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Food Chemistry 1 > P4. Meat - Muscle contraction > Flashcards

P4. Meat - Muscle contraction Flashcards

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1
Q

Red meat generally refers to?
- encompasses 6 types of meat

A
  • refers to mammalian skeletal muscle tissue consumed as food
  • encompasses beef/veal, buffalo, mutton/lamb, goat, pork and horse (NO POULTRY)
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2
Q

most of the meat consumed is from ________ animals. why?

A
  • young animals
  • bc strengthening of muscles with time leads to tougher meat
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3
Q

why is color of fresh meat red to reddish pink?

A

owing to large concentration of myoglobin (oxygen storage protein) present in muscle

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4
Q

what other tissues/components may also be present in red meat? (5)

A
  • bone
  • connective tissue
  • adipose tissue
  • nerves
  • blood
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5
Q

factors that affect gross composition of red meat (6 + 3 ish)

A
  • species
  • breed
  • age
  • sex
  • nutrition of live animal
  • muscle condition in live animal (related to level of activity)
  • anatomical location of retail cut
  • extent of trim (fat)
  • methods of processing/cooking
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6
Q

composition of lean tissue for meat (5)

A
  • water (around 70-74%)
  • protein (around 20-21%)
  • lipid (around 5-6%)
  • ash (1%)
  • carbs, vitamins, other soluble organic constituents (1% of skeletal muscle)
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7
Q

water accounts for >___% of lean tissue by weight
- water is either ________ (to what? or ______ (trapped within what?)
- _______ water serves as what? when?

A
  • > 70%
  • bound (to proteins)
    free (trapped with muscle cells)
  • free water serves as medium in which nutrients and other solutes are dissolved and transported
  • when animal is alive
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8
Q

how is protein content typically derived in proximate analysis of meat?
- percent of ______ is multiplied by ______ –> bc?

A
  • from determination of muscle nitrogen content by Kjeldahl analysis
  • percent of nitrogen multiplied by 6.25 –> based on average nitrogen content of protein (16%)
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9
Q

is the proximate analysis of protein in meat accurate?

A
  • as much as 10% of muscle N originates from non-protein sources (ie nucleic acids and free aa)
  • thus, true protein content of red meat is somewhat lower than usually reported (19% vs 21%)
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10
Q

lipids can account for __-___% of fresh weight of separable lean tissue
- minimal values (___-___%) represent what? present in all living cells?
- larger values indicate what?

A
  • 1-13% of fresh weight
  • 0.5-1% represent membrane phospholipids
  • presence of variable amounts of neutral storage lipids which are primarily TG
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11
Q

what does ash refer to when analyzing meat content? (2)

A
  • refers fo inorganic residues, remaining after muscle sample is incinerated at extremely high temps
  • represents mineral component of muscle (Ca, Mg, Fe)
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12
Q

main carb in muscle?
vs main carb in meat? why?

A
  • glycogen (short term energy storage)
  • lactate bc during conversion of muscle to meat, glycogen is largely converted to lactate by anaerobic glycolysis (by bacteria and microorgs and enzymes that are in the “dead” body)
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13
Q

why is red meat an excellent source of protein in human diet?

A

because dietarty requirements for essential aa reflect the considerable skeletal muscle content of our own bodies

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14
Q

proteins in skeletal muscle can be separated, based on their _____A_____ into 3 classes:
- what?
- percent of total muscle protein?
- _____A_____?

A
  • solubility
    1. sarcoplasmic: 30%, soluble (float in cytoplasm)
    2. myofibrillar: 50-60%: soluble in concentrated salt solutions (0.3M NaCl) –> otherwise, they precipitate
    3. Stromal: 10-20%, insoluble –> attaches muscle tissue to bone
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15
Q

sarcoplasmic proteins are dissolved in what?

A

cytoplasm/sarcoplasm inside muscle cell

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16
Q

sarcoplasmic proteins
- 2 ex
- involved in (2)
- colors of fresh, cooked and cured meat products are due to ?

A
  • myoglobin and glycolytic enzymes
  • regulation of cell and energy homeostasis
  • due in large part to myoglobin content and oxidation state of iron in the heme group associated with myoglobin (Fe2+ = red, Fe3+ = brown)
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17
Q

why is veal a paler color compared to adult beef?

