Lecture 13 Flashcards
What 3 filament structures is the cytoskeleton composed of?
Microtubules
Actin filaments
Intermediate filaments
What are some properties of Intermediate filaments?
strong, flexible, ropelike
provides mechanical strength against physical stress
What protein do intermediate filaments use to connect to other filaments?
Plectin
what is the architecture order of Intermediate filaments?
Monomers -> dimers -> tetramer ->filament unit
True or false?
Intermediate filaments require ATP and/or GTP?
False
What controls assembly and disassembly of Intermediate filaments?
phosphorylation and Dephosphorylation
What are 2 types of Intermediate filaments?
Keratin containing and Neurofilaments
what and where are keratin containing filaments commonly found? what are they commonly attached to?
Structural proteins of epithelial cells
commonly attached to nuclear envelope
Where are Neurofilaments commonly located? how are they orientated?
in the cytoplasm of the neurons
orientated parallel to the axon
What is actin structures involved in?
intracellular motile processes
what 3 ways can actin filaments be organized in?
Ordered arrays
highly branched networks
tightly anchored bundles
True or false?
Actin filaments are not a major contractile muscle protein?
False, they are a major contractile protein
True or false?
Actin is a major protein in every eukaryotic cell?
True, they are
how is actin filaments assembled and disassembled?
ATP binds to Actin resulting in the filament length increasing
will keep increasing until ATP conc. decreases
will begin ‘treadmilling’ once reaction on both ends remains constant
What can influence Actin filament assembly / disassembly rates? why is this required?
a number of different proteins
Required for cell locomotion, change in cell size, phagocytosis, cytokinesis
What is a molecular motor than operates with actin filaments?
Myosin motors
What direction do Myosin motors move in?
Towards the ‘barbed’ end of the actin filament
What characteristic do all myosins share? what 2 binding sites are there?
A motor head
a binding site for the actin filament
a binding site for ATP consumption to drive the motor
where on myosin motors do varieties occur?
the tail portions of the molecule
What are the 2 types of Myosin motors?
Conventional (Type II) and unconventional
What are Conventional motors commonly used for?
muscle contraction
splitting of cell during division
generating tension at focal adhesions
cell migration
turning behavior at growth cones
What is the structure of Conventional Myosins?
pair of heads
pair of necks
2 light chains
2 intertwined long heavy chains
In what direction do myosin molecules assemble on filaments?
with the tails pointed towards the center and the heads pointed away from the center
Why is the bipolar center of a filament important for myosin heads?
so the heads on opposite ends of the filament have the ability to pull actin filaments towards one another
In what way to unconventional myosins move? What molecule is it similar to?
“hand-over-hand” - one of the 2 heads must be bound at all times to a polarized track
(similar to kinesin)
True or False?
Skeletal muscle fibers are uni-nucleated cells
False, they are multi-nucleated
what strands do each muscle fiber contain?
myofibrils
what are the contractile units in myofibrils?
sarcomeres - repeating linear array of contractile units
How are sarcomeres organized?
Unit screeches from Z-line to Z-line
Dense middle region (H zone / A band)
I band (thin filaments only)
H zone (thick filaments only)
A band region (excluding H-zone) is where thin and thick filaments overlap
How do the regions change during muscle contraction in a sarcomere?
H (thick filaments) and I band (thin filaments) decrease as the filaments regions overlap each other through Actin-movement
Z lines (edge of the unit) move inward towards edge of A-band
What 3 things to thin filaments contain?
Actin, tropomyosin and troponin
What is Troponin?
protein complex that contacts both actin and tropomyosin
What is tropomyosin?
molecule that fits securely into thin filament (interacts with 7 actin units)
How do myosin heads engage with filaments during contraction? what is it similar to?
each myosin head binds to a thin filament
when bound, a conformational change occurs that moves the thin actin filament
all the myosin heads act in sync in a continuous motion
what determines the behavior and organization of actin filaments inside cells?
integrations with actin binding proteins determine the organization and behavior
what are the 9 categories actin binding proteins can be divided into based on function?
Nucleating
Monomer-sequestering
End-blocking
monomer-polymerizing
Actin filament depolymerizing
cross-linking
filament-severing
membrane binding
What are some activities where cell locomotion is important?
Tissue / organ development
formation of blood vessels
development of axons
wound healing
protection against infection
what is the fibroblast locomotion leading edge called?
Lamellipodium
What is a growth cone?
A highly motile region of the cell that explores the environment
Describe the structure and functions of intermediate filaments.
▪ Explain the structure and function of actin and myosin and how
they interact.
▪ Describe the molecular components of muscle.
