C6: Cytoskeleton Flashcards by Jasmine Marta

A ___ is present in the cytoplasm of all cells, including bacteria, and archaea

cytoskeleton

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It is a complex, dynamic network of interlinking protein filaments that extends from the cell nucleus to the cell membrane

cytoskeleton

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It gives the cell its shape and mechanical resistance to deformation, and through association with extracellular connective tissue and other cells it stabilizes entire tissues.

cytoskeleton

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The ___ is the collective name for all structural filaments in prokaryotes

prokaryotic cytoskeleton

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play essential roles in cell division protection, shape determination, and polarity determination in various prokaryotes.

Cytoskeletal elements

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Prokaryotic cytoskeleton (5)

FtsZ
MreB
CRESCENTIN
ParM and SopA
MinCDE system

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The first identified prokaryotic cytoskeletal element, forms a filamentous ring structure located in the middle of the cell called the Z- ring that contricts during cell division.

FtsZ

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acts as an organizer protein and is required for cell division; homologous to eukaryal tubulin

FtsZ

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is a bacterial protein believed to be analogous to eukaryal actin

MreB

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determines cell shape by mediating the position and activity of enzymes that synthesize peptidoglycan and by acting as rigid filament under the cell membrane that exerts outward pressure to sculpt and bolster the cell.

MreB

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condenses from its normal helical network and forms a tight ring at the septum in Caulobacter crescentus right before cell division.

MreB

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is also important for polarity determination in polar bacteria, as it is responsible for the correct positioning of at least four different polar proteins in C. crescentus.

MreB

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____ (encoded by ___ gene) is an analogue of eukaryotic.

Crescentin; creS

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has a rather large primary homology with IF proteins in addition to three-dimensional similarity

Crescentin

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is a cytoskeletal element that possesses a similar structure to actin, although it behaves functionally like tubulin.

ParM

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___ and ___ that are responsible for R1 plasmid separation.

ParR; parC

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is a filament system, that properly
positions the septum in the middle of the cell in Escherichia coli.

MinCDE system

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inhibits the formation of the septum by prohibiting the polymerization of the Z-ring.

MinC

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_____ form a helix structure that winds around the cell and is bound to the membrane by MinD.

MinC, MinD, and MinE

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function is for the maintenance of cell-shape by bearing tension;

INTERMEDIATE FILAMENTS

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Organise the internal tridimensional structure of the cell, anchoring organelles and serving as structural components of the nuclear lamina.

INTERMEDIATE FILAMENTS

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also participate in some cell-cell and cell matrix junctions.

INTERMEDIATE FILAMENTS

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are most commonly known as the support system or “scaffolding” for the cell and nucleus while also playing a role in some cell functions.

Intermediate filaments

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form cell-cell connections and anchor the cell-matrix junctions that are used in messaging between cells as well as vital functions of the cell.

intermediate filaments

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intermediate filaments are in general present in mesenchymal cells.

Vimentin

is present in general in epithelial cells.

Keratin

type of IF giving structural support to the nuclear envelope

lamin,

, play an important role in structural and mechanical support of muscle cells

desmin

All intermediate filaments start from a fibrous subunit. This then coils around another filamentous subunit to form a coined-coil ___

dimer, or protofilament

Using proteins called ___, the intermediate filaments can be connected to one another to form sheets and meshes

plectins

can also connect the intermediate filaments to other parts of the cytoskeleton, while other proteins can help to attach the IF cytoskeleton to the cell membrane (e.g., desmoplakin)

Plectins

aid in cytokinesis and cell motility; Involved in cytoplasmic streaming

microfilament

They are also part of muscle cells and allow these cells to contract, along with myosin.

microfilament

Cytoskeletal opposites of the intermediate filaments

ACTIN FILAMENTS

They are strands are made up of small globular actin (g-actin) subunits.

ACTIN FILAMENTS

the largest of the cytoskeleton's fibers at about 23 nm.

MICROTUBULES

hollow tubes made of alpha and beta tubulin

MICROTUBULES

Most of the microtubules in an animal cell come from a cell organelle called the

centrosome

important in forming the spindle apparatus (or mitotic spindle)

microtubules

involved in transporting molecules within the cell and in the formation of the cell wall in plant cells.

microtubules

Microtubule are mostly found as large 13-stranded (each strand is called a ____) hollow tube structures.

protofilament

Dimers of ____ polymerize to form microtubules

α- and β-tubulin

a phenomenon in microtubules wherein, tubulin subunits will both associate and dissociate from the plus end of the protofilament.

Dynamic Instability

__ is fairly strong, but not very flexible; Depolymerization also occurs.

microtubule

almost all microtubules have their (-) end in a perinuclear area known as the

MTOC, or microtubule organizing center.

