Actin Filaments (Microfilament) - Cytoskeleton Flashcards
What is the most important components of Action that make microfillaments unique in the cytoskeleton?
Actin makes microfillaments:
The smallest
The most flexible
What are microfilaments made up of?
monomers (G-actin)
What is microfilaments plymerized to?
polymer (F-actin)
What is the monomers of microfilaments?
G-actin
What is the polymer of microfilaments?
F-actin
What do two polymers of F-actin form in a microfilament?
double-helix
What makes up a double- helix in a microfilament?
two polymers of F-actin
Explain the formation of a microfilament.
A microfilament is made up of monomer G-actin, that polymerize to an F-actin, creating a polymer. Two F-actin polymers twisted together create a double-helix, creating a microfilament.
What are the 3 main key functions of the cytoskeleton?
1) maintain cell shape
2) allow key movements
3) adapt to compressive forces
How are microfilaments involved in cell migration?
microfilaments can polymerize, squeeze in, and changes morphology to fit through tiny spaces
What is Diapedesis and actins associates?
white blood cells change shape through actins to squeeze through the tiny intracapillary clefts
Why would a white blood cell want to perform cell migration?
to move out of the blood stream and into interstial spaces to fight pathogens
What is microfilaments role in cell division?
microfilaments seperate one cell by forming a constriction ring, allowing actin to pinch the cell in half producing two daughter cells.
What stage of mitosis does actin form a constriction ring?
during cytokinesis
How are microfillaments related to cell extension?
Actin are involved in the formation of Microvilli and Stereocilia.
What are the two main parts of the cell membrane in microvilli and stereocilia?
Apical: top portion
Basal: bottom portion
What occurs on the Apical surface of microvilli and stereocilia?
Actin forms a core of fingerlike projections or extensions, allowing movement
Which cell has a a smaller extension on apical surface?
Microvilli
Stereocilia
Microvilli
Which cell has a larger extension on apical surface?
Microvilli
Stereocilia
Stereocilia
What is Microvilli’s role in the gastrointestinal tract?
food passing through GI tract come into contact with microvilli, increasing surface area for digestion
What is Stereocilias role in the inner ear?
the stereocilia movement opens up channels in the inner ear for balance (vestibular) and hearing (cochlear)
What is microfilaments role in muscle contraction?
microfilaments in muscles are know as Myofilaments (Actin + Myosin). The mysion clicks on with action, pulling the actin strans closer to other actin strands, causing shortening of myofilaments. = muscle contraction and relaxation.
(heavily involved in ATP production)
What is a myofilament?
the microfilament of a muscle cell, made up of actin and myosin
What does mysosin do in a muscle cell?
clickes on actin to pull actin strands closer together (shortening myofilaments) to cause muscle contraction/ reflaxation
What role does microfilaments play in cell junctions?
prevents cell seperation through tight junctions and adheren junctions
Whar are actin filaments key in the cell function formation?
actin strands help stick cells together and prevents seperation.
What role does microfilamanets play in membrane transport?
actin responsible for invagination/ fuses on cell membrane allowing endosomes to perform endocytosis or extocytosis.
What is actin assembled into filaments called?
F-actin
Which has an ATP inding site?
G-actin
F-actin
G-actin
Where is the ATP binding site located in a monomer G-protein?
between domains II and IV
Actin filaments are:
non-polar
polar
polar
(-) end: ATP binding cleft (gobular heads of myosin)
(+) end: Barbed end (gobular heads of myosin)
What end of actin filaments is pointed, where ATP binding cleft is located?
(-) end
What end of actin filaments is the barbed end?
(+) end
G-actin has intrinsic ATPase activty, thus is usually bound to:
ATP
ADP
both
both ATP and ADP
Where does polymerization and depolymerization occur in microfilaments?
at the ends of the filaments (not the middle)
What are the three phases of polymerization?
1) nucleation
2) elongation
3) steady-state
Which phase of polymerization occurs slowly?
nucleation
Which phase of polymerization occurs relatively rapidly?
elongation
When does elongation occur?
Only when g-protein concentration is above a critical concentration. (Cc)
What phase of actin polymerization does elongation occur?
when G-actin concentration in above a Cc
