Proteins III Flashcards
__________ contains 12% solids, of which 3.5 is protein
Fluid milk
Milk proteins have high nutritive value (good AA balance), surpassed only by ____________ which are a good source of ___________
egg albumin
lysine
Milk proteins can be categorized into two groups: ________ and _______ proteins
caseins
whey
__________ is a general term for milk proteins having an isoelectric point at pH 4.5
Casein
________ are isolated by adjusting the pH of milk to 4.5 by using acid, while _________ are left in solution
Casein
whey
What are the most common caseins?
- As1-casein
- B-casein
What is the most common whey protein?
B-Lactoglobulin
O. Hammarsten (1877) outlined a procedure to separate ______, _______, and _________
casein
lactalbumin
lactoglobulin
Skim milk is diluted, and then acidified with ________; ________ flocculates, while the ______ proteins stay in solution
acetic acid
casein
whey
Established that ______ is insoluble in weakly acidic media
casein
Casein is a ____________ with the phosphate attached to _______
phosphoprotein
serine
Classify the types of casein in order of most present to least present.
as1 > B > K > as2 > γ
____ and ____ casein are differentiated from each other by their sensitivity to the presence of Ca2+ ions
as1
K
____ casein will precipitate in the presence of Ca2+, while ____ casein does not
as1
K
Micelles dissociate if _____ is dialyzed from the solution, and will reform if ____ is added back
Ca2+
Ca2+
_________ are responsible for the opaque whiteness of milk, an optical effect due to light scattering (properties from casein)
Micelles
The opaque whiteness of milk is due to ____________
light scattering of casein micelles
Calcium sensitive ____ is surrounded by _____
as1 casein
K casein
Paracasein is another form of casein that is obtained by _________
rennin
______ is a proteolytic enzyme obtained from the ____ stomach of the calf
Rennin
fourth
Rennin attacks ______ at a specific site, cleaving off a ____________________
K-casein
glycomacropeptide
When ______ is added into a milk solution, the micelles are destabilized and they associated to form a curd, which forms ______________
rennin
paracasein
The formation of ___________ is the first step in cheese making
paracasein
Acid/Isoelectric casein and paracasein are similar physically because they aren’t ________________
temperature sensitive
In the __ variation of as1 casein, AA residues 14-26 are missing
A
In the __ variation of as1 casein, the peptide chain has 199 AA residues
B
In the __ variation of as1 casein, Glu-192 is replaced by Gly-192
C
In the __ variation of as1 casein, Ala-53 is replaced by phosphothreonine
D
All the variations of ___________________ contain 8 phosphoserine residues, 7 of which are localized between 43 and 80
as1-casein
________ contains a portion with 12 carboxyl groups from _____________ and _____________ residues, making it extremely ______
as1-casein
glutamic acid
aspartic acid
polar
In _______, AA 100-199 are _______ and responsible for the self-association tendencies of the protein despite the repulsive forces between the _________ groups, and the lack of ___________ residues
as1-casein
apolar
phosphate
cysteine
The ________ residues distributed along the chain in as1 casein hinders the ordered structure
proline
In as1-casein, the hydrophilic segment is connected to a____________
hydrophobic B-sheet region
In as1-casein, the hydrophobic B-sheet region is connected to the region that contains the ____________, which is connected to a short ________
phosphate
a-helical segment
In as1-casein, the a-helical segment is connected to a very hydrophobic ______________ domain, which contains extended __________
carboxy-terminal
B-strands
The carboxy terminal segment of as1-casein is very ____________
hydrophobic
In as1-casein, - 15% of the peptide chain is _________, and 22% has a ____________
a-helical
B-structure
__________ consists of 207 AA residues
as2-casein
___________ has a pronounced dipolar structure due to the concentration of _______ groups in the region of the N-terminal, and ________ groups in the region of the C-terminal
as2-casein
anionic
cationic
______ contains 11 phosphoserine and 2 cysteine residues
as2-casein
________ precipitates with Ca2+ more easily than as1-casein
as2-casein
______ is the most hydrophobic casein
B-casein
_______ has 209 AA residues (A-variant)
B-casein
___________ contains 5 phosphoserine residues that are localized between 1 and 40, which contains practically all the __________ sites of the molecule
B-casein
ionizable
In B-casein, 136-209 contain residues with _______ side chains
apolar
Which casein acts like soap?
