Proteins V Flashcards
Connective tissue are also called ______ proteins
stromal
___________ transmit the mechanical force of contraction from muscle fibers to produce movements of the bones to which they are attached
Connective tissue
Connective tissue is (elastic/inelastic)
inelastic
______ represents 90% of the stromal proteins, while _______ constitutes 10%
Collagen
elastin
_________ is found in connective tissues throughout the body, including bone, tendon, cartilage, blood vessels, skin, and teeth, as well as the endomysium, perimysium, and epimysium of muscle.
Collagen
________ refers to a family of at least 27 different, but closely related, extracellular proteins
Collagen
The basic unit of collagen is ______, which consists of 3 ____________
tropocollagen polypeptide chains (a-chains)
________ consists of two polypeptide chains of identical sequence termed a1, and another chain termed a2, and is the dominant type in meat
Type 1 collagen
_________ consists of three identical chains of a1
Type III collagen
Most _______ contain about 33% glycine, 12% proline, 11% alanine, 10% hydroxyproline, 1% hydroxylysine, and small amounts of polar and charged amino acids
collagens
What is the most present AA in collagen?
Glycine
Which amino acid is virtually absent from collagen?
Tryptophan
Which AA is sometimes used as a criterion of purity for collagen preparations?
Tryptophan
In collagen chains, a repeating sequence of ___-X-Y is often seen, where X is often ____ and Y is often _____ or ______
Glycine
Proline
Hydroxyproline
Hydroxylysine
The a-chains of collagen are (left/right)-handed helixes
left
In the a-chains of collagen, glycine is present at every _____
third
_____ is the only amino acid that can be accomodated in the interior of collagen
Glycine
In the collagen structure, the side chain of every ____ residue points toward the very tightly packed center of the coiled-coil
third
In collagen, hydrogen bonding occurs between the ____ of a _____ and the _____ of the adjacent X residue on another chain
N-H
glycine
C=O
The triple helix of collagen is also stabilized by H-bonds involving the _______ residues
hydroxyproline
The collagens are grouped according to the _____________
supramolecular structures they adopt
What are the 4 types of collagen?
- Striated and fibrous
- Non-fibrous and network-forming
- Microfibrillar or filamentous
- Fibril-associated
The ______ group of collagen consist of repeating bands every 67-70 nm, originating from head-to-tail orientation of collagen molecules which form staggered side-by-side arrays
striated and fibrous
The ________ group of collagen are stabilized and strengthened by the intra and intermolecular covalent crosslinks
striated and fibrous
In live animals, the number of ___________ increases over time, which contributes to the _______ of meat from older animals
covalent collagen crosslinks
toughness
In muscle, collagen is associated with the epimysium (Type __ only), and the perimysium (Type __ and ___, with some Type __)
I
I
III
V
Type I collagen is associated with _______
epimysium
Types I, III, and V collagens belong to the _______
fibrous and striated collagens
Type I, III, and some Type V is associated with the _______
perimysium
The innermost part of the endomysium consists primarily of _____ collagen, which forms a sheet-like _________
Type IV
non-fibrous network (group 2)
Elastin differs from collagen in its _______
elasticity
_________ return to their original shape after being stretched to several times their original size
Elastin fibers
_______ are found in tissues requiring elasticity, such as the walls of _________
Elastin fibers
arteries and elastic ligaments
The main AA in elastin is ____, and large amounts of _______ are also found
glycine
proline, alanine, nonpolar aliphatic AA
Elastic lacks ______ and _______ AA
hydroxyproline
hydroxylysine
____________ are characterized by large numbers of lysinorlysine and desmosine crosslinks
Elastin fibers
_________ arise from crosslinking between allysine, which is formed by _____ of lysine residue by lysyl oxidase, and an adjacent unmodified lysine residue
Lysinorlysine
oxidation
Desmosine crosslinks are derived from ____ lysine chains
four
___________ are likely to be involved in restoring elastin fibers to their original shape and size following deformation
Desmosine
The biochemical changes that are responsible for the conversion of muscle to meat are not completed until up to __ weeks later
2
What is the specific function of muscle?
To convert chemical energy into mechanical energy.
What is the immediate source of chemical energy?
ATP
What happens initially with the cessation of blood flow that occurs at slaughter? How long does this last?
Myofibers utilize the oxygen bound to myoglobin to support aerobic metabolism (5 minutes)
______ serves as a rapidly accessible reservoir of high-energy phosphate for regeneration of ATP through the action of the enzyme _______
CrP
creatine kinase
________ also contributes to the generation of ATP
Adenylate kinase
After the exhaustion of CrP, creatine kinase, and adenylate kinase, what becomes the dominant metabolic pathway for the generation of ATP?
