meat science exam 3 Flashcards
general composition of meat
70 - 75% water, 20 - 25% proteins, 1 - 6% lipids (differences in IM fat), 1% carbs, 1& inorganic constituents (iron, vit. B 12)
what are the three groups of proteins
sarcoplasmic proteins (25 - 30%, water soulble, enzymes, myoglobin) myofibrillar proteins (50-50%, salt soluble, actin & myosin) stomal proteins (connective tissue 10 - 20%, insoluble, require stong acid/alkali, collagen, elastin)
muscle structure & function
muscle comprises 30 to 40% of animals body mass (largest organ mass in the body of vertebrates) primary functions are movement, support, maintenance of body temp, & dietary protein source (muscle –> meat) pH changes from 7.0/7.2 to 5.4/5.8
basic muscle types
skeletal = voluntary, cardiac & smooth = involuntary
skeletal muscle is surrounded by _____ and contains ____ (level 1)
epimysium, muscle fascicles
muscle fascicle/bundle is surrounded by ____ and contains _____ (level 2)
perimysium, muscle fibers
muscle cell (fiber) is surrounded by ______ and contains _____ (level 3!)
endomysium, myofibrils
myofibrils are surrounded by ______ and contain _______ (level 4)
sarcoplasmic reticulum, sarcomeres (Z line to Z line)
sarcomere
5ht level and the contractile unit
muscle fibers
encased and ‘harnessed’ by highly organized network of connective tissue (leaves 1 - 3)
connect tissue (CT) is subdivided into ‘sheaths’ that encase
the entire muscle = epimysium, bundles of muscle fibers = perimysium, individual muscle fibers = endomysium
endomysium
the endomysium interfaces and forms an attachment with the basement membrane which is attached to the cell membrane (sarcolemma) & transmits force of contraction to the skeleton
where is IM fat/marbling located
located in perimysium, marbling in meat consists of groups of IM fat cells deposited in the perimysium in CLOSE PROXIMITY TO BLOOD VESSELS
the structural unit of a collagen fibril is
tropocollage
a tropocollagen molecule is
a triple helix consisting of three polypeptide (AA bonds) chains (alpha chains), repeating tripeptide, Gly-X-Y where X & Y are frequently proline and hydroxyproline
as collagen matures what happens
it forms stable cross-links which increases is tensile strength, older animals will have tougher cross-linkages
muscles and collagen content
psoas major has 350ug/g of hydroxyproline vs superficial digital flexor/shank has 1,430 ug/g of hydroxyproline which makes it tougher
what is elastin
‘rubbery’ protein that is abundant in structures that require the ability to stretch (ex: nuchal lig. arteries & veins, abdominal wall, lungs, skin)
what unique amino acids does elastin contain
desmosine and isodesmosine which forms cross lines, is very resistant to extremes in alkalinity, acidity, and heat - very stable protein (more so than collagen)
elastin and stretching
elastin fibers are capable of stretching to several times their original length but quickly resume their original length when tension is released
muscle cell = myofiber
long cylindrical shape, length ranges from a few mm to several cm, diameter ranges from 10 to more than 100 microns, multinucleated (nuclei located at periphery just beneath the sarcolemma) designed to shorten, resulting in movement
sarcolemma
cell membrane
sarcoplasm
cytoplasm of muscle cell (water, proteins, lysosomes, glycogen granules, lipid droplets, ribosomes)
myofibrils
contractile machinery of cell comprised of repeating contractile units called sarcomeres
sarcoplasmic reticulum & transverse tubules
highly developed ER, unique to muscle cells
sarcoplasmic reticulum function
membrane around the myofibril that sits just under the endomysium, stores calcium/Ca+ in relaxed muscle
transverse tubules function
t-tubules, invaginations of the sarcolemma that form a “communication channel” into the interior of a muscle fiber
structure and banding feature of myofibrils
myofibrils occupy over 80% of cell volume, show distinct light and dark bands (striations), reflects presence of 2 major filaments dark/A band and light/I band
what bisects the I band?