B-casein
Polar head and an apolar tail
______ contains 9% a-helical structure and 25% B-structure
B-casein
In B-casein, - increasing the temperature results in an increase in _____________, with no decrease in ____________ content
B-structure
a-helical
In B-casein, the ___________ originates in an aperiodic part of the chain
B-structure
Like _______-casein, _______-casein contains no cysteine residues
as1
B
Unlike _____-casein, ______-casein does not self-associate spontaneously
as1
B
________-casein precipitates in the presence of Ca2+ ions found in milk
B-casein
When _______-casein precipitates with Ca2+, at temperatures of < 1oC, the calcium salt is quite soluble
B
A1 and A2 B-casein are genetic variants of _______ that differ only by one amino acid
B-casein
Company marketing with predominantly __ protein claims that milk containing __ proteins are harmful, but there is insufficient evidence to prove
A2
A1
_________ are degradation products of B-casein formed by milk proteases
gamma-casein
________-casein has 169 residues
K
_____-casein is a monomer
K
____-casein contains 2 cysteine residues, and is only accessible under reducing conditions
K
Normally, __-casein occurs as a trimer or as higher oligomers by the formation of ________bonds
K
disulfide
In ___-casein, varying amounts of carbohydrate are bound to the peptide chain through Threonine residues at positions 131, 133, 135, or 136 (A variant)
K
___-casein can be separated electrophoretically into various components that have the same AA composition, but differ in the carbohydrate content
K
Which casein has a 3D horse and rider model?
K
In the horse and rider model of __-casein, the ___-terminal makes up the horse, the ____-terminal makes up the rider, and the two legs of the horse are made of _______
K
N
C
B-structures
___-casein contains 16% a-helical structure and 27% B-structure
K
In the horse and rider model of __-casein, the legs are very _____________ and are an area of interaction with other caseins
K
hydrophobic
____-casein is the only constituent of casein that remains soluble in the presence of Ca2+ ions in milk
K
Aggregation of ____-casein and ____-casein with ____-casein prevents their coagulation in the presence of Ca2+ ions
as1
B
K
10% of the total casein fraction is present in milk as _________, usually designated as _______ caseins
monomers
serum
A(n) _______ in H+ and Ca2+ promotes casein micelle formation
increase
A(n) _________ in citrate promotes casein micelle formation
decrease
A(n) _________ in phosphate promotes casein micelle formation
decrease
A(n) _________ in temperature promotes casein micelle formation
increase
Dialysis of casein complexes against a ___________ (citrate, phosphate) would shift the equilibrium completely to _________
chelating agent
monomers
The diameter of micelles has a mean of ______
150 nm
Micelles are held together by _______, ________, and ________
hydrophobic interactions
electrostatic interactions
hydrogen bonds
In the case of casein micelles, _______________ are minimal at temperatures below 5oC
hydrophobic interactions
The electrostatic interactions in casein micelles are mostly between ________ and ________ that form bridges between __________ and ________ residues
calcium
calcium phosphate
phosphoserine
glutamic acid
What are the two types of subunits of casein micelles?
