Lipids

Question 1

Physiological roles of lipids

Answer 1

1: in adipose tissues, triglycerides (fats) store energy
2: in cellular membranes, phospholipids constitute a barrier b/w intracellular and extracellular environments
3: cholesterol is a special lipid that serves as a building block for the hydrophobic steroid hormones

Question 2

Fatty Acid Structure

Answer 2

long unsubstituted alkanes that end in a carboxylic acid
chain typically 14-18 carbons long, synthesized 2 C at a time from acetate, only even-numbered FAs are made in human cells
saturated: all C covalently bound to max # of H, no C-C double bonds
unsaturated: 1 or more double bonds in the tail (double bonds almost always Z or cis)

Question 3

Triaglycerols/Triglycerides (TGs)

Answer 3

storage form of the FA is fat
3 FAs esterified to a glycerol molecule (glycerol: 3C triol)
3 hydroxyl groups that can be esterified to FAs

Question 4

Lipases

Answer 4

enzymes that hydrolyze fats

Question 5

Why triglycerides stored in fat cells as energy source

Answer 5

fats more efficient energy storage molecules: packing and energy content
packing: hydrophobicity allows fats to pack together much more closely than carbohydrates (carbs carry greater water-of-solvation: water molecules H-bonded to hydroxyl groups)
energy content: fat molecules store more energy than carbs

Question 6

Lipid Bilayer Membranes

Answer 6

membrane lipids = phospholipids
lipid bilayer: hydrophobic interactions drive formation of bilayer, once formed is stabilzied by van der Waals forces b/w the long tails

Question 7

Would a saturated or unsaturated FA residue have more van der Waals interactions with neighbouring alkyl chains in a bilayer membrane?

Answer 7

double bonds in phospholipid FAs tend to increase membrane fluidity, prevents membrane from solidifying by disrupting orderly packing of hydrophobic tails

decreasing length of FA tails also increases fluidity

Question 8

Fluidity of lipid bilayer

Answer 8

to increse fluidity:
increased double bonds
decreased length of FA tails
at low temp., cholesterol increases fluidity - membrane antifreeze

to decrease fluidity:
at high temp., cholesterol decreases fluidity

*cholesterol keeps fluidity at an optimal level

Question 9

Terpenes

Answer 9

member of a broad class of compounds built from isoprene units (C5H8) w/ general formula: (C5H8)n
can be linear or cyclic
need at least 2 isoprenes to make a terpene
classified by # of isoprene units they carry:
- monoterpens - 2 isoprene units
- sesquiterpene - 3 isoprene units
- diterpene - 4 isoprene units
- triterpene - 6 isoprene units (e.g., squalene)
waxes, precursors to ring lipids (e.g., cholesterol)

Question 10

Terpenoids

Answer 10

both terpene-like and terpene-not like regions
built from isoprene skeleton and functionalized with other elements (e.g., O, N, S, etc.)
e.g., vitamin A

Question 11

Steroids

Answer 11

hydrophobic

all steroids have basic tetracyclic ring system, based on structure of cholesterol

Question 12

Cholesterol

Answer 12

important component of lipid bilayer, precursor to steroid hormones, bile salts
obtained from diet and synthesized in liver
carried in blood packaged with fats and proteins into lipoproteins
4 ring structure: 3 6C rings and 1 5C ring

Question 13

Steroid Hormones

Answer 13

made from cholesterol

e.g., testosterone, estradiol