The Cytoskeleton Flashcards
What is the cytoskeleton?
A dynamic network of interconnected filaments and tubes that extend throughout the cytosol (and some organelles) of eukaryotes
T or F: All eukaryotes and prokaryotes have microtubules and microfilaments.
False. Only eukaryotic cells have them
What do animal cells have in addition to microtubules and microfilaments?
Intermediate filaments
What are the four primary functions of the cytoskeleton?
- Structural support
- Spatial organization within the cell
- Intracellular transport
- Contractility and motility
What is the structure of a microtubule?
Hollow and tube-like
What are microtubules made up of?
Tublin dimers
What are tublin dimers composed of?
Alpha- and beta- tubulin
What are alpha/beta heterodimers composed of?
An alpha-tublin polypeptide chain and a beta-tublin polypeptide chain
How are heterodimers aligned to create structural polarity?
In the same direction (head to tail)
What are protofilaments in microtubules composed of?
alpha/beta heterodimers
How many protofilaments create the hollow cylinder of a microtubule?
13
What is structural polarity important for in microtubules?
Microtubule growth and the direction of movement of material along it
Which of the three cytoskeleton fibres have the largest diameter?
Microtubules
What is the primary function of microtubules?
Help maintain the cell shape and internal structure
What are the two types of microtubules?
- Axonemal microtubules
- Cytoplasmic microtubules
How do axonemal microtubules and cytoplasmic microtubules differ in terms of their organization?
- Axonemal: highly organized and stable
- Cytoplasmic: loosely organized and very dynamic
Which type of microtubule is part of structures involved in cell movement?
Axonemal microtubules
Which type of microtubule is found in cilia?
Axonemal microtubules
What are cilia?
Hair-like structures that extend from the surface of cells
What are the two types of cilia?
- Motile
- Nonmotile
What function do motile cilia often perform?
Propel the movement of cells of the fluid surrounding them
What function do nonmotile cilia often perform?
Often serve a sensory function
Which type of microtubule is located in the cytosol?
Cytoplasmic microtubules
T or F: Microtubules and microfilaments undergo dynamic assembly and disassembly.
True
T or F: The formation of microtubules isn’t regulated/controlled.
False. It is regulated/controlled
What is the difference between the plus and minus end of microtubules and microfilaments?
- Plus end: fast-growing
- Minus end: slow-growing
What is the term used to describe the rapid shrinkage at the plus end of a microtubule?
Catastrophe
What is the microtubule-organizing centre?
The central site of microtubule assembly
T of F: The microtubule-organizing centre is found in both prokaryotes and eukaryotes.
False. MTOC is only found in eukaryotic cells
What are the two most important microtubule-organizing centres?
Basal bodies and centrosomes
What is the microtubule-organizing centre for animal cells?
Centrosomes
What is involved with dynamic instability?
Cycles of rapid depolymerization followed by slower polymerization in the plus end of microtubules
What does the dynamic instability of microtubules allow for during cell division?
Allows spindle microtubules to quickly find and attach to chromosomes
What are the two classes of microtubule-associated proteins (MAPs)?
- Non-motor
- Motor
Which type of microtubule-associated protein controls microtubule organization in the cytosol?
Microtubule-associated non-motor proteins
What type of microtubule-associated protein often contribute to the growth and disassembly of microtubules?
Microtubule-associated non-motor proteins
Defective Tau protein in neurons causes neurofibillary tangles and leads to what?
Alzheimer’s and other forms of neurodegenerative disorders
Which type of microtubule-associated protein powers intracellular transport?
Microtubule-associated motor proteins
What are microtubule-associated motor proteins able to generate between microtubules?
A sliding force
What are the two main types of microtubule-associated motor proteins?
- Kinesin
- Dynein
What is the difference between kinesin and dynein in terms of the direction of their movement?
- Kinesin: Plus end directed (moves to plus end)
- Dynein: Minus end directed (moves to minus end)
What occurs during the force-generating step when motor MAPs cause movement?
ATP binds to the leading head and induces a conformation change that swings the training head 180 degrees toward the (+) end of the microtubule
What is the difference between the leading head and the training head during movement along a microtubule?
- Leading head: Whichever head is closest to the (+) end
- Trailing head: Whichever head is closest to the (-) end
What are melanophores?
Specialized skin cells that produce the pigment melanin
What type of organism possesses melanophores?
Some vertebrates
What do melanophores do with the pigment they have produced?
They keep it in granules and move them around inside in response to hormones or neuronal signals
What does the redistribution of melanin in vertebrates with melanophores allow them to do?
Change colours
How do melanin granules in melanophores move back and forth along microtubules?
They are transported by kinesin and dynein
What happens to melanin granules in melanophores in the dark?
They are dispersed outwards, causing the organism to be darkly coloured
Which motor MAP is responsible for dispersing melanin granules?
Kinesin
What happens to melanin granules in melanophores in the light?
They are aggregated to the centre of the organism, causing it to be lightly coloured
What are intermediate filaments composed of?
intermediate filament protein subunits
Intermediate filaments are exclusive to which type of cell?
multicellular animal cells
What does it mean for intermediate filaments to be non-polar?
They have no plus or minus ends
Why are intermediate filaments not used for transport?
Because they are non-polar
Karatins compose intermediate filaments in which cell type?
Epithelial cells
Viementins compose intermediate filaments in which cell type?
Fibroblasts
Neurofilaments compose intermediate filaments in which cell type?
Neurons
Where are intermediate filaments composed of lamins located?
The nucleus
Which fibre of the cytoskeleton is composed of a double helix of actin monomers?
Microfilaments
Which fibre of the cytoskeleton is the thinnest?
Microfilaments
Which of the three cytoskeleton fibres are involved in muscle contraction and cytokinesis?
Microfilaments
What is the central component of microfilaments?
Actin
What are the two ways in which actin can exist within a cell?
- As a monomer (G-actin)
- As a polymer (F-actin)
What is G-actin?
A single unit/monomer of actin
What is F-actin?
An actin filament/polymer
T or F: F-actin appears as a single strand of subunits.
False. F-actin appears as TWO strands of subunits
How many subunits of G-actin does one F-actin unit have?
28
What is phalloidin?
A class of toxins (phallotoxins)
What is a major symptom of phalloidin poisoning?
Acute hunger
How does phalloidin affect F-actin?
It binds to and stabilizes F-actin and prevents the depolymerization of actin fibres
Are F-actin filaments polar or non-polar?
Polar (have plus and minus end)
In terms of microfilament growth, what occurs once a stable actin trimer has been established?
There is rapid elongation
What regulates the organization of F-actin microfilaments?
Actin-binding proteins
What is the Arp 2/3 complex?
A branching facilitator
What does the Arp 2/3 complex do?
Helps create branching points for the polymerization of new actin fibres
What does the polymerization and branching of microfilaments play a central role in?
Directed cell motility
What is a lamellipodium?
An actin projection on the leading edge of a cell
What is profilin?
An actin-binding protein that enhances the growth of filaments
What is cofilin?
An actin-binding protein that disassembles actin filaments
What does a capping protein do to a microfilament?
Prevents the exchange of a subunit at the plus end
What are myosins?
A superfamily of motor proteins associated with microfilaments
Which direction do mysoins move along microfilaments?
Toward the plus end
What are the two broad groups myosins can be divided into?
- Conventional myosins
- Unconventional myosins
Which type of myosin is the primary motor for muscle contraction?
Conventional myosins
Which type of myosin generates force and contributes to motility in non-muscle cells?
Unconventional myosins
