Proteins II Flashcards
Proteins that are made up of only amino acids are termed _________
simple proteins
Proteins of most interest from a food science perspective are _______ and ________
albumins and globulins
_________ are proteins that are soluble in neutral distilled water
Albumins
__________ are proteins that are soluble in neutral, dilute salt solution, but not in distilled water
Globulins
B-lactoglobulin from milk and myosin/actin from meat are examples of ________
globulins
_________ are proteins that are soluble in dilute acid or base, but not in neutral solutions
Glutelins
Gliadin from wheat is an example of ___________
prolamines
_________ are proteins that are soluble in 50-90% ethanol and insoluble in water
Prolamines
__________ are proteins that are insoluble in water and neutral salts
Scleroproteins
_________ are proteins that are resistant to enzymatic hydrolysis
Scleroproteins
________ are generally structural proteins (keratin, collagen)
Scleroproteins
_________ are basic proteins, which contain large amounts lysines and arginines
Histones
Histones contain large amounts _______ and _______
lysines
arginines
________ are proteins that are soluble in water and precipitated by ammonia
Histones
_________ proteins contain additional chemical moieties other than amino acids
Conjugated
The non-amino acid component of conjugated proteins is termed the _________ group, and it can drastically modify the properties
prosthetic group
How are simple proteins classified?
Based on their solubility
How are complex proteins classified?
Based on their prosthetic groups
________ are proteins that are complexed with lipids; generally, with triglycerides and phospholipids
Lipoproteins
_______ are abundant in nature and have good emulsifying properties (ex: egg yolk proteins)
Lipoproteins
_______ are proteins that are complexed with carbohydrate
Glycoproteins
In glycoproteins, the carbohydrate is generally attached to the _____ group of ______ or _____ by an __-glycosidic bond
OH
serine
threonine
O
In glycoproteins, the carbohydrate is generally attached to the _____ group of _______ by an __-glycosidic bond
amide
asparagine
N
________ are proteins that are complex with a metal ion, which is generally loosely chelated
Metalloproteins
Fe2+ in myoglobin and hemoglobin, where Fe2+ is chelated by a porphyrin ring structure is an example of a ____________
metalloprotein
Numerous _______ have metal ions as prosthetic groups
enzymes
_________ are proteins that are conjugated to inorganic phosphates
Phosphoproteins
Casein and the enzyme renin are examples of _________
phosphoproteins
In phosphoproteins, the phosphate is generally linked to proteins by the ___ group of _______ or _________
OH
serine
threonine
The more (simple/complex) a protein is, the more susceptible it is to its environment
complex
Proteins are much (less/more) sensitive to their environment than lipids and carbohydrates
more
Proteins can undergo drastic changes in structure (_________) under relatively mild conditions
Denaturation
Does denaturation break peptide bonds?
No, the primary structure remains intact
Denaturation influences the ______ and _______ structures
secondary and tertiary structures
Casein has little _________ structure, and hence does not denature readily even when boiled
secondary
Unfolding of the tertiary structure/unraveling of the secondary structure makes the peptide bonds more accessible to ____________
proteolytic enzymes
Denaturation of a protein generally results in a reduction in _________
solubility
Denaturation results in generally ________ viscosity, and gelation may occur
increased
_________ is no longer possible following denaturation
Crystallization
____________ may be decreased or lost following denaturation
Enzymatic activity
If denaturation is extensive, the __________ form can be completely unraveled and its ________ structure badly disrupted
globular
secondary
When the globular form is unraveled due to denaturation, ___________ groups are exposed, which can react with each other so that _______ or ________ takes place
reactive groups
polymerization
aggregation
Some proteins form _____ when denatured, while others _______
gels
precipitate
In denaturation, milk and acid produces a _____, while heating collagen produces a ______
curd
gel
______ causes denaturation because an increase in kinetic energy of molecules results in the disruption of _____________, which are relatively weak
Heat
hydrogen bonds
A shift in pH affects the overall charge of the molecule, which influences the ______________________ to the _______________, and can cause denaturation
electrostatic bond contribution
tertiary structure
