lecture7_lipids.pptx

(1)

(2)

lipids

• _{Common defining feature of lipids is their}

insolubility in water

• _{But can be dissolved in nonpolar solvents such}

(3)

Functions:

• _{Structural components of cell membranes}

(e.g. Phospholipids and sphingolipids)

(4)

CLASESS

1. Fatty acids and their derivatives 2. Triacylglycerols

3. Wax esters

(5)

(6)

(7)

(8)

Packing of fatty acids

• _{Fully saturated fatty acids in the extended}

form pack into nearly crystalline arrays,

stabilized by many hydrophobic interactions.

• _{The presence of one or more cis double bonds}

(9)

Fatty acids can be:

• _Saturated

• _Unsaturated

– _{Cis configuration}

(10)

• _{Nonessential fatty acids – can be synthesized} • _{Essential fatty acids – must be obtained from}

the diet

– _{E.g. linoleic acid and linolenic acid}

– _{Sources: vegetable oils, nuts, and seeds}

– _{Contributes to proper membrane structure, and}

(11)

Functions of fatty acids

• _{In vertebrates, free fatty acids (unesterified fatty}

acids, with a free carboxylate group) circulate in the blood bound noncovalently to a protein carrier,

serum albumin.

• _{However, fatty acids are present in blood plasma}

mostly as carboxylic acid derivatives such as esters or amides.

• _{Lacking the charged carboxylate group, these fatty}

(12)

(13)

(14)

Triacylglycerols

• _{Esters of glycerol}

with three fatty acid molecules

• _{Referred to as fats}

(15)

• _{Fats – solid at room temperature, contains a}

large proportion of saturated fatty acids

• _{Oils – liquid at room temperature because of}

(16)

Functions of triacylglycerol

(17)

1. Storage and transport form of fatty acids

Triacyglycerol store more energy than glycogen:

1. Because they are hydrophobic, they coalesce into compact, anhydrous droplets within cells, storing an equivalent amount of energy with glycogen but in about 1/8 of glycogen’s volume.

Adipocytes – cell which store fats

(18)

2. Provide insulation in low temperature by

preventing heat loss

2. Provide insulation in low temperature by

preventing heat loss

3. In plant, provides an important energy

reserves in fruits and seeds.

(19)

(20)

(21)

(22)

Wax

• _{Complex mixture of nonpolar lipids}

• _{Protective coating on leaves, stems, and fruit of}

plants, and skin an fur of animals

• _{Main constituent of waxes: esters composed of}

long chain fatty acids and long-chain alcohols

• _{Also contains hydrocarbons, alcohols, fatty}

acids, aldehydes, and sterols

(23)

Examples of waxes

• _{Carbauba wax – produced by the leaves}

of Brazilian wax palm

_{Main Consituent: ester melissyl cerotate}

CH₃(CH₂)₂₄ – COO – (CH₂)₂₉CH₃

• _Beeswax

(24)

• _{wax extracted from spermaceti oil (from}

whales; see Box 10–1) are widely used in the manufacture of lotions, ointments, and

polishes.

(25)

(26)

Phospholipids: characteristics

• _{Amphipathic: have hydrophobic and}

hydrophilic domains

_{Hydrophobic domain – composed mainly of}

hydrocarbon chain of fatty acids

_{Hydrophilic – or polar head group – contains}

(27)

(28)

Phospholipids: roles

• _{Structural components of membranes}

• _{Emulsifying agents and surface active agents}

When phospholipids are present in

sufficient

(29)

(30)

Types of phospholipids

1. Phosphoglycerides – contains glycerol, fatty acids, phosphate, and alcohol (e.g. choline)

(31)

1. phosphoglyceride

The simplest

phosphoglyceride

(32)

(33)

(34)

2. sphingolipids

(35)

sphingomyelin

• _{Sphingomyelins resemble phosphatidylcholines in}

their general properties and three-dimensional

structure, and in having no net charge on their head groups

• _{Sphingomyelins are present in the plasma}

membranes of animal cells and are especially

prominent in myelin, a membranous sheath that

surrounds and insulates the axons of some neurons— thus the name “sphingomyelins.”

