Question | Answer |
What do peptides do? | involved in active transport of amino acids
involved in many redox-type reactions |
How many Amino Acids are in polypeptides? | <50 amino acids |
How many Amino Acids are in proteins? | >50 amino acids |
parts of an amino acid | -alpha amine group
-alpha carboxyl group
-R side chain |
taste of L-amino acids | bitter or neutral taste |
taste of D-amino acids | sweet taste |
which stereochemistry of amino acid are mostly susceptible to enzyme-catalyzed polymerization? | L-amino acids |
How are D-Amino acids formed? | made by heat/alkaline treatment (racemization)
-microorganisms provide a source
-these amino acids present in fermented foods/beverages may largely originate from bacteria |
isoelectric point | -pH at which the dipolar ion is electrically neutral |
Zwitter Ion | amino acid where there is no net charge |
pka1 | pH at which concentrations of COO- and COOH are equal |
pka2 | pH at which the concentration of NH3+ and NH2 are equal |
pka3 | pka value of an ionizable group from the R group |
estimation of the isoelectric point of amino acids w/ no charged side chain | (pka1+ pka2)/2 |
estimation of the isoelectric point of acidic amino acids | (pka1 + pka3)/2 |
estimation of the isoelectric point of basic amino acids | (pka2 + pka3)/2 |
which part of the amino acid represents the beginning of the polypeptide? | the amino-terminal group |
Which part of the amino acid represents the end of the polypeptide? | the carboxyl-terminal group |
which part of the amino acid does not participate in peptide bonds? | -The R group
- R remains available for additional chemical reactions |
What are the 2 ways that amino acids are classified? | -according to their polarity
-according to their nutritional aspects |
How do you use polarity to classify amino acids? | -charge of the side chains at physiological pH
-charged and polar
-uncharged and polar
-unpolar and hydrophobic |
How do you classify amino acids by their nutritional aspects? | -essential
-semi-essential
-non-essential |
How is Aspartic Acid (Asp) classified by its polarity? | -has extra carboxyl group
-charged and polar |
How is Glutamic Acid (Glu) classified by its polarity? | -has extra carboxyl group in side chain
-charged and polar |
How is Lysine (Lys) classified by its polarity and its nutritional aspects? | -has extra amino group in side chain
-participates in Maillard Reaction due to extra amino group being highly reactive
-Maillard reaction also needs reducing sugar
-also involved in protein crosslinking via lysinoalanine
-essential amino acid |
How is Arginine (Arg) classified by its polarity and its nutritional aspects? | -can accept another proton
-charged and polar
-non-essential (possibly semi-essential) |
How is Histidine (His) classified by its polarity and its nutritional aspects? | -extra electron pair
-charged and polar
-essential (possibly semi-essential) |
How is Asparagine (Asn) classified by its polarity and its nutritional aspects? | -withdraws electron from amino group, so it can't accept protons
-uncharged and polar
-non-essential |
How is Glutamine (Gln) classified by its polarity and its nutritional aspects? | -uncharged and polar
-non-essential |
How is Cysteine (Cys) classified by its polarity and its nutritional aspects? | - Sulfhydral group is side chain
-can form crosslinks
-uncharged and polar
-disulfide bonds act as covalent bonds in protein structures
-component of keratin
-semi-essential
-synthesis from methionine partially possible |
How is Glycine (Gly) classified by its polarity and its nutritional aspects? | -Hydrogen is side chain
-uncharged and polar
-non-essential |
How is Serine (Ser) classified by its polarity and its nutritional aspects? | -additional hydroxy group in side chain
-partially esterified with phosphoric acid
-part of active site of some enzymes
-uncharged and polar
-non-essential |
How is Threonine (Thr) classified by its polarity and its nutritional aspects? | -has methyl-hydroxide as side chain
-uncharged and polar
-essential |
How is Tyrosine (Tyr) classified by its polarity and its nutritional aspects? | -aromatic ring as side chain
-uncharged and polar
-semi-essential
-synthesis from phenylalanine partially possible |
How is Alanine (Ala)classified by its polarity and its nutritional aspects? | -methyl group as side chain
-nonpolar side chain
-hydrophobic
-non-essential |
How is Valine (Val) classified by its polarity and its nutritional aspects? | -2 methyl groups as side chain
-nonpolar side chain
-hydrophobic
-essential |
How is Leucine (Leu) classified by its polarity and its nutritional aspects? | -non-polar side chain
-hydrophobic
-essential |
How is Isoleucine (Ile) classified by its polarity and its nutritional aspects? | -has 2nd Chiral Carbon in side chain
-non-polar side chain
-hydrophobic
-essential |
How is methionine (Met) classified by its polarity and its nutritional aspects? | -has sulfur in side-chain
-non-polar side chain
-oxygen and heat sensitive
-involved in the sunlight off-flavor of milk