Anaerobic glycolysis utilizing glycogen reserves stores in the muscle
For every 2 molecules of ATP produced in anaerobic glycolysis utilizing glycogen, _____ molecule(s) of ______ is produced, which accumulates in the muscle and ______ the pH
1
lactic acid
lowers
When a pH of 5.5 is reached, many of the ______ enzymes are deactivated, and no further ______ can take place
glycolytic
glycolysis
In the delay phase, the level of ATP remains at >95% of the initial level, indicating that the rate at which _________ is nearly equal to the rate at which it is _________
ATP is generated
consumed
The _________ occurs because the muscle cells still function adequately as long as ATP levels remain high, and hence the muscle remains pliable and undergoes lengthening when subjected to stretch.
delay phase
Muscle cells still function adequately as long as _____ remain high
ATP
The ______ may last up to 12 hours
delay phase
The delay phase ends when ______ becomes depleted, because _________ alone cannot produce ATP fast enough to match the rate at which it is being hydrolyzed in the cell
CrP
anaerobic glycolysis
Depletion of ATP reduces the ability of the _________ to reduce the ___________ concentration to the submicromolar range, and thereby maintain the muscle in a _____ state
calcium pump protein
sarcoplasmic Ca2+
resting
Depletion of ATP results in an inability to dissociate ____ from ____ and hence the muscle cannot relax, which is the onset of _____
myosin
actin
rigor mortis
Muscle cramps are similar to ________: when people exercise for too long, ________ cannot keep up with the muscle’s ATP demand
rigor mortis
anaerobic glycolysis
As ATP levels continue to fall, there is a continuous increase in the number of _____ cross-bridges with _____ that are locked because of a lack of ATP.
myosin
actin
There is a corresponding increase in rigor development, as measured by the decrease in ________, and there may be some _________ shortening
extensibility
sarcomere
_________ is an increase in resistance of the muscle to lengthen when stretched
extensibility
The degree of ________________ that takes place during this rigor phase is closely related to meat toughness.
sarcomere shortening
The final phase of conversion of muscle to meat is referred to as ______ or ________
aging
rigor resolution
During the ___________, partial degradation of the structure of the myofilament framework by endogenous _______ enzymes occurs.
resolution phase
proteolytic
During the resolution phase, some of the muscle ______ is gradually regained, and there is a corresponding increase in meat _______
extensibility
tenderness
The length of the ______ usually is a few days in pork and lamb, and up to 2 weeks in beef
resolution phase
Among the muscle proteases that may play a role in postmortem muscle protein degradation, _______ have been the most studied.
calpains
______ are calcium-activated proteases that are most active in the _____ pH range and are regulated by a variety of factors, including calcium, phospholipids, and calpastatin, a widely distributed calpain-specific protein inhibitor.
Calpains
neutral
________ and ________ are ubiquitously expressed in tissues, suggesting that they are involved in basic and essential cellular functions mediated by Ca2+ signaling pathways
u-calpain
m-calpain
u-calpain and m-calpain are composed of homologous _______ subunits, and different ________ subunits
regulatory
catalytic
In skeletal muscle cells, the ubiquitous calpains tend to be concentrated in the _________
Z-discs
_______ is specific to skeletal muscles
Calpain 3
_______ binds to titin, and carries 3 unique sequences
Calpain 3
_______ are activated as the Ca2+ concentration in the ________ increases postmortem.
Calpains
sarcoplasm
_______ cause rapid and complete loss of the _____ owing to the degradation of troponin-T, titin, and nebulin as well as other minor proteins closely associated
Calpains
Z-discs
Once calpains are activated, ____ and _____ are passively released from the sarcomere and become substrates for other proteolytic enzymes
actin
myosin
______ are lysosomal proteases that act on numerous muscle proteins.
Cathepsins
Unlike calpains, _______ are maximally active at the _____ pHs characteristic of meat in the ______ phase
cathepsins
acidic
resolution
_____ are more important than _____ during the resolution phase
Calpains
cathepsins
Postmortem tenderization is _____-mediated, a characteristic only associated with the _____ proteolytic system in skeletal muscle.
Ca2+
calpain
Animals overexpressing the inhibitor _______, postmortem protein degradation is reduced
calpastatin
The _______ is a large and ubiquitous ATP-dependent proteolytic system that may also be involved in myofibrillar protein degradation during aging of meat.
proteosome
The ______ is able to degrade ___ and ____ in vitro; however, it is not able to degrade intact ______.
proteosome
actin
myosin
myofibrils
_______ initiate myofibrillar degradation, resulting in release of actin, myosin, and other proteins from the ______, which may then be hydrolyzed by the ______.
