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1) Introduction to Food Science > Chapter 11: Proteins: Amino Acids and Peptides > Flashcards

Chapter 11: Proteins: Amino Acids and Peptides Flashcards

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1
Q

Describe PKU.

A

Individuals with PKU must not consume phenylalanine (since it is not synthesized). Tyrosine is a byproduct of phenylalanine. When no Phe is available, additional Tyr must be consumed to meet the body’s needs (conditionally essential AA).

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2
Q

Which plant source is known for its high quality? How is it treated? Which amino acid is limiting?

A
  • Soybeans
  • Must be heat processed for several hours to destroy toxic compounds that prevent the complete digestion of proteins
  • Low in methionine
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3
Q

Which amino acid is often limiting in cereal grain? Which others are limiting in plant-based products?

A

Cereal: Lysine
Others: Tryptophan, Threonine

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4
Q

Name some combinations that provide adequate amounts of AA.

A
  • Whole-wheat bread + peanut butter
  • Rice and red beans
  • Refried beans and corn tortilla
  • Hummus (chickpeas + sesame seeds)
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5
Q

Which amino acids are used in lipoprotein clusters?

A

AA with nonpolar side chains, positioned toward the outsides of the molecules, allowing them to attract cholesterol molecules

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6
Q

Which AA have a hydroxyl group?

A

Serine, threonine, tyrosine (causes a polar nature)

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7
Q

What are proteins composed of?

A

Carbon, Hydrogen, Oxygen, Nitrogen, usually Sulfur

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8
Q

What else can be contained in protein composition?

A

Iron, Copper, Phosphorus, Zinc

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9
Q

What is the basic subunit of proteins?

A

Amino acids

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10
Q

Name the 3 parts of the amino acid.

A
  • Side chain of C and H
  • Carboxyl group (COOH)
  • Amine group (NH2)
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11
Q

Which part of the amino acid acts as the acid? As the base?

A

Acid: carboxyl group
Base: amine group

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12
Q

How do amino acids combine?

A

carbonyl carbon and amide nitrogen combine and form a peptide bond through condensation (released water)

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13
Q

Define polypeptide.

A

Chain of amino acids bound together by peptide bonds.

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14
Q

How many AA are in most proteins?

A

100 to 150 AA

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15
Q

How are AAs classified?

A

1) By their nutritional use

2) By the chemical nature of their side chain

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16
Q

Compare dispensable and indispensable AA.

A

Dispensable/nonessential: made by the body (11)

Indispensable/essential: not made by the body and must be supplied by the diet (9)

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17
Q

Name the 9 essential amino acids.

A

Histidine, Isoleucine, Leucine, Lysine, Valine, Methionine, Phenylalanine, Threonine, Tryptophan

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18
Q

What causes conditionally indispensable AA?

A

Certain conditions prevent the body from producing enough dispensable AA and they have to be obtained from the diet
(not in healthy individuals)

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19
Q

Compare complete and incomplete protein sources.

A

Complete: contain all the indispensable AA
Incomplete: grains and vegetables are short one or more of the essential AA

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20
Q

How do vegetarians get complete proteins?

A

Combining sources (ex: beans + rice)

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21
Q

Name the 4 types of amino acid side chains.

A
  • Nonpolar
  • Uncharged polar
  • Positively charged
  • Negatively charged
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22
Q

Which amino acid side chains are less soluble in water?

A

Nonpolar sidechains

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23
Q

Which amino acid side chains will form hydrogen bonds and are attracted to polar molecules?

A

AA with neutral sidechains

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24
Q

Which amino acid side chains can function as buffers?

A

Positively and negatively charged

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25
Q

Name 3 reasons why protein structure is complex.

A

1) Number of amino acids
2) Order in which they combine
3) Interaction of the sidechain

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26
Q

Define primary structure.

A

The order the amino acids occur in the sidechain; results from chain of peptide bonds.

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27
Q

Define secondary structure.

A

Refers to the shape of sections of the protein

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28
Q

Define tertiary structure.

A

Refers to the 3D structure of an entire AA chain

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29
Q

Name the 3 types of secondary structure

A

1) Helix: repeating coil
2) Random coil: tangled and twisted
3) Pleated sheet: like a paperfan

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30
Q

Differentiate the 2 types of tertiary structure.

A

1) Globular proteins do not form gel networks (do not hold water)
2) Fibrous proteins form gel networks, long elastic, usually made from helix-shaped strands

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31
Q

How do H-bonds form in proteins?

A

Form between the H-atom of one chain and the hydroxyl group of another

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32
Q

Name the 2 functions of H-bonds in proteins.

A
  • Basic to the stability of 2nd and 3rd structures

- Make some proteins water soluble

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33
Q

Define disulfide cross-links

A

Covalent bonds between 2 protein molecules at side chains with sulfur

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34
Q

What is the function of disulfide cross-links?

A

The more stable disulfide bonds, the more stable the molecule

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35
Q

How can we break disulfide bonds?

A

Sodium hydroxide (Lye)

36
Q

How do hydrophobic interactions form in proteins?

A

Form between sidechains that are nonpolar

37
Q

Name 2 examples of hydrophobic interactions in food.

A
  • Caseins in milk (cheese curds)

- Whey, by-product of cheese production

38
Q

Define myoglobin.

A

The iron binding protein pigment in muscle that provides colour

39
Q

When is myoglobin bright red, purplish and brown?

A

Bright Red: when O molecule is attached
Purplish: when O molecule is not attached
Brown: after prolonged exposure to O

40
Q

Define oxidation and reduction reactions.

