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In nature are fatty acids generally found in their free form or incorporated into triacylglycerols?
They are normally found incorporated into triacycglycerols
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What are the 2 basic forms fatty acids come in?
Saturated and Unsaturated
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Describe saturated fatty acids
- simplest and least reactive
- Chain series of methyl groups terminating in an carboxyl group
- Structurally a zig-zag but linear overall
- Weak acids
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What length of saturated fatty acids are liquid at room temperature?
C12
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Why does water solubility decrease with increasing chain length?
Increasing hydrophobicity as the methyl chain extends and dominates the more polar carboxyl group
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Which fatty acids are slightly miscible with water?
C4-C8
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What special properties do the monovalent salts of free fatty acids have?
They are water soluble, with strong surface tension reducing properties (bubbles!!)
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Why cant soaps be used as emulsifiers?
Although they are excellent emulsifiers, they taste awful
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When do you get soapy off flavors in food?
When metal ions in food react with a free fatty acid
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What is soap scum?
Divalent ion salts are largely insoluble so when it reacts with hard water it makes soap scum
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What are the two naming systems for fatty acids?
- Trivial names
- Systematic names (IUPAC)
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Which names tend to predominate?
Trivial Names
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What is the common name of 'ethanoic acid'?
Acetic acid
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What is the common name of butanoic acid?
Butyric acid
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What is the common name of hexanoic acid?
Caproic acid
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What is the common name of octanoic acid?
Caprylic acid
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What is the common name of decanoic acid?
Capric acid
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What is the common name of dodecanoic acid?
Myristic acid
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What is the common name of hexadecanoic acid?
palmitic acid
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What is the common name of octadecanoic acid?
Steric acid
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What is the common name of eicosanoic acid?
arachidonic acid
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What is the common name of docosanoic acid?
Behnic acid
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What are fatty acids with one double bond called?
Monounsaturated
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What does a cis double bond do to the molecular structure?
Introduces a kink which can make an L or U shape, depending on where the double bond is located
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What does a single trans bond make a fatty acid look like?
Appear more like a saturated fatty acid than an unsaturated fatty acid
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What is the order of melting points?
Cis < Trans < Saturated
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Is it easier for trans-monounsaturated or cis-monounsaturated to for a crystal latice?
Trans-monounsaturated (mono-cis = bandaids)
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What is a common and generally unavoidable side effect of hydrogenation?
Conversion of cis isomers to trans
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Fun Fact: cis-trans conversion to a large degree is the main mechanism by which oils are converted into plastic fats during hydrogenation, moreso than the accompanying desired reduction in the overall degree of unsaturation
YAY!!
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Why are trans fatty acids consider to be un-natural fatty acids?
Because they are not found in nature
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Are trans fatty acids metabolized more like saturated or unsaturated fatty acids?
More like saturated eventhough they are unsaturated
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Why does butter naturally contain trans fatty acids?
Due to bio-hydrogenation of cis fatty acids to trans by reumen miroorganisms
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What does positional isomerism affect?
The physical properties of monounsaturated fats, because of where the double bond is located
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In IUPAC nomenclature, where is the double bond position counted from?
carboxylic end
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Which is a more significant variable: positional isomerism or cis/trans configuration
cis/trans configuration is more significant
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What is an example of when the position of a double bond an be very important?
Omega-3 fatty acids
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What are the two basic forms of how double bonds are situated relative to each other?
- unconjugated: they are separated by methylene carbon
- Conjugated: next to eachother
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Are most natural polyunsatured FAs conjugated or unconjugated?
Unconjugated
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What is the most famous naturally occuring conjugated fatty acid?
Conjugated linoleic acid (CLA) which has both cis and trans double bonds
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What is special about CLA (Conjugated Linoleic Acid)?
It is considered to have anti-carcinogenic effects, anti-arteriosclerotic effects, help the immune system and affects energy metabolism
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Are conjugated or unconjugated FAs more thermodynamically stable?
Conjugated
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Are conjugated or unconjugated FAs more susceptible to autoxidation?
conjugated
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What is an active methylene group?
- The methyl group in linolenic acid that is positioned between double bonds which are conjugated on one side and unconjugated on the other
- Contributes substantially to reversion phenomenon
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What are the most common unsaturated fatty acids?
Oleic, Linoleic, Linolenic
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How is the presence of a double bond indicated in the nomenclature?
- Ending becomes -enoic instead of -anoic
- If there is more than one double bond, the count is given before the suffix
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How is the location of the double bond indicated in the nomenclature?
Counting from the carboxyl end, put the number of the carbon that the double bond starts at before the full name
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How do you indicate cis/trans configuration in the nomenclature?
Put either cis or trans before every number
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What is the omega carbon?
The last carbon which tells you to count from the CH3 end instead
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Why are omega-3 fatty acids considered beneficial?
They slow the development of arteriosclerosis
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What does straight chain variety mean?
The fatty acid has no branches or side groups or chains
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Describe branched chain fatty acids
- They have a hydrocarbon branch in the chain
- They contain a cyclopropene ring
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Why is the cyclopropene ring bad for chicken eggs?
It makes pasty and rubbery yolks and causes egg color problems
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Describe hydroxy acids
- Contain a hydroxyl group in the fatty acid chain (very reactive)
- Found in the oil of the castor bean tree
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What are acetylinic fatty acids?
Contain a triple bond
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What are some other functional groups which may be present in the fatty acid chain?
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