Lipids: Fatty Acid Structure Flashcards
Two main classes of lipids:
1) Fatty acids
2) Isoprenoid
Naming fatty acids:
2 naming conventions
1st naming convention
Naming fatty acids:
2 naming conventions
2nd naming convention
Unsaturated fatty acids:
Double bonds can be cis or trans.
Unsaturated fatty acid:
Cis
Creates a “bend” in the structure.
Naturally made fat
Unsaturated fatty acids:
Trans
Have tighter bonds and “straight”
Some are made naturally by the gut bacteria (meat products)
The rest are made commercially as a by-product of partial hydrogenation
What does the bend on a cis bond do to membrane fluidity?
The “bends” cause kinks in the aceyl chains of phospholipid bilayers of membranes causing the junctions to become loose. This increases membrane fluidity.
Partial hydrogenation targets cis-bonds in fatty acids to:
Add hydrogens and turn oils into solid fats.
How can partially hydrogenated fats be labelled as 0 trans fat?
Using reduced pressure and blending oil reduces the trans fat content.
Less than 0.5 grams per serving can be labelled as “0% trans fat.”
Associated with increased risk of coronary heart disease
Fatty acid synthesis:
Occurs in cytoplasm (16:0 palmitate)
Substrates: Acetyl CoA & malonyl CoA
(malonyl CoA= acetyl CoA w/ extra CO2 group)
Fatty acid synthase:
Enzyme for fatty acid synthesis:
Exists as a dimer (two fatty acid chains can be made at once)
Contains two S groups: one from cysteine, one from B5
(cis binds acetyl groups, and B5 binds malonyl groups)
B7: biotin:
Coenzyme of fatty acid synthesis:
helps add CO2 to acetyl CoA to make malonyl CoA (malonyl CoA)
B5:
part of fatty acid synthase:
also part of acetyl CoA and malonyl CoA
B3:
NADPH
reduces the fatty acid chain
Which pathway provides NADPH?
Pentose phosphate pathway
How do you get to a 16 carbon chain?
You repeat the elongation cycle.
How do you get the chain off the enzyme?
Use water to break the bond:
hydrolysis
How do you make the chain bigger than a 16C chain?
Elongate using enzymes embedded in the ER membrane.
How do you make odd-numbered fatty acid chains?
Starting with propionyl CoA (3C) rather than acetyl CoA (2C) in step one can make odd-numbered chains.
How do you get unsatturated fatty acids?
Some from the ER: desaturase enzymes use NAD (P) H (B3) to create double bonds
Some are essential, only get them from diet desaturase enzymes are only found in plants.
Essential fatty acids:
needed to support the cardiovascular, immune, reproductive, and nervous systems.
How do you regulate fatty acid synthesis?
Glucagon: released when blood sugar is low
Insulin: released when blood sugar is high
Epinephrine: released during sympathetic responses
-Synthesis is oppositely regulated to break down (beta ox)
-Synthesis promotes storage of fats as TG’s
Glucagon promotes beta ox (and therefore decreases fatty acid synthesis)
Glucagon plays a crucial role in promoting beta-oxidation by increasing the availability of FFAs, removing regulatory barriers, and directly activating enzymes involved in the process. Provides the body with an alternative source of energy when glucose is limited.
Inhibits acetyl CoA carboxylase:
Glucagon & epinephrine
Activates acetyl CoA carboxylase:
Insulin
Acetyl CoA carboxylase catalyzes:
It catalyzes the first committed step in fatty acid synthesis: the addition of bicarbonate to acetyl-CoA to make malonyl CoA.
Triglycerides:
Three fatty acids are attached to a glycerol backbone via an ester linkage.
Provides energy and insulation.
Which packs tighter? triglycerides of glycogen and why?
Triglycerides: because it is more hydrophobic than glycogen. Can attract more hydrophobic molecules and exclude water.
