Myofibrillar Proteins and Meat Composition

Question 1

Chemical composition of mammalian skeletal muscle

Answer 1

1. Water (75%)
2. Protein (18.5%)
3. Lipids (3%)

Question 2

Thick vs Thin Myofilaments

Answer 2

Thick: 14-16nm diameter, mainly made of myosin protein
Thin: 6-8nm diameter, mainly made of actin protein

Question 3

Types of meat proteins

Answer 3

1. Stromal (15%)
2. Sarcoplasmic (30%)
3. Myofibrillar (55%)

Question 4

Types of myofibrillar proteins

Answer 4

1. Contractile (myosin and actin)
2. Regulatory (troponin and tropomyosin)
3. Structural (titin, nebulin, intermediate filaments)

Question 5

Binding sites on myosin heads

Answer 5

ATP and actin

Question 6

G-actin vs F-actin

Answer 6

G-actin is the monomer (globular)
F-actin is the polymer (fibrous)

Question 7

Tropomyosin

Answer 7

Protein found on F-actin that covers the binding site

Has a length of 7 G-actin monomers

Question 8

Troponin

Answer 8

Protein found in the grooves of actin that regulates Ca dependent activation of muscle contraction

Found every 7-8 G-actins

Question 9

Subunits of troponin

Answer 9

TnT - binds tropomyosin
TnI - inhibits myosin-actin cross bridge
TnC - binds Ca ion

Question 10

Titin

Answer 10

protein that provides scaffold for alignment of thick filaments during myofibrillar and sarcomere formation

Elastic in I band, inelastic in A band

Question 11

Nebulin

Answer 11

protein that aligns thin filaments during myofibril formation and anchors it to Z disk

Question 12

Intermediate Filaments

Answer 12

desmin, filamin, paranemin, synemin

connects adjacent myofibrils