lecture 7 Flashcards
(40 cards)
what is acytlation?
a rxn where an acetyl group (CH₃CO) is added to a protein, usually to specific amino acids like lysine( ε-amino group) or the N-terminal of a protein. It replaces the positive amino group with a negative group→result is protien is more negatively charged
what are the effects of acyetlation?
Improves solubility, as the addition of a bulky group, increases repulsion between protiens. It inhibits gelation. And it shifts the pI of the protien to a lower pH meaning it will better dissolve in acidic conditions
what is succinylation
a rxn where a succinyl group (a molecule with two carboxylic acid groups) is added to a protein, usually attaching to amino acids like lysine, histidine, cysteine, tyrosine, serine, or threonine.
what are the effects of succinylation?
This reaction increases protiens negative charge and enhances repulsion as well as increases the hydrophilic nature if the protien. This increases solubility. Improves emulsifying and foaming. As it enhances gelation due to hydrophilic/hydrophobic balance changing and since there are many functional OH groups allows for more crosslinkinh. And it decreases digestability and bioavability
what is phosphorylation?
is a rxn where a phosphate group is added normally from phosphoric acid,this phosphate group will be covalently attached to the protien typically at a OH group called o phosphorylation or amino group(NH2) called N-phosphorylation
what are the effects of phosphorylation?
It introduces a negative charge, which shifts the isoelectrical point to a lower pH. It increases solubility because of increased polarity. This also allows for these amino acids to form cross links, enhancing the stability of gels
what are the sensitivities of pH of O-phosphorlyated resides vs N-phosphorlated?
- o= stable at acidic pH
- stable at basic pH, can be dephosphorylated in acidic pH
how are carboxyamidomethyl formed?
The protien is reacted with iodacetamide at a pH of 8-9, and acetamide will be added which stabilizes the thiol group, preventing disulfide bonds from forming.
what are CAM modiifications used for?
Crucial for identfication and quantification of protien for anylasis as it prevents formation of disulfide bonds, which make the protien easier to denature and digest when working with them in experiments
what happens during the formation of lysinoalanine?
- protiens are exposed to alkaline conditions and heated, the amino acids will undergo chemical changes
- intermediate formations: serine/cystine residues reaction to form unstable intermediates
- serine looses water to form Dehydroalaline
- cystine looses hydrogen sulfide to form dhydroalaline as well
- cross linking with lysine: The ε-amino group of lysine reacts with dehydroalanine to form lysinoalanine through a covalent bond.
what is the result of lysinoalanine formation?
Reduces protien quality as it reduces digestability and bioavability. It is also a saftey concern because it can have potential toxic effects it too high
what is alkylation?
is a reaction where an alkyl group (methyl, ethyl.) is added covantely to the side chain of an amino acid . This is irreversabile
what is the result of alkylation
Impairs nutritional qulaity as it reduces the avaibility of essential amino acids like lysine and cystine for digestability and bioavilibility. They are more resistant to digestive enzymes. they also improve emulsfying as the added groups are better at stabilization due to increased hydrophobicity. In terms of solubility it could decrease or increase solubility based on size of group and nature of group. Overall since they are hydrophobic and the larger they are, they will decrease solubility.
what are the two types of alkylation?
reductive and non reductive (malliard)
what are the steps of reductive alkylation?
- addition of an alkyl group from an aldehyde/ketone will react with α- or ε-amino group at a pH of 9 this will form a schiffs base
- reduction: a reducing agent like borohydride or cyanoborohydride this will “lock in” the schiffs base and it cannot keep going in the malliard rxn
how is a disulfide bond formed and broken
formed through oxidation which links thiol groups on 2 cystine residues. To break this very strong bond it is done via reduction where a free cys is added
what is the benefit of disulfide bonds?
enhances heat stability, viscosity, foaming and gelling properties
what is chemical crosslinking?
it is the covalent attachment of one functional group of a side chain to another molecule which can be intra or intermolecullary
what is the benifit of chemical crosslinking?
it makes it possible to stabilize tertiary and quaternary structures which improves stabilization of foams, gels, and emulsions
explain the cross linking of acidic and basic amino acids
when heated lysine can form covalent cross links with aspartic/glutamic acid which forms an isopeptide bond
what is schiffs base (formula)
R1-CH=N-R2
in short what is the malliard reaction
It is a reaction that occurs during cooking between amino acids and reducing sugars(have aldehyde free), which involves a series of complex reactions that result in the browning of food and the creation of flavours
what are the steps of the malliard reaction?
- formation of schiffs base: a reducing sugar reacts with an amino group foroming a schiffs base
- amadori rearrangement: the schiffs base undergos rearrangment which forms the amadori compound (ketoamine), which is a more stable intermediate
- decomposition: the amadori compounds break down by dehydration and fragmentation into reactive intermediates like dicarbonyl compounds like HMF, pyruvate aldehyde. Which begin to form flavours
- formation of flavor and brown pigments: the reactive intermediates condense and polymerize to form melanodins which are responsible for the brown pigments. These reactions also form flavor compounds
what is the effect of substrate concentration on enzyme activity?
- At low substrate concentrations, the reaction rate (V₀) increases almost linearly as more substrate binds to the enzyme.
- At high substrate concentrations, the enzyme becomes saturated, and the reaction rate approaches a maximum velocity (Vmax).
