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What is an example of a protein acting as a regulating agent or hormone?
Insulin
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What is an example of a protein acting as a defense mechanism?
Antigens and antibodies
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What is an example of proteins that carry oxygen and carbon dioxide?
myoglobin and hemoglobin
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What does the idea of protein functionality refer to for a food scientist?
Use of physico-chemical properties of the molecule to produce a specific state of affairs or function in a food system
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What are some examples of protein functionality?
- Water binding
- Emulsification
- Gel formation
- Coagulation
- Dough formation
- Structure formation - edible foams (meringue)
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Which protein has the ability to hydrate and leaven flour in the form of dough?
Gluten - a protein with peculiar elastic properties not associated with other grain flours
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Milk proteins and soybean proteins have the ability to form what?
A curd
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What is an endogenous enzyme?
An enzyme contained within the source (can cause autolytic degradation)
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What is an exogenous enzyme?
Introduced into the system by an outside source, such as a microorganism that will contaminate the system
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What is an important use of proteases for food science?
To tenderize meat
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What is an important use of lipases for food science?
To speed up flavor development
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What is an important use of amylases for food science?
To manufacture corn syrup/sugar
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What is an important use of glucose oxidase for food science?
To remove headspace oxygen from food packages
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What are the protein breakdown products?
Amino acids and peptides
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What can protein hydrolysates be used for?
To make meaty, brothy flavors
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How are meat analogs made?
Can be made from soy protein using extrusion technology
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What is surimi?
Proteins extracted from fish tissue to formulate analogs (avatars) of crab meat and scallop
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Proteins are generally considered to be made up of how many basic amino acids?
20
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What is the secret to the success of living systems?
Their ability to ''build'' an almost infinite variety of protein structures
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What constitutes an amino acid?
To be considered an amino acid both the NH2 and COOH functional groups have to be attached to the same carbon, termed the alpha carbon
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What is unusual about amino acid behavior as a function of pH?
- If one places an amino acid in a strongly acidic environment (pH<1) and titrates with a strong base the amino acid can give up 2 H+ as the pH rises toward 14
- First one from the carboxylic acid group and then one from the amino group
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What is the formula for calculating the pKA1 for an amino acid?
- pKA1 occurs in COOH group
- pKA1 = -log([H+][AA+] / [AA+ or -]
- 50% positive and 50% neutral form
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What is the formula for calculating the pKA2 for an amino acid?
- pKA2 occurs in the NH2 group
- pKA2 = -log([H+][AA+ or -] / [AA-])
- 50% neutral and 50% negative
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What is the formula for calculating the pK1 for an amino acid?
- pK1 is the isoelectric point
- pK1 = overall charge = 0
- pK1 = (pK1 + pK2) / 2
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What are amino acids like at low pH?
- Amino acid is predominantly protonated
- Predominantly positively charged (COOH/NH3+)
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What happens to the amino acids as pH rises (with more OH-)?
Hydrogens are stripped away by the addition of base to become negatively charged (COO-/NH2)
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In what form does the amino acid exist at the isoelectric point?
It does not have the expected standard neutral structure (form A), but exists as form B, the Zwitterion
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What is the Zwitterion like?
- Individual amino acids exist as Zwitterions as they transition from an overall positive charge at low pH to negative charge at high pH
- Never exist as uncharged neutral species
- It is neutral overall in terms of charge, but the molecule is in effect ionic in nature
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What does the ionic nature of the amino acid make it like?
All amino acids have more the attributes of a salt which gives ionic character to the organic molecule
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What unusual physical properties to the amino acids have due to their ionic character?
- A crystalline structure
- Are soluble in water
- Are very stable
- Only decompose at relatively high temperatures
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Why are amino acids said to be amphoteric?
They have both basic and acidic functional groups within the same molecule
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What are the different classifications of amino acids?
- Those with aliphatic side chains
- Hydroxylic side chains
- Carboxylic side chains
- Basic side chains
- Aromatic side chains
- Sulfur containing amino acids
- Imino acids
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What are two amino acids which fall into the aliphatic amino acid category?
- Glycine (R group = H)
- Alanine (R group = CH3)
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What is the simplest amino acid?
Glycine
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Do amino acids typically have optical isomers? Why?
- Yes, all except glycine
- Because all the other amino acids have one or more asymmetric carbons with 4 different substituent groups
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What does it mean that amino acids have optical isomers?
Can rotate plane polarized light
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- Chiral structures are mirror images and are non superimposable, like your hands
- This is because they are 3D structures not just 2D crosses
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How can you determine the configuration of a compound?
You can compare it to a reference compound (glyceraldehyde) in terms of its symmetry
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What is the compound that we use to compare compounds to in order to decide if they are D or L?
Glyceraldehyde
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Based on the reference compound, how do we know if the compound is in dextro or levo form?
- If the OH group is on the right of the n-1 carbon, then it is dextro
- If the OH group is on the left of the n-1 carbon, then it's levo
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What does synthetic production of amino acids generally lead to?
Racemic mixtures of D and L isomers, of which only half can contribute to protein synthesis
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