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2) Food Chemistry I > Proteins V > Flashcards

Proteins V Flashcards

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1
Q

Connective tissue are also called ______ proteins

A

stromal

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2
Q

___________ transmit the mechanical force of contraction from muscle fibers to produce movements of the bones to which they are attached

A

Connective tissue

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3
Q

Connective tissue is (elastic/inelastic)

A

inelastic

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4
Q

______ represents 90% of the stromal proteins, while _______ constitutes 10%

A

Collagen

elastin

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5
Q

_________ 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.

A

Collagen

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6
Q

________ refers to a family of at least 27 different, but closely related, extracellular proteins

A

Collagen

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7
Q

The basic unit of collagen is ______, which consists of 3 ____________

A 
tropocollagen
polypeptide chains (a-chains)
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8
Q

________ consists of two polypeptide chains of identical sequence termed a1, and another chain termed a2, and is the dominant type in meat

A

Type 1 collagen

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9
Q

_________ consists of three identical chains of a1

A

Type III collagen

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10
Q

Most _______ contain about 33% glycine, 12% proline, 11% alanine, 10% hydroxyproline, 1% hydroxylysine, and small amounts of polar and charged amino acids

A

collagens

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11
Q

What is the most present AA in collagen?

A

Glycine

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12
Q

Which amino acid is virtually absent from collagen?

A

Tryptophan

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13
Q

Which AA is sometimes used as a criterion of purity for collagen preparations?

A

Tryptophan

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14
Q

In collagen chains, a repeating sequence of ___-X-Y is often seen, where X is often ____ and Y is often _____ or ______

A

Glycine
Proline
Hydroxyproline
Hydroxylysine

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15
Q

The a-chains of collagen are (left/right)-handed helixes

A

left

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16
Q

In the a-chains of collagen, glycine is present at every _____

A

third

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17
Q

_____ is the only amino acid that can be accomodated in the interior of collagen

A

Glycine

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18
Q

In the collagen structure, the side chain of every ____ residue points toward the very tightly packed center of the coiled-coil

A

third

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19
Q

In collagen, hydrogen bonding occurs between the ____ of a _____ and the _____ of the adjacent X residue on another chain

A

N-H
glycine
C=O

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20
Q

The triple helix of collagen is also stabilized by H-bonds involving the _______ residues

A

hydroxyproline

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21
Q

The collagens are grouped according to the _____________

A

supramolecular structures they adopt

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22
Q

What are the 4 types of collagen?

A
  • Striated and fibrous
  • Non-fibrous and network-forming
  • Microfibrillar or filamentous
  • Fibril-associated
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23
Q

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

A

striated and fibrous

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24
Q

The ________ group of collagen are stabilized and strengthened by the intra and intermolecular covalent crosslinks

A

striated and fibrous

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25
Q

In live animals, the number of ___________ increases over time, which contributes to the _______ of meat from older animals

A

covalent collagen crosslinks

toughness

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26
Q

In muscle, collagen is associated with the epimysium (Type __ only), and the perimysium (Type __ and ___, with some Type __)

A

I
I
III
V

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27
Q

Type I collagen is associated with _______

A

epimysium

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28
Q

Types I, III, and V collagens belong to the _______

A

fibrous and striated collagens

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29
Q

Type I, III, and some Type V is associated with the _______

A

perimysium

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30
Q

The innermost part of the endomysium consists primarily of _____ collagen, which forms a sheet-like _________

A

Type IV

non-fibrous network (group 2)

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31
Q

Elastin differs from collagen in its _______

A

elasticity

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32
Q

_________ return to their original shape after being stretched to several times their original size

A

Elastin fibers

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33
Q

_______ are found in tissues requiring elasticity, such as the walls of _________

A

Elastin fibers

arteries and elastic ligaments

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34
Q

The main AA in elastin is ____, and large amounts of _______ are also found

A

glycine

proline, alanine, nonpolar aliphatic AA

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35
Q

Elastic lacks ______ and _______ AA

A

hydroxyproline

hydroxylysine

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36
Q

____________ are characterized by large numbers of lysinorlysine and desmosine crosslinks

A

Elastin fibers

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37
Q

_________ arise from crosslinking between allysine, which is formed by _____ of lysine residue by lysyl oxidase, and an adjacent unmodified lysine residue

A

Lysinorlysine

oxidation

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38
Q

Desmosine crosslinks are derived from ____ lysine chains

A

four

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39
Q

___________ are likely to be involved in restoring elastin fibers to their original shape and size following deformation

A

Desmosine

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40
Q

The biochemical changes that are responsible for the conversion of muscle to meat are not completed until up to __ weeks later

A

2

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41
Q

What is the specific function of muscle?

