Cytoskeleton Flashcards by Grace Smith

What are cytoskeletal strands made of?

In general, cytoskeletal strands are made of chains of globular protein or bundles of fibrillar protein

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What functions does the cytoskeleton serve?

Implicated in:
● Cell shape
● Cell division
● Movement
○ of cell contents
○ of the cell

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What is GFP?

Green fluorescent protein from green fluorescent jellyfish
-used to colour proteins for observation

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Function and Superfamiliy

FtsZ

Protein of the tubulin superfamily
-forms a band around the midpoint of the cell during division (the “Z ring”)
-creates a strangulation in the cell

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What happens if you inhibit FtsZ?

Results in filamentous morphology and lysis
- it stretches then eventually breaks
-this is an avenue of research to treat resistant bacteria

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Function and Superfamiliy

MreB

Protein of the actin superfamily
-Gives rod-shaped bacteria their rod shape
-Probably used as a guiding scaffold in the deposition of new cell wall during growth

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Function

RodZ

Not actually part of the cytoskeleton

Transmembrane protein that works in conjunction with MreB to shape the Prokaryotic cell; not part of the cytoskeleton but it provides a binding site for MreB

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Function and Superfamiliy

ParM

Protein of the actin superfamily

Moves plasmids to opposite ends of the cell prior to division
-only for low count plasmids

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Function

Crescentin

A coiled-coil filamentous protein, bending bacilli into a curved shape

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Mobility

the cell can move

e.g.: red blood cells (The cell is mobile)

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Motility

the cell can move by itself

e.g.: Escherichia coli bacteria (The cell is motile)

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Flagellum

A hollow-tube filament made of self-organising flagellin proteins

A basal apparatus (motor) anchored in the cell wall, protruding into the cytoplasm (in prokaryotes)

-NOT PART OF THE CYTOSKELETON IN PROKARYOTES

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peritrichous

Flagellar Arrangment

flagella are all around the perimeter of the cell

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Which direction does e-coli rotate its flagellum to “run”

Counter-clockwise

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Which direction does e-coli rotate its flagellum to “tumble”

Clockwise

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Chemotaxis

Movement directed by the concentration gradient of chemicals

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Type IV pili

Retractile protein filaments that move the cell like a grappling hook or Spiderman’s web

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Archaea flagella

Shorter and simpler in structure than bacterial flagella

Archaeal flagellin is similar to the type IV pilin of bacteria
-Powered by ATP
-Uncertain as to how the motor is constructed

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Periplasmic flagella

Known also as axial filaments
-Found in spirochaetes
-They are “external” structures: internal to the outer membrane, but external to the plasma membrane
-They make the entire cell rotate in a corkscrew motion

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What are the 3 classes of cytoskeletal fibres in Eukaryotes

-Microtubules (tubulin family)
-Microfilaments (actin family)
-Intermediate Filaments

Microtubules (polarity and family)

(tubulin family)
○ Polar (directional)
○ Globular monomers

Microfilaments (polarity and family)

(actin family)
○ Polar (directional)
○ Globular monomers

Intermediate Filaments (polarity)

○ Apolar
○ Filamentous monomers

What are microtubules (MTs) made of?

Hollow tubes made of tubulin heterodimers
-Stiff structural tubes
-resists compressive forces

They move cell contents and also the cell

Are microtubules involved in transport?

Microtubules serve as tracks for vesicle transport Motor proteins attach to both the microtubules and a cargo to transport it along to a specific destination

Are motor proteins polar?

Yes

# Which end does it move towards and what type of transport is it Kinesin

moves toward the positive end (anterograde transport) - ATP powered

# Which end does it move towards and what type of transport is it Dynein

moves toward the negative end (retrograde transport) - ATP Powered

What are Eukaryotic cilia and flagella are made of? What is their configuration?

They are made of microtubules Both structures are ATP-powered and share the same configuration. -Basal body: 9 triplets, no central tubule (9+0) -Motile portion: 9 doublets, 2 central tubules (9+2)

Basal body configuration | Flagella

9 triplets, no central tubule (9+0)

Motile portion configuration | Flagella

9 doublets, 2 central tubules (9+2)

Does Eukaryotic cilia and flagella have the same structure?

Yes, but their size and movement are different Flagellum: undulates side to side (think flutter kick) Cilium: beats asymmetrically (think whip kick)

What radiates from Microtubule Organizing Centers (MTOCs)

Microtubules (the centrosome functions as the MTOC in many eukaryotic cells)

Which class of cytoskeletal fibre guides chromosomes during mitosis?

Microtubules Microtubules are part of the spindle apparatus (cell division lectures)

Microfilament monomer

G-actin is the protein monomer of microfilaments | Think globular actin

Microfilament polymer

G-actin is polymerized into F-actin to form filaments | Think filamentous actin

Basic functions of microfilaments

● Microfilaments provide tensile strength to various parts of the cell ● They help shape the cell ● They provide movement to the cell and to the cell membrane

What superfamily are microfilaments?

actin filaments

Does F-actin formation require ATP?

yes

What supports microvilli on intestinal cells internally

Microfilaments

Which system is used for cell motion and muscle contraction?

An actin-myosin system

Amoeboid movement

The most common type of “crawling” movement in Eukaryotes is likely driven by actin filaments and myosins pulling on them, forming pseudopodia

Cytoplasmic Streaming

an actin-myosin system -cell contents circulate throughout the cell -common in plant cells

Can some bacteria manipulate the actin-based cytoskeleton?

Yes Ehrlichia chaffeensis (Gram-negative) “hijacks” the cytoskeleton of neutrophils to find other neutrophils for infection -like zombies

Intermediate filaments (IFs)

Large family of more than 50 proteins They twist to form cable-like structures of very high tensile strength They help toughen parts of the cell and to morph the cell into a specific shape Animal-only structure!

What are desmosome fibers are made of?

Desmosome fibers are made of keratin, an IF protein

What is made of extracellular keratin IFs?

Extracellular keratin forms tough structures like claws, horns, beaks, feathers, hair, nails, etc.

Lamin

the protein that forms the nuclear lamina -a type of IF

What moves the flagellum and how does it do it

Dyneins move the flagellum Dyneins attached to a neighbouring doublet “walk” on the surface of the microtubule facing it