MTOC contains a structure known as the __.

centrosome

components of centrosome (2)

centriole- pericentriolar material (PCM)

- two short barrel-shaped microtubules based structures positioned perpendicular to each other

centriole

facilitates microtubule nucleation

Y-tubulin ring complex

“railroad tracks”= ___ “trains” = ____

“railroad tracks”= microtubules “trains” = kinesins and dyneins

“streets”= ___ “trucks”= ___

“streets”= microfilament “trucks”= myosin

____ drive towards (+) end or cell periphery ____ go toward (-) end or towards the MTOC

KINESINS DYNEINS

an arrangement of alternating fibers of f-actin ("thin fibers") and myosin II ("thick fibers").

SARCOMERE

Sarcomere is one of many connected together to form a __ (extends the length of mucle cell).

myofibril

are responsible for muscle contraction.

Sarcomeres

a fibrous protein that lies in the groove of an actin microfilament and blocks access to the myosin binding site.

TROPOMYOSIN

attaches to the microfilament in conjunction with a multi-subunit troponin complex.

TROPOMYOSIN

- calcium binding protein subunit that initiates the sequence of conformational changes on the thin filament

Troponin-C

a gigantic protein (the largest known, at nearly 3 MDa); can be thought of as something of a bungee cord tether to the myosin

TITIN

prevent the forces generated by the myosin from pulling the fiber apart

TITIN

Nerve cell releases neurotransmitters such as ___ which bind to receptors (AChR) on the muscle cell.

acetylcholine (ACh),

Membrane attachment to the cytoskeleton is necessary for

force transmission.

Signaling from membrane receptors can induce cytoskeletal rearrangements via

adapter proteins.

were one of the early experimental systems for studying cytoskeleton-membrane interactions.

Erythrocytes

__ and __ are important linkage proteins connecting transmembrane proteins to microfilaments.

Ankyrin, spectrin

are used to connect extracellular substrates to the cytoskeleton and enhance signal transduction.

Scaffolding proteins

control cytoskeletal polymerization, depolymerization, bundling, and network formation.

Accessory proteins

promotes actin polymerization by exchanging ATP with ADP and enhancing addition to microfilaments

Profilin

regulates microfilament assembly by sequestering G-actin and releasing it via profilin.

Thymosin B4

___ and ___ can sever actin microfilaments by altering subunit conformation.

Gelsolin and severin

___ and __ are microtubule-severing proteins

Spastin and katanin

sequesters tubulin dimers and is regulated by phosphorylation.

Op18 (stathmin)

__, ___, and ___ promote microtubule assembly and stability.

MAP1, MAP2, and tau

Several proteins crosslink (6)

F-actin, fimbrin, alpha-actinin, b-spectrin, dystrophin, and filamin.

the ability of an organism to move independently, using metabolic energy.

MOTILITY

is genetically determined, but may be affected by environmental factors.

MOTILITY

refers to an organism's ability to move food through its digestive tract.

MOTILITY

responsible for protrusion of the front end of migrating cells.

RAPID POLYMERIZATION

accounts for the ability of cells to migrate in a specific direction.

CHEMOTAXIS

Cellular swimming: Their beating pattern is then coordinated at the cellular level, most often in a wave-type of manner known as the

metachronal wave

Other strategies of swimming include the elegant movement used by Eutreptiella - called .

metaboly

2 types of cell motility

cell swimming cell crawling

is the common mechanism employed by most eukaryotic animal cells as they move through animal tissues, constituted of other cells or filaments of the extracellular matrix.

Cell crawling

They either move by means of wormlike cycles of extensions and contractions of their cell body or of some specific protrusions, or slide without visible means of protrusion, a process also referred to as gliding.

cell crawling

slide without visible means of protrusion, a process also referred to as .

gliding

The best characterized crawling mechanism is the so called

amoeboid motility.

Two-dimensional protrusions

lamellipodia, filopodia or microspikes

Flat veil-shaped projections called ___, as they occur keratocytes' in fibroblasts' or fish motility for wound healing.

lamellipodia

Long thin projections called either ____, and which occur for example in neuronal growth-cone progressions.

filopodia or microspikes

process of amoeboid motility can be decomposed into three to five steps that occur simultaneously

1. Extension 2. Adhesion 3. Translocation 4. De-adhesion

The first process opf amoeboid motility is ____, where the membrane is pushed forward by means of the polymerization of cytoskeletal filaments.

Protrusion

Then the protrusion adheres to the __ via the formation of ___, and subsequent contraction of the cellvvcytoskeleton drags the cell body forward.

substrate; anchoring points

are dynamic events that occur within the cytoskeleton of eukaryotic cells.

Microtubule growth and catastrophes

The ____ refers to their ability to alternate between phases of growth and shrinkage

dynamic instability of microtubules

___, also known as actin-based gels or actin networks, are dynamic and organized structures formed by a protein called actin.

Actin gels

Actin can exist in two primary forms:

globular (G-actin) and filamentous (F-actin).

are involved in cell motility, including processes like crawling, muscle contraction, and the formation of cellular protrusions

Actin gels

in the cytoskeleton refers to the movement of cellular structures and organelles within a cell that is powered by motor proteins associated with the cytoskeleton.

Motor-driven motility

____ explain various biophysical processes. These models involve the movement of proteins, ion transport, and rotary-motor processes.

Isothermal rectifying models