BIOC 503 - Fatty Acids

lipids

organic biomolecules that are soluble in organic, apolar solvent BUT insoluble or barely soluble in water

glycolipids

lipids attached to sugar residues

fatty acids

carboxylic acid with hydrocarbon chain

• chain ranges from 4 to 36 carbons

short chain

fatty acids with a hydrocarbon chain made of LESS THAN 6 carbon atoms

medium chain

fatty acids with a hydrocarbon chain made from 8 TO 12 carbon atoms

long chain

fatty acids with hydrocarbon chain made FROM 14-24+ carbons atoms

acetic acid

2 carbons short chain fatty acid

• still soluble in water because of the short hydrocarbon chain

butyric acid

4 carbons short chain fatty acid

lauric acid

12 carbons medium chain fatty acid

palmitic acid

16 carbons long chain fatty acid

stearic acid

18 carbons long chain fatty acid

even, acetyl-CoA

fatty acids always have an ___ number of carbons because they are synthesized from ___ which has a 2 carbons skeleton

saturated

fatty acid that only contain single C-C bond in their hydrocarbon chain

• tend to aggregate

• tend to have linear structure

unsaturated

fatty acid containing one or more double C=C bond in their hydrocarbon chain

• double bond creates kink

• the extra space between fatty acids offers more flexibility

• majority of fatty acids are ___

• can be in cis or trans configuration

cis configuration

adjacent carbons are on the same side of the double bond

• relative distance 3.1A

• majority of fatty acids

• 30 degrees kink

trans configuration

adjacent carbons are on opposite sides of the double bond

• still kinked but roughly linear structure

• larger distance 3.8A

kink

double bond(s) of unsaturated fatty acids create a ___ in hydrocarbon chain

short-hand nomenclature

delta or omega notation to name fatty acids

delta nomenclature

(# carbons: # double bonds)Δ (position of double bond) (cis or trans configuration)

• Carbon #1 is the carboxy carbon

omega nomenclature

(# carbons: # double bonds)ω (position of double bond)

• carbon #1 is the end of hydrocarbon chain

• ALWAYS IN CIS CONFIGURATION

essential

___ fatty acids cannot be synthesized by the body, and thus need to be acquired from the diet

EPA

20:5 fatty acid mainly found in fish oil

• precursors to prostaglandins

DHA

22:6 fatty acids which is an important membrane component

4-5, ionized

the pKa of fatty acids usually stands between ___ which means that they are ___ at biological/neutral pH

pKa-2

99% of fatty acids are protonated at pH =___

pKa+2

99% of fatty acids are ionized at pH = ___

weak

fatty acids are ___ acids as they have a relatively medium-high pKa compared to others

hydrophilic, hydrophobic

fatty acids are made of a ___ head group, which is polar and charged, and a ___ tail

factors of fatty acids solubility

1- carbon chain length

2- ionization

2- double bonds

longer

the ___ the hydrocarbon chain of fatty acids, the LESS soluble they are

more

IONIZED fatty acids tend to be ___ soluble

partial polarity

double bonds help with fatty acid solubility by adding ___ to the carbon chain

decrease

double bonds ___ the melting point of fatty acids as kinks create space between lipid molecules and add fluidity

liquid

fatty acids that are ___ at room temperature have a LOWER melting point

solid

fatty acids that are ___ at room temperature have a HIGHER melting point as saturated fatty acids pack into aggregates

factors affecting fatty acids MP

• number of carbon (more carbons = higher MP)

• double bonds/unsaturation (more C=C = lower MP)

inert, active

the hydrocarbon chain of fatty acids tend to be biochemically ___ beside the double bonds, while the head group is biochemically ___

reactions involving double bonds

• hydrogenation

• autooxidation

reactions involving carboxyl group

• amidation

• esterification

hydrogenation

add hydrogen atoms to double bonds in fatty acid hydrocarbon chain using a metal catalyst

• alters physical properties and biological activities of molecule

• ADD STABILITY, which makes transport and storage easier & less susceptible to autooxidation, change consistency

• can lead to cis-trans isomerization when reaction is only partial, which is bad for human health

• increase saturated fat content, which is bad for human health

10

Rule of thumb: susceptibility of fatty acid to autooxidation INCREASES about __ folds for EACH double bond in the hydrocarbon chain\

• starts with rate of 1 for 0 double bond

autooxidation

fatty acids double bonds in carbon chain oxidizes in presence of molecular oxygen (O2), which creates hydroperoxide

• hydroperoxide = reactive oxygen species (ROS) which causes membrane, proteins, and DNA damage

• antioxidants prevent ROS damage and formation

esterification

fatty acid carboxy group reacts with an alcohol to form an ester-linkage

amidation

fatty acid carboxy group reacts with an amine to form an amide-linkage

• same linkages used in peptide bonds

ester-linkages

the prefixes mono-, di-, and tri- for glycerides refer to the number of ___

• can go up to 3 because of glycerol backbone?

second

triacylglycerols often have a double bond in the ___ position

functions of triacylglerols

• storage of energy (when all 3 ester-linkages are made (max capacity), no hydroxy group anymore, so not water soluble, no water needed, and better use of space)

• insulation

lipases

enzymes breaking the ester-linkages in fatty acids to make soap and detergent using water aka saponification reaction