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Food Chemistry 1 > P2. Structure + classification > Flashcards

P2. Structure + classification Flashcards

1
Q

proteins are continually being synthesized and broken down in any living system - consequently, there are ____ _______ ______ and _________ present in most food systems

A
  • free amino acids
  • peptides
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2
Q

most famous flavor potentiator? has been linked with ?

A

monosodium glutamate (MSG)
- has been linked to Chinese Restaurant Syndrome –> may affect portion of the population adversely

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3
Q

what are used extensively as flavoring agents to provide meaty or brothy flavour to soups, etc.?
- example?

A

protein hydrolysates (acid or enzymatic hydrolysates)
- soy sauce

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4
Q

meat also contains an appreciable amount of _____ ________ _______, which provide flavor as well as a source of __________ reactions products

A
  • free amino acids
  • Maillard
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5
Q

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

A
  • sulfur containing amino acids (methionine, cysteine)
  • hydrogen sulfide (H2S)
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6
Q

bitter flavors can arise in proteinaceous systems (like cheese) due to what?

A

low molecular weight hydrophobic peptides

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7
Q

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 ________ _______

A
  • putrefactive
  • deamination or decarboxylation
  • microbial enzymes
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8
Q

what is putrefaction?

A

when microbial enzymes degrade proteins into free amino acids and it releases odors

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9
Q

what is the primary structure of proteins?

A

L-amino acids are linked together in a unique manner, by means of a peptide bond
(chain of connecting amino acids)

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10
Q

what is a peptide bond?

A

special form of amide bond where alpha amino group is linked to the alpha carboxyl group of the next amino acid

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11
Q

each polypeptide chain starts on __-hand side with free ________ group –> which terminus?
vs polypeptide ends on __-hand side with free _______ group –> which terminus?

A
  • starts on L-hand side with free amino group –> N terminus
  • ends on R-hand side with free COOH group –> C-terminus
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12
Q

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 ______

A

double bond
- restricted to a maximum angle of 6°
- effectively planar

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13
Q

peptide bond: which 2 atoms are always trans to each other?

A

oxygen of carboxylic group and H of amino group

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14
Q

does primary structure contribute to protein functionality?

A

not really…

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15
Q

3 main types of secondary structure

A
  • alpha helix
  • beta sheet
  • suprahelix
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16
Q

if the primary structure were the only structure available, all proteins would be highly _________ (_____ and _______)

A

asymmetric
- long and thin

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17
Q

due to (2 + 1 ish), the protein polymer elongates and tends to _______ upon itself, producing a ?

A
  • L-chiral form of amino acids
  • and steric hindrance
  • (also the 6° rotation of peptide bond)
  • twist upon itself
  • producing a helical structure
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18
Q

how is helical structure stabilized?

A
  • by hydrogen bonding due to repetitive proximity of peptide carbonyl oxygen (e- rich) and H from the peptide nitrogen 4 residues away
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19
Q

H-bonding in alpha helix acts as a __________-like force to lock protein in helical conformation where each turn of helix involves _____ aa residues

A
  • zipper-like force
  • 3.6
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20
Q

what repeating sequence of polar and non-polar aa residues favors formation of alpha helical structure?

A

PNPPNNP

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21
Q

which 2 amino acids don’t contribute to helix formation? why not?

A
  • proline and hydroxyproline
  • because they don’t have true amine group to contribute
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22
Q

if proline or hydroxyproline is present in the aa chain, the helical structure will be ________ at that point

A

disrupted

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23
Q

silk of spiders/insects contain lots of ?

A

beta-sheet structure

24
Q

what are b-strands?
+ how many aa residues in length?

A
  • extended structure involving hydrogen bonding btw segments of the polypeptide chain
  • 5-15 aa
25
Q

formation of beta sheet favored by what sequence of polar and non-polar aa residues:

A

NPNPNPN

26
Q

what are the 2 subforms of beta sheets?

A
  • parallel
  • antiparallel
27
Q

differences (2) between parallel and anti-parallel beta sheets

A

Parallel:
- N terminals are on same side
- angled H-bond
Antiparallel:
- N and C terminals are on same side
- straight H-bond

28
Q

stability difference between alpha helix and beta sheet?

A
  • beta sheets closer together than alpha helix = more stable but not as soluble as alpha helix
29
Q

suprahelix is found in _______ –> very _______, ________ protein

A

collagen
- tough, inelastic protein

30
Q

what is a suprahelix? (2)
- large amounts of which aa?

A
  • major structural animal protein composed of large amounts of glycine and proline/hydroxyproline
  • 3 separate macromolecules, of which 2 are identical are intertwined to form a suprahelix
31
Q

suprahelix:
- the basic unit is ____________, the suprahelix is held together by ___________ btw chains, with H-bonds being supplied by _______

A
  • topocollagen
  • H-bonds
  • glycine
32
Q

disrupted collagen is extensively used in food industry as a _________ ______ (ie: __________)

A
  • gelling agent
  • gelatin
33
Q

what is the protein’s tertiary structure? Goal?

