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FST 100A > Proteins > Flashcards

Proteins Flashcards

1
Q

When is lipid autoxidation termination favored? What occurs as a result of the reaction?

A

-high levels of radicals present of low oxygen levels
-lipid radical reaction comes to an end, not end of oxidation as a whole
-covalently linked lipids are produced

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2
Q

What three things can initiate lipid autoxidation?

A
  1. transition metals
  2. ionizing radiation (UV light)
  3. heat (reduces energy barrier to break double bond)
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3
Q

Besides autoxidation, name the two other oxidation methods. What happens in them? What are some of their defining features?

A
  1. photosensitizer-induced oxidation = singlet oxygen forms from metal-containing compounds reacting,
    -radical forms at double bond
    -no initiating ROS required
  2. lipoxygenase enzymes = present in many animals/plants
    -contains iron catalytic site to form alkyl radical
    -commonly inactivated by blanching
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4
Q

What five things can inhibit oxidation of lipids?

A
  1. amber bottles = to filter UV light
  2. bleaching = removes photosensitizers
  3. blanching = inactivates oxidizing enzymes
  4. chelators = molecules that bind to metal to make them unable to oxidize lipids
  5. antioxidants = slow rate of oxidation reactions
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5
Q

What are the two antioxidant mechanisms? How do they work?

A
  1. quench singlet oxygen = oxygen returns to triplet/ground state and absorbed energy is dissipated as heat (ex. of quencher = ascorbic acid)
  2. compete for free radicals = antioxidants can neutralize or “quench” free radicals, preventing or slowing down the chain reactions that free radicals can initiate
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6
Q

What kind of compounds are a major class of anti-oxidants? What makes them good anti-oxidants?

A
  1. phenolic compounds
    -form resonance hybrids which stabilizes their radical
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7
Q

What makes an antioxidant good at preventing oxidation?

A

-must easily form radicals, but remain stable

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8
Q

What is a limiting factor in frying? Why are plant lipids not great for frying?

A

-smoke point
-plant lipids oxidize faster

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9
Q

What occurs in a lipid hydrolysis reaction?

A

-can be catalyzed by an acid or base (saponification)
-carbonyl serves as site for nucleophilic attack
-reaction is not stereospecific, all fatty acids are removed

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10
Q

What are the products of a base catalyzed lipid hydrolysis reaction (saponification)?

A

-glycerol and fatty acid soaps

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11
Q

Describe an enzyme-catalyzed lipolysis reactions. What are the products?

A

-lipase enzymes catalyze hydrolysis
-used in lipid digestion
-stereospecific, sn-2 is kept
-produces short-chain fatty acids, monoglycerides, diglycerides, overall amphiphilic molecules

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12
Q

What occurs in an esterification/interesterification lipid reaction? How does it impact the physical properties of lipids?

A

-esterification = condensation reaction (reverse of lipolyis)
-interesterification = fatty acids are removed and randomly reattached to glycerol backbone
-can be carried out by base-catalyzed hydrolysis or lipases as an alternative to partial hydrogenation
-alters crystallization/melting behavior
-creates good shortenings

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13
Q

What occurs in a hydrogenation reaction? What is the product?

A

-a metal catalyst adsorbs diatomic hydrogen and forms hydrogen radicals
-the acyl lipid chain then adsorbs to catalyst by breaking double bond (makes unsaturated fats saturated)
-the hydrogen is added across the double bond
-creates shortenings

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14
Q

What are some of the properties of nonpolar (hydrophobic) uncharged amino acids?

A

-large R-groups = taste bitter
-Tyr and Trp have some minor hydrophilic groups, but they are largely hydrophobic
-smaller R-groups = taste sweet
-Gly and Ala have relatively small interactions with water

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15
Q

What are some of the properties of charged amino acids

A

-bulky but interact well with water
-contain R groups which can be protonated/deprotonated
-acidic = negatively charged, have acidic taste (glutamic and aspartic acid
-basic = positively charged, have bitter taste (arginine, lysine, histidine)

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16
Q

What are some of the properties of polar (hydrophilic) uncharged amino acids?

A

-polar groups are able to form hydrogen bonds
-positive interactions with water
-generally taste sweet
-exception = methionine is hydrophobic and bitter

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17
Q

Describe Aspartame’s structure. What are some of its defining features?

