Moir's Marvellous Muscles Flashcards
What is the diameter of microfilaments?
a) 25 nm
b) 8 nm
c) 8 micrometers
d) 20 micrometers
B) 8nm
Which statement is incorrect?
a) Actin is very highly conserved in eukaryote cells
b) 6 genes encode actin, including 2 non-muscle types
c) There is usually variation of 15-20 residues in the forms of actin
d) Mutations in actin are often lethal.
c is incorrect
there is actually only 4 or 5 amino acid variation
Which is true about actin polymerisation?
a) ATP hydrolysis is required for actin polymerisation
b) monomers are preferentially added to the pointed end
c) monomers are added to the pointed and barbed ends at equal rates
d) Momomers are preferentially added to the barbed end
d) Momomers are preferentially added to the barbed end
Hydrolysis of ATP is not required for actin polymerisation.
Under normal conditions, during equilibrium of actin polymerisation:
a) G-actin and f-actin are at equal concentrations
b) Only filaments are present in the cell until monomers are needed
c) the equilibrium is largely in favour of monomers
d) the equilibrium is largely in favour of filaments
d is correct: the equilibrium is highly in favour of filaments.
There is a ‘pool’ of actin monomers always in the cell in case a filament needs to be formed at short notice.
The stability of the filament is determined by:
a) Whether ATP is bound to the pointed end
b) Whether ATP is bound to the barbed end
c) The concentration of magnesium in the cell
d) The rate at which monomers bind to the filament
a) whether ATP is bound to the pointed end
Once the monomer at the pointed end hydrolyses ATP, it falls off. The filament is stable as long as the pointed end monomer binds ATP.
Which of these statements are correct?
i) the rate of polymerisation increases rapidly once a trimer of monomers is formed.
ii) G-actin can be a limiting factor in polymerisation
iii) Initially, polymerisation is energetically unfavourable
iv) There is no lag phase in actin polymerisation
a) All of the above
b) i, ii and iv
c) i, ii and iii
d) i and iv
c) i, ii and iii are correct.
Profilin is an actin binding protein responsible for..
a) monomer binding
b) filament capping
c) gel forming
d) contraction
a) monomer binding
Which actin binding protein is responsible for ‘bundling’ the filaments together?
a) myosin
b) gelsolin
c) tropomyosin
d) fimbrin
d) fimbrin
Thymosin B4…
a) severs filaments that are bound together
b) inhibits actin polymerisation
c) stimulates actin polymerisation
d) binds actin filaments together
b) Thymosin B4 inhibits actin polymerisation, by sequestering actin monomers, thereby reducing the amount of monomers available to form a filament.
This is important in preserving a ‘pool’ of actin monomers.
Which statement is incorrect?
a) The Dystrophin gene is the longest gene in the human genome
b) Major cause of muscular dystrophy are insertions in the dystrophin gene
c) The gene is largely introns
d) Duchenne muscular dystrophy is the more severe form of the disease
b is incorrect.
The major cause of muscular dystrophy are deletions or point mutations in the dystrophin gene, rather than insertions.
Duchenne MD is the result of
a) insertions in the dystrophin gene
b) point mutations
c) frameshift within the gene
d) inversions in the gene
c) Duchenne MD is the result of frameshifts within the dystrophin gene
What is necessary for profilin to promote filament formation?
a) Binding of Mg2+
b) Binding of phosphatidyl inositol biphosphate
c) Binding of GTP
d) Alcohol.
b) Binding of phosphatidyl inositol biphosphate (PIP2)
What is the core protein in microvilli?
a) actin cross-linked by fimbrin
b) actin cross-linked by profilin
c) actin capped with capping protein
d) Actin with gel-forming proteins
a) actin cross-linked by fimbrin
Fimbrin links f-actin together, which allows the generation of higher order structures such as microvilli and actin cables.
What is filamin?
a) an actin-binding gel protein
b) an actin-binding ‘bundling’ protein
c) A network of f-actin held together by gel proteins
d) A network of f-actin held together by bundling proteins
c) A network of f-actin held together by gel proteins
Gelation proteins create networks of F-actin e.g. filamin
Why is gelsolin an important component of serum?
a) It prevents the formation of actin clots by binding actin monomers so that they won’t form filaments
b) It prevents formation of actin clots by severing actin filaments
c) It forms actin networks
d) It has helicase activity
b) gelsolin prevents formation of actin clots by severing actin filaments
At what angle do branches grow from the sides of existing actin filaments?
a) 45 degrees
b) 90 degrees
c) 70 degrees
d) 60 degrees
c) 70 degrees
The branched actin networks at leading edge of
migrating cells are very important for cell movement and the precise delivery of ‘cargo’
What is dystrophin’s role in skeletal muscle?
a) anchors actin filaments to the cell membrane
b) anchors myosin filaments to the cell membrane
c) regulates the length of the actin filaments
d) regulates the length of the myosin filaments
a) dystrophin anchors actin filaments to the cell membrane.
