meat and poultry tech

1. STRUCTURE OF
MUSCLE

2.  Skeletal muscle– 35-65% of carcassweight of
meat animals
 Epimysium-CTsheathcovering the entire muscle
 Perimysium-CTsheathsurroundinfbundlesofMF
 Endomysium-surroundsindividual musclefibres

4. Musclefiber/ Myofiber/ Muscle cell
 Structural unit of muscle fiber
 75-92% of total muscle volume
 Long,unbranched,multinucleated, thread like cells
 10-100 µmdiameter
Sarcolemma
 Musclecell membrane(elastic in nature)
 Motor nerve fiber endingsterminate onsarcolemmaat
myoneural junction
 Motor end plate- structuresat myoneuraljunctionform
a raised moundonthe musclesurface

5. Myofibril
 Organelle uniqueto muscle
 Longthin rods(1-2 µmdiameter) with their long
axis parallel to the long axis of the fiber
 Musclefiber of 50 µmdiameter has1000-2000
myofibrils
 Crossstriated myofibrils remain embedded in the
cytoplasm of muscle fiber

6. Myofibrillar crosssection-highly organized array of
dots of two distinct sizesthat comprises of
a. Thickfilaments – arranged parallel to eachother,in
exact alignment acrossentire surfaceof myofibril
b. Thin– aligned acrossmyofibril, parallel to each
other and the thick filaments
Thickand thin filaments overlap at certain regions –
hencebanded/ striated appearance (alternate light
and dark areas)

7.  Lightband- singly refractive , isotropic, I band
 Dark band- doubly refractive, anisotropic,Aband, denser
 Zdisk- dark thinband that bisectsI band
 Sarcomere- Repeating structural unitof myofibril, basic
unitwhere musclecontraction and relaxation occurs.It is
unitof myofibril between two Zdisks(½ I Band+A
band+½ I band)
 Sarcomerelength – 2.5 µm(resting stage)
 H zone- regionAband where only thick filaments are
present
 Pseudo H zone- region of Aband containing only rod
portion of myosin molecules, no heads present
 M line-

9. Myofilaments
Thickfilaments- constituteA band
 14- 16 nmin diameter, 1.5 µmin length
 Predominantprotein- myosin
Thin filaments-
 6-8 nmin diameter, 1 µmoneither side of Zdisk
 constituteI band and extend beyond I band intoA
band
 Predominantprotein- actin

10. Zdiskultrastructure
 Anactin filament ononeside of the Zdisk lies
between two actin filaments onopposite side of Z
disk
 Actin filaments do not passthroughthe Zdisk
 Zdisk ismade of Zfilaments, connectwith actin
filaments oneither side of Z disk.
 1 actin filament connectsto 4 Zfilaments that pass
throughZdisk and thenconnectswith an actin
filament in the adjacent sarcomere

11. Proteinsof myofibril
 More than20 proteins where 6 constituteapp 90%
of total myofibrillar proteins (MP)
 Myosin,actin, titin, tropomyosin,troponin and nebulin
 On basisof function-
Contractile- actin , myosin
Regulatory- tropomyosin, troponin
Cytoskeletal- titin , nebulin ( integral to structure
of Z disk)

12. Contractile proteins
1.Actin- 20% of MP
Globular shapedapp 5.5 nmin diameter
G shapedactin- monomeric form
G actin monomerspolymerize to form Factin
2 strandsof Factin are spirally coiled around one
another to form “super helix”

13. 2.Myosin- Fibrousprotein , 45% of MP
 Elongated rod shapedwith a thickenedportion at
oneend (head)
 Head region isdouble headed and projects
laterally from the long axis of the filament

14.  Portion between head and tail isknownasneck
 Myosinfilaments are arranged in opposite directions on
either side of M line.
 Mysoinheads- active site whichforms crossbridges with
actin filaments during contraction
 Myosinwhensubjectedto proteolytic digestion splits into
two fractions ie. Lightmeromyosinand heavy
meromyosin
 Pseudo H zone- centre of the A band myosin filaments
contain only rod portion of myosin molecules, no heads
present

17. Regulatory proteins
Tropomyosin- 5 % of MP
,Liesin closecontact with actin
filament
Each strand lies alongside, within each groove of actin
super helix
Single molecule extends length of 7 G-actin mol .
Troponin-5% of MP
 Presentat well defined intervals in grooves of actin
filament
 Liesalong the tropomysoin strands
 1 molof troponin for every 7-8 G actin molecules
* refer previous slide for representation

18. Cytoskeletal proteins
 Titin-mostabundant, 10% of MP
.
 3rd filament
 Largestpolypeptide known(25000 aa)
 Extendlongitudinally in eachhalf sarcomerefrom M
line to Z disk
Portion of titin in
A band is inelastic
and that in I band
is elastic

