Cells alive 3- cytoskeleton Flashcards
what are the functions of the cytoskeleton?
- support
- movement
- resistance to mechanical forces
what are the 3 types of filaments in a cytoskeleton?
-microfilaments
- intermediate filaments
- microtubules
what are the monomers in microfilaments?
actin
what size are microfilaments
v small: 5-9nm
what are microfilaments made of and how are they assembled?
made of globular proteins called actin which assemble into two stranded helical polymers
where do you find microfilaments?
they are dispersed through the cell but concentrated beneath the cortex
how are microfilaments distributed?
the actin anchors to the mesh proteins in the cortex and distribute like a web
what is the function of microfilaments?
cell shape and motility
are microfilaments dynamic?
yes
what is the size of intermediate filaments?
10nm diameter (hollow tube)
are intermediate filaments more or less dynamic than microfilaments?
less
what is the structure of intermediate filaments?
extended alpha-helical regions wind together into dimers which then associate into tetramers, these wind together to form rope-like fibres
what is a dimer?
2 joined monomers
what is a tetramer
4+ subunits
give examples of intermediate filaments
keratins in epithelial cells
desmin in muscle cells
what is the function of intermediate filaments?
mechanical support of cell structures
what is the size of microtubules?
25nm in diameter
what are microtubules made of?
globular proteins called tubulin
what is the minimal subunit of microtubules?
dimer of alpha beta subunit
how is tubulin formed?
alpha and beta tubulin subunits dimerise to form tubulin
what is the structure of microtubules?
- long and straight
- one end (-) is attached to a microtubule organising centre (MTOC) while the other end (+) grows and shrinks
what protein “walks” along the microtubule
motor proteins
are intermediate filament monomers globular?
no
typically microtubules are attached to one point within the cell; what is it called?
microtubule organising centre
true or false…Monomers are added to the filaments of the cytoskeleton by covalent interactions.
false
within the cytoskeleton what is the concentration at which the rate of monomer addition equals the rate of removal known as?
The critical concentration
Microtubules and actin filaments have a fast growing and a slow growing end. Name 2 mechanisms by which this is achieved
- conformation change
- nucleotide hydrolysis
Name one toxin or drug which affects the assembly or disassembly of the cytoskeleton.
vincristine
Which of the following are examples of cytoskeletal motor proteins?
- tublin
- dynein
- actin
- myosin
- kinesin
- dynein
- myosin
- kinesin
what are the cytoskeletal elements to these motor proteins
- dyneins
- myosins
- kinesins
dyneins = microtubules
kinesins = microtubules
myosins = actin filaments
Put the following in order:
Myosin head bound to actin filament…
ATP hydrolysed
Myosin head changes shape to move forwards
Phosphate released and mysoin reattaches to actin
Myosin releases actin
ADP released and conformation change (power stroke)
Myosin binds ATP
- myosin binds ATP
- myosin releases actin
- ATP hydrolysed
- myosin head changes shape to move forwards
- phosphate released and myosin reattaches to actin
- ADP released and conformation change (power stroke)
Name two organelles which are held in position by the actions of motor proteins on microtubules.
golgi
endoplasmic reticulum
Cytoskeletal elements are central to cell motility. Match the form of motility to the element:
- flagella and cilia
- muscle contraction
- cell crawling
- microvilli in gut
with
actin filaments
microtubules
intermediate filaments
flagella and cilia = microtubules
muscle contraction = actin filaments
cell crawling = actin filaments
microvilli in gut = actin filaments
What is the order of the three cytoskeletal elements in order of size? (smallest to largest)
microfilaments, intermediate filaments, microtubules
What is the main role of microtubules?
Organelle positioning and intracellular transport
Actin filaments and microtubules have fast growing ends. How is this achieved?
nucleotide hydrolysis
Myosin, Kinesin, and Dynein are examples of what?
motor proteins
Motor proteins on microtubules hold the following organelle(s) in position:
ER
Golgi
Chromosome
All of the above
all of the above
What is vincristine?
a chemotherapy drug that inhibits tubulin polymerisation
What is the default route taken by a protein once it has completed its journey through the Golgi?
constitutive exocytosis
How are cells protected from their own lysosomal hydrolases?
these enzymes only work within a membrane at a specific pH range
What coat does your protein need if it wants to go from the ER to the Golgi?
COP II
What coat does your protein need if it wants to go from the Golgi to the ER?
COP I
What coat does your protein need if it wants to go from the plasma membrane to the endosome?
Clathrin
What is the name of the protein that links clathrin to the cargo receptor?
adaptin
What is the name of the protein that cleaves off the newly formed vesicle?
dynamin
What is the process via which certain components can be retrieved from the plasma membrane following exocytosis?
endocytosis
How is myosin moving along actin filaments related to muscle contraction?
When a myosin head pulls against actin the sacromere shortens.
It is chains of sacromeres that form myofibrils which bundle together to form muscle fibres that stretch the length of the muscle cell.
How do kinesins move along microtubules?
It has two globular heads that interacts with the cytoskeleton.
Kinesin moves from the negative end of the microtubule to the positive.
The globular heads use ATP hydrolysis to power the conformation changes that walk the motors along the microtubules.
Each head attahes and releases itself alternately, like moving one foot then the other.
How are kinesins moving related to intracellular transport and organisation?
The motor proteins are attached to the organelle or vesicle that they are moving so that as the motor protein moves, so does the organelle.
What are the types of cellular motility?
Cell crawling
Phagocytosis
Microvilli
How are microvilli related to cellular motility?
Bundles of actin fibres extend to the tip and there are myosins attached to the cell membrane that ‘walk’ along the actin filaments, causing the microvillus to wave.
What is it called when filaments polymerise and depolymerase rapidly?
nucleation
Explain what nucleation is.
Hardest part because bonds between subunits need to be broken.
Occurs in lag phase.
What occurs in growth phase?
elongation
At equilibrium, what is the critical concentration?
How do you work it out?
The concentration of monomers free in the cytoplasm after elongation
cc = Koff/Kon
cc is often greater at one end, which elongates faster. If the concentration of free monomers drops then this end also depolymerises fastest. This is the plus end.
Give 3 examples of how the cytoskeleton can hold a tissue together?
Tight junctions seal epithelial membranes and limit the passage of molecules. They contribute to the maintenance of cell polarity
Anchoring junctions (can attach cells to each other using adherins junctions and desmosomes. They can bind cells to the extracellular matrix using local adhesions and hemi-desmosomes
Gap junctions (directly connect cytoplasm of adjacent cells, hollow junction is made from connexins
What type of myosin makes muscles contract?
myosin II
what motor proteins bind to microtubules and where do they move?
kinesin moves from - to +
dynein moves + to -