(36)

(37)

cerobrosides

• _{Cerebrosides have a single sugar linked to}

ceramide;

• _{those with galactose are characteristically found}

in the plasma membranes of cells in neural tissue, and those with glucose in the plasma membranes of cells in nonneural tissues.

• _{Example: galactocerebroside – entirely found in}

the cell membranes of the brain

(38)

(39)

Gangliosides

• _{Gangliosides, the most complex sphingolipids, have}

oligosaccharides as their polar head groups and one or more residues of N-acetylneuraminic acid

(Neu5Ac),a sialic acid (often simply called “sialic acid”), at the termini.

• _{Sialic acid gives gangliosides the negative charge at}

pH 7 that distinguishes them from globosides.

(40)

Importance of Sphingolipids

• _{Apparently (from reading your}

book), when Johann Thudichum discovered sphingolipids at the turn of the 20th century, he had no idea why they were present. That’s why the name is derived from the Sphinx.

• _{We now know that many are}

involved as cell surface recognition sites.

• _{One well-known function of}

(41)

Importance of Sphingolipids

• _{Many are involved as cell surface}

recognition sites.

• One well-known function of sphingolipids is that they function as cell surface

antigens, defining the various blood types.

• _{The human blood groups are determined}

in part by the type of sugars located on the head groups. In the ABO system, the determinating gene is located on

chromosome 9, and encodes one of several glycosyltransferases.

• _{If the gene encodes a protein that}

transfers an N-acetylgalactosamine group, this corresponds to the A antigen.

• If the gene encodes a protein that transfers a galactose group, this corresponds to the B antigen.

• _{If the gene does not encode an active}

(42)

Sphingolipids at Cell Surfaces Are Sites of

Biological Recognition

• _{In humans, at least 60 different sphingolipids have been}

identified in cellular membranes.

• _{Many of these are especially prominent in the plasma}

membranes of neurons, and some are clearly recognition sites on the cell surface, but a specific function for only a few sphingolipids has been discovered thus far.

• _{The carbohydrate moieties of certain sphingolipids}

(43)

• _{Gangliosides are concentrated in the outer surface of cells,}

where they present points of recognition for extracellular molecules or surfaces of neighboring cells.

• _{The kinds and amounts of gangliosides in the plasma}

membrane change dramatically during embryonic development.

• _{Tumor formation induces the synthesis of a new complement}

of gangliosides, and very low concentrations of a specific ganglioside have been found to induce differentiation of cultured neuronal tumor cells.

• _{Investigation of the biological roles of diverse gangliosides}

remains fertile ground for future research.

(44)

Other roles:

• _{Some glycolipids may bind bacterial toxins, as}

well as bacterial cells, to animal cell membranes.

• _{Example- the toxins that causes cholera,}

(45)

Sphingolipid storage disease

• _{Lysosomal storage disease is caused by a}

hereditary deficeincy of an enzyme required for the degradation of a specific metabolite.

• _{Several lysozyme storage disease are}

associated with sphingolipid metabolism.

• _{Example . Tac-Sachs diease due to}

(46)

(47)

Sterols

• _{Sterols are structural lipids that}

are present in the membranes of most eukaryotic cells.

• _{The general sterol has four fused}

rings, three of which are

six-membered, and one of which is five-membered.

• _{The main body of sterols is}

planar.

• _{Cholesterol is shown at the left.} • _{Sterols can modulate the fluidity}

of membranes.

• _{Many hormones are derivatives}

(48)

Steroid Hormones

• Steroids are oxidized derivatives of sterols. Can you determine where oxidation occurs from the precursor sterol? Can you describe how many electrons are involved in the

oxidation?

• Steroids have the main body of sterols, but do not have the alkyl chain, like in cholesterol. This makes them more polar than cholesterol. • Steroid hormones move through the

blood stream primarily attached covalently or noncovalently to protein carriers.

(49)

Lipids as Signals, Cofactors & Pigments

Beyond the Passive Roles of Lipids in Storage & Structure

• Active roles for lipids and their derivatives

_{Intracellular signaling – Phosphatidylinositol} _{Paracrine hormones – Eicosanoids}

_{Steroid hormones –polar cholesterol derivatives} _{Vitamins – A, D, E, and K}

(50)

(51)

(52)

(53)

(54)

(55)