Calpains
sarcomere
proteosome
Postmortem metabolism leads to a (increase/decrease) in pH from the physiological value of _____ to _____
decrease
- 4
- 5
The natural __________ postmortem is beneficial because it retards microbial growth and thereby extends shelf life
reduction in pH
The final postmortem pH of meat is close to the isoelectric point of ________, _________ interactions become favored instead of __________ interactions, resulting in a decrease in water-holding capacity and some exudation of water from the tissue
myosin
protein-protein
protein-water
The extent to which _________ affects the economic value of the meat, simply because meat is sold by weight
water is extuded
Antemortem depletion of ___________ may result from pre- slaughter stressors (including cold, damp weather), exercise, or excessive fasting.
glycogen stores
Following slaughter, the lack of adequate ________ reserves results in early termination of _______, so the final pH of the meat remains relatively ____
glycogen
glycolysis
high
What causes dark, firm, and dry (DFD) meat?
- Lack of glycogen
- Early termination of glycolysis
- High pH (> 6.0)
The final pH of meat affects its _____ because the charge on the proteins remain ____, thereby maximizing separation of muscle myofibrils, and reducing light _______
color
high
scattering
Active mitochondrial respiration at a ___ ph reduces the fraction of __________ in the tissue
higher
oxymyoglobin
What is the consequence of reduced oxymyoglobin in the tissue?
The color of DFD meat ranges from slightly dark to extremely dark or nearly black
What is the color of DFD meat?
The color of DFD meat ranges from slightly dark to extremely dark or nearly black
Upon cooking of meat, a ______ increase in meat toughness occurs with increasing temperature.
biphasic
A _____ increase in toughness occurs over the range of 40- 50 °C, attributed to thermal denaturation of ___ and ___, which shrink and form a ____ within the myofiber that accounts for the increased toughness.
sharp
actin
myosin
gel
Upon gelation after heating to 40-50oC, some of the water previously associated with the myofiber is apparently forced out by shrinkage of the _______, thus accounting for some of the loss of fluid observed over this temperature range.
endomysium
The second sharp increase in toughness during heat at 65-75oC results from the shrinkage of _________ associated with the ________ that denature and are gradually converted to ________
collagen fibers
perimysium
gelatin
The shrinkage of the __________ generates a substantial force that expels a large amount of fluid from the myofibers in the second phase as compared to the first phase.
perimysial fibers
Does the first or second phase of heating release more fluid?
The second
As heating of the meat (especially above 70 °C) is prolonged, tenderness gradually _________, due to the partial hydrolysis of heat-labile crosslinks between _______, and to _____ hydrolysis
increases
collagen chains
peptide
The balance between the degree of toughening induced by shrinkage of _______ and _______ fibers and the weakening of _______ and _______ via hydrolysis contributes to the ultimate texture of the product.
myofibrils
perimysial
collagen
myofibrils
When a fresh meat product is heated, an initial lightening of the color occurs due to the precipitation of _______ within the myofibers, which changes the perception of the color
proteins
Most of the color changes upopn heating of fresh meats are due to chemical changes in the _______ and depend to some extent on the chemical state of _____
myoglobin
iron
_________ is one of the most heat-stable of the muscle proteins and retains its structure and color properties up to at least 50 °C.
Myoglobin
With prolonged heating and increasing temperature, there is a gradual change of the _________ color of fresh meats to a ________ color.
reddish-pink
greyish-brown
Fe(III) is _____, Fe(II) bound to O2 is _____, Fe(II) bound to water is ______
metmyoglobin
oxymyoglobin
deoxymyoglobin
The change in color due to heating is primarily due to denaturation of ______ and change in the oxidation of its _____ group, but some browning also results from the ____________
myoglobin
heme
Maillard reaction
Premature browning may occur as a result of the greater sensitivity of _______ and ________ to thermal denaturation as compared to __________
metmyoglobin
oxymyogloin
deoxymyoglobin
Causes of persistent red color in cooked fresh meat include ____ meat pH, the presence of carbon monoxide or oxides of nitrogen formed during cooking, and differing concentrations of ______.
high
myoglobin
Many of the cooked meat flavor compounds, including pyridines, pyrazines, thiophenols, and thiazoles are formed via the ____________
Maillard reaction pathway
The presence and abundance of Maillard reaction precursors include _______ components, such as peptides, amino acids, nucleotides, and _________ components including fatty acids
water-soluble
non-polar