The C-terminal of dystrophin binds to the cell membrane and the N-terminal binds to the actin filament
Which statement regarding myosin is correct?
a) there are 14 subclasses of myosin
b) all isoforms of myosin interact with actin through their tail domains
c) Their cellular roles differ depending
on their tail domains.
d) Their cellular roles differ depending
on their head domains.
c) is correct: the myosin isoform’s cellular roles differ depending on their tail domains.
a - there are 20+ subclasses
b - all isoforms of myosin interact with actin through their head domains
Myosin I and V are required for: a) Movement of vesicles b) Sarcomere structural stability c) the formation of actomyosin contractile bundles in non-muscle cells d) cell division
a) Myosin I and V are required for the movement of vesicles.
Which myosin is important for the formation of actomyosin contractile bundles in non-muscle cells?
a) Myosin I
b) Myosin VI
c) Myosin II
d) Myosin III
c) Myosin II is important for the formation of actomyosin contractile bundles in non-muscle cells (essential for cell movement & cell division).
The tail of myosin II
a) has helicase activity
b) is a coiled-coil tail
c) Is very short
d) Is the longest of the myosin sub-classes
b) Myosin II has a coiled-coil tail
Which is the only myosin that can assemble into a filament?
a) Myosin I
b) Myosin II
c) Myosin IV
d) Myosin V
b) Myosin II
Only myosin II has an unbroken coiled-coil tail and therefore is the only myosin that can assemble into a filament.
Some other myosins (eg myosin V) have regions of coiled-coil that are interspersed by nonhelical regions (usually because of proline) and so form a dimer but not a filament.
A few myosins cannot form a dimer and are therefore monomeric (eg myosin I)
Which of these statements are true regarding Nebulin and Titin:
i) They are ‘giant proteins’
ii) They regulate the lengths of actin and myosin filaments
iii) They act in skeletal and cardiac muscle
iv) Titin acts on the actin filaments and nebulin on the myosin filaments
a) all of them
b) i and ii
c) i, ii and iv
d) i, ii and iii
d) i, ii and iii are correct.
Titin acts on the MYOSIN filaments and nebulin on the ACTIN filaments
The calcium concentration in resting muscle is:
a) 10^-5M
b) 10^-9M
c) 10^-8M
d) 1.0M
c) 10^-8M
The calcium concentration in contracting muscle is:
a) 10^-5M
b) 10^-8M
c) 10^-7M
d) 0.1M
a)10^-5M
Myosin moves along F-actin by:
a) Binding and releasing calcium
b) the hydrolysis of MgATP into MgADP
c) Binding and releasing ATP
d) The hydrolysis of GTP into GDP
b) Myosin heads process along actin filaments by hydrolysing MgATP to MgADP in the presence of actin
Which statement regarding the regulation of contraction is incorrect?
a) Striated muscle regulation involves the inhibition of
the actin-activated ATPase
b) Contraction is a delayed response
c) tropomyosin is a regulatory protein in contraction
d) the troponin complex is regulatory in contraction
b) is incorrect
Contraction is actually an instant response.
Both tropomyosin and the troponin complex are regulatory in contraction.
Striated muscle regulation involves the inhibition of
the actin-activated ATPase. Release of calcium activates contraction- it releases the inhibition
What is the incidence of inherited heart disease caused by mutations in myosin & actin?
a) 1/1000
b) 1/750
c) 1/500
d) 1/400
c) 1/500
Which statement regarding myosin and cell locamotion is correct?
a) Myosin I is found at the rear of the cell and pushes it forward
b) Myosin II is found at the leading edge of the cell
c) lamelipodia are formed at the trailing edge of the cell
d) different isoforms of myosin within a cell can be isolated using antibodies
d) is correct: Can localise different isoforms of myosin within a cell using specific myosin antibodies.
Myosin I is localised at the leading edge of the cell, allowing the cell to send out lamelipodia so that the cell moves forward.
Myosin II is confined to the rear of the cell and pushes the back of the cell along the surface.