A

The reversible process of adding and removing oxygen.

Oxidation adds oxygen, Reduction removes it

41
Q

When are nitrites used?

A

added during the curing process to preserve meats

42
Q

Define cured meats

A

ham and bacon, very stable, pink-red colour

43
Q

Define denaturation

A

Any change in the shape of a protein molecule without breaking the peptide bonds

44
Q

Name the 3 characteristics of denaturation.

A
  • Loosening or unfolding of the tertiary and sometimes secondary structure
  • Sometimes reversible
  • Involves only H-bonds
45
Q

The breaking of which reaction is irreversible?

A

Breaking disulfide cross-links

46
Q

Define coagulation. What does it result from?

A

Permanent denaturation, which results when liquid or semiliquid proteins form solid or semisoft clots

47
Q

Name 3 effects of coagulation a protein.

A
  • Changes its physical characteristics
  • Alters the ability to bind with water
  • Interferes with biological interactions of enzymes
48
Q

Name a denatured protein that can return to its original state?

A

Beaten egg whites

49
Q

What kind of protein holds their new shape?

A

Coagulated proteins, ex: cooked eggs

50
Q

Name the 3 methods to physically denature proteins

A

1) Temperature changes
2) Mechanical actions
3) Sound waves and irradiation

51
Q

How do heat and cold affect proteins?

A

Heat: speeds up denaturation
Cold: may cause curdling

52
Q

What mechanical actions disrupt protein structures? What strengthens gluten?

A

Disrupt: beating, rolling, kneading

Strengthens gluten: kneading

53
Q

How do sound waves/irradiation disrupt protein structures?

A

Prolonged exposure at high levels is needed

54
Q

Name the 2 methods to chemically denature proteins.

A

1) Change in pH

2) Exposure to mineral salts or metals

55
Q

Name examples of products in which acids have denatured milk proteins.

A

Sour cream, buttermilk, yogurt

56
Q

What kind of salts can denature proteins?

A

Sodium and potassium salts

57
Q

What are the 4 factors food scientists examine to determine how effective proteins work in a product?

A
  • Water absorption
  • Solubility
  • Viscosity
  • Stability in acids and alkalis
58
Q

Name the 5 functions of protein in food.

A

1) Proteins form gels
2) Proteins change texture
3) Proteins emulsify
4) Proteins form foams
5) Proteins develop gluten

59
Q

Define a protein gel

A

Mixture of fluids locked in a tangled mesh of denatured and coagulated protein

60
Q

What are the 2 parts of protein gels?

A

1) 3D molecular structure

2) Liquid attracted to the protein

61
Q

What do acids do to gelatin? What can develp?

A

Acids soften gelatin, which may develop syneresis if stored or cooked for too long

62
Q

What increases gel stability?

A

Mineral salts, hard water, more gelatin, slow coolin rates

63
Q

What decreases gel stability?

A

Acids, sugars, food pieces, rapid cooling

64
Q

How is protein gel formed from muscle tissue?

A

When salt is added to destabilize proteins

65
Q

How can globular proteins change texture?

A

Spun into fibers under the right conditions

66
Q

Name 2 examples of texturizing.

A
  • Soy protein to create meat substitutes by denaturation or heat-coagulation under pressure
  • To produce processed cheeses
67
Q

What kind of protein can act as an emulsifier?

A

Denatured protein

68
Q

How do proteins act as emulsifiers?

A

Polar side chain attracts water-based liquid and nonpolar side attracts oil

69
Q

How can casein act as an emulsifier?

A

Pressure used in homogenization of milk ENABLES casein to act as an emulsifier

70
Q

What makes extraction of oils from seeds more difficult?

A

Protein’s ability to form an emulsion

71
Q

Define a foam.

A

Gas suspended in liquid or semi-solid

72
Q

How are foams formed?

A

By bubbling gas through a mixture, beating or whipping, and depressurization

73
Q

Give examples of foams.

A

Meringue, foam cakes, marshmallows, soufflés, bread

74
Q

Give examples of good foaming agents.

A

Albumin in egg whites and milk

75
Q

What is gluten?

A

Strongly cohesive and elastic protein

76
Q

How is gluten formed?

A

When a high protein flour is combined with moisture and stirred or kneaded

77
Q

What does gluten’s strength result from?

A

Disulfide cross-links formed during kneading

78
Q

What happens to gluten when baked?

A

Gluten coagulates when baked

79
Q

What damages high protein foods?

A

High temperature and prolonged cooking

80
Q

What happens when high protein foods are damaged?

A

Protein molecules shrink and squeeze out H2O, resulting in a dry, rubbery, tough product

81
Q

Name 6 functions of protein as a nutrient.

A

1) Support growth and repair
2) Fight disease
3) Maintain fluid and mineral balance
4) Maintain pH balance
5) Control bodily functions
6) Provide energy

82
Q

How do proteins function as buffers?

A

Pick up and release acids and bases (side chain)

83
Q

How do proteins control bodily functions?

A

Proteins are apart of hormones that maintain body functions and enzymes (chem reactions)

84
Q

How do proteins provide energy? What is a byproduct? How does it affect health?

A

AA -> Energy (produces ketones and ammonia - strains kidneys)

85
Q

Name 2 ways food scientists are developing affordable proteins.

A

1) Developed grains (triticale)

2) Using biotechnology

86
Q

What is a health concern of protein?

A

Allergies

1) Introduction to Food Science (20 decks)

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