Review Notes: Catabolism of fatty Acids - Overview

Roles of Lipids

lipids = biological molecules that are soluble in organic solvents

• DONT former plymers

roles of lipids

1. Membrane structure

2. Cholesterol:

   1. membrane structure - 95% of cholesterol is in membrane

   2. precursor of bile acids

   3. precursor of steroid hormones (cause of cardiovascular disease)

→ produces hormones & vitamins

3. Second messensgers (ex. diacylglycerol)

4. Produce vitamins (A,D,E, K)

5. very important energy stores

Fatty acids Catabolism

Triaglycerols relationship with Fatty acids

Esterification = forms TAGs from fatty acids

Lipolysis = breakdown TAGs into fatty acids

Fatty acid relationship with A-CoA

FA synthesis = uses A-CoA +ATP to form fatty acids

Beta-oxidation = breaks down FA into A-coA

• A-CoA can be used in CAC to generate energy

• A-CoA can be used to irreversibly form cholesterol (no pathway to break, thus excrete as bile salts to lower high cholesterol)

• A-CoA can be used to form ketone bodies (reversible)

Fatty Acids

Fatty acids = hydrocarbon derivatives

• 4-36 carbons long (most common are C16 & C18)

• amphiphatic/amphiphillic: consist of a polar head group & non-polar hydrocarbon tail

  • longer chain FA are amphipathic bc they contain a longer NONpolar tail

  • shower chain FA are amphiphilic bc they have a shorter NONpolar tail

• Types:

  • saturated = NO double bonds (fully saturated w hydrogens)

  • Cis-unsaturated (most common) = double bond w hydrogens on same side of DB

    • assumed

  • trans-unsaturated = double bond w hydrogen on OPP sides of DB

    • MUST be told & indicated

• most fatty acids are deprotonated at c1 (carboxyl group), thus have a (-) charge

• FA’s are formed from TAGs via lipolysis or from A-CoA using ATP

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Q.

LDL = ”bad” cholesterol that forms plaque

HDL = “good” cholesterol that helps stop forming plaque

Numbering of Fatty Acids

start numbering at carbonyl carbon (c1) → alpha → beta….

• last carbon is omega

note: omega-# indicates that the DB is # carbons from the omega (last) carbon of the FA

ex. omega-3 fatty acid = 1st DB is 3C from the omega carbon

note: 1% of diet needs to be omega-3 fatty acids & we don’t need more

Q. is this an omega-9 fatty acid?

No, this is a omega-3 fatty acid

• C18 with 3 double bonds, thus ∆9,12,15

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note: linolenate is an essential fatty acid that we get from plants in our diet

note: most PUFA’s have NON conjugated double bonds - thus have 2+ single bonds b/w DB’s

Indicating Trans vs. Cis double bonds of Fatty Acids

Cis double-bond = H’s on same side of DB

• DONT have to indicate its cis

• # of carbons in total : # of DB ^ ∆# of c w DB

trans double-bond = H’s on OPP side of DB

• NEED to indicated its trans before ∆

• # of carbons in total : # of DB trans^ ∆# of c w DB

What affects the melting point of Fatty acids?

→ length of chain & presence/absence of DB’s affect FA melting points:

• longer chains have higher Mp

• saturated chains have higher Mp

  • presence of DB’s prevents FA from coming together → decreasing van Der Waals interactions b/w chain that decreases Mp

longer chain & less DB = more solid

shorter chain & more DB = less solid

Triacylglycerols (TAGs)

Triacylglycerols = fatty acid esters of glycerol

• consist of FA chains connected via ester bonds to a 3C glycerol backbone

  • form TAGs via esterification rxn in which the acyl group is left behind when glycerol is added to FA

• purpose: TAGs/fat are our main energy store, NOT carbohydrates

• fat is stored primarily in adipose tissue (also release hormone like muscle does)

Types:

1. Mixed TAGs = 2 diff FA attached to glycerol backbone

2. Simple TAGs = ALL 3 FA are identical

Role of Leptin

Leptin = monomeric protein w only alpha-helices & loops

• binds to receptor in thalamus to sya you’re full

• possible obesity treatment, but has little effect bc few humans have mutated leptin protein, instead we have more mutations in the leptin receptor (harder to treat)

Many foods contain TAGs: example

shows:

• longer chain & less DB = more solid

• shorter chain & more DB = less solid

ex. beef fat has a longer chain saturated than butter, thus its more solid

ex. olive oil has more unsaturated thus its more liquid than beef fat & butter