A

To convert chemical energy into mechanical energy.

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42
Q

What is the immediate source of chemical energy?

A

ATP

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43
Q

What happens initially with the cessation of blood flow that occurs at slaughter? How long does this last?

A

Myofibers utilize the oxygen bound to myoglobin to support aerobic metabolism (5 minutes)

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44
Q

______ serves as a rapidly accessible reservoir of high-energy phosphate for regeneration of ATP through the action of the enzyme _______

A

CrP

creatine kinase

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45
Q

________ also contributes to the generation of ATP

A

Adenylate kinase

46
Q

After the exhaustion of CrP, creatine kinase, and adenylate kinase, what becomes the dominant metabolic pathway for the generation of ATP?

A

Anaerobic glycolysis utilizing glycogen reserves stores in the muscle

47
Q

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

A

1
lactic acid
lowers

48
Q

When a pH of 5.5 is reached, many of the ______ enzymes are deactivated, and no further ______ can take place

A

glycolytic

glycolysis

49
Q

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 _________

A

ATP is generated

consumed

50
Q

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.

A

delay phase

51
Q

Muscle cells still function adequately as long as _____ remain high

A

ATP

52
Q

The ______ may last up to 12 hours

A

delay phase

53
Q

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

A

CrP

anaerobic glycolysis

54
Q

Depletion of ATP reduces the ability of the _________ to reduce the ___________ concentration to the submicromolar range, and thereby maintain the muscle in a _____ state

A

calcium pump protein
sarcoplasmic Ca2+
resting

55
Q

Depletion of ATP results in an inability to dissociate ____ from ____ and hence the muscle cannot relax, which is the onset of _____

A

myosin
actin
rigor mortis

56
Q

Muscle cramps are similar to ________: when people exercise for too long, ________ cannot keep up with the muscle’s ATP demand

A

rigor mortis

anaerobic glycolysis

57
Q

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.

A

myosin

actin

58
Q

There is a corresponding increase in rigor development, as measured by the decrease in ________, and there may be some _________ shortening

A

extensibility

sarcomere

59
Q

_________ is an increase in resistance of the muscle to lengthen when stretched

A

extensibility

60
Q

The degree of ________________ that takes place during this rigor phase is closely related to meat toughness.

A

sarcomere shortening

61
Q

The final phase of conversion of muscle to meat is referred to as ______ or ________

A

aging

rigor resolution

62
Q

During the ___________, partial degradation of the structure of the myofilament framework by endogenous _______ enzymes occurs.

A

resolution phase

proteolytic

63
Q

During the resolution phase, some of the muscle ______ is gradually regained, and there is a corresponding increase in meat _______

A

extensibility

tenderness

64
Q

The length of the ______ usually is a few days in pork and lamb, and up to 2 weeks in beef

A

resolution phase

65
Q

Among the muscle proteases that may play a role in postmortem muscle protein degradation, _______ have been the most studied.

A

calpains

66
Q

______ 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.

A

Calpains

neutral

67
Q

________ and ________ are ubiquitously expressed in tissues, suggesting that they are involved in basic and essential cellular functions mediated by Ca2+ signaling pathways

A

u-calpain

m-calpain

68
Q

u-calpain and m-calpain are composed of homologous _______ subunits, and different ________ subunits

A

regulatory

catalytic

69
Q

In skeletal muscle cells, the ubiquitous calpains tend to be concentrated in the _________

A

Z-discs

70
Q

_______ is specific to skeletal muscles

A

Calpain 3

71
Q

_______ binds to titin, and carries 3 unique sequences

A

Calpain 3

72
Q

_______ are activated as the Ca2+ concentration in the ________ increases postmortem.

A

Calpains

sarcoplasm

73
Q

_______ 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

A

Calpains

Z-discs

74
Q

Once calpains are activated, ____ and _____ are passively released from the sarcomere and become substrates for other proteolytic enzymes

A

actin

myosin

75
Q

______ are lysosomal proteases that act on numerous muscle proteins.

A

Cathepsins

76
Q

Unlike calpains, _______ are maximally active at the _____ pHs characteristic of meat in the ______ phase

A

cathepsins
acidic
resolution

77
Q

_____ are more important than _____ during the resolution phase

A

Calpains

cathepsins

78
Q

Postmortem tenderization is _____-mediated, a characteristic only associated with the _____ proteolytic system in skeletal muscle.