A
  • because myoglobin content tends to be in lower abundance in young animals
  • not old enough to have produced a lot of myoglobin
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18
Q

myoglobin has primarily ______ structures
- contains a ________ ring which contains _______

A
  • helical
  • porphyrin ring
  • contains a heme
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19
Q

myofibrillar proteins:
in muscle tissues, where salt concentration is ______ (above or below their solubility?), myofibrillar proteins are assembled into what?
- role?

A
  • 0.15M (below solubility of 0.3M)
  • into complex quaternary structural filaments
  • regulate, support or perform mechanical work of contraction
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20
Q

which proteins (2) account for ___ of total protein in skeletal muscle (for mechanical work)

A
  • myosin and actin (contractile proteins)
  • 65% of total protein
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21
Q

what regulates myosin and actin activity? (2)

A

troponin complex and tropomyosin

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22
Q

what is included in myofibrillar protein (6)

A
  • myosin
  • actin
  • troponin complex (C, I and T)
  • tropomyosin
  • titin
  • nebulin
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23
Q

behavior of myofibrillar proteins is important in fresh meats bc ?

A

because extent of contraction and rigor mortis development are critical in successful conversion of muscle to meat, as well as in processed meats

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24
Q

what is rigor mortis? can eat?

A

when muscle becomes very stiff after death (animal can’t make ATP anymore) –> can’t eat it –> need to wait for it to resolve before eating

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25
Q

what do stromal proteins form?
- these ________ proteins contribute to what?

A
  • fibrous connective tissues that strengthen and protect muscles
  • insoluble
  • meat toughness
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26
Q

what is the most prevalent of stromal proteins?
- this protein is also the most what?

A
  • collagen!
  • also the most abundant protein in animal body
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27
Q

although collagen makes only a small/big contribution to total skeletal muscle protein, importance of collagen is highlighted by the fact that ?

A
  • small
  • processing and cooking methods for meat are designed to disrupt and partially solubilize collagen fibers (hydrolyze = more tender)
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28
Q

3 sources of non-protein nitrogen in skeletal muscle?

A
  • creatine
  • amino acids
  • nucleic acids and nucleotides
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29
Q

total content of non-protein N only accounts for ___% of net weight of muscle
- however, which 2 sources are key components in what?

A

1.6%
- creatine and nucleotide ATP are key components in development of rigor mortis

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30
Q

skeletal muscles consist of a ________ arrangement of what?

A
  • parallel
  • of elongated multinucleated cells called myofibers (muscle fibers)
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31
Q

individual myofibers range from ___ to ____ um in width and from what to what in length? sometimes spanning what?

A
  • 10-100 um in width
  • few mm to several cm in length
  • sometimes spanning entire length of muscle
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32
Q

hierarchical structure of skeletal muscle? (3 layers)

A
  • each myofiber is encase in layer of connective tissue called endomysium
  • groups of myofibers are organized into primary and secondary bundles (fascicles) that are segregated by another layer of connective tissue called perimysium (surrounds muscle bundle)
  • final layer of heavy connective tissue sheaths, called epimysium surrounds the whole muscle –> those sheaths merge with connective tissue tendons to link muscles to bones
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33
Q

muscle is infiltrated by complex system of _________ (2 functions) and of ___________ (2 ish fcts)

A
  • complex system of nerves –> regulation of muscle contraction + maintenance of muscle tone
  • vascular syste through which blood provides O2 and nutrients while removing metabolic end products
34
Q

what (2) combine to provide necessary framework for maintaining the structural integrity of tissues within muscle?

A

perimysium and endomysium

35
Q

adipose tissue may be embedded in what?
- visible through ____A____
- abundance of ___A_____ used as an indicator in what?

A
  • perimysium
  • marbling
  • marbling = indicator in visual appraisal of meat quality
36
Q

muscle cells functions via ?, triggered by what? –> leads to what (2)
- this function requires what?

A
  • via translation of electrochemical impulses, triggered by neural stimulation at the neuromuscular junction
  • into increased intracellular calcium concentrations that in turn trigger muscle contraction (VS absorb calcium = muscles relax)
  • this function requires a unique cellular structure
37
Q

myofibers are bound by what? (2 names) –> differs from other membranes?

A
  • by plasma membrane (sarcolemma)
  • differs from other outer membranes
38
Q

what conducts stimulus for contraction into interior of myofiber? (4 steps)

A
  • invaginations of sarcolemma penetrate into myofiber (like fingers poking into a balloon)
  • these inward extension of sarcolemma form a network of transverse tubules (T-tubules) distributed along length of myofiber
  • T-tubules are in physical contact at periodic intervals with extensive highly developed intracellular membrane network called sarcoplasmic reticulum
  • SR network encircles contractile organelles + functions as a reservoir of calcium ions which serve as trigger for muscle contraction
39
Q

What is SR network? (IMPORTANT)
- serves as what? which triggers what?

