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Nutrition 244 > Protein Structure > Flashcards

Protein Structure Flashcards

1
Q

Why are proteins difficult to cook?

A

They are sensitive to heat.

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2
Q

What elements make up protein?

A

C, O, N, H

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3
Q

What are the building blocks of proteins?

A

Amino acids

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4
Q

What does an AA contain?

A

Acid group

Amine Group

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5
Q

What is the variable factor for an AA? What is its importance?

A

The side chain.

It gives the AA its unique identity and will determine how it will react chemically.

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6
Q

How many AA are there?

A

20-23 AA, depending on how you classify them.

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7
Q

What are the nutritional classifications of amino acids?

A
  1. Essential AA -> must come from diet

2. Non-essential AA -> body can make these

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8
Q

What are the 9 essential AA?

A

Phenylalanine
Valine
Threonine

Tryptophan
Isoleucine
Methionine (has a sulfur group)

Histidine
Leucine
Lysine

PVT TIM HaLL

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9
Q

What are the two ways we categorize protein quality?

A
  1. Complete Protein

2. Incomplete Protein

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10
Q

What is a complete protein?

A

It has all of the essential amino acids.

Most animal proteins are complete.

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11
Q

What is an incomplete protein?

A

It doesn’t have all of the essential amino acids.

Most plant proteins are incomplete.

They will typically have protein complementation.

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12
Q

What is protein complementation?

A

It is combining plant protein sources to make a complete protein.

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13
Q

Look at the chart for protein complementation.

A

Look at the chart for protein complementation.

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14
Q

What are two ways that amino acids can be classified?

A
  1. Isoelectric Point

2. Side-Chain Group

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15
Q

What is the isoelectric point?

A

The pH at which it has no net charge.

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16
Q

What is a side chain?

A

An R-group that gives the AA its identity.

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17
Q

What are the four different categories of side chains?

A
  1. Polar Side Chain
  2. Uncharged-Polar Side Chain
  3. Non-polar/Hydrophobic Side Chain
  4. Imino Acid (2 Amine Structures)
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18
Q

Describe Polar Side Chains.

A

Easily ionized.

Enter into ionic bonding.

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19
Q

Describe Uncharged Polar Side Chains.

A

Nonionized side chains.

Enter into hydrogen bonding.

Those containing sulfur enter into covalent bonding (disulfide bridges).

These are also known as neutral AA.

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20
Q

Describe Non-Polar Hydrophobic Side Chains.

A

Enter into hydrophobic interacts.

Fat-soluble Amino acids.

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21
Q

Describe Imino Acid Side Chains.

A

They contain a secondary amine group.

The amine is typically tied up in a ring structure.

Very important in COLLAGEN.

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22
Q

What amino acids have a polar side chain? (5)

A

Acid AA -> Aspartic Acid and Glutamic Acid

Basic AA -

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23
Q

What amino acids have a polar side chain? (7)

A

Serine, Threonine, Tyrosine, Glycine, Tryptophan, Cysteine, and Methionine.

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24
Q

What amino acids have a nonpolar/hydrophobic side chain? (5)

A

Alanine, Valine, Leucine, Isoleucine, and Phenylalanine.

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25
Q

What amino acids have an imino acid side chain? (2)

A

Proline and Hydroxyproline.

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26
Q

What is a peptide bond?

A

It is a bond between amino acids, forming a protein chain.

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27
Q

What type of bond is a peptide bond?

A

A covalent bond.

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28
Q

Describe a peptide bond.

A

Acid group of AA is bonded to the amine group of the other AA.

This occurs via hydrolysis with the removal of a water.

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29
Q

What are the four level of protein structures?

A
  1. Primary
  2. Secondary
  3. Tertiary
  4. Quaternery
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30
Q

What is the primary structure of a protein? What interactions do you see here?

A

It is a sequence of AA in a linear structure.

Held together by peptide bonds between AA via covalent bonds.

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31
Q

What is the secondary structure of a protein? What interactions do you see here?

A

It is how the protein TWIST or COILS.

Formed by hydrogen bonding between the amide and the carboxyl oxygen.

32
Q

What are the three types of secondary structures?

A
  1. Alpha-helix
  2. Beta-sheets
  3. Random Coil
33
Q

What is the tertiary structure of a protein? What interactions do you see here?

A

It is how the protein FOLDS around and OVER ITSELF.

Highest level of structure achieved by most proteins.

Held together by all types of bonds.

  1. Hydrogen Bonding
  2. Ionic Bonding (salt bridges)
  3. Covalent (disulfide bonds)
  4. Hydrophobic Interactions.
34
Q

What is the driving force of folding tertiary proteins?

A

Protection of hydrophobic amino acids.

35
Q

What is the bonding dependent on?

A

The side chain.

36
Q

What is the quaternary structure of a protein?

A

These are protein that exist in subunits.

Many subunits aggregate to form a quaternary structure.

37
Q

What are examples of quaternary structures?

A

Hemoglobin

Soy Proteins

Casein.

38
Q

What are the three types of proteins found in foods?

A
  1. Globular
  2. Fibrous
  3. Conjugated.
39
Q

What are globular proteins? Are they are soluble?

A

They form a circle (by folding over itself)

They are more water-soluble (hydrophobic AA are in the center)

40
Q

What are some examples of globular proteins?

A

Albumins, globulins, enzymes.

41
Q

What are fibrous proteins? Are they soluble?

