Test 3. Lecture 27 Flashcards
Actin filaments are organized into:
•__________—filaments are cross-linked
into closely packed parallel arrays.
• ____________—filaments are cross-linked
in arrays that form 3-D meshworks with the
properties of semisolid gels.
Actin bundles
Actin networks
cross-linking protiens have at least two domains that bind actin
__________are small, rigid proteins that force filaments to align
closely.
Proteins that organize actin filaments into networks tend to be large flexible proteins
that cross-link perpendicular filaments.
Actin-bundling proteins
Two types of actin bundles:
1. __________—closely spaced filaments aligned in parallel, with the same
polarity, with barbed ends adjacent to the plasma membrane.
__________ is a bundling protein in parallel bundles; first isolated from INTESTINAL MICROVILLI
2.___________—more widely-spaced filaments, cross-linked by
_________
Increased spacing between filaments allows the motor protein myosin to interact
with the actin filaments.
Parallel bundles
Fimbrin
Contractile bundles
α-actinin.
In actin networks, proteins such as \_\_\_\_\_\_\_\_\_\_ form flexible cross-links. A filamin dimer is a flexible \_\_\_\_-shaped molecule with actin-binding domains at the end of each arm.
filamin
V- shaped
Actin filaments are concentrated AT CELL PERIPHERY where they form a 3-D
network beneath the plasma membrane.
This network and associated proteins (________) determines cell
shape and is involved in activities such as movement.
Red blood cells (erythrocytes) are useful for studies of the cortical
cytoskeleton.
They have no nucleus or organelles, so plasma membranes and associated
proteins are easily isolated.
They also lack other cytoskeletal components, so the cortical cytoskeleton is
the principal determinant of cell shape
the cell cortex
__________ is a member of the calponin family of actin-binding proteins.
It is a tetramer of two polypeptide chains, α and β. The ends of the spectrin
tetramers associate with short actin filaments, resulting in the spectrinactin
network.
Spectrin
__________links the spectrin-actin network and the plasma membrane by
binding to spectrin and a transmembrane protein (band 3).
Ankyrin
Most cells have specialized plasma membrane regions that form contacts with :
1.
2.
3.
These regions are also attachment sites
for actin bundles, evident in fibroblasts
maintained in tissue culture.
Cultured fibroblasts secrete extracellular
matrix proteins that stick to the dish.
- adjacent cells,
- the extracellular matrix, or
- other substrata (such as the surface of a culture dish).
The fibroblasts attach to the matrix via binding of transmembrane proteins
(________)
.
The sites of attachment (___________) are also attachment sites for large actin bundles called ____________
___________, cross-linked by α-actinin and stabilized by tropomyosin.
Two other proteins,______ and ________ are involved in binding stress fibers.
integrins
focal adhesions
stress fibers.
Stress fibers are contractile bundles
talin and vinculin
“attachment of actin filaments to adherens junctions”
In sheets of epithelial cells, cell–cell contacts (adherens junctions) form a
continuous ___________around each cell.
adhesion belt
“attachment of actin filaments to adherens junctions”
Contact is mediated by transmembrane proteins called ________. They
bind to cytoplasmic _________-, which anchor actin filaments to the plasma
membrane.
cadherins
catenins
Cell surfaces have a variety of protrusions involved in cell movement, phagocytosis, or functions such as absorption of
nutrients.
These extensions are based on _________, in relatively permanent or
rapidly rearranging bundles or networks.
___________ are fingerlike extensions;
abundant on cells involved in absorption.
1. Microvilli of epithelial cells lining the
intestine.
2. They increases the surface area for
absorption by ten to twentyfold.
actin filaments
Microvilli
Intestinal microvilli contain closely
packed parallel bundles of 20 to 30
________________.
actin filaments
The filaments are cross-linked by
__________ and __________
The actin bundles are attached to the
plasma membrane by the Cabinding
protein calmodulin in
association with myosin I.
fimbrin and villin.
Other surface protrusions are transient and form in response to
environmental stimuli.
____________ are extensions of moderate width, responsible for
phagocytosis and the movement of amoebas.
_____________ are broad, sheetlike extensions at the leading edge of
fibroblasts.
Many cells also extend _____________, thin projections of the plasma membrane
supported by actin bundles.
Pseudopodia
Lamellipodia
filopodia
Cell movement or extension of cellular
processes involves a coordinated
series of movements.
Cell locomotion Movement across a surface proceeds in 3 stages: 1. 2. 3.
– Extension of the leading edge – Attachment of leading edge to the substratum – Retraction of the rear of the cell into the cell body
Formation of cell surface protrusions in response to extracellular stimuli
is regulated by Formation of cell surface protrusions in response to extracellular stimuli
is regulated by ____________
Rho proteins
Rho proteins activate ___________, which stimulate the __________
complex and initiate growth of branched actin filaments.
WASP proteins
Arp2/3
- _________ is a __________—a protein that converts chemical energy (ATP) to
MECHANICAL ENERGY, generating force and movement. - Skeletal muscles are bundles of ___________, large cells formed by fusion of
many cells during development. - Most of the cytoplasm consists of _____________, BUNDLES OF THICK MYOSIN FIlAMENTS AND THIN ACTIN FILAMENTS
and thin actin filaments.
Each myofibril is a chain of contractile units called __________, which give skeletal
and cardiac muscle their striated appearance.
- Myosin
molecular motor - muscle fibers
- myofibrils
sarcomeres
Electron microscopy
- Actin Filaments are attached at their ________ to the _________
- myosin filaments are anchored at the __________
- I band, only actin filaments; A band a myosin filaments; overlap in the peripheral region of the A band
1.barbed ends
z disk
\
2. M line
The __________________ of muscle contraction
1. during contraction, _______ shorten, bringing _______ closer
- no change in width of ___________, but _________ almost disappear
- The actin and myosin filaments slide past one another so that the actin filaments move into A band and H zone
- The molecular basis for this is the binding of myosin to actin filaments, allowing myosin to function as a motor that drives filament sliding
- During contraction, sarcomere shortens, brining z disc closer together.
- no change in width of A band, but I bands and H zone allmost disappear
MYOSIN II: ______________, has 2 heavy chains and 2 pairs of light chains
- the heavy chains have a globular head region and a long alpha helical tail
- the tails twist around each other in a coiled coil
the type in muscle
” organization of actin and myosin filament”
_____________: several hundred myosin molecules in parrallel staggered array
_____________ , forming cross-bridges between thick and thin filaments
the oriientation of filaments reverses at the M line
thick filaments
globular heads bind actin