A
  • sarcoplasmic reticulum (muscle equivalent of endoplasmic reticulum)
  • encircles contractile organelles + functions as a reservoir of calcium ions which serve as trigger for muscle contraction
40
Q

3 types of proteins in sarcoplasmic reticulum
- all of them need: ?

A
  1. proteins in interior (lumen) of SR bind calcium ions while muscle is at rest
  2. proteins form channels that open in response to electrochemical stimulus –> allow diffusion of calcium ions from within SR to the sarcoplasm (cytoplasm) –> triggers muscle contraction
  3. proteins pump calcium back into lumen of SR during relaxation
    - need ATP!
41
Q

what organelles fo the muscle cells possess? (7 ish)

A
  • nuclei (multiple, usually dispersed to periphery + found immediately beneath sarcolemma)
  • sarcoplasmic reticulum (endoplasmic reticulum)
  • sarcolemma (plasma membrane)
  • sarcoplasm (cytoplasm)
  • T-tubules
  • mitochondria –> energy transducers for myofiber
  • lysosomes
  • myofibrils!
42
Q

function of lysosomes in muscle cells?

A
  • serve as major reservoir for family of proteolytic enzymes known as cathepsins, which play catabolic role in protein turnover
43
Q

why are myofibers usually multinucleated?

A
  • multiple nucleis bc of path by which skeletal muscle cells develop
44
Q

sarcoplasm contains varying amounts of (2) –> both for ________?
- quantity depends on?
- also contains (5 ish)

A
  • glycogen and lipid droplets –> energy!
  • depends on type of muscle fiber and on nutritional and exercise/resting state of individual
  • contains myoglobin (oxygen storage protein) + various enzymes + metabolic intermediates + nucleotides, aa, etc…
45
Q

3 types of myofibers? + functions

A
  1. Type 1: slow red
    - slow contracting, red myofibers
    - contain greater amounts of oxidative organelles and fuels such as mitochondria, myoglobin and lipids
  2. Type 2a: fast red
  3. Type 2b: fast white
    - fast contracting myofibers are more equipped for anaerobic metabolism fueled by carbohydrates (ie birds to fly, 100m sprint)
46
Q

what consists of 80-90% of volume of muscle cell?

A

myofibrils (contractile organelles of muscle cells)

47
Q

myofibrils are composed of (2) in a highly specific structural organization that is what?

A
  • thin and thick protein filaments (myofilaments)
  • basis for muscle cell function
48
Q

fundamental structural unit of myofibrils is ?

A

sarcomere

49
Q

when longitudinal sections of skeletal muscle are viewed under microscope –> what (2) can be seen + characteristics

A
  • A bands (anisotropic): consists of overlapping thin and thick filaments + brighter middle region called H-zone where only thick filaments
  • I bands (isotropic): only thing filaments
50
Q

boundaries of sarcomeres are defined by what? what are they? (3)

A
  • by Z-discs
  • narrow, dark, electron-dense center of I band = Z-disc
  • Z-disc represent junction between 2 sarcomeres
  • matrix of proteins that constitute the Z-disc serves as anchoring structure for proteins of thin filaments that emanate from both sides of Z-disc
51
Q

at center of H-zone is a dark/light zone analogous to Z-disc called ?
- consists of what? + function

A
  • M line
  • consists of proteins that maintain structural arrangement of thick filament proteins + serve as anchoring point for protein titin which spans sarcomere form M-line to Z-disc
52
Q

4 major components of sarcomere:

A
  1. Z-discs define boundaries of sarcomere
  2. thin filaments = anchored at Z-disc
  3. thick filaments in central region that partially overlap with thin filaments
  4. titin filaments that span from Z-disc to M line (from Z-Z through the M-line)
53
Q

what is the sliding filament theory of muscle contraction? (3)

A
  • sarcomere lengths, defined as distance btw adjacent Z-discs, depend on state of contraction of myofiber or stretching force applied to it
  • lengths of both thin and thick filaments remain CONSTANT, independant of whether muscle is stretched, contracting or in resting state
  • thin and thick filaments interdigitate in such a way that thick filament (myosin) is surrounded by an array of 6 thin filaments (actin?)
  • when contraction takes place, thin and thick filaments slide past each other such that thin filaments (I bands) at opposite ends of sarcomere move toward each other = shortening of sarcomere length
54
Q

who (2) investigated structural mechanism of skeletal muscle contraction?