A

These proteins provide structure (tough proteins).

They are insoluble in water.

42
Q

What are some examples of fibrous proteins?

A

Collagen
-forms a triple helix, holds muscle fibers together

Elastin
-connects bone to muscle

43
Q

What are conjugated proteins?

A

Protein bound to SOMETHING ELSE.

Proteins can form complexes with many other molecules.

44
Q

What are some examples of conjugated proteins?

A

Glycoproteins, Lipoproteins, Metalloproteins, Phosphoproteins.

Look at notes for more specifics.

45
Q

What are the five chemical reactions of proteins?

A
  1. Hydrolysis
  2. Buffering
  3. Denaturation
  4. Browning Reaction
  5. Enzymatic Reactions.
46
Q

What is hydrolysis?

A

The splitting of a large molecule into smaller molecules by the addition of a molecule of water. Typically aided with energy input.

Hydrolysis is breaking of the peptide bond when talking about proteins.

The net result is a shorter protein chain.

47
Q

After hydrolysis, what is the net result?

A

A shorter peptide chain.

It will INCREASE solubility, making it easily dispersable.

It will DECREASE the ability of the protein to thicken.

48
Q

What are the two types of hydrolysis? Name some examples.

A
  1. Acid Hydrolysis
    - marinages with vinegar
  2. Enzyme Hydrolysis
    - meat tenderizers (papain, bromelain, ficin
    - Cheese production (rennet)
49
Q

How can proteins act as buffers?

A

They are amphoteric.

They can act as a weak acid or a weak base. The free carboxyl group can donate a H+, while a base can accept a H+, respectively.

50
Q

What is the role of a buffer?

A

It resists changes in pH.

51
Q

What is the isoelectric point? What can it effect if you’re at this point?

A

The pH at which a protein has NO CHARGE.

It can effect ionic and hydrogen bonding properties, effecting the shape of the protein.

The protein will be most susceptible to precipitation and/or denaturation.

52
Q

What is denaturation?

A

Unfolding of the protein, which will change its structure an shape.

This is an irreversible reaction.

53
Q

What are the 5 causes of denaturation?

A
  1. Heat or Cold
  2. UV light
  3. Mechanical Treatments (beating, whipping, chearing)
  4. Extreme pH
  5. 70% Alcohol
54
Q

What is the result of denaturation? (3)

A
  1. Increase in viscosity.
    - proteins unfold and become larger or less compact
  2. Decrease in water holding capacity
    - loss of moisture during cooking
  3. Increase susceptibility to proteolysis.
    - unfolding of protein exposes more surface area for enzyme action.
55
Q

What are the two types of browning reactions?

A
  1. Non-enzymatic browning

2. Enzymatic browning

56
Q

What is non-enzymatic browning?

A

The Maillard Browning Reaction.

57
Q

What are the requirements for the Maillard Browning Reaction? (2)

A
  1. Protein or Amin Group

2. Reducing Sugar.

58
Q

What are the requirements for the enzymatic browning? (4)

A
  1. Enzyme (protein)
  2. Oxygen
  3. Substrate
  4. Mixing of Reactants.
59
Q

What are enzymes?

A

They are protein catalysts what speed up chemical reactions.

60
Q

How do enzymes work?

A

They use a “lock-and-key” mechanism.

The specific shape of the enzyme fits into the substrate.

The enzyme will produce the end product.

61
Q

What is unique about the enzyme after it has done its role.

A

It is unchanged by the process, meaning it can go on and react again.

62
Q

What does the environment have to be for an enzyme to function?

A

Enzymes function at specific ranges of temperature and pH

Optimal Conditions:

  • 95C-104C
  • Neutral pH
63
Q

Describe the structure of an enzyme.

A

It has a protein portion and a nonprotein portion.

64
Q

What is important about the nonprotein portion of an enzyme?

A

It is necessary for enzyme to be active.

It can have a cofactor (mineral) or a coenzyme (vitamin)

65
Q

What is a holoenzyme?

A

Protein portion + nonprotein portion.

66
Q

What are some enzymes used by the food industry?

A

Rennet -> cheese
Papin -> meat tenderizer
Glucose Oxidase -> removal of glucose from egg whites.

67
Q

Why do enzymes have to be controlled?

A

To prevent product deterioration.

Lipoxygenase in milk or soybeans will cause off flavors.

Blanching veggies before freezing.

68
Q

What are some enzymes used in quality testing?

A

Alkaline Phosphatase -> determines if pasteurization is complete.

Xanthine Oxidase -> tests freshness of fish

69
Q

What are the five functions of protein in food?

A
  1. Foam formation
  2. Thickening agents
  3. Gel formation
  4. Structure
  5. Edible Film.
70
Q

What if the function of protein in foam formation?

A

They have the ability to form stable foams.

Egg whites
Gelatin

71
Q

Stable foams provide foams with what features?

A

Stable foams provide a light airy product with a large volume.

72
Q

What is the function of protein as a thickening agent?

A

Egg proteins when denatured by heat act as a good thickener.

73
Q

What is the role of protein in Gel formation?

A

Some proteins can form gels.

Gelatin
Casein
Egg protein

74
Q

What is the role of protein in providing structure?

A

They are responsible for the textural characteristics of baked goods.

75
Q

What is the role of protein in edible film formation?

A

Some proteins can form edible films.

Via…
Gluten from wheat
Zein from corn
Casein and whey from milk

Nutrition 244 (12 decks)

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