P2. Structure + classification
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proteins are continually being synthesized and broken down in any living system - consequently, there are ____ _______ ______ and _________ present in most food systems
• free amino acids • peptides
most famous flavor potentiator? has been linked with ?
monosodium glutamate (MSG) - has been linked to Chinese Restaurant Syndrome –> may affect portion of the population adversely
what are used extensively as flavoring agents to provide meaty or brothy flavour to soups, etc.? - example?
protein hydrolysates (acid or enzymatic hydrolysates) - soy sauce
meat also contains an appreciable amount of _____ ________ _______, which provide flavor as well as a source of __________ reactions products
• free amino acids • Maillard
which type of amino acids provide flavor or bad smell due to their breakdown when being cooked, mainly due to the release of _______ _______ and its reaction products
• sulfur containing amino acids (methionine, cysteine) • hydrogen sulfide (H2S)
bitter flavors can arise in proteinaceous systems (like cheese) due to what?
low molecular weight hydrophobic peptides
amino acids are generally considered to be precursors of __________ odors and flavors in meat and fish - these odors and flavors are due to compounds produced by enzymatic _________ (IMPORTANT) or ________ of free amino acids by ________ _______
• putrefactive • deamination or decarboxylation • microbial enzymes
what is putrefaction?
when microbial enzymes degrade proteins into free amino acids and it releases odors
what is the primary structure of proteins?
L-amino acids are linked together in a unique manner, by means of a peptide bond (chain of connecting amino acids)
what is a peptide bond?
special form of amide bond where alpha amino group is linked to the alpha carboxyl group of the next amino acid
each polypeptide chain starts on __-hand side with free ________ group –> which terminus? vs polypeptide ends on __-hand side with free _______ group –> which terminus?
• starts on L-hand side with free amino group –> N terminus • ends on R-hand side with free COOH group –> C-terminus
peptide bond has a partial _______ _________ character - so, rotation of peptide bond is __________ to a maximum of ___ ° –> so the -C-CO-NH-C unit is effectively ______
double bond - restricted to a maximum angle of 6° - effectively planar
peptide bond: which 2 atoms are always trans to each other?
oxygen of carboxylic group and H of amino group
does primary structure contribute to protein functionality?
not really…
3 main types of secondary structure
• alpha helix • beta sheet • suprahelix
if the primary structure were the only structure available, all proteins would be highly _________ (_____ and _______)
asymmetric - long and thin
due to (2 + 1 ish), the protein polymer elongates and tends to _______ upon itself, producing a ?
• L-chiral form of amino acids • and steric hindrance • (also the 6° rotation of peptide bond) • twist upon itself • producing a helical structure
how is helical structure stabilized?
• by hydrogen bonding due to repetitive proximity of peptide carbonyl oxygen (e- rich) and H from the peptide nitrogen 4 residues away
H-bonding in alpha helix acts as a __________-like force to lock protein in helical conformation where each turn of helix involves _____ aa residues
• zipper-like force • 3.6
what repeating sequence of polar and non-polar aa residues favors formation of alpha helical structure?
PNPPNNP
which 2 amino acids don’t contribute to helix formation? why not?
• proline and hydroxyproline • because they don’t have true amine group to contribute
if proline or hydroxyproline is present in the aa chain, the helical structure will be ________ at that point
disrupted
silk of spiders/insects contain lots of ?
beta-sheet structure
what are b-strands? + how many aa residues in length?
• extended structure involving hydrogen bonding btw segments of the polypeptide chain • 5-15 aa