Lecture 13

Question 1

What 3 filament structures is the cytoskeleton composed of?

Answer 1

Microtubules
Actin filaments
Intermediate filaments

Question 2

What are some properties of Intermediate filaments?

Answer 2

strong, flexible, ropelike
provides mechanical strength against physical stress

Question 3

What protein do intermediate filaments use to connect to other filaments?

Answer 3

Plectin

Question 4

what is the architecture order of Intermediate filaments?

Answer 4

Monomers -> dimers -> tetramer ->filament unit

Question 5

True or false?
Intermediate filaments require ATP and/or GTP?

Answer 5

False

Question 6

What controls assembly and disassembly of Intermediate filaments?

Answer 6

phosphorylation and Dephosphorylation

Question 7

What are 2 types of Intermediate filaments?

Answer 7

Keratin containing and Neurofilaments

Question 8

what and where are keratin containing filaments commonly found? what are they commonly attached to?

Answer 8

Structural proteins of epithelial cells
commonly attached to nuclear envelope

Question 9

Where are Neurofilaments commonly located? how are they orientated?

Answer 9

in the cytoplasm of the neurons
orientated parallel to the axon

Question 10

What is actin structures involved in?

Answer 10

intracellular motile processes

Question 11

what 3 ways can actin filaments be organized in?

Answer 11

Ordered arrays
highly branched networks
tightly anchored bundles

Question 12

True or false?
Actin filaments are not a major contractile muscle protein?

Answer 12

False, they are a major contractile protein

Question 13

True or false?
Actin is a major protein in every eukaryotic cell?

Answer 13

True, they are

Question 14

how is actin filaments assembled and disassembled?

Answer 14

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

Question 15

What can influence Actin filament assembly / disassembly rates? why is this required?

Answer 15

a number of different proteins
Required for cell locomotion, change in cell size, phagocytosis, cytokinesis

Question 16

What is a molecular motor than operates with actin filaments?

Answer 16

Myosin motors

Question 17

What direction do Myosin motors move in?

Answer 17

Towards the ‘barbed’ end of the actin filament

Question 18

What characteristic do all myosins share? what 2 binding sites are there?

Answer 18

A motor head
a binding site for the actin filament
a binding site for ATP consumption to drive the motor

Question 19

where on myosin motors do varieties occur?

Answer 19

the tail portions of the molecule

Question 20

What are the 2 types of Myosin motors?

Answer 20

Conventional (Type II) and unconventional

Question 21

What are Conventional motors commonly used for?

Answer 21

muscle contraction
splitting of cell during division
generating tension at focal adhesions
cell migration
turning behavior at growth cones

Question 22

What is the structure of Conventional Myosins?

Answer 22

pair of heads
pair of necks
2 light chains
2 intertwined long heavy chains

Question 23

In what direction do myosin molecules assemble on filaments?

Answer 23

with the tails pointed towards the center and the heads pointed away from the center

Question 24

Why is the bipolar center of a filament important for myosin heads?

Answer 24

so the heads on opposite ends of the filament have the ability to pull actin filaments towards one another

Question 25

In what way to unconventional myosins move? What molecule is it similar to?

Answer 25

"hand-over-hand" - one of the 2 heads must be bound at all times to a polarized track (similar to kinesin)

Question 26

True or False? Skeletal muscle fibers are uni-nucleated cells

Answer 26

False, they are multi-nucleated

Question 27

what strands do each muscle fiber contain?

Answer 27

myofibrils

Question 28

what are the contractile units in myofibrils?

Answer 28

sarcomeres - repeating linear array of contractile units

Question 29

How are sarcomeres organized?

Answer 29

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

Question 30

How do the regions change during muscle contraction in a sarcomere?

Answer 30

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

Question 31

What 3 things to thin filaments contain?

Answer 31

Actin, tropomyosin and troponin

Question 32

What is Troponin?

Answer 32

protein complex that contacts both actin and tropomyosin

Question 33

What is tropomyosin?

Answer 33

molecule that fits securely into thin filament (interacts with 7 actin units)

Question 34

How do myosin heads engage with filaments during contraction? what is it similar to?

Answer 34

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

Question 35

what determines the behavior and organization of actin filaments inside cells?

Answer 35

integrations with actin binding proteins determine the organization and behavior

Question 36

what are the 9 categories actin binding proteins can be divided into based on function?

Answer 36

Nucleating Monomer-sequestering End-blocking monomer-polymerizing Actin filament depolymerizing cross-linking filament-severing membrane binding

Question 37

What are some activities where cell locomotion is important?

Answer 37

Tissue / organ development formation of blood vessels development of axons wound healing protection against infection

Question 38

what is the fibroblast locomotion leading edge called?

Answer 38

Lamellipodium

Question 39

What is a growth cone?

Answer 39

A highly motile region of the cell that explores the environment

Question 40

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.