Chapter 26: Lipids

1
Chapter 26 Lipids
Biomolecules that are more soluble in nonpolar or
weakly polar solvents than they are in water
glyceryl tristearate - a triglyceride or fat
2

• Acetyl Coenzyme A
• Fats, Oils, and Fatty Acids
• Phospholipids
• Waxes
• Prostaglandins
• Terpenes and the Isoprene Rule
• Isoprene units and terpenes
• Isopentenyl pyrophosphate
• Carbon-carbon bond formation in terpene
  biosynthesis
• Steroids
• Cholesterol
• Vitamin D
• Bile acids
• Corticosteroids
• Sex hormones
• Carotenoids
• Fat-soluble Vitamins

3

• Acetyl Coenzyme A

4

• Acetyl Coenzyme A

5

• Fats, Oils, and Fatty Acids

glycerine (glycerol)

• a triglyceride
• animal fat
• Rs more saturated
• higher melting point
• (solid at RT)
• vegetable oil
• Rs more unsaturated
• lower melting point
• (liquid at RT)

fatty acids
6

• Fats, Oils, and Fatty Acids

• fatty acids
• most have even numbered chains, between 12 and 20
  carbons
• cis isomer predominates in unsaturated fatty
  acids
• more unsaturation ? lower melting point

stearic acid (180) m.p. 70ºC oleic acid
(9-181) an ?-9 fatty acid m.p. 16ºC linoleic
acid (9,12-182) an ?-6 fatty acid m.p.
-5ºC linolenic acid (9,12,15-183) an ?-3 fatty
acid m.p. -11ºC
7

• Fats, Oils, and Fatty Acids

• stearic acid
• packs better intocrystal lattice
• m.p. 70ºC

• oleic acid
• m.p. 16ºC

• linoleic acid
• packs least well intocrystal lattice
• m.p. -5ºC

8

• Fats, Oils, and Fatty Acids

9

• Fats, Oils, and Fatty Acids

10

• Fats, Oils, and Fatty Acids
• Fatty acid biosynthesis

11

• Fats, Oils, and Fatty Acids
• Triglyceride biosynthesis

12

• Phospholipids

phosphoric acid esters
hydrophilic head group
glycerol
carboxylic acid esters

• along with proteins, are major constituent of
  cell membranes in plants and animals

hydrophobic tail - consists mostly of palmitic
(160) stearic (180) and oleic (181) acids
13

• Phospholipids

Cell membranes
proteins
lipid bilayer
cholesterol
phospholipid
14

• Waxes

15

• Prostaglandins

• originally isolated from semen and thought to be
  produced only in the prostate gland
• now known to be present in almost all animal
  tissues
• functions
• smooth muscle contraction
• inhibition of platelet aggregation
• lowering of blood pressure
• induction of labor
• all based on the prostanoic acid structure

16

• Prostaglandins

• synthesized in the body from 20-carbon
  polyunsaturated fatty acids

17

• Prostaglandins

• stimulates contraction of uterine muscle
• used as an abortifacient
• but very rapidly degraded in the body

• the synthetic prostaglandinCarboprost is 10 to
  20 timesmore potent, and also degradesmuch more
  slowly in the body

18

• Terpenes and the Isoprene Rule
• Isoprene units and terpenes

• terpenes
• volatile components of essential oils
• made up of isoprene units, usually joined
  head-to-tail

myrcene (bayberry oil)
farnesol (musk mallow)
19

• Terpenes and the Isoprene Rule
• Isoprene units and terpenes

Classification of terpenes Class Number of
isoprene units monoterpene 2 sesquiterpene 3 diter
pene 4 sesterpene 5 triterpene 6 tetraterpene 8
20

• Terpenes and the Isoprene Rule
• Isoprene units and terpenes

21

• Terpenes and the Isoprene Rule
• Isopentenyl pyrophosphate

22

• Terpenes and the Isoprene Rule
• Carbon-carbon bond formation in terpene
  biosynthesis

23

• Steroids

• Cholesterol, hormones, bile acids
• all have this tetracyclic ring structure
• most have methyl groups at C-10 and C-13

• most steroids have all-trans ring fusions
• groups at the points of ring fusion are axial
  (anti)
• as a result the ring system is nearly flat and
  quite rigid

24

• Steroids
• Cholesterol

• precursor to other hormones
• essential component of biological membranes (140
  g in healthy adult)
• transported in the blood as a soluble complex
  with lipoproteins
• low-density lipoproteins (LDL) can be deposited
  in blood vessels
• high-density lipoproteins (HDL) minimize deposits

25

• Steroids
• Vitamin D

vitamin D3 is involved in the regulation of
calcium and phosphorus metabolism - essential
for preventing rickets
26

• Steroids
• Bile acids

• produced in the liver, stored in the gall
  bladder, secreted into the intestine
• anions at bile and intestinal pH
• help to emulsify dietary fats and aid in their
  digestion

27

• Steroids
• Corticosteroids

• produced in the adrenal cortex
• control electrolyte balance, regulate metabolism
  of carbohydrates, decrease inflammation, involved
  in reaction to stress, allergic response

28

• Steroids
• Sex hormones

• androgens (male sex hormones)
• produced in the testes
• responsible for development of male sex
  characteristicsestrogens (female sex
  hormones)
• produced in the ovaries
• responsible for development of female sex
  characteristics
• progesterone suppresses ovulation

• synthetic substances such as 17-ethynylestradiol
  are more potent at suppressing ovulation
• important as oral contraceptives

29

• Carotenoids

• natural pigments characterized by tail-to-tail
  linkage between two 20-carbon units
• absorb light in the visible portion of the
  spectrum due to the extended conjugation
• therefore colored

30

• Fat-soluble Vitamins

found in carrots and someyellow and green
vegetables
found in fish-liver oils and dairy products
31

• Fat-soluble Vitamins

32

• Fat-soluble Vitamins

• occurs in fish oil and some vegetable oils, and
  in leafy green vegetables
• functions as an antioxidant - traps peroxy
  radicals (ROO) formed during enzyme-
  catalyzed oxidation

• essential for blood clotting

33

• Fat-soluble Vitamins

• Passes through GI tract untouched
• carries some fat-soluble vitamins with it
• products containing Olestra usually have higher
  levels of fat-soluble vitamins added to them to
  make up for this loss