Z line = key primary structural element of the myofibril, z line to z line = sarcomere, lateral boundaries of repeating contractile units
what is the H zone & H pseudo zone
H zone = light band within dark A band, where there is no overlap of thick and thin filaments there is only thick filaments. Pseudo H zone = dark region bisecting H zone
M line
very thin, dark line within the pseudo H zone important structurally, M line “holds” thick filaments in position
contractile proteins in myofibril
actin (thin filament) & myosin (thick filament)
regulatory proteins in myofibril
tropinin & tropomyosin (thin)
structural/cytoskeletal proteins
alpha-actinin (z-line, integral) titin (z-line to m-line, spring) nebulin (parallels thin f., actin forms around) myomesin (m-line) desmin (peripheral to z-line)
myosin, contractile protein
70-80% of myofibril protein, thick filament, burns ATP for muscle contraction, myosin head moves back and forth to perform a muscle contraction
actin, contractile protein
20-25% of the myofibril protein, think filament, globular G-protein, arranged like a twisted peral necklace f-protein, myosin head attached to the actin at the myosin binding site
thin filament structure
composed of a ‘super helix’ of F-actin (polymerized form of G-actin) include ‘regulatory proteins’ tropinin T, I, C and tropomyosin
tropomyosin
thin protein that lays around the actin proteins, regulatory protein
troponin
comprised of three subunits = troponin T (bound to tropomyosin) troponin C (binds Ca+) troponin I (inhibitory subunit that prevents interaction between actin and myosin)
what happens when Ca+ is released
when Ca+ is present, tropomyosin slides away from the myosin-binding sites on actin molecules, permitting formation of actomyosin bonds
titin
SPRING! argest protein discovered, extends from z-line to m-line, attaches thick filaments to z-line, molecular spring, maintains passive muscle tension, relaxation, keeps arcomere in alignment
nebulin
originated at z-line and extends along thin filament, throughout to provide template for building and maintaining F-actin and may be involved in connecting thin filament to z-line
I band
light band, contains only thin filaments. actin troponin tropomyosin titin & nebulin
h zone
light zone in middle of A-band, thick filaments only
A band
dark bands, contain thick and think filaments, actin myosin M line
M line
middle of H-zone, center of sarcomere, holds thick filaments in position
Z line
in middle of I band, holds thin filaments
what is the first sequence of events in muscle contraction?
a signal/acation potential (AP) reaches motor end plate at neuromuscular junction
what is the second step in muscle contraction
acetyl choline (ACH) released into the synaptic cleft, sarcolemma is depolarized (Na+ flux into fiber)
what happens at the arrival of action potential and release of ACH
signal passed to sarcolemma, ACH binds to receptors on sarcolemma causing resting potential to change (Na+ flux into myofibers K+ leaves myofibers) sarcolemma depolarizes, AP passes in both directions along sarcolemma, depolarization causes the SR yo release Ca++ into cytosol
what goes into myofibrils during AP and what leaves
sodium Na influx to myofibrils and potassium K leaves myofibrils
what is the third step in muscle contraction
AP transmitted via T-tubules to SR
what is the forth step in muscle contraction
Ca++ released from SR terminal cisternae into sarcoplasm, the depolarization of the SR causes release of Ca++
what does calcium bind with during contraction?
troponin C, which causes a shift in the troponin tropomyosin complex
what is the fifth and sixth step of muscle contraction
Ca++ binds to toponin C, tropomyosin shifts exposing myosin binding site
what happens to myosin after calcium binds
myosin ATPase activated and ATP hydrolyzed into ADP and Pi = myosin ready to bind
what is the thick and thin filament interaction during contraction
tropomyosin shifts exposing myosin binding sites, actin-myosin crossbridge formation
the ATPase activity of myosin
ATP bind to the myosin head, ATP hydrolysis to ADP + pi “cocks” the myosin head, the myosin head attached to the exposed binding site of actin, weak bond, Pi leaves the myosin head causing the “power stroke” ADP is released causing strong myosin-actin bond. Then ATP reattaches to the myosin head, releases mysin head from the myosin-actin binding site
what happens during muscle relazation?
cholinesterase released, acetylcholine breakdown, sarcolemma and T-tubules re-polarized, SR pump activates and Ca++ returned to SR terminal cisternae, actin-myosin cross bridge formation terminated, return of tropomyosin to myosin binding site, Mg++ complex formed with ATP, passive sliding of filaments, sarcomeres return to resting state
what are the different muscle fiber types and how to they differ?
