chapter 8 summary

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Lecture 1 : chapter 8

*what are lipids ?

lipids are organic compound that are insoluble in water but can be dissolved

in organic solvents like alcohol , aceton,…

* but why ? Lipids are compounds that consist mostly of nonpolar groups.

They have limited solubility in water, but dissolve freely in organic

solvents.

*they are classified according to chemical structure :

open-chain compounds : cyclic forms:

with polar head groups and fused rings

nonpolar long tails like fatty acids , triglycerides derived from

sphingolipids , glycolipids ,phosphoacylglycrols cholesterol

lipid soluble vitamins ,PGs ,LTs ,TXs

Lipids types :

Fatty acids : amphipathic compounds because the carboxyl

group is hydrophilic and the hydrocarbon tail is hydrophobic

*the hydrophobic tail

is usually unbranched

RـــــــCOOH

*fatty acids come from either hydrolysis of TAG or phospholipids of the

membrane

Amphipathic : تعني ان المركب يحتوي على مواد ذائبة في الماء ومواد

ر ذائبة في الماءيغ



Saturated fatty acids Contain only single bonds in straight structure

Like the fat Unsaturated fatty acids Contain at least on double bond ,

2 conformation : cis >> produces kink

Trans >> straight

Lower melting point(the more double bonds the more

the lower melting point)

Like the oil

Nomenclature : we put the number of carbon and then the number of double

bonds

Triacylglycerols : Glycerol is a simple compound that contains three hydroxyl groups . When all three of the alcohol groups form ester(polar) linkages with fatty acids, the resulting compound is a triacylglycerol; an older name for this type of

Essenti

al FAs

Unsaturated fatty acids can be

converted to Saturated fatty

acids by hydrogenation



compound is triglyceride.

Phospholipids : Result from esterification)forming ester bond) by phosphoric acid rather than fatty acid on one of the alcohols

*phosphoric acid is triprotic( and thus can form more than one ester

linkage. One molecule of phosphoric acid can form ester bonds both to

glycerol

and to some other alcohol, creating a phosphatidyl ester

المقصود ان الفوسفريك اسيد قادر على عمل اكثر من استير على عكس الفاتي اسيد القادر على عمل رابطة واحدة فقط

Classification of phosphatidyl ester The classification of a phosphatidyl ester depends on the nature of the substance that

is esterified to the phosphate group (R group )

Store energy in the adipose tissue ,

each gram produces 9Kcal of energy !

Glycerol used in creams and lotions

Ester bond is formed when we lose OH

from one side and H from the other side

to form RـــــOـــــــR



المقصود انه يتم تصنيفهم بناء على المركب المرتبط بذرة االكسجين

these compounds have long, nonpolar, hydrophobic tails and polar, highly

hydrophilic head groups and thus are markedly amphipathic

*the polar head is negatively charge at neutral Ph

*they are important in biological membrane

Waxes :



Mixture of esters of long chain FAs and alcohols

*The only function is

protective I n plant and

human

Sphingolipids :

Formed form

sphingosine + FA

*no glycerol

Sphingosine is amino

alcohol (alcohol (OH)

+amine(NH3)) .

When only linked to FA at the amino

group >ceramide(the simplest

sphingolipid).

When linked to FA and phospahric acid on the alcohol and the phsopharic

acid esterfied with choline(amino alcohol) >> myelin .

*sphingolipids are important in nervous system and found in both animals and plants

*how to make sphingolipid ?

1- sphingosine (which is alcohol amine) react with FA at the amine

group

2- the type of sphingolipid is determined by the molecule at the

alcohol group



Glycolipids : a compound in which a carbohydrate is bound to

an alcohol group of the lipid by a glycosidic linkage.