A

-dipeptide of Asp + Phe with methyl groups on carboxylic acid of Phe
-relative sweetness intensity of about 200 (200x sweeter than sucrose)
-used in diet beverages
-hydrolyzes at high temperatures (not good for baking)

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18
Q

Describe some of the features of a peptide bond.

A

-rigid and planar
-limits rotation of bonds about alpha carbon
-almost exclusively in trans-configuration

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19
Q

Protein folding depends on ____________, environmental interactions, and bond formation.

A

-primary structure

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20
Q

Describe the secondary structure of a protein.

A

-alpha helix forms
-intra-coiling hydrogen bonding in backbone
-beta sheets form hydrogen bonds with neighboring portions of strands
-similar R-groups cluster on one side of strands

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21
Q

Describe the tertiary structure of a protein. What three types of proteins fall under this category?

A

-globular = compact, most common food proteins, bury hydrophobic groups in protein core
-fibrous = elongated, mainly hydrophilic, common to have repeating structures linked together
-random coil proteins = less defined structural motifs, often poor water solubility

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22
Q

Describe the quaternary structure of a protein. What are some examples?

A

-can consist of several subunits
-ex. glycinin, hemoglobin, collagen

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23
Q

Describe the general structure of a globular protein? What are some examples?

A

-spherical, hydrophobic core
-highly water soluble
-ex. B-lactoglobulin, alpha-lactalbumin, egg proteins

24
Q

Describe the structure of B-lactoglobulin.

A

-small, B-barrel
-hydrophobic core
-one free cysteine (contributes to gelation)
-can unfold at interface to act as an emulsifier or foam-stabilizer

25
Q

Describe the structure of alpha-lactalbumin.

A

-small, high helix content
-native structure has high heat-stability
-binds calcium to deliver it in body

26
Q

What are the two proteins that make up egg white proteins? Describe their structure/features.

A

-ovalbumin = 2 cysteines available for disulfide bonding, heat denaturation at 70-80 C, forms gel
-ovomucin = large, lots of interaction with water (viscous)

27
Q

Describe the structure of egg yolk proteins.

A

-high content of lipoproteins
-rich in phospholipids

28
Q

Why are eggs good for foam formation? What can inhibit this?

A

-their proteins create disulfide bonds that stabilize air bubbles
-the bonds can then rearrange to form more extensive cross-linking
-metal ions or acid can inhibit disulfide bond formation (prevents over-whipping)

29
Q

Describe the general structure of a fibrous protein? What are some examples?

A

-takes on tertiary and quaternary structures
-highly hydrophilic
-often contains multiple polypeptide chains
-ex. collagen, tropomyosin, actin

30
Q

Describe the structure of collagen.

A

-Gly-X-hPro repeats
-triple helix structure
-high tensile strength
-many structures covalently link to form full collagen molecule

31
Q

Describe the structure of tropomyosin.

A

-mainly extended helices
-hydrophobic seam between helices
-elongated fibers

32
Q

What is a main class of unstructured proteins? Describe its structure/properties.

A

-poorly defined tertiary structure
-insoluble, but forms smaller micelles
-high protein content
-assists in delivery of calcium and phosphate
-calcium phosphate stabilizes alpha/beta casein core and k-casein occupies surface

33
Q

What are the structures/properties of B-casein and K-casein?

A

-B-casein = many prolines, charge, and polar groups prevent globular structure
-K-casein = charged, much more hydrophilic, plays important role in micelle stability and coagulation in dairy

34
Q

What are the two water insoluble proteins found in gluten? What are their structures? What is the general structure of gluten?

A

-gliadin = mainly alpha helices, random coil
-glutenin = larger, mainly random coil with few helices provides strength/elasticity
-gluten has few charged groups, is rich in glutamine, proline, and has a poorly defined tertiary structure
-gluten network forms disulfide bonds in water to create network

35
Q

What effects does protein denaturation have on a protein?

A

-loss of native functionality
-increased entropy
-reduced solubility, hydration, and enzyme activity

36
Q

What five features can induce protein denaturation? How do they do this?

