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food chem
Proteins
| 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 |
Created by:
kemplea
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