* when alcohol (OH) from a lipid (like

sphingosine) binds to

sugar(monosaccharides ) this form

glycolipid

For example cereamide + sugar(glu or

galactose) > glucocerebroside

*cerebrosides are important for

nerves and brain

*when add complex carbohydrate

moiety (more than 3 sugars) it’s

called gangliosides

ceramid

e



Steroids: a group of lipids that have a fused-ring structure of three six-

member rings (A, B, C), and one five-member ring (D)

Six member and five member mean>> number of ribs of the ring ! >> ستة

اضالع وخمسة اضالع

*all steroids are derived from cholesterol

*cholesterol contains only one hydroxyl group so it’s highly hydrophobic

and it’s very important component of cell membrane in animals (not

prokaryotes) and can be deposited in case of atherosclerosis(تصلب الشرايين(

Summary for key points

*lipids are water insoluble but can be dissolved because mainly of nonpolar

compounds but can be soluble in organic solvents

* lipids can be open chain or fused rings(steroids )

type summary



FA *Saturated (single bonds,high melting point) ,nonsaturated(double bonds ,

cis ,trans , low melting pint) *Contain carboxyl group , can make ester bonds with alcohol on glycerol or sphingosine *released from degradation of TAG or Phospholipids *named as number of carbons : number of double bonds

TAG *Glycerol+3 FA by esterification reaction *glycerol released for TAG defradation *important for energy storage *hydrolyzed by Lipase(inside)>> outside the body by acids or bases(saponification)

phosphpolipids

Glycerol+2 FA + one phosphate * classified according to what binds the phosphate (phosphatidyle esters) >>phosphatidylX

wax Long chain alcohol + long chain FA * protective

Sphingolipid

Sphingosine+ FA ester on amine group +group on the alcohol * classified according to what bind the alcohol(H ,sugar , phosphocholine)

Glycolipid Carbohydrate (glu or gala.)+ alcohol by glycosidic link like ceramides Complex sugers + alcohol >> gangliosides

Steroids 3 sixed rings + one fived ring All are derived from cholesterol which is found in animal membranes All have the same structure and differ only by side chains Examples : sex hormones( testosterone , estradiol , vitamin D3)

Biological membrane

Composed from lipids and proteins which interact with each other to

determine function >isolation of the cell extracellular matrix , regulate

transportation of specific substance , contain important enzymes

component details

lipids *composed of phosphoglycerides(phospholipid))amphipathic),glycolipids,cholesterol



* the lipids arranged in bilayer(held together by non-covalent bonds like van dar

waals and hydrophobic interaction) where : 1-The outer layer toward the external environment(water) so it’s polar , and composed of the heads of the phospholipids and mixture of lipids , contain bulky molecule. 2- the inner layer composed of non-polar tails because it’s hydrophobic environment And mixture of lipids that may differ from the external layer , contains smaller molecule . and contain cholesterol The non-polar tails are FAs that may be : Saturated >> linear arrangement>> more rigid membrane Unsaturated(cis) >> produce kink >> more fluid membrane Normally the bilayer is more fluid than rigid

* cholesterol : - is found in the internal layer

-found only in animal cells , not plants , not the prokaryotes(bacteria) -stabilizes the extended straight chain arrangement of saturated fatty acid by van

der waals interaction >> so no cholesterol = more fluidity --

-- plants contain more unsaturated FA ,and bacteria don’t contain steroids at all

so their membrane is the most fluid

*as temperature increases ,the membrane more disordered and more fluid



proteins *Peripheral proteins (found on the surface of the membrane)

bound to polar head groups of lipid by electrostatic interactions or polar interactions (or both)

can be removed by raising the ionic strength of the medium (1 M NaCl)>so this will remove the interaction between the proteins and lipids. *Integral proteins: Span the membrane from exterior to interior and are bound tightly to the membrane

can be removed by harsh treatment with detergents or sonication(ultrasound)

removal generally denatures without pure removal ! * proteins are found as alpha helical or beta pleated sheet and this minimize contact of polar residues with the non-polar lipids

بوالر , لهذا البروتين بكون الفا او بيتا لتقليل التفاعل بينهم -يعني البروتين بوالر والغشاء نون *Proteins also can be

anchored or fixed to the lipid via covalent bonds From cysteins or free amino groups to one of several lipid anchors *Common anchors

include:

Myristoyl and Palmitoyl

*N-myristoylationcan be via

N-terminal gly residue

Thioester linkage occur at cys residue

Transition temperature is the temperature at which there is cooperative transition of the

fluidity of the membrane , and it’s higher for more rigid membranes and less for more fluid

membranes.