Contains K-casein
Does not contain K-casein
_________ are arranged on the surface of submicelles
K-casein molecules
The ________ C-terminals of K-casein protrude from the surface, which prevents further aggregation
hydrophilic
The hydrophilic _________ of K-casein prevent further aggregation
C-terminal
Aggregation of the submicelles proceeds until the entire surface of the forming micelle is covered with ________
K-casein
_______ is 5 nm thick
K-casein coverage
A small part of _______ is also found inside the micelle
K-casein
______ has a role in stabilizing casein micelles
K-casein
Due to its role in stabilizing casein micelles, cleaving of _______ causes the casein proteins to __________, and separate from the whey
K-casein
coagulate
Rennet contains the precursor of the enzyme _________, an acid protease having specificity for __________
chymosin
K-casein
________ specifically recognizes the sequence from His-98 to Lys-11 in _______, and selectively cleaves the peptide bond between Phe-105 and Met-106
Chymosin
K-casein
Chymosin cleaves K-casein into ___________ and a ___________
para-K-casein
glycomacropeptide
Chymosin releases a soluble ___________ while the __________ precipitates in the presence of Ca2+ ions
glycomacropeptide
para-K-casein
What are the two largest components of whey protein?
- B-lactoglobulin (10%)
- B-lactalbumin (2%)
________ is 10% of the total milk protein, and 58% of the ____ protein fraction
B-lactoglobulin
whey
_____ has 162 AA
B-lactoglobulin
In B-lactoglobulin, ___ variant has an aspartic acid, while the ___ variant has a glycine
A
B
_____ contains 2 disulfide bonds, 1 free sulfhydryl group, and no phosphorus
B-lactoglobulin
Which milk protein has a dynamic disulfide bond?
B-lactoglobulin
Below pH 3.0 and above pH 8.0, __________exists as a ______
B-lactoglobulin
monomer
Between pH 3.1 and 5.1, at low temperatures and high concentration, B-lactoglobulin associates to form an _______
B-lactoglobulin
octomer
Which milk protein can oligomerize?
B-lactoglobulin
This oligomerization is mediated through ______ groups
carboxyl
The ___ variant of B-lactoglobulin forms more readily than the ___ variant since it has an extra ______ group
A
B
carboxyl
At the pH of milk, _________ tends to form a ______
B-lactoglobulin
dimer
The _______ of __________ are spherical with diameters of about 18 angstroms
dimers
B-lactoglobulin
The _______ structure of B-lactoglobulin is homologous to that of ____-binding proteins
secondary
retinol
The secondary strand of ___________ contains 9 strands of B-structure
B-lactoglobulin
Which milk protein associates to form a barrel with _______ and a lid with _______?
B-lactoglobulin
B-structures
a-helix
The center of the barrel of _______ is hydrophobic and is involved in the binding of hydrophobic molecules
B-lactoglobulin
The biological role of B-lactoglobulin, manufactured in the __________, is _________
mammary gland
unknown
B-lactoglobulin is effective at binding __________
retinol
__________’s _________ pocket is effective at binding retinol
B-lactoglobulin
hydrophobic
It is speculated that the binding of ________ may have a regulatory role in the mammary gland
vitamin A
Because of its prevalence in bovine milk, the properties of whey protein in the food industry are largely the properties of _______________
B-lactoglobulin
___________ compose 2% of total milk protein and 13% of total whey protein
a-Lactalbumin
____ has 123 AA
a-Lactalbumin
________ has 4 disulfide linkages and no phosphate groups
a-Lactalbumin
__________ modifies the activity of galactosyl transferase
a-lactalbumin
a-lactalbumin modifies the activity of _______________
galactosyl transferase
The transfer of UDP-galactose to N-acetylglucosamine groups (glucose) is slow without __________________
a-lactalbumin
________________ adds UDP-galactose to glucose and produces _______ and UDP, which is faster when __________ is attached
galactosyl transferase
lactose
a-lactalbumin
40% of the residues of the AA sequences of _____________and _____________ are the same, including the cysteine residues, and 20% of the residues are similar
a-lactalbumin
lysozyme
a-lactalbumin is related to ________
lysozyme
________ helps synthesize the linkage that _________ cleaves
a-lactalbumin
lysozyme
Do a-lactalbumin and lysozyme work on the same substrates?