Proteins with significant quantities of ___________, ___________, and ___________ are especially susceptible to changes in pH
aspartic acid, glutamic acid, and lysine
Many soluble proteins ________ when they are subjected to environmental conditions close to their isoelectric point
precipitate
___________ are compounds that can effectively compete with the peptide linkage for hydrogen bonds can readily disrupt both tertiary and secondary structure
Hydrogen bond breakers
Urea is an example of a ___________
hydrogen bond breakers
Hydrogen bond breakers disrupt ____________ and ____________ structures
secondary
tertiary
Urea is commonly used to denature proteins for analysis by __________
electrophoresis
_______ and _______ can disrupt H-bonds by _______________ of a protein
Alcohol
acetone
partial dehydration
The degree of structure modification of alcohol/acetone is (less/more) severe than urea
less
_____________ and _____________ are commonly used to precipitate enzymes from solution for isolation with minimal denaturation
Alcohol
acetone
___________ have both hydrophilic and hydrophobic moieties
Detergents
__________ can bridge the hydrophobic and hydrophilic regions of a protein and result in the opening of the structure of the protein
Detergents
SDS is a ____________ and is often used for analysis by ___________
detergent
electrophoresis
_________________ make the environment hydrophobic, which can turn the protein macromolecule inside out and denature
Organic solvents
_______________ can make enzymes work in opposite ways
Organic solvents
Certain proteins can reduce surface tension, resulting in the formation of a ____
foam
Each air bubble in a foam has a thin __________ that separates the two environments: _________ water and __________ air
membrane
hydrophilic
hydrophobic
At the interface in a foam, protein molecules rearrange themselves to _______________
reduce their free energy
Foods that contain appreciable amounts of protein generally undergo browning when they are heated under _________________________, which is known as the _________ Reaction or ______________
low-moisture conditions
Maillard
Non-Enzymatic Browning
Non-Enzymatic Browning involves the reaction of an ___________ group of a reducing sugar and a _____________ group of an amino acid or peptide or protein
aldehyde
free amino
The initial Maillard reaction forms _________
Glycosylamine
Glycosylamine undergoes a series of reactions called _____________
Amadori rearrangement
Amadori rearrangements involves the loss of _______ from within the sugar portion of the molecule
water
In the Maillard reaction, after the loss of water, the sugar portion undergoes _______ and breaks up ____________ (produces aroma/flavor) that readily polymerize into ___________
scission
low-molecular weight compounds
brown pigments
The brown pigments in the Maillard reaction are called __________
melanoidins
In terms of the protein, the net result of the Maillard reaction is that ______ will be “_______”
Lysine
bound
The “bound” Lysine from the Maillard reaction causes _________ that limits _______________ of the protein
steric hindrance
enzymatic digestion
Enzymatic action will stop ___ amino acid on either side of the bound Lysine, leaving an indigestible ______, which is poorly absorbed and used by the body
one
tripeptide
Non-enzymatic browning can adversely affect the ___________ value of proteins
nutritional
What is PER?
Protein Efficiency Ratio
PER (increases/decreases) due to the Maillard reaction
decreases
What is PER’s equation?
Weight gained/Weight of protein consumed
Amino acids with a ____________ group can also undergo reactions with reducing sugars at high temperatures
secondary amine
Argine, Tryptophan, Histidine, Glutamine, and Asparagine all have a ___________ group
secondary amine
If reducing sugars are mainly absent, the cross-linking of proteins can occur at higher temperatures by the formation of _____ bonds between ____ and _____ groups on side chains of AA
amide
COOH
NH2
Do cross-linking reactions form peptide bonds?
No, since they do not involve an alpha-carbon
Can amide bonds formed from cross-linking reactions be hydrolyzed by digestive proteolytic enzymes?
No, since they do not have peptide bonds
Enzymatic action of cross-linked amide bonds will stop at ___ amino acid on either side of the cross-linked amino acids, leaving an indigestible ___________
one
hexapeptide
The preparation of protein concentrates and isolates often calls for the treatment of proteins with _____ in the presence of ____ to modify their properties
alkali
heat
In harsh conditions, “new” ___________ can form if free AAs are present or produced
amino acids
Is the formation of Lysinoalanine beneficial?