A

Huxley and Hanson

55
Q

muscle contraction:
- lengthening or shortening of distance btw Z-discs
- increasing or decreasing overlap of thin and thick filaments

A
  • shortening
  • increasing overlap
56
Q

muscle stretching:
- lengthening or shortening of distance btw Z-discs
- increasing or decreasing overlap of thin and thick filaments

A
  • lengthening
  • decreasing –> thin filaments of sarcomere slide away from each other as they move along A-band
57
Q

extent to which thin and thick filaments overlap has great practical significance with respect to meat _________
- short sarcomeres result from what –> correlated with what?

A
  • meat tenderness
  • from contraction as muscle is converted to meat
  • correlated with toughness
58
Q

thin filaments of sarcomere primarily consists of 4 proteins

A
  1. actin (contractile protein)
  2. tropomyosin (regulatory protein)
  3. troponin (regulatory protein)
  4. nebulin (cytoskeletal protein)
59
Q

thick filaments are primarily composed of what?
- what is also associated with thick filaments?

A
  • myosin
  • titin
60
Q

actin = _____ most abundant protein in muscle
- constitute ____% of myofibrillar protein content
- at high/low ionic strength, actin exists primarily as ______, a __________ _________ with MW of ____ kDa

A
  • second
  • 20%
  • low ionic strength
  • G-actin, a globular monomer with MM of 42 kDa
61
Q

at physiological ionic strength, G-actin monomers become what?
- one end of each thin filament is attached to what? how are thin filaments placed compared to M-line?

A

polymerized head-to-tail into F-actin –> forming 2-stranded, double helical assemblies that constitute the backbone of thin filament
- attached to Z-line
- because of directional nature of thin filaments, filaments on opposite sides of M-line are directed toward each other within a given sarcomere

62
Q

2 functions of actin in myofibril?

A
  1. actin binds to myosin (thick filament) during muscle contraction, forming cross-bridges btw thin and thick filaments
  2. actin binds to regulatory proteins tropomyosin and troponin
63
Q

tropomyosin (MW?) exists in myofiber as __________ polymer
- this short/long, ________-like structure runs length of what, spaning what?

A
  • a head-to-tail polymer
  • long ribbon-like structure runs entire length of thin filament, spanning 7 actin monomers
64
Q

what are the 3 subunits of troponin?

A
  • troponin-T (TnT, MW = 30.5 kDa) –> binds troponin complex to tropomyosin
  • troponin-C (TnC, MW = 18 kDa) –> binds Ca2+ ions
  • troponin-I (TnI, MW = 20.9 kDa) –> inhibits actomyosin ATPase (stops ATP from being hydrolyzed = keep muscle relaxed)
65
Q

how do tropomyosin and troponin bind?
how many of each protein bind together?

A
  • troponin binds near head-tail junctions of tropomyosin molecules
  • 1 troponin complex per tropomyosin molecule = 1 troponin per 7 actin
66
Q

what mechanism allows actin to bind to myosin? (2 steps)

A
  1. upon neural stimulation at neuromuscular junfction, Ca2+ ions are released inside cell
  2. when TnC binds to Ca2+ ions, this causes a conformational change in the binding of TnT to tropomyosin
  3. this alters binding btw tropomyosin and actin monomers in thin filaments = allows actin to bind to myosin
67
Q

myosin is the ______ abundant muscle protein, constituting ___% of muscle myofibril
- MW?
- consists of __ polypeptide chains –> describe

A
  • the most abundant
  • 43% of muscle myofibril
  • 521 kDa!
  • 6 polypeptide chains
  • 2 heavy chains (223 kDa)
  • 4 light chains (15-20 kDa)
68
Q

myosin stabilized by what?
- structure of ______-_____ ____

A

by interactions btw aa side chains
- coiled-coil rod

69
Q

myosin molecule is highly symmetric/asymmetric?
- describe

A
  • asymmetric!
  • at amino end of heavy chain, protein exhibits globular structure called myosin head
  • from the compact/folded domain of the head, the polypeptide chain extends in a long, rod-like, helical tail
  • helical tails of 2 myosin heavy chains intertwine to form a helical coiled-coil
70
Q

underphysiological conditions (within muscle cell), side-by side myosin molecules do what?
- what happens to myosin heads?