Type I, type IIA, Type IIX or Type IID, Type IIB. each differ by metabolism (energy they use) and job they perform, most muscles contain all four fiber types
Type I
slow twitch, marathon runner, small muscle diameter, high myoglobin = aerobic, very oxidative metabolism (greater concentration of capillaries) very little glycolytic activity and glycogen, produce less force, greater lipid content, very resistant to fatigue, sustained use (posture, masseter in bovine, flight muscles in migratory birds) chicken thigh, IM fat
Type IIA
moderate myoglobin content, moderate contraction speed, small fiber diameter, moderate lipid content, moderate fatigue resistance, oxidative metabolism, very little glycogen content or glycolytic metabolism, have larger blood supply network than type IIB, normal everyday muscle contraction, can take advantage of both aerobic and anaerobic metabolism (fast oxidative glycolytic FOG fibers)
Type IIX (D)
low myoglobin content, moderate fiber diameter, moderate contraction speed, very little fatigue resistance, very little oxidative metabolism, moderate glycogen content and glycolytic activity, low lipid content, once thought to be a transitional fiber type but now considered 4th fiber type, athletes that combine both strength and endurance = baseball
Type IIB
low myoglobin content, large fiber diameter, very little fatigue resistance, fast contraction speed, little oxidative metabolism, high glycogen content and glycolytic metabolism = anaerobic, very little lipid content, short burst of activity, contract quickly and fatigue quickly, produce more force with each contraction, lower concentration of capillaries, body builders/powerlifters, chicken breast
type I vs type IIB (myoglobin, redness, mitochondria, capillaries, lipid content, glycogen level)
myoglobin: I > II, redness: I > II, mitochondria: I > II, capillaries I > II, lipid content I > II, glycogen level II > I
what are the sources of ATP for muscle contraction and relaxation
direct phosphorylation, anaerobic glycolysis, oxidative phosphorylation
phosphagen system
anaerobic, short-term ATP demand, only last about 30 seconds and has steep drop off
glycogen-lactic acid system
anaerobic, short term ATP demand, lasts about 45 seconds (30 - 60sec), slower drop off than phosagen, energy source of glucose (glucose –> glysolysis –> pyruvic acid –> lactic acid) 2 ATP per glucose
aerobic respiration
long term ATP demand, energy source of glucose pyruvic acid, fatty free acids from adipose tissue, amino acids from protein catabolism, oxygen required and produces 38 ATP per glucose with energy duration of hours
how does exsanguination affect O2
blood removal interrupts supply of O2 to the muscles, the muscles attempt to maintain homeostasis during early postmortem period
during exsanguination how does metabolism change
shifts energy metabolism from aerobic (TCA cycle) to anaerobic (glycolysis pathway)prevents recycling metabolic by-products
how does glycogen metabolism affect muscle pH decline
PM glycolysis produces lactic acid and becuase there is no opportunity to recycle LA it accumulates in the muscle (lactate + H+) the accumulation of the H+ ions causes muscle pH to decline from initial value of 7.0/7.2 to 5.4/5.5
what affects muscle pH decline?
rate and extend of pH decline differs among animals due to differences in muscle glycogen load at harvest (related to genetic effects and pre-harvest activity/stress) & carcass chill rate
normal animal pH decline
slow and steady with initial pH of 7.0 to 7.2 then final pH of 5.4 to 5.6 about 6 to 24 hr PM
creatine phosphate (CP)
one of the two primary energy sources for maintaining PM homeostasis, for short term high rates of energy production
rigor mortis “stiffness of death”
when CP and glycogen stores have been exhausted the muscle slowly depletes ATP and permanent actomyosin cross-bridges (rigor bonds) are formed, accompanied by loss of extensibility and muscle shortening
what are the three phases of rigor mortis?