No, since it is unnatural and poorly absorbed; may be toxic (renal failure)
Lysinoalanine is produced under ____________
very harsh conditions
Strongly alkaline environments can lead to ___________ of amino acids
racemization
Racemization converts _________ to _____ mixtures
L-amino acids
D-L
____________ results in the loss of effectiveness of amino acids as building blocks for protein synthesis
Racemization
__________ are abundant in living tissue and are secreted by microorganisms
Proteolytic enzymes
__________ results in a reduction in molecular weight and loss of functionality
Proteolysis
________ may lead to bitter hydrophobic peptides
Proteolysis
__________ causes the tenderization of meat by papain
Proteolysis
_________ is associated with microbial spoilage of high-protein foods
Putrefaction
_________ involves degradation of free amino acids, produced by _______ enzymes secreted by _________
Putrefaction
proteolytic
spoilage microorganisms
The free amino acids are attacked by ___________ and ___________ in putrefaction
microbial deaminases
decarboxylases
________ remove amine groups and _________ remove carboxyl groups from free amino acids in ___________
Deaminases
decarboxylases
putrefaction
The products of _________ are volatile and rather repulsive odiferous compounds
Putrefaction
In putrefaction, at lower pHs, ________ are the most active, while at higher pHs, the _________ are the most active
decarboxylases
deaminases
The deaminase and decarboxylase reactions in putrefaction reduce ________ and increase________
molecular weight
volatility
________ are generally responsible for high-protein systems becoming putrefactive
Microorganisms
_____ are especially susceptible to putrefaction
Fish
Fish undergo an enzymatic reaction that produces putrefactive-like compounds: conversion of ________ to ______ by the enzyme ______________________
TMAO (no smell)
TMA (volatile and putrefactive)
Trymethylamine-N-oxide reductase
Production of ____ in fish correlates well with the rise in the microbial population and the overall rise in putrefactive compounds
TMA
Measuring ____ provides an indication of freshness of fish
TMA
Decarboxylase enzymes are inhibited by ______
DMFO
Most proteins are ____________ and can bind water
hygroscopic
______ proteins play an important role in absorbing and retaining moisture in bread; maintaining a soft texture
Milk
Addition of _____ protein to hamburger helps retain moisture, making the burger juicier
soy
The water-binding capacity is strongly associated with the ____ species present (NH3+ and COO-) and _______ bonding sites (C=O, N-H) that are readily hydrated
ionic
hydrogen
The water-binding capacity may also be associated with the presence of a ___________ in the protein as a _______ group
polysaccharide
prosthetic
Water, having a strong _________________, can form a hydration shell around polar groups
dipole moment
A ______________________illustrates the equilibrium moisture associated with a material as a function of relative humidity at a constant temperature
moisture sorption isotherm
What are the three types of water-binding?
- Bound-water
- Water-associated with bound water
- Free-water
_______________ is hydrogen bonded to the protein or a hydrate of an ionic species, and is an integral part of the molecular structure that cannot be removed
Bound water
________________ is more mobile, yet still somewhat structure
Water-associated with bound water
_______________ is unstructured, quite mobile, and can be removed relatively easily
Free water
________ is the region where proteins show their water absorption capacity
Free water
A protein’s ability to bind water is a function of its __________composition, overall structure (including ______ groups), and ______
amino acid
prosthetic groups
charge
_____________ processes may involve substantial changes in factors that clearly affect protein structure (temperature, pH, ionic strength)
Water-removal
_________ has very little effect on the nutritional quality of proteins because no heat is involved
Freezing
_______ can cause major structural changes in proteins
Freezing
In tissue systems (meat, fish), _________ can cause extensive denaturation due to changes in ionic strength and pH caused by local concentration effects and the removal of water from the microenvironment of the protein molecule
freezing
The extent of __________ is often dependent on the _____ of freezing
denaturation
rate
The changes from freezing are exemplified by the loss of __________________ (manifested by the development of freezer drip) and often result in a loss of desirable texture
water-binding capacity
Deteriorative effects of dehydration processes may be due to _________ and/or _________
denaturation
browning
_____________ is one of the best methods of drying in terms of maintaining protein functionality, nutritional quality, and enzyme activity (expensive)
Freeze drying
What are the two types of water-removal processes?
- Freezing
- Dehydration
There might be ___________ during freezing, but there is little browning due to ________________________
denaturation
low temperature of sublimation
In the case of ______, freeze drying is optimal in terms of retaining water-binding capacity of the proteins
meat
____________ is used extensively for protein solutions (milk, egg whites)
Spray drying
In __________, some denaturation may take place due to higher temperatures and shear at the nozzle
spray drying
In ______________, some browning in the case of egg whites and milk take place due to the presence of glucose and lactose (Maillard reaction)
spray drying
____________ causes extensive denaturation and browning if sugars are present
Drum drying