No
Most proteins are (more/less) stable in the presence of calcium due to the ability of calcium to promote the formation of __________________ with most proteins
less
ionic intermolecular cross-links
Ionic intermolecular cross-links between proteins and calcium hold the molecules in proximity and increases ____________________
the likelihood of aggregation upon heating
____________ is unusual since the molecule is more stable to heat in the presence of calcium
a-lactalbumin
a-lactalbumin uses calcium to form _________________ bonds that tend to make the molecule resistant to thermal unfolding
intramolecular ionic
Milk protein that is more stable to heat in the presence of calcium: ____________
a-lactalbumin
Bovine Serum Albumin isolated from milk is identical to BSA from ___________
blood serum
Where is bovine serum albumin synthesized?
- Not synthesized in the mammary gland
- Enters milk through the bloodstream
_________ has 17 disulfide linkages, 1 free sulfhydryl group, and no phosphorus
Bovine Serum Albumin
In blood plasma, _______ is a carrier of free fatty acids
albumin
Which molecule binds hydrophobic molecules in milk?
albumin
________ and ________ are used in the manufacture of paper for coating to improve the adhesion of ink to the surface, in waterproof glue, to make fabrics water-repellent, etc.
Caseins
caseinates
_______ is recovered by coagulation, achieved by _______ or _______ treatment
Casein
acidification
enzymatic
Acid coagulation of casein is achieved by ________________ or by direct addition of acids to the milk at 35-50oC to attain a pH of 4.5
lactic acid fermentation
_________ coagulation is achieved at 45oC, while _________ coagulation is achieved from 35-50oC
Enzymatic
acid
To terminate enzymatic coagulation, the milk is ___________
heated to 65oC to inactivate the enzyme
Following coagulation of casein, it is separated from the milk in a ___________, _____, and ______
sedimentation centrifuge
washed
dried
Enzymatic coagulation produces ________, while acid coagulation produces ________
rennet casein
acid casein
To produce a casein product that is soluble or readily dispersible, the casein is dispersed in ______ and treated with ______ at 90oC and pH 6.2-6.7
water
alkali
What is the product of casein solubilization?
Sodium caseinate or calcium caseinate
Following its solubilization, sodium caseinate is ________
spray-dried
______ is considered valueless since it is too high in salt to be consumed in large amounts
Whey
Spray-dried _____ and ___ products are used in formula, baked goods, candies, beverages, and animal feed
whey
whey
(WPC/WPI) contain less protein than (WPC/WPI)
WPC
WPI
How is whey usually dried? What is a technique that can reduce the cost?
- Spray drying
- Reverse osmosis
Reverse osmosis is used for the drying of ________, using a ___________ that holds back _____________
whey
perm-selective barrier
proteins, lactose, salt
In __________ the pressure exceeds the osmotic pressure
reverse osmosis (hyperfiltration)
Whey protein concentrates are produced by ____________
ultrafiltration
What does ultrafiltration allow to pass through?
Lactose, salt, water
Holds back proteins
The amount of lactose removed in whey processing depends on the ___________ and _____________
the number of ultrafiltration stages
the amount of wash water
Which method is highly detrimental to whey?
- Steam injection
- Precipitation of the denatured proteins
- Sedimentation centrifuge
- Drying
For the recovery of _____ from whey protein concentrations, the filtrate obtained in the _________ step can be concentrated by _________using a membrane the selectively holds back the lactose while allowing the ____ to pass through
lactose
ultrafiltration
reverse osmosis
salts
The lactose concentrate recovered from reverse osmosis is _____ and cooled slowly to induce ____________
seeded
sugar crystallization
Lactose can be recrystallized to yield a _________, which is used as a ________
raffinate
filler in tablets
___________ require extensive processing (ultrafiltration, microdialysis, and ion exchange) to obtain a highly-purified protein
WPI
___________ are produced by the enzymatic treatment of WPI to break the proteins into peptides that are more easily digested, while the nutritional quality of the protein remains high
Whey protein hydrolysates
____________ are less likely to trigger allergic reactions than _________________; they are used often in infant formulas
Whey protein hydrolysates
non-hydrolyzed whey protein