A

the way the whole peptide chain folds itself into its 3D shape to reduce its free energy

34
Q

tertiary structure:
if protein has large number of hydrophobic aa, they will prefer to be in a __________ environment and will tend to ____________ with each other if exposed to a _______ environment, creating a tertiary structure with a __________ core

A
  • hydrophobic
  • associate with each other if exposed to a polar environment
  • hydrophobic core
35
Q

tertiary structure:
1. groups that have opposite charges such as (2), can form _________ bonds (at pH 7)
2. additional H-bond can take place any time ?
3. ________ bonds can also form –> typically a _________ linkage btw 2 ___________

A
  1. COO- and NH3+
    - electrostatic bonds
  2. anytime a H and O are in proximity
  3. covalent bonds
    - typically disulfite linkage (S-S) btw 2 cysteines
36
Q

what are the 5 types of bonds that maintain tertiary structure?

A
  • hydrophobic interactions
  • van der waals interactions
  • hydrogen bonds
  • disulfite bridge
  • ionic bond/electrostatic interaction
37
Q

as a globular protein is synthesized in cell:
3 steps

A
  • elongation represents primary structure
  • would then form into alpha-helix
  • then form specific tertiary structure that depends on its environment and types of bonding available to take a shape that produces the lowest free energy form
38
Q

what is the quaternary structure of proteins?

A

represents 2 or more tertiary globular proteins associating as a group to form dimers, tetramers or octamers

39
Q

what are the forces/interactions contributing to quaternary structure/difference btw tertiary structure? (IMPORTANT)

A
  • same as tertiary structure except no covalent bond/disulfite bonds: electrostatic, h-bond, hydrophobic, van der waals
40
Q

secondary structure refers to _______, ________ arrangements in space of ________ aa residues in polypeptide chain
- maintained by __________ btw (2)

A
  • regular, recurring arrangements
  • adjacent aa
  • maintained by H-bonds between amide H and carbonyl O of peptide backbone
41
Q

what are simple proteins?
what are the 6 classes of simple proteins?
which are the 2 of most interest from food science perspective?

A
  • proteins made up of only amino acids
    1. albumins
    2. globulins
    3. glutelins
    4. prolamines
    5. scleroproteins
    6. histones
  • albumins and globulins
42
Q

what are albumins, globulins, glutelins soluble in? + examples

A
  1. albumins: soluble in neutral distilled water
  2. globulins: soluble in neutral, dilute salt solutions, but NOT distilled water
    ex.: b-lactoglobulin from milk + myosin/actin from meat
  3. glutelins: soluble in dilute acid or base, but NOT neutral solutions
    ex.: glutenin from wheat
43
Q

what are prolamines, scleroproteins and histones soluble in? + examples

A
  1. prolamines: soluble in 50-90% ethanol and insoluble in water
    ex.: gliadin from wheat (generally hydrophobic)
  2. scleroproteins: insoluble in water and neutral salts –> resistant to enzymatic hydrolysis –> generally structural proteins that anchor bone and tissue (keratin, collagen)
  3. histones: contain large amounts of lysine and arginine = basic –> soluble in water and precipitated by ammonia
44
Q

what is beta-lactoglobulin soluble in?

A
  • globulin
  • soluble in neutral, dilute salt solutions. not distilled water
45
Q

what is collagen soluble in?

A
  • scleroprotein
  • insoluble in water and neutral salt
  • resistant to enzymatic hydrolysis
46
Q

what is glutenin from wheat soluble in?

A
  • glutenin
  • soluble in dilute acid or base, but not neutral solutions
47
Q

what are conjugated proteins?

A

proteins that contain additional chemical moieties other than aa

48
Q

the non-aa component of a conjugated protein is called ___________ _______ –> can drastically modify (2) properties of a protein

A
  • prosthetic group
  • physical and chemical properties of a protein
49
Q

4 classes of conjugated proteins

A
  1. lipoproteins (FA or lipid)
  2. glycoproteins (sugar moiety)
  3. metalloproteins
  4. phosphoproteins (phosphorus group)
50
Q

Lipoproteins:
- proteins complexed with ? generally (2)
- abundant in nature?
- emulsifying properties?
- ex.:

A
  • lipids, generally TG and phospholipids
  • yes!
  • good emulsifying properties
  • ex.: egg yolk proteins and some milk proteins
51
Q

glycoproteins:
- proteins complexed with ? which can range from what to what?
- conjugated moiety generally attached to what? by what bond? (2 answers)

A
  • with carbohydrates, ranging from simple sugars to hetero/polysaccharides
  • to OH group of serine or threonine by O-glycosidic bond OR to amide group of asparagine by N-glycosidic linkage
52
Q

metalloproteins
- proteins complexed with a ________ _____ which is generally loosely _______
- examples:
- numerous ______ have ______ ______ as prosthetic groups

A
  • metal ion, loosely chelated
  • Fe2+ in myoglobin and hemoglobin, where Fe2+ is chelated by porphyrin ring structure
  • enzymes have metal ions
53
Q

phosphoproteins:
- proteins conjugated to ________ ________
- best examples are (2)
- _______ group is generally linked to proteins by the ____ group of (2 aa)

A
  • inorganic phosphates
  • casein and rennin enzyme
  • phosphate group linked by OH group of serine or threonine
54
Q

casein has a lot of ______ _______ which can sequester _______

A

inorganic phosphates
- sequester calcium

55
Q

many proteins contain ________ prosthetic groups.
- proteins then become very complex in terms of ________ makeup and _________ + more susceptible to its ____________

A
  • 2 or more
  • chemical makeup and reactivity
  • environment

Food Chemistry 1 (22 decks)

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