A

Ca2+

calpain

79
Q

Animals overexpressing the inhibitor _______, postmortem protein degradation is reduced

A

calpastatin

80
Q

The _______ is a large and ubiquitous ATP-dependent proteolytic system that may also be involved in myofibrillar protein degradation during aging of meat.

A

proteosome

81
Q

The ______ is able to degrade ___ and ____ in vitro; however, it is not able to degrade intact ______.

A

proteosome
actin
myosin
myofibrils

82
Q

_______ initiate myofibrillar degradation, resulting in release of actin, myosin, and other proteins from the ______, which may then be hydrolyzed by the ______.

A

Calpains
sarcomere
proteosome

83
Q

Postmortem metabolism leads to a (increase/decrease) in pH from the physiological value of _____ to _____

A

decrease

  1. 4
  2. 5
84
Q

The natural __________ postmortem is beneficial because it retards microbial growth and thereby extends shelf life

A

reduction in pH

85
Q

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

A

myosin
protein-protein
protein-water

86
Q

The extent to which _________ affects the economic value of the meat, simply because meat is sold by weight

A

water is extuded

87
Q

Antemortem depletion of ___________ may result from pre- slaughter stressors (including cold, damp weather), exercise, or excessive fasting.

A

glycogen stores

88
Q

Following slaughter, the lack of adequate ________ reserves results in early termination of _______, so the final pH of the meat remains relatively ____

A

glycogen
glycolysis
high

89
Q

What causes dark, firm, and dry (DFD) meat?

A
  • Lack of glycogen
  • Early termination of glycolysis
  • High pH (> 6.0)
90
Q

The final pH of meat affects its _____ because the charge on the proteins remain ____, thereby maximizing separation of muscle myofibrils, and reducing light _______

A

color
high
scattering

91
Q

Active mitochondrial respiration at a ___ ph reduces the fraction of __________ in the tissue

A

higher

oxymyoglobin

92
Q

What is the consequence of reduced oxymyoglobin in the tissue?

A

The color of DFD meat ranges from slightly dark to extremely dark or nearly black

93
Q

What is the color of DFD meat?

A

The color of DFD meat ranges from slightly dark to extremely dark or nearly black

94
Q

Upon cooking of meat, a ______ increase in meat toughness occurs with increasing temperature.

A

biphasic

95
Q

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.

A

sharp
actin
myosin
gel

96
Q

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.

A

endomysium

97
Q

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 ________

A

collagen fibers
perimysium
gelatin

98
Q

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.

A

perimysial fibers

99
Q

Does the first or second phase of heating release more fluid?

A

The second

100
Q

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

A

increases
collagen chains
peptide

101
Q

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.

A

myofibrils
perimysial
collagen
myofibrils

102
Q

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

A

proteins

103
Q

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 _____

A

myoglobin

iron

104
Q

_________ is one of the most heat-stable of the muscle proteins and retains its structure and color properties up to at least 50 °C.

A

Myoglobin

105
Q

With prolonged heating and increasing temperature, there is a gradual change of the _________ color of fresh meats to a ________ color.

A

reddish-pink

greyish-brown

106
Q

Fe(III) is _____, Fe(II) bound to O2 is _____, Fe(II) bound to water is ______

A

metmyoglobin
oxymyoglobin
deoxymyoglobin

107
Q

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 ____________

A

myoglobin
heme
Maillard reaction

108
Q

Premature browning may occur as a result of the greater sensitivity of _______ and ________ to thermal denaturation as compared to __________

A

metmyoglobin
oxymyogloin
deoxymyoglobin

109
Q

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 ______.

A

high

myoglobin

110
Q

Many of the cooked meat flavor compounds, including pyridines, pyrazines, thiophenols, and thiazoles are formed via the ____________

A

Maillard reaction pathway

111
Q

The presence and abundance of Maillard reaction precursors include _______ components, such as peptides, amino acids, nucleotides, and _________ components including fatty acids

A

water-soluble

non-polar

2) Food Chemistry I (31 decks)

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