delay phase = muscle remains extensible and elastic, onset phase = muscle begins to lose extensibility, completion phase = ATP is depleted, muscle is inextensible
what happens to sarcomeres as muscle goes into rigor
sarcomeres shorten as muscle goes into rigor, peak toughness is at 40% shortening
sarcomere shortening and temperature
degree of sarcomere shortening is temperature dependent, 15-20* C is optimal rigor temp - minimal sarcomere shortening, chilling muscles to temperatures of <15*C while ATP is still present results in “cold-shortening “ (pork less susceptible than beef or lamb) 21
which animals are electrically stimulated pre-rigor and why?
beef and lamb carcasses experience are pre-rigor electrical stimulation which depletes ATP supplies before muscle goes into rigor which PREVENTS COLD SHORTENING
sarcomere length differences among muscle
muscles differ in chill rate and in degree of tension exerted on myofibrils during onset of rigor based on locomotion/use for example gluteus medius sarcomere length is 1.66 microns vs psoas major is 2.94 microns
contractile state and tenderness
sarcomere shortening between 20 & 40% of resting length increases meat toughness
changes during postmortem aging that improve tenderness (actin myosin)
actin-myosin interactions (rigor bonds) are weakened 24 to 36 hrs postmortem non-enzymatic change resulting in slight improvement in tenderness
changes during postmortem aging that improve tenderness (enzymatic degradation)
enzymatic degradation of key structural proteins (postmortem proteolysis) during early PM period = calpains
changes during PM aging that improve tenderness (CT)
perimysium and endomysium are weakened during extended aging perions > 10 days
postmortem muscle proteolysis, calpain system
calpain protease system (endogenous enzyme dependent on Ca++ for activity, most active at pH 7) has calpain 1 calpain 2 calpain 3 and calpastatin which is the inhibitor. calpains degrade proteins directly attached to, closely associated with or near the Z-line
proteolytic effect of calpains
degradation of key structural proteins increases meat tenderness, calpains degrade intermediate filaments that link myofibrils to one another - desmin, sever the connection of myofilaments to the z-line - titin & nebulin, cause alpha-actinin to be released from z-line (a-actinin is NOT DEGRADED by calpains) degrade costameres (linkage of myofibrils to sarcolemma) vinculin & dystrophin, myofilaments breakaway z-line
are actin and myosin bonds influenced by calpain system?
NO
calpastatin
regulatory protein, controls actions (inhibits) calpains, calpastatin levels decrease over time
if there is increased calpastatin then what happens to tenderness
decreases tenderness
what breed/genotype and sex factors increase calpastatin activity
bos indicus influence in cattle, callipyge gene in sheep, intact males (testosterone)
what pre-harvest stress and growth modifiers increase calpastatin activity
epinephrine from pre-harvest stress and beta-agonist growth modifiers (ractopamine hydrochloride or zilpaterol hydrochloride)
high calpastatin activity does what to the rate of tenderization during PM aging
slows the rate of tenderization
what is callipyge gene
callipyge gene = much higher calpastatin activity
changes in CT with PM aging
degradation of CT is associated with tenderization effects observed with extended aging periods, CT is not affected about 10 days PM but weakens thereafter
PM changes in meat toughness
24 hr PM is peak on WBSFwith rigor shortening, dops odd after with early PM proteolysis (24-72ish hrs) when weakening of CT > 10 days PM
muscle specificity
actomyosin effect: sarcomere length, muscle fiber diameter. background effect: connective tissue. bulk density/lubrication effect: IM fat
what causes differences in CT amount?
muscle to muscle differences of locomotion vs support, genetic effects with dilution of CT
what is myostatin
“muscle stop” growth differentiation factor inhibits myogenesis, expression of myostatin = muscle growth stops
what happens with myostatin mutation or suppression
mutation or suppressed, expression of myostatin gene = more muscle less fat and animals have more muscle fiber since the muscle isn’t told to stop growing, it will also create more tender beef
we don’t use because animals get too big to handle
