protein 2 Flashcards
What is the name of the proteins that are made of only amino acids
simple proteins
Complete : albumins are soluble in _____
neutral distilled water
Complete : globulins are soluble in _____ and insoluble in ____
neutral dilute salt water
Glutelins are proteins that are soluble in _____ but not in _____
acid or base insoluble in neutral solutions
prolamines are proteins that are soluble in ____ and insoluble in _____
50-90% ethanol water
histones are proteins that are soluble in ____ and precipitated by ______
soluble in water precipitated by ammonia
What are the proteins that are the most interest from the food science perspective
albumins and globulins
What are the two major amino acids compose the histones
arginine and lysine
Scleroproteins are proteins that are insoluble in _____ and in _____ and resistant to ____
water and neutral salts resistant to enzymatic hydrolysis
What are conjugated proteins?
proteins that contain a non-amino acid part (prostetic group)
What are the 4 classes of conjugated proteins seen in class
- metalloproteins ** 2. phosphoproteins 3. glycoproteins 4. lipoproteins
What is a prosthetic group?
group attached to a protein that is not an amino acid.
In the case of glycoproteins. what is the amino acid that the sugar will be attached ti if it forms a o-glycosidic bond
serine, tyrosine (but aromatic doesn’t favor tyrosine) threonine
T or F : lipoproteins can make great emulsifiers
true, because they are often attached to phospholipids
In the case of glycoproteins. what is the amino acid that the sugar will be attached ti if it forms a n-glycosidic bond
asparagine
What are the two amino acid that can link the phosphate for the phosphoproteins
OH group of serine and threonine
T or F : the more the protein are susceptible to their environment and the more they can be complex
true
T or F : proteins are more sensitive to their environment than lipids and carbohydrates
true
What is the definition of denaturation
change in the structure or the conformation of a protein because of the distruction of the forces between a.a. Does not involve breaking the peptide bond
What are the interactions that denaturation disrupt?
- hydrogen bonds 2. electrostatic bonds 3. hydrophobic bonds 4. van der waals 5. covalent bonds (only the S-S not the peptidic)
what are the variables of the sensitivity to denaturation?
- chain length 2. amino acid composition 3. complexity of structure 4. prosthetic groups 5. environmental conditions
T or F : denaturation can be reversible if it the bonds didn’t destroy in the 2˚ structure
true
When the conformation of a protein is changed, many of its _____ properties are also changed
physical
(2) Denaturation of protein generally results in a reduction in its _____
solubility
Why do we digest food more easily when we cook it?
because we make the peptides bonds more accessible by the denaturation
What is the most important factor contributing to denaturation
heat
why does caseins don’t denature easily
because they have little to no secondary structure.
What are the factors that can lead to denaturation
- changes in pH 2. changes in ionic strength (hydrogen bond breakers) 3. chemical agents (ethanol/acetone, urea) 4. Detergents 5. organic solvents 6. surface forces 7. combination of the above
Proteins with significant quantities of _____(3 amino acid) are especially susceptible to changes in pH
aspartic acid, glutamic acid and lysine
Why does urea can denature proteins?
because the NH2 compete with the peptide linkage for hydrogen bonds that can readuly disrupt the 3˚ and 2˚ structures.
how does acetone and alcohol works to disrupt the h-bonds in a protein
partial dehydration of the protein.
T or F : casein can be denatured by heat
false
How can you take all the protein out of solution of milk?
with boiling (whey proteins) and acid (casein)
Which one is the more severe in the structure modification : urea or acteone/alcohol
urea
How does detergents work in denaturing proteins
they have both hydrophilic and hydrophobic parts so they open the structure of the protein.
Complete : SDS is a ____ and results in the opening of the structure of the protein
detergents
How does organic solvent works to denature proteins?
they turn the environment hydrophobic so the protein’s hydrophobic region can be exposed
T or F : in a organic solvent, lipase can add FFA to glycerol
True in some cases
How does surface force denature proteins?
air bubbles are incorporated into the proteins. The hydrophobic part is is facing the air and this change in arrangement cause denaturation. (foaming)
What are the protein reactions seen in class
- non-enzymatic browning 2. cross-linking 3. formation of lysinoalanine 4.racemization of a.a
What is the definition of hygroscopic
substance tending to absorb moisture from the air.
Which amino acids participate in non-enzymatic browning ?
the major one is lysine. Other that can react at high temperature are arginine, glutamine, asparagine, histidine and tryptophan.
Complete : maillard reaction involves the reaction of an _____ of a ______ and a free ____of an amino acid or the free amino group on a peptide or protein
aldehyde (R-CH=O) group
reducing sugar
amino group
The first product of the maillard reaction is a :
glycosylamine and water
The second product of the maillard reaction is :
amadori compound
What is the problem with the maillard reaction
‘Bound’ lysine causes steric hindrance that limits enzymatic digestion of the protein. The enzyme will not hydrolyse the peptide linkage between the lysine and other neighboor a.a. and you’ll be left with a-L-a that won’t be digested
Roasted cereals would make the PER ___ (decrease or increase)
PER is the weight gain by wt protein consumed. Since lysine is not present, the PER will decrease because less weight gain
What explains the brown color in the maillard reactions
the formation of melanoidin
What is cross-linking?
amide bonds forming between the NH2 and and COOH of SIDE CHAINS of amino acids
What are the two carboxylic amino acids that can participitate in cross-linking reactions
aspartic acid and glutamic acid
What is the indigestible product of the cross-linking and of the maillard reaction ?
cross-linking : hexapeptide (X1-X2-X3
l
X4-X5-X6)
maillard : tripeptide (A-L-A)
In the formation of lysinoalanine, what are the starting amino acids?
Cystine and lysine
The formation of lysinoalanine occurs under alkaline or acidic conditions?
alkaline conditions (OH deprotonate the H from the cystine).
What are the conditions to have a racemization?
alkaline conditions
What are the degradative reactions of proteins?
- proteolysis (break in the peptidic linkage)
- putrefaction (deaminase and decarboxylase)
At lower pHs, the ______ are the most active, while at higher pHs the ______ are the most active.
decarboxylase
deaminases
Why does the putrefaction release odors?
because the decarboxylation and deamination lowers the molecular weight of the proteins and can make them volatile
Complete : cadaverine and putrescine are by-product of ______
putrefaction (decarboxylation)
What is the reaction by wich there is a fishy smell produced in old fish
The enzyme trimethylamine-N-oxide reductase is produced by enzymes
What can you add in bread to make it more moist?
milk proteins
What are the three water form?
- bound water
- hydrate water
- free water
T or F : freezing can cause denaturation
true because of the salt being concentrated.