A
  1. temperature = proteins unfold and increase in entropy
  2. pH = alters surface charge, can cause repulsion
  3. salts = binds to charged residues, can cause aggregation
  4. interfaces = hydrophobic interfaces (oil, air) can stabilize hydrophobic regions
  5. solvents = hydrophobic solvents (ethnol) can reduce hydrophobic interactions
37
Q

Which protein is less soluble and more heat stable? Whey proteins or globular plant proteins?

A

-globular proteins are less soluble and more heat stable

38
Q

If the pH of a molecule is above the isoelectric point, the NET charge will be _______________.

A

-positive

39
Q

What does “salting in” mean in the context of denaturing proteins? “Salting out”?

A

-salting in = moderate salt level can improve solubility of proteins
-salting out = too much salt can reduce solubility

40
Q

When are the following proteins soluble?
-albumins
-globulins
-prolamins
-glutenin’s
-fibrous proteins

A

-albumins = soluble in water at neutral pH
-globulins = soluble in dilute salt
-prolamins = soluble in alcohol
-glutenin’s = soluble in a strong acid/base
-fibrous proteins = soluble in hot water

41
Q

How are dairy products formed through curdling?

A

-casein micelle is destabilized
-proteins aggregate and trap fat in the protein network
-acidification and enzyme modification is used

42
Q

How are whole-muscle proteins impacted by cooking?

A

-the structural hierarchy of actin/myosin remains intact
-water is held between structures by capillary forces
-myofilaments can swell, encouraged by salt (myosin helices denature)

43
Q

How are the myofibrillar proteins in processed meat products extracted? How are they impacted by cooking?

A

-extracted with salt and fine chopping
-cooking = proteins denature and crosslink; fats integrate into this gel texture to hold water

44
Q

What is gelatin made from?

A

-partially hydrolyzed collaged made with strong acidic or basic conditions

45
Q

What does a high bloom strength mean for gelatin?

A

-higher molecular weight and a stronger gel

46
Q

What two major fractions of globulin proteins are soy proteins high in? What are their structures?

A

-glycinin = large, 2-3 disulfide bonds
-B-conglycinin = no disulfide bonds

47
Q

How is tofu made?

A

-soybeans are first processed (chopped) and heated
-the globular proteins are denatured and enzymes form aggregates
-hydrophobic groups are exposed to improve aggregation and gelation
-aggregated proteins are coagulated with either salt or acid-induced gels

48
Q

How do salt and acid-induced gels help coagulation in the making of tofu?

A
  1. salt = forms salt bridges, promotes aggregation, but needs divalent cations
  2. acid-induced gels = creates fine texture and increases water content (creates silken tofu)
49
Q

What are the three main protein reactions? What do they do?

A
  1. hydrolysis = breakdown of peptide bond between amino acid backbones
  2. redox reactions = formation/breaking of disulfide bonds between cysteine residues
  3. enzymatic cross-linking = transglutaminase enzyme catalyzes formation of isopeptide bond (between amino acid side chains)
50
Q

What are the consequences of protein hydrolysis?

A

-loss of native functionality (could impart new properties)
-generates flavor compounds
-allows for absorption of amino acids in the GI tract

51
Q

What are the consequences of protein redox reactions?

A

-alters inter- and intra- molecular bonding arrangement
-stabilizes (native) tertiary structures
-alters the functionality of foods (ex. gluten formation)

52
Q

What are the industrial food applications of enzymatic cross-linking of proteins?

A

-increased firmness and water holding
-restructuring of meats
-improved quality

53
Q

What are the three main categories of food enzymes?

A
  1. proteases = break proteins
  2. amylases = cleaves polysaccharides
  3. lipases = assists in digestion of lipids
54
Q

What are the two types of amylase enzymes? How do they differ in functionality?

A
  1. endoenzymes = cleave within polysaccharide chains into smaller polymers
  2. exoenzymes = cleave terminal ends of polysaccharide chains into sugars
55
Q

How do lipase enzymes break down lipids?

A

-attack glycerol/fatty acid ester bond
-enzyme remains in water phase where bile salts can emulsify lipids
-hydrophobic region of triglyceride comes to the interface, causes opening of catalysis site for nucleophilic attack

FST 100A (1 decks)

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