-involved in cooking off-flavor (cabbage-like)
-hydrophobic
-essential |
How is phenylalanine (Phe) classified by its polarity and its nutritional aspects? | -phenolic side chain
-non-polar side chain
-hydrophobic
-essential
-aromatic amino acid |
How is Tryptophan (Trp) classified by its polarity and its nutritional aspects? | -double ring side chain
-non-polar side chain
-hydrophobic
-easily destroyed by oxidative reactions in processing
-essential |
How is Proline (Pro) classified by its polarity and its nutritional aspects? | -amide ring in side chain
-nonpolar side chain
-hydrophobic
-non-essential |
What makes an essential amino acid "essential"? | -amino acids that can't be synthesized by human cells |
What makes a non-essential amino acid? | -amino acids that can be synthesized by human body
-example: by either transamination or amination of keto acids |
What is phenylketonuria? | -inherited invorn error of metabolism
-defect in the enzyme phenylalanine hydroxylase
-causes accumulation of phenylalanine in the brain
-causes mental retardation
-causes epileptic seizure
-incidence of 1 in 10,000 births in caucasians and east asia |
What is phenylalanine hydroxylase? | -enzyme that converts dietary phenylalanine to tyrosine
-this enzyme is lacking in phenylketonuria |
What is the possible cause of mental retardation in PKU? | -phenylalanine transporters in brain all being occupied, so other amino acids can't get through blood-brain barrier
-less synthesis of synapses |
What is a diagnostic tool that is used to determine PKU? | -detection of phenylketones in urine is diagnostic tool
-phenylpyruvate |
Sweetener that contains phenylalanine | -aspartame |
What is tyrosinase? | -enzyme that works in conjuntion w/ tyrosine
-responsible for melanin production
-responsible for formation of skin color
-has 2nd hydroxy group
-converts to quinone
-causes reaction similar to enzymatic browning
-happens after exposure to UV light |
What is tyramine? | -biogenic amine formed by the decarboxylation of tyrosine
-higher concentration may lead to headaches due to interfering w/ receptors in human bodies
-tyrosine decarboxylated
-especially in microorganisms (fermented products like blue cheese |
Which Amino Acid is responsible for formation of sunlight off-flavor of milk? | -methionine
-caused by exposure to UV light and riboflavin as sensitizer
-forms methional |
What is methional? | -product formed by UV-exposure of methionine
-responsible for sunlight off-flavor of milk |
which Amino Acid is responsible for the formation of cabbage-like cooking off-flavor? | -methionine causes this
-caused by dimethylsulfide formation |
Which amino acid can be catalytic active residues in active site of some enzymes? | -serine
-interacts with peptide linkages, so it can eventually be cleaved |
cystine | -disulfide that is formed by the oxidation of cysteine
-can be formed even under mild oxidative conditions |
When can the reduction of cystine to cysteine occur? | -this conversion is possible using borohydride or thiol reagents |
What percentage of cysteine is keratin composed of? | 9-10% |
what amino acid is part of MSG? | -glutamic acid |
monosodium glutamate | -flavor enhancer
-enhances meat flavor
-taste is confirmed by umami
-used as additive in frozen, dehydrated, or canned meat products
-promotes sensory perception of meat-like aroma notes |
What is "China Restaurant Syndrome"? | -hypersensitive people suffer from drowsiness, headache, and stomache ache
-caused by a sensitivity to MSG |
What food ingredients contain Glutamic Acid? | -MSG
-hydrolyzed corn protein
-hydrolyzed soy protein
-hydrolyzed wheat protein
-these ingredients are used as flavor-enhancers and to promote sensory perception of meat-like aroma |
What is lysinoalanine? | -forms crosslinking of proteins
-can be formed at high temps
-can be formed at room temp under alkaline conditions
-additional amino group of lysine involved |
What are biogenic amines? | -bacterial metabolites having their origin from amino acids
-formed by decarboxylation |
What is Histamine? | -biogenic amine formed by the carboxylation of histidine
-found in high concentrations in tuna and mackerel
-found in long-ripened cheese and fermented food products |
What is histadine decarboxylase? | -enzyme responsible for the conversion of histidine to histamine
-found in various bacteria |
Scromboid food poisoning | -also known as histamine fish poisoning
-causes headache, flushing, abdominal cramps, etc.
-not from uncomplicated histamine poisoning, but is generally associated with high levels of histamine (>50 mg/100g) |
What is glutathione? | -major antioxidant in body
-made up of glutamic acid, cysteine,m and glycine
-found in high amounts in beef and broccoli
-involved in active transport of amino acids
-involved in many redox reactions
-hydrophilic |
What is the importance of the Hydrophilic nature of glutathione? | -can be conjugated with xenobiotic compounds
-this allows increase of hydrophilicity for excretion through bile |