A

coalesce via their tail portions to form thick filaments
- myosin head project radially from thick filament shaft and are directed toward the thin filaments

71
Q

how are thick filaments arranged compared to M-line?

A

just like thin filaments, thick filaments are arranged in bipolar fashion –> myosin molecules on opposite sides of M-line point in opposite directions

72
Q

2 functions of myosin

A
  • important structural constituent of muscle
  • acts as an ATPase enzyme, splitting ATP and liberating chemical energy that is transformed by the protein into mechanical energy
73
Q

myosin head
- site for (2)
- what can they do during contraction?

A
  • active site for ATPase and site of force transduction
  • are able to link to actin molecules of thin filaments and form cross-bridges
74
Q

what gives rise to process of contraction and relaxation of muscle?

A

ability of myosin heads to repeatedly form and break cross-bridges

75
Q

titin is the _________ single polypeptide chain known (MW?)
- titin spans ______ of a sarcomere, running from _______ to _______
- appears to act as what that does what?
- may also serve as a template for what?

A
  • largest (3 000 kDa!)
  • half of a sarcomere: running from Z-line to M-line
  • act as cytoskeletal structure that maintains integrity of thick filaments
  • template upon which myosin molecules form thick filament during muscle cell differenciation and development
76
Q

how come titin may be involved in restoring resting sarcomere length when muscle relaxes?

A

evidence that portion of titin located in gap btw thick filament and z-line is elastic

77
Q

when the muscle cell is at rest, ________ sterically blocks what _______ ________ from binding to the _______-binding sites of the ______ filament
- upon stimulation of a muscle fiber by the nerve, the neurochemical impulse is transmitted into fiber by what?
- this triggers what?

A
  • tropomyosin sterically blocks myosin heads from binding the myosin-binding sites of the actin filament
  • T-tubules
  • T-tubules in turn, trigger release of Ca2+ from lumen of the SR
78
Q

when T-tubules release Ca2+, concentration of Ca2+ in the sarcoplasm rises at least ____-fold
- some of these Ca2+ bind to ____ –> causes 2 things

A
  • 100-fold
  • TnC, causing conformation change in TnT, the tropomyosin binding subunit
  • as a result of the conformational change, position of tropomyosin is shifted to a location deeper in the actin filament
  • this exposes myosin binding sites on the actin monomers
79
Q

4 steps of myosin-actin interaction/contraction cycle (schéma)

A
  1. myosin heads hydrolyze ATP and become reoriented and energized
  2. myosin heads bind to actin molecules of the thin filament, forming crossbridges btw thin and thick filaments (using E provided by ATPase activity of myosin)
  3. myosin crossbridges rotate toward center of sarcomere (power stroke) (when ADP is released, 45° shift = slides myosin deeper in the actin
    - contraction cycle continues if ATP is available and Ca2+ level in sarcoplasm is high
  4. As myosin heads bind ATP, crossbridges detach from actin
80
Q

during contraction cycle, myosin heads are __________ to thick filament axis
- upon binding to actin, myosin heads swivel to approximately ___° angle, pulling thin filaments past the thick filaments toward __________ (power stroke)
- with myosin heads on opposite sides of M-line pulling thin filaments toward ________, sarcomere ___________
- at this point, ______ binds to myosin head, causing what?
- ATP is then _________ to provide E for what? the head is now poised to …

A
  • perpendicular
  • 45°
  • toward M-line
  • pulling thin filaments toward middle, sarcomere shortens
  • ATP binds to myosin head, causing detachment of head from actin
  • ATP is then hydrolyzed to provide E for structural rearrangement of myosin head back to the 90° state
  • head is now poised to bind another actin monomer on thin filament and thus allowing another incremental shortening
81
Q

what happens when no neuronal stimulation anymore?
- how/using what?

A

Ca2+ concentration is lowered to resting levels by action of a Ca2+ pump protein that transports Ca2+ ions back into SR
- ATP provides chemical energy needed for transport of Ca2+ from relatively low Ca2+ concentration in sarcoplasm to much higher concentration in lumen of SR

82
Q

what happens to troponin and tropomyosin when Ca2+ is pumped back into storage?

A
  • troponin resumes its original (no calcium) conformation
  • thus, tropomyosin returns to its original position on the actin filament, thereby blocking myosin binding sites and causing the muscle to relax

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