19.  Bindsto theoutsideshaft of the thick filament and C
protein that encirclesand stabilizes the thick
filament
 Providesscaffold for alignment of filaments during
myofibril and sarcomere formation
 Mature myofibrils- maintainsstructureand integrity
of myofibrils

20.  Nebulin – 4% of MP
 Located closeand parallel to actin filament
 Extendsalong the length of the thin filament fromA
band to Z disk
 Developing muscle-organization of thin filaments
 Mature muscle-servesasscaffold for stability of
thin filaments, anchorsthin filaments to Zdisk

21.  Cprotein- 2% , Hprotein- 1%, Myomesin-2%,
Mprotein-1%, skelemin-1%-stabilize the rod
portion of myosin molecules
 Aplha actinin (2%), Cap z (1%)- integral
componentsof Zdisk

22. Sarcoplasmic reticulum and Ttubules
 SRisa membranoussystemof tubulesand cisternae
that forms closely meshednetwork around each
myofibril
 Ttubules-associated with sarcolemma
Elements of SR
 Longitudinal tubules-thintubulesoriented in the
direction of myofibrillar axis
 Fenestratedcollar- Inthe Hzoneregion the longitudinal
tubulesconvergeforming a perforated sheet
 Terminalcisternae- At junctionof A and I band the
longitudinal tubulesconvergeand join with a pair of
larger, transversly oriented tubular elements

23.  Longitudinal tubulesextend from fenestrated collar
to terminal cisternae in both directions
 Ttubule runstransverselyacrossthe sarcomereat
A-I band junctionand lies between two tubular
elementsof the terminal cisternae pair
 Triad- structureformed by a T-tubuleand terminal
cisternae oneither sides.Thisislocated at A-I
junction.It isresponsible for regulation of excitation-
contraction coupling, whereby a stimulusexcitesthe
muscleand causesit tocontract.

25.  Mitochondria- located in sarcoplasm,power house
of the cell
 Lysosomes-smallvesicleslocated in the sarcoplasm.
Contain enzymescapable of digesting cell.
Cathepsins(proteolytic enzyme)isof major
importance
 Golgi complex- secretory cells

26.  Smooth muscle- only a smallproportion of meat,
hassingle nucleus,centrally located. SRisless
developed, myofilaments lessordered.Actin and
myosinare presentin sameproportion asin skeletal
musclebut nostriations.
 Cardiac muscle- uniqueproperty of rhythmic
contractability, centrally placed nucleus,less
branched fibers, striated appearance. T-tubulesare
larger in diameter, occurat Zdisk.Terminal
cisternae isabsent.Intercalated disk are present
acrossthe entire fiber

27. Connective tissue
 CTsurroundingmuscles,musclebundlesand muscle
fibers isfibrous, k/a connectivetissueproper
 Bone, cartilage- supportive CT
ground substanceplusembedded cells
CTproper
extracellular fibers

28. Ground substance
 Viscoussolutioncontaining soluble glycoproteins
referred to asproteoglycans (core protein attached
to glycosaminoglycans)
 Containssubstratesand end products of CT
metabolismsuchastropocollagen andtropoelastin
 Glycosaminoglycans– hyaluronic acid and
chondroitin sulphate

29. Extracellular fibers
 Collagen and elastin
 Collagen- mostabundant protein in animal body ,
significantly influencesmet tenderness
 20-25% of total body protein
 Principal structural protein of CT
 Glycprotein that contain smallamountsof glucoseand
galactose
 Glycine- mostabundant aa , 1/3 rd of total aa
 Hydroxyproline and proline – another 1/3rd ,
hydroxyproline isconstant(13-14%) componentof
collagen, doesnot occurin other animal proteins

30.  Tropocollagen – structural unit of collagen fibril
 Tropocollagen moleculesare composedof three α
chainsto form a triple helix
 Accordingly 12 types of collagen out of which type
I, III, IV, V and VII are associated with CTof skeletal
muscle.
 Insolubility and high tensilestrength of collagen
fibers isdue to intermolecular crosslinkages which
increasesand becomesmorestable with age. Hence
meat from aged animalsistougher.

31. Elastin
 Lessabundant CT
,rubbery protein presentin
arterial walls and ligaments,framework of diff
organs
 Glycine- mostabundantaa
 Desmosineand isodesomineare 2 uniqueaa
presentin elastin
 Insolubility – presenceof high contentof nonpolar
aa.

32. Connectivetissue cells
 Fibroblasts- synthesize precursorsof extracellular
componentsof CTie. Tropocllagen,tropoelastin and
ground substance
 Mesenchymalcells- precursorsof fibroblasts and
adipoblasts
 Adipose cells- deposition of fat