Contractile proteins

Question 1

What is the cytoskeleton?

Answer 1

System of filaments scaffolding the cell that helps with structural, spatial and mechanical functions

Question 2

What is a major component of the cytoskeleton?

Answer 2

Actin

Question 3

What determines the shape of the cell and its ability to divide?

Answer 3

Actin and actin binding proteins

Question 4

What uses ATP hydrolysis to move filaments and move organelles along filaments?

Answer 4

Myosin (motor protein)

Question 5

Each subunit of actin is bound to what and called?

Answer 5

G-actin (globular actin) is bound to an ATP

Question 6

G-actin subunits assemble into what and are bound to what?

Answer 6

F-actin (filamentous actin) is bound to ADP after it hydrolyzed it to help form a filament

Question 7

Which end of the F-actin grows faster?

Answer 7

Plus end grows faster and minus end grows slower

Question 8

Why is polarity of the F-actin important?

Answer 8

It is important for assembly and for establishing a direction of movement of myosin relative to actin

Question 9

What are the phases of F-actin polymerization?

Answer 9

Nucleation (lag phase)
Elongation (growth phase)
Steady state (equilibrium phase)

Question 10

Describe the polymerization of F-actin

Answer 10

G-actin subunits form an oligomer of 3 subunits and then logarithmically grow fast into F-actin

Question 11

What is the critical concentration of actin?

Answer 11

When the rate of polymerization is equal to the rate of dissociation of actin (steady state)

Question 12

Where is actin the most abundant?

Answer 12

Right beneath the plasma membrane to provide mechanical support, cell shape and enables cells to migrate, engulf, divide

Question 13

Actin binding proteins

Answer 13

Organize f-actin into bundles/networks that can then perform the functions of actin - have to have 2 actin binding domains

Question 14

What are the 2 types of actin bundles?

Answer 14

Parallel bundle and contractile bundle

Question 15

What protein is used in the parallel bundle?

Answer 15

Fimbrin

Question 16

Describe parallel bundles?

Answer 16

Actin filaments + fimbrin; Tightly packed to prevent myosin 2 from entering; seen in microvilli to increase surface area, nutrient uptake and signaling of the cell

Question 17

What protein is used in the contractile bundle?

Answer 17

Alpha-actinin

Question 18

Describe contractile bundles?

Answer 18

Actin filaments + alpha-actinin; loosely packed to allow myosin 2 to enter; seen in the contractile ring used in mitosis to divide the cell

Question 19

Compare the size of alpha-actinin

Answer 19

Larger protein in order to increase the distance between actin filaments

Question 20

What are actin networks?

Answer 20

Actin filaments held together by large actin binding proteins such as filamin that creates a 3D meshwork in order to withstand force and determine stability of membrane

Question 21

What is spectrin?

Answer 21

Actin binding protein in RBCs that also binds ankyrin and protein 4.1 to control cell deformability/flexibility

Question 22

Hereditary spherocytosis

Answer 22

Mutations in spectrin, ankyrin, protein 4.1 that results in impaired deformability/flexibility leading to unstable RBCs = spherical RBCs

Question 23

What are the symptoms of HS?

Answer 23

Jaundice, splenomegaly, anemia and spherical RBCs

Question 24

What are myosin proteins?

Answer 24

Motor proteins that move along actin filaments via ATP hydrolysis

Question 25

What are the 3 domains of a myosin protein?

Answer 25

Head, neck, tail

Question 26

Purpose of the myosin head?

Answer 26

Contains actin binding sites and ATP binding sites as well as ATPase activity

Question 27

Purpose of myosin neck?

Answer 27

Flexible region that binds myosin light chain peptides

Question 28

Purpose of myosin tail?

Answer 28

Intertwine, bind membrane and organelles

Question 29

What are the 3 types of myosin?

Answer 29

Myosin 1, 2, 5

Question 30

Describe myosin 1

Answer 30

One head | Function = membrane association and endocytosis

Question 31

Describe myosin 2

Answer 31

2 heavy chains each with head and neck domain; tail homodimerizes Function = contraction

Question 32

Describe myosin 5

Answer 32

2 heavy chains and 6 light chains per neck, end of tails associate with specific receptors on organelles Function = organelle transport

Question 33

What direction do myosin proteins move?

Answer 33

Towards the plus end of actin

Question 34

How is the powerstroke related to the myosin neck?

Answer 34

The longer the myosin neck, the greater the rate of movement

Question 35

What are the important proteins within the sarcomere?

Answer 35

Cap Z, Tropomodulin, nebulin, Titin

Question 36

Cap Z function

Answer 36

Stabilizes plus end of sarcomere

Question 37

Tropomodulin function

Answer 37

Stabilizes minus end of sarcomere

Question 38

Nebulin function

Answer 38

Extends along the length of the actin filament; length determines the length of the actin filament

Question 39

Titin function

Answer 39

Stabilizes myosin and prevents overstretching

Question 40

What can titin mutations cause?

Answer 40

Cardiomyopathies - harder for heart to pump blood

Question 41

How do non-muscle cells contract?

Answer 41

Actin-myosin structures are formed in a transient manner as needed by the cell

Question 42

Describe the dystrophin protein?

Answer 42

Links the cytoskeleton (actin) of muscle fibers to the cell membrane/connective tissue Acts as a shock absorber during contraction and stabilizes the sarcolemma to prevent injury to the muscle fibers

Question 43

What are the 2 types of duchenne's muscular dystrophy?

Answer 43

Duchennes and beckers muscular dystrophy

Question 44

How is duchenne's muscular dystrophy inherited?

Answer 44

X-linked recessive that causes muscle wasting

Question 45

What kind of mutations does duchenne's muscular dystrophy have?

Answer 45

Out of frame mutants that create little to no dystrophin

Question 46

What kind of mutations does becker's muscular dystrophy have?

Answer 46

In frame mutants that create a smaller protein with partial function

Question 47

What is the current treatment for duchenne's muscular dystrophy?

Answer 47

Gene therapy, dystrophin replacement, drugs to prevent exon skipping