Function of the plasma proteins

1- transport : polar and large molecule need to enter the cell , but

they can’t pass through the membrane directly , they use

transporter protein

Active means against concentration gradient passive

Needs energy and carrier protein

Primary >uses ATP directly and contains multiple subunits

> ATPase activity and carrier subunit

> like Na-K ATPase

Secondary > uses electrochemical gradient that created by primary active

transport and uses energy

Indirectly , by moving one substance down the

Gradient and the other against the gradient

Flip flop migration of lipid molecules from one layer to another layer is limited(occurs occasionally)

•Lateral motion within one layer frequently occurs specially in fluidic bilayer

Fluid mosaic model : explain how the membrane exists and formed

Mosaic : implies that the two components exist side byside without forming some other

substance of intermediate nature Fluid: lateral motion in lipid bilayers also occurs in

membranes. The proteins “float” in the lipid bilayer and can move along the plane of the

membrane



More details :

Secondary active transport in bacteria :

Bacteria transport lactose to the cell

against the concentration gradient , so

it needs a substance to be moved

down the gradient which is H+

BUT HOW BACTERIA CREATE THE

GRADIENT OF THE H+ :

Bacteria will pump H+ out the cell

by primary active transport > now

H+ is more outside the cell > it will enter through galactoside permease

down the gradient and create energy that’s used by the same transporter to

transport lactose

Passive transport :

No need for energy , down the electrochemical gradient

Two types : 1- simple diffusion : a molecule or ion moves through an opening Without interaction with other molecules Small uncharged molecules O2,N2,CO2 The rate of movement is controlled by conc. Difference across Membrane> the more the difference the more the rate 2- facilitated diffusion : a molecule or ion is carried across a membrane by carrier/channel proteinTransport driven by concentration difference. Interaction occur but no energy required



Large polar molecules and ions like Glucose movement from blood to RBCs Blotting the rate of transport by facilitated diffusion against substance concentration give a hyperbolic relationship

This means a presence of carrier that might get saturated. But no saturation in simple diffusion with linear relationship

Membrane receptors : The second function of membrane proteins But what is a receptor ??

a receptor is a large protein that's on the surface of the cell or inside the

cytoplasm , and interact with specific active substance that change its

activity and initiates an action within the cell



Features of receptors :

1- Large proteins 2- Interact with specific substance that has the same shape that fit in the

receptor 3- Receptors action can be

inhibited by poison (inhibitor)

4- Mostly integral and lose function when isolated

5- Very few present in cell membrane

Example of receptors :

Cholesterol is transported in

the blood in with LPL protein

because it's hydrophobic.

To enter the cell the protein

portion of LDL binds to a

receptor on the cell surface ,

and the complex is endocytosed , and the receptor will be recycled.

*excess cholesterol decrease the number of these receptors and

associated with atherosclerosis or heart diseases

LDL protein

contain mainly

cholesterol

LDL-

receptor

complex

Receptor is

recycled



Lipid soluble vitamins :

vitamin details

Vitamin A

*derived from b-carotene which is an extensively unsaturated hydrocarbon (the precursor of Vit A) *b-carotens converted in the liver to vit A(retinol) *Vitamin A is abundant in carrots and other vegetables *the aldehyde form Vit A ( Retinal) play important role in vision when bound to protein called opsin to form the visual pigment called rhodopsin *the aldehyde is formed by dehydrogenase and it's found as cis or trans *The aldehyde group of retinal forms an imine (also called a Schiff base) with the side-chain amino group of a lysine residue in rod-cell opsin



Vit. D *derived from cholesterol(steroid) * regulates Ca++ and phosphate in the body and it's important for the bones *cholesstrol>dehydrochoesterol> then By uvl >cholecalciferol(vit d3 the modt abundaunt form)>hydorlyxated in the liver on 25-carbon>then hydorxylated on cabon1 in the kidney >to form the active form *deficiency leads to rickets in children and infants



Vit.E *The most active vitamin E is a tocopherol Vitamin E is an antioxidant(reducing agent) >means it reacts with oxidizing agents so it will be oxidized instead of our cells and this will protect us

*React and remove a very reactive and highly dangerous substances known as free radicals

Free radicals has at least one unpaired electrons which accounts for their reactivity

In rats Vit E is required for reproduction and prevention of muscular dystrophy

Vit.K It's composed of bicycled rings +isoprene units(long unsaturated

hydorocarbbons) *the rings contain Contain 2 carbonyl groups. (polar part) