Proteins Flashcards
What are the various nutritional roles of proteins?
- provide amino acids 2. give nitrogen 3. give energy (debatable)
Complete : nutritionist approach proteins for their ___ while food scientist approach protein for their ___
- nutritional value 2. functionality
What is a protein functionality?
the function or property the protein give in a food product.
What is one function of the protease in food processing
tenderize meat
What is one function of the lipases in food processing
flavor development in cheeses
What is one function of the amylases in food processing
to manufacture corn syrup/sugars
What is one function of the glucose oxidase in food processing
to remove the head space oxygen from food packages.
What is the amino acid you loose when roasting cereals?
lysine
What is surimi?
crab meat analog made from pollock
T or F : Only compounds that have an amino (NH2) and a carboxylic acid (COOH) group attached to the same carbon (the alpha-carbon) are considered to be amino acids.
T
complete : at low pH, the amino acid is ____
protonated (COOH/NH3)
Complete : since amino acid have both a base and an acid they are ___
ampholytes or amphoteric
T or F : structure at the isoelectric point is neutral
false, it is a zwitterion but it is not neutral.
What is the form of the amino acid glycine at neutral pH
What is the form of the aa glycine at low pH ?
What is the form of the aa glycine at high pH ?
Can a zwitterion be neutral?
Zwitterions are simultaneously electrically charged and electrically neutral.
What are the three physical properties of amino acids at the pI
- decompose at high temperatures
- soluble in water
- have a crystalline structure
What is the only amino acid that doesn’t have a asymetric carbon?
Glycin (2H)
What are optical isomers?
mirror images of a compound. They are not superimposable (cannot be flipped over to superimpose unpon one another.
Complete : since the alpha carbon is asymetric, the a.a. show _____ and rotate ____
optical isomerism
plane-polizired light in opposite directions
What is the reference compound that was determined to give the configurations D and L?
Glyceraldehyde.
The glyceraldehyde is L, when the OH is on the ____, the aldehyde is on the ____ and the alcohol is on the ___
OH on the left
aldehyde on the top
alcohol on the bottom
In L amino acid, the ___ is on the left, the ___ is on the top, and the ___ is on the bottom
NH3 on the left
Carboxylic on the top
R group on the bottom
What enamtiomer is this glyceraldehyde?
L
Which enamtiomer of amino acid is this?
L-amino acid
which enamtiomer of amino is this?
L
T or F : all proteins are synthesized from the D amino acids
false, in the L form
What amino acid supplement should you buy (assume same price), synthetic or the ones from protein hydrolysis
The one from protein hydrolysis because if you take synthetic 50% of the amino would be in the D-form (unusable). (racemic mixture)
What is a racemic mixture?
In chemistry, a racemic mixture, or racemate (/reɪˈsiːmeɪt, rə-, ˈræsɪmeɪt/), is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule.
What are the 7 categories of amino acids?
(1) Amino acids that have aliphatic side chains
(2) Amino acids that have hydroxylic side chains
(3) Amino acids that have carboxylic side chains
(4) Amino acids that have basic side chains
(5) Amino acids that have aromatic side chains
(6) Sulfur-containing amino acids
(7) Imino acids
What are the three amino acids with OH groups
- serine
- threonine
- tyrosine
What are diester linkages?
linkage with one phosphate group in between two hydroxyl amino acids (either serine threonine or tyrosine). These bonds play a role in the 3D structure of proteins and make them less susceptible to denaturation.
Why are casein stable to heat?
because of the presence of diester linkages.
Which are the three amino acids that can be glycolysated or phosphorylated?
the ones with an OH group (hydroxyl group). Threonine, tyrosine and serine
What is the linkage between a sugar and a serine ?
o-glycosidic linkage
Complete : proteins that contains significant amounts of aspartate and glutamate will have a ____ isoelectric point
low
T or F: At pH 7 and above, most of these free carboxyl groups would be negatively charged - affects protein conformation as a function of pH.
under certain conditions, when the amino acids are burried inside the proteins, the proteins structure can sheild the COOH from ionization.
what are the two amino acids from which an NH2 can be added to form two new amino acids
glutamatic acid —> glutamine
asparatic acid –> asparagine
What are the amino acids that can participate in the non-enzymatic browning?
all the amino acids with a amine in their side chain. (lysine, glutamine, asparagine, histidine, arginine)
What are the two conditions that can cause the asparagine or glutamine to be hydrolyse into aspartic or glutamic acids
heat and acidic contions.
What is the reaction by which the asparagine become aspartic acid?
What is the reaction by which the glutamine become glutamate?
Which one is more polar : positive polar amino acids or negative polar amino acids
the positive (amide groups) are more water solulble
What is the link between the sugars and the amide bonds in the maillard reactions
N-glycosidic bonds
Which group of amino acids have has higher pka value?
the amino groups.
What is the name of the very basic group on the amino acid arginine
guanidino group
what is the name of the group in the histidine
imidazole
What is the name of the group that is particular in proline and hydroproline
imino.
What is the function of the proline and hydroxyproline (imino amino acids)
interrrupt the natural tendency of the alpha helix.
What are the two reactions responsible for the odors in putrefaction?
deamination and decarboxylation of free amino acids
T or F : the peptide bond can happen naturally
false, needs enzymes
what is the convention to write the chain of proteins
n on the left and c on the right
T or F : the peptide bond can rotate
false.
What is the reason of the secondary structure?
the peptide bond can’t rotate (charality) and creates an angle of 6˚ and causes stearic hindrance
Where are the hydrogen bonds in the a-helix
between the nitrogen of one amino acid and the carboxylic of 4th amino acids after
Complete : The helical structure is stabilized by _______ due to the repetitive proximity of the peptide carbonyl oxygen (electron-rich) and the hydrogen from the peptide nitrogen four residues away.
hydrogen bonding
What is the sequence that is responsible for the helical structure of the amino acid chain
P-N-P-P-N-N-P-
What are the two amino acid that doesn’t participitate in the helical structure
proline and hydroxyproline
What is the sequence of the ß-sheets
-N-P-N-P-N- (alterning polar and non-polar amino acids)
How many amino acids is there in the ß-strands?
5-15 amino acids
What are the three secondary structures configurations
- alpha-helix
- ß-sheets
- suprahelix
What is the difference in configuration of the anti-parallale and parallel beta-sheets ?
in the parralel ß-sheets, the R groups are pointing in the same direction.
What are the three amino acids that are in the suprahelix 2˚ structure
proline, hydroxyproline and glycine.
complete : structures that alternate the polar and non polar amino acids have the propensity to form ____
ß-sheets
What bonds are responsible for the secondary structre
hydrogen bonding
what bonds are responsible for the tertiary structure
- electrostatic bonds (ionic bonds between the r chains that are positive and negative)
- hydrogen bonds
- disufide bonds (covalent)
4 hydrophobic interactions and van der waals interactions
What is the amino acid responsible for the disulfide linkages?
cystein
T or F : the tertiary structure give the enzyme its functionality
true
T or F : the 4˚ contains S-S bonds
false
What are the bonds/forces in the 4˚ structure
- electrostatic bonds (ionic bonds between the r chains that are positive and negative)
- hydrogen bonds
- hydrophobic interactions
- van der waals