Triglyceride synthesis:
Lipogenesis
liver and adipocytes: cytosol of cells
Starts with addition of 2 fatty acids to a glycerol backbone.
Makes substrates: glycerol -3- phosphate backbone, 3 fatty acyl CoAs.
Transfer 2 fatty acid chains to the backbone sequentially
Replace the phosphate on the backbone witht he 3rd fatty acid chain
What enzyme adds a phosphate to glycerol?
Glycerol Kinase
Adipose and liver convert DHAP from ______ to glycerol 3 phosphate using _________.
cytosol and mitochondria of cells
using glycerol 3 phosphate hydrogenase (GPDH)
Fatty acids are added to a CoA carrier using _____
ATP
A: Pyruvate
B: acetyl CoA
C: Polyphenol sulfide
D: pyruvate carboxylase
E: acetyl CoA
F: acetly coA carboxylase
G: NADPH; fatty acid synthesis, steroid hormone production
Phospholipids & glycosphinolipids
Phosphoglycerides:
Made: ER
First three steps: acylation of glycerol 3 phosphate, phosphorylation of diacylglycerol, attachment of a head group to phosphatidic acid
Glycerol-3-P is made from ____ in liver and adipose tissue. Liver can also make it from______.
Pyruvate; DHAP
Fatty acids are activated by attachment to a _____ carrier.
acyl carrier protein (ACP)
_____ fatty acids are sequentially added to the glycerol 3 p
saturated fatty acids
Adding the head group on a phospholipid:
First, a CMP is added to create a good leaving group
Next, the CMP is removed to add head group attached via nucleophilic substitution.
Sphingolipids:
Sphingomyelin:
Phosphate-alcohol head group
Backbone= sphingosine (part of ceramide)
Has two fatty acid tails:
-one is sphingosine backbone
-One is added to sphingosine to make a ceramide
Found in cell membranes: important component of myelin
Tay-Sach’s disease:
Glycosphingolipids
accumulation of sphingolipids
Accumulates lyssosomes due to an enzyme deficiency
Most severe excess occurs in the brain
Build up leads to neuronal damage: neurodegeneration can lead to death by 5 years of age.
Eicosanoids: Derived from arachidonic acid or similar 20 C fatty acids
Include prostaglandins
Physiological functions depend on type:
-Vasodilation
-Vasoconstriction
-Platelet aggregation
Waxes:
Mixtures of nonpolar molecules, including fatty acids linked to long-chain hydrocarbon alcohols via ester bonds
Categories of isoprenoids:
1) Terpenes
2) Mixed terpenes
3) Steroids
Terpenes:
Isoprene units linked together
Smallest terpene= 2 isoprene units linked together=monoterpene
Names of common terpenes:
-farnescene
-squalene
-beta carotene
Mixed terpenes:
Terpenes with non-terpene component attached :
-CoQ
-Vit K
-Farnesylated proteins
Steroids:
Complex molecules made from 6 isoprene units
Made from cholesterol
Cholesterol synthesis review:
Most cholesterol synthesis occurs in the liver:
-Makes bile
-Make lipoproteins: LDL to cary cholesterol to tissues
LDL binds to a receptor on the cell and is internalized, broken down within the cell, and cholesterol is released.
Familial hypercholesteremia:
inherited defect of LDL receptors:
leads to an increase in circulating LDL, and therefore cholesterol, in the blood
-Increases risk of myocardial infarction
Cholesterol is a precursor to steroid hormones:
al animal steroids are derived from cholesterol.
Cholesterol is converted to pregnenolone, which is then converted to various other steroids hormones
Plant sterols have a similar structure to cholesterol:
Used in plant membranes
can compete with intestinal cholesterol absorption.
(helps lower LDL cholesterol levels)
Cardiac glycosides are derivatives of plant sterols:
Note the lipid attached to the carbohydrate: this is an isoprenoid ring structure.
Digoxin: used to treat heart failure and atrial fibrilation