What is the diameter of a microtubule?
a) 8nm
b) 5nm
c) 20nm
d) 25nm
d) 25nm
Where are transient microtubules found?
a) In cells undergoing division
b) the neuronal axon
c) cilia
d) flagella
a) In cells undergoing division
More stable MTs are found in non-differentiating cells, forming structures such as cilia and flagella.
They also are an integral part of the neuronal axon.
Microtubules are assembled from..
a) monomers
b) homodimers
c) heterodimers
d) trimers
c) Microtubules are assembled from an alpha,beta heterodimer of tubulin.
Microtubules cannot form from homodimers or monomers.
Alpha-tubulin..
a) binds GTP reversibly
b) binds GTP irreversibly
c) hydrolyses GTP to GDP
d) hydrolyses GTP to GMP
b) Alpha-tubulin binds GTP irreversibly.
Each alpha-beta tubulin dimer binds 2molecules of GTP.
One GTP binding site is in alpha tubulin and this binds
GTP irreversibly. The second site is on beta-tubulin and
this binds GTP reversibly and hydrolyses it to GDP.
How many protofilaments are in a microtubule?
a) 100
b) 13
c) 25
d) 80
b) 13
MTs are long, hollow cylinders made up of 13 protofilaments
The protofilment end with beta-tubulin is the:
a) slow-growing + end
b) slow-growing - end
c) fast-growing + end
d) fast-growing - end
c)
Because all protofilaments in a microtubule have the same orientation one end of the microtubule is ringed by a-tubulin and the other by b-tubulin. The two ends differ in their rates of assembly. The end with b- tubulin is the fast growing (+) end.
GDP-tubulin at the + end of a protofilament…
a) stabilises the MT
b) destabilises the MT
c) causes rapid lengthening of the MT
d) causes the GDP to be released
b) GDP-tubulin at the + end destabilises the MT
GTP-tubulin stabilises the MT whereas GDP-tubulin causes disassembly. If (+) end becomes capped with GDP tubulin it causes instability and rapid disassembly.
Cells can assemble and disassemble MTs - necessary for cell division.
Which statement regarding kinesins is INCORRECT?
a) Kinesins are processive (+) end directed motor proteins
b) There are 2 classes of kinesins
c) Mitotic kinesins transport vesicles and organelles.
d) All kinesins contain a globular head
c) is incorrect
Cytosolic kinesins transport vesicles and organelles.
Kinesins are processive (+) end directed motor proteins - they move cargo away form the nucleus, towards the + end of the MT. Dyneins are (-) end directed motor proteins involved in intracellular transport and in cell movement.
How is cargo delivered to a precise location from microtubules?
a) Kinesin carries it along the branched microtubule to its destination
b) Kinesin and Myosin carries it along the branched microtubule to its destination
c) Myosin takes it from Kinesin and carries it along branched actin filament to its destination
d) Kinesin carries it along branched actin filament to its destination.
c) Myosin takes it from Kinesin and carries it along branched actin filament to its destination
Microtubules do not branch, actin filaments are highly branched.
Myosin V associates with a microtubule and waits for kinesin carrying a cargo – the cargo is transferred to myosin V which then delivers cargo precisely to target by
moving along actin.
Which statement regarding microtubule associated proteins (MAPs) is INCORRECT?
a) One of the two domains of MAPs binds to the microtubule only.
b) The ‘arm’ domain can bind to membranes, intermediate filaments, or other microtubules.
c) Incorrect polymerisation of MAP1 is linked to neurodegenerative disorders such as Alzheimers
d) The length of the projective domain controls the spacing of adjacent microtubules.
c) is incorrect.
Incorrect polymerisation of Tau, not MAP1, is linked to neurodegenerative disorders such as Alzheimers
What is Taxol’s role in chemotherapy?
a) It inhibits polymerision of tubulin into microtubules
b) It causes depolymerisation of microtubules
c) It stabilises microtubules by inhibiting shortening
d) It inhibits the hydrolysis of ATP
c) Taxol stabilises MTs by inhibiting shortening. However, it does have side effects as it effects all cells.
What is Colchicine’s role in chemotherapy?
a) It inhibits polymerision of tubulin into microtubules
b) It causes depolymerisation of microtubules
c) It stabilises microtubules by inhibiting shortening
d) It inhibits the hydrolysis of ATP
b) Colchicine causes depolymerisation of MTs and cells
become blocked in mitosis – but it is very toxic.
