin and vimentin-related filaments (connective-tissue cells, muscle cells, neuroglial cells)
3.) Neurofilaments (nerve cells)
4.) Nuclear Lamins (Strengthen the nuclear membrane) |
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Term
| Describe the rare human genetic disease epidermolysis bullosa simplex (EBS) |
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Definition
| A mutations in the keratin genes interferes with the formation of keratin filaments in the epidermis, the skin is highly vulnerable to mechanical injury, gentle pressure can rupture cells and cause the skin to blister |
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Term
| The intermediate filaments in the tough nuclear lamina are called... |
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Definition
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Term
| When are intermediate filaments arranged in a 2-D mesh? |
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Definition
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Term
| What controls the disassembly and reassembly of the nuclear lamina? |
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Definition
| The phosphorylation and dephosphorylation of the lamins by protein kinases. The phosphorylation causes a conformational change which weakens the binding between tetramers and causes the filament to fall apart |
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Term
| What are the long and relatively stiff hollow tubes of protein that can rapidly disassemble in one location and reassemble in another? |
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Definition
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Term
| In a typical animal cell, microtubules grow out from a small structure near the center of the cell called the ____________. |
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Definition
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Term
| What part of the cytoskeleton is mainly responsible for anchoring membrane-enclosed organelles and for guiding intracellular transport? |
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Definition
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Term
| When a cell enters mitosis, the cytoplasmic microtubules disassemble and reassemble into an intricate structure called the __________ ___________. |
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Definition
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Term
| What forms cilia and flagella? |
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Definition
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Term
| Describe the subunits of microtubules: |
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Definition
| Molecules of tubulin, each one of which is itself a dimer composed of alpha-tubulin and beta-tubulin. The tubulin dimers stack together noncovalently into 13 parallel protofilaments, which form the hollow tube |
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Term
| Describe the structural polarity of microtubules |
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Definition
Each protofilament has an alpha-tubulin exposed at one end and a beta-tubulin exposed at the other end.
The BETA end is the PLUS end
The ALPHA end is the MINUS end |
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Term
| How does a microtubule grow? |
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Definition
| From an initial ring of 13 tubulin molecules; tubulin dimers are added individually. In vitro, tubulin is added bi-directionally, but it's added faster on the BETA-tubulin end (this is why it is called the PLUS end) |
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Term
| Why is the polarity of a microtubule so important?> |
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Definition
| It is crucial for the assembly of microtubules, as well as for their functions, i.e. defining a direction for intracellular transport |
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Term
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Definition
| Typically present on one side of the nucleus when the cell is not dividing; contains hundreds of ring-shaped GAMMA-tubulin structures, each ring-shaped gamma-tubulin is a starting point, or "nucleation site" for the growth of one microtubule |
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Term
| In what direction do the microtubules grow of the the centrosome? |
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Definition
| The alpha-beta-tubulin dimers add to the gamma-tubulin ring in a specific orientation, resulting in the minus end of each microtubule being embedded in the centrosome and growth only occurs at the plus end, the outward-facing end |
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Term
| Why are the nucleating sites formed by gamma-tubulin so important? |
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Definition
| It is difficult (energetically) for a cell to start a new microtubule from scratch, by assembling a ring of alpha-beta-tubulin and then adding dimers. The concentration of free alpha-beta-tubulin in vivo is too low to drive the difficult first step of assembling the new ring |
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Term
| Describe the dynamic instability of microtubules. |
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Definition
| A microtubule can grow (by sequentially adding dimers of tubulin), then, quickly, the microtubule can rapidly shrink inward by losing subunits from the free end, and then it could start to grow again, it can even disappear completely |
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Term
| What controls the dynamic instability of microtubules? |
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Definition
| Tubulin molecules' intrinsic ability to hydrolyze GTP. A free tubulin dimer has one GTP bound which is hydrolyzed to GDP shortly after the subunit is added to a growing microtubule. The growth can go faster than the hydrolysis, creating the GTP cap at the end of the rope |
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Term
| What is faster: movement along microtubules or free diffusion? |
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Definition
| Movement along microtubules |
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Term
| What is saltatory movement? |
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Definition
| The small, jerky steps taken by mitochondria and other small membrane-enclosed organelles. |
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Term
| How do motor proteins work? |
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Definition
| They bind to actin filaments or microtubules and use the energy derived from repeated cycles of ATP hydrolysis to travel along the MT in a single direction. They also attach to other cell components, and transfer them as "cargo" |
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Term
| What are the 2 families of motor proteins which travel along microtubules, and which direction do they move? |
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Definition
Kinesins (move toward PLUS end)
Dyneins (move toward the MINUS end, the centrosome) |
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Term
| T/F Both kinesins and dyneins have two globular ATP-binding heads and a tail |
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Definition
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Term
| Describe the proteins associated with dynein. |
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Definition
| Dynactin associates the motor protein with the microtubule, spectrin and anchorin connect the cargo with the motor protein. |
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Term
| What is the main motor protein involved in cilia movement? |
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Definition
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Term
| Microtubules are cross-linked with ______ to cause the curling of flagella |
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Definition
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Term
| What are the 2 types of Microtubule Associated Proteins? (MAPs) |
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Definition
1.) stabilizing MAPs (e.g. MAP1)
2.) destabilizing MAPs (e.g. catastrophin) |
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Term
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Definition
| It is a microtubule associated protein which binds to the PLUS end of a MT after the GTP cap goes away and stops the pulling apart of the MTs. |
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Term
| T/F When one side of a flagella is active, the other side is also active to promote symmetrical movement. |
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Definition
| FALSE! The other would be shut down (inactive) so that the flagella don't just stay still |
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Term
| Describe the separation of the mitotic spindle. What causes it? How are the chromosomes separated? What happens to the kinetochore? |
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Definition
| An abundance of the MAP catastrophin at the PLUS end of a MT in the mitotic spindle disrupts the MT and dynein pulls the kinetochore as cargo, and separates the chromosomes. |
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Term
| Describe actin filaments (structure) |
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Definition
| They are helical polymers of actin molecules. They are more flexible than microtubules and are often found in bundles or networks associated with the plasma membrane |
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Term
| Are actin filaments polarized? |
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Definition
| Yes, there is fast- and a slow-growing end |
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Term
| What controls the assembly and disassembly of actin filaments? |
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Definition
| The hydolysis of ATP tightly bound to each actin monomer |
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Term
| What controls the varied forms and functions of actin filaments? |
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Definition
| Multiple actin-binding proteins. They control the polymerization of actin filaments, cross-link the filaments into loose networks or stiff bundles, attach them to membranes, or move them relative to one another |
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Term
| What is the cell cortex? What is its purpose? |
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Definition
| A network of actin filaments underneath the plasma membrane which is responsible for the shape and movement of the cell surface, including the movements involved when a cell crawls along a surface. |
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Term
| Describe the migration of a cell. |
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Definition
| A variety of actin-binding proteins drive the leading edge of the cell forward, adhere to the substratum, and retract the trailing edge. All these processes are triggered by external stimuli working via small GTP-binding proteins |
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Term
| What's up with myosins? What do they do, how do they do it... |
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Definition
| Myosins are motor proteins that use the energy of ATP hydrolysis to move along actin filaments; they carry organelles along actin-filament tracks or cause adjacent actin filaments to slide past each other in contractile bundles. |
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Term
| How are actin-filaments associated with muscle contractions? |
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Definition
Huge arrays of overlapping actin filaments and myosin filaments generate contractions by sliding over one another
Muscle contraction is initiated by a sudden rise in cytosolic Ca++, which delivers a signal to the contractile apparatus via Ca++ binding proteins |
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