lecture 6-physiochemical and functional properties Flashcards
what functional properties does size affect? and in what way
- solubility→ smaller protiens are more soluble
- foaming capacity→ smaller protiens have a higher more rapid forming foaming capacity
- emulsifying capacity→ smaller protiens are better in emulsions
- viscosity→ larger protiens increase viscosity due to network formation
- swelling power→ larger protiens form more stable gels due to their network forming ability
What affects the charge of protiens
the amino acid composition (only 5 out of 21 AA are charged), and the nature and number of ionizable R groups (side chains) of some amino acids
explain how an amino acid is amphoteric
amphoteric means the amino acid can act as an acid and base this is because it has two ionizable groups; the amino group which can accept a proton and the carboxyl groupo which can donate a proton. only the terminal groups can ionize since not involeved in peptide bonds
how is a zwitterion formed?
In an aqueos solution amino acids can loose a proton from the carboxyl group and gain a proton on the amino group making a zwitterion which has a positive and negative charge
what can amino acids do in their zitterion form?
They have a buffering capacity as they can act as an acid or base and can therefore help maintain the pH
what happens to protiens in an acidic medium and what is the net charge and result of this?
In an acidic enviroment there is a lot of protons (H+) floating around and the basic groups on the protien (amino group) can accept these protons resulting in the protien gaining positive charges. The result is a net positive charge, allowing for repulsion
what happens to protiens in a basic medium and what is the resulting net charge?\
In a basic medium there are fewer protons floating around so the acidic group (COOH) will loose their protons (COO-) this means the protien will have more negative charges because the acidic proton donated their protons and the result is a net negative charge.
in acidic and basic medium which groups are dissocaited?
acidic medium= basic groups
basic medium=acidic groups
if the isoelectrical point happens at a pH less than 7 what does that mean
the number of acidic groups is greater than the number of basic groups and the protien is nuetral at an acidic pH
if the isolectrical point happens at a pH more than 7 what does that mean?
the number of basic groups is greater than the number of acidic groups and the protien is neutral at a basic pH
in terms of hydrophobicity what is generally true in a folded protien?
the hydrophorbic residues are in the core so solvent getting to there is low and hydrophilic residues are located at the surface and can be easily acessed by solvents. There are some hydrophobic groups that can be located on the surface but this should be kept to a minimum as it can affect function
what is hydrophobicity responsible for forming?
the formation of irreversible aggregates after denaturation. When a protien is denatured the protien is unfolded exposing the hidden hydrophobic groups which can stick to other hydrophobic patches on other protiens resulting in protiens clumping together= aggregation. These aggregates are irreversable, this can negatively affect the protiens stability
what is the only amino acid with free SH to form disulfide bonds?
cystine
how are disulfide bonds beneifiicla to protiens
They add covalent crosslinks to the protien which increase stability.
what is the process of breaking and forming disulfide bonds?
oxididation-reduction process
what is denaturation and what is the result?
the process that changes the molecular structure of a protien without breaking any peptide bonds (loss of 4,3,2 structures), this results in loss of biological activity and significant changes in some physical/functional properties like decrease in solubiluty
how is denaturation caused?
Physically done by:
- temperature which breaks hydrogen bonds
- pH breaks electrostatic and hydrogen bonds
- UV light breaks disulfide bonds
- mechanical stress breaks hydrogen bonds
CHemically done by:
- organic solvents which break ionic and hydrogen bonds
- gunidine hydrochloride
- detergents like SDS which break hydrogen bonds
- salts and urea which break ionic bonds
what are the 2 types of denaturation
- reversible: once denaturing agent is removed the orginal interactions between amino acids can return the protien to its orginal conformation and can resume function like when I straighten my hair
- irreversible: it cannot be reversed this can be because unfolded peptide chain is stabilized by interactions with other chains, unfolding reactive groups may be exposed that before were blocked or burried or disulfide bonds have formed like in the case of egg white being heated
what are advantages/uses of denaturation of protiens?
- can destory enzyme activity which is important in food processing
- can destroy ANF
- can change texture which may be desired
what is protien aggregation?
it is the process by which misfolded protiens (denatured protiens) adopt a conformation that causes its polymerization into aggregates, basically means protiens clump together
what are the driving forces in protien aggregation?
covalent (disulfide bonds) and non covalent cross links (ionic, hydrogen, hydrophobic and van der waals interactions)
what is a benefit of aggregation or a use of it?
increases viscosity, allows for emulsions to be formed and be stabled as well as for gels
what is a disadvantage of aggregation?
It is related to harmful subtance AGE (advanced glycation end products) which is the result of sugars interacting with protiens/fats in the bloodstream. High levels are linked to inflamation, oxidative stress, alheizmers, diabetes, heart disease, renal failure
what are factors that affect aggregation and how so
- temperature→ increased temperature→denaturation→increased aggregation
- pH→at pI more easiliy will protiens aggregate
- ionic strength
- concentration
- pressure→high pressure→change in protien structure→aggregation
- protien source
- mechanical stress→ more collisions→greater chance of aggreagtion
