Lipids

Lipids

• long-term energy storage

• do not consist of polymers

• insoluble in polar substances

• structural components of cells –

ex. phospholipids are the major building block in cell membranes

• "messengers" (hormones)

Lipid Construction

• Lipids are composed of three fatty acids covalently bonded to a 3-carbon glycerol

• The fatty acids are composed of CH2 units, and are hydrophobic/not water soluble

Fats• Fats

– Are constructed from two types of smaller molecules, a single glycerol and usually three fatty acids

(b) Fat molecule (triacylglycerol)

H HH H

HHH

HH

HH

HH

HH

HOH O HC

C

C

H

H OH

OH

H

HH

HH

HH

HH

HH

HH

HH

H

HCCC

CC

CC

CC

CC

CC

CC C

Glycerol

Fatty acid(palmitic acid)

H

H

H

H

HH

HH

HH

HH

HH

HH

HH

HH

HHHH

HHHHHHHHHHHH

H

HH

H HH

H HH

HH

HH

HH

HH

HHHHHHHHHHH

HH

H

H H H H H H H H HH

HH H H H

H

HH

HHHHHH

HHHHH

HH

HO

O

O

O

OC

C

C C C C C C C C C C C C C C C C C

C

CCCCCCC

CCCCCCCCC

C C C C C C C C C C C CC

CC

O

O

(a) Dehydration reaction in the synthesis of a fatEster linkage

Figure 5.11

• Saturated fatty acids– Have the maximum number of hydrogen

atoms possible– Have no double bonds

(a) Saturated fat and fatty acid

Stearic acid

Figure 5.12

Saturated Fats

• Unsaturated fatty acids– Have one or more double bonds

(b) Unsaturated fat and fatty acidcis double bondcauses bending

Oleic acid

Figure 5.12

Unsaturated Fat

• Saturated refers to the "saturation" of the molecule by hydrogen atoms

• The presence of a double C=C covalent bond reduces the number of hydrogens that can bond to the carbon chain, hence the application of the term "unsaturated“.

• Fatty acids can be saturated (meaning they have as many hydrogens bonded to their carbons as possible) or unsaturated (with one or more double bonds connecting their carbons, hence fewer hydrogens).

• Fat - solid at room temperature (saturated)• Oil - liquid (unsaturated)

Phospholipids

• Phospholipids– Have only two fatty acids– Have a phosphate group instead of a third

fatty acid

• Phospholipid structure– Consists of a hydrophilic “head” and

hydrophobic “tails”

CH2

O

PO O

O

CH2CHCH2

OO

C O C O

Phosphate

Glycerol

(a) Structural formula (b) Space-filling model

Fatty acids

(c) Phospholipid symbol

Hy

dro

ph

ob

ic t

ail

s

Hydrophilichead

Hydrophobictails

–

Hy

dro

ph

ilic

he

ad CH2 Choline

+

Figure 5.13

N(CH3)3

• The structure of phospholipids– Results in a bilayer arrangement found in cell

membranes

Hydrophilichead

WATER

WATER

Hydrophobictail

Figure 5.14

Cholesterol and steroids

• Steroids - lipids characterized by a carbon skeleton consisting of four fused rings

HO

CH3

CH3

H3C CH3

CH3

Figure 5.15

• One steroid, cholesterol– Is found in cell membranes– Is a precursor for some hormones

HO

CH3

CH3

H3C CH3

CH3

Figure 5.15

Cholesterol

• Excess cholesterol in the blood has been linked to atherosclerosis, hardening of the arteries.

Functions of Fats and Oils

• Long term energy storage • Animals convert excess sugars (beyond

their glycogen storage capacities) into fats • Plants store excess sugars as starch,

although some seeds and fruits have energy stored as oils - corn oil, peanut oil, palm oil, canola oil, and sunflower oil

• Fats store six times as much energy as glycogen.

• Insulation - heat retention• Cushion – protection (body organs, fetus)• Structural components of cells - Phospholipids

and glycolipids – cell membranes• Phospholipids are modified so that a

phosphate group (PO4-) is added to one of the fatty acids.

• The addition of this group makes a polar "head" and two nonpolar "tails".

• Waxes – cuticle -waxy layer covering the leaves and stems of many land plants; and protective coverings on skin and fur of animals

• Hormones – body regulation