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food chem

Proteins

QuestionAnswer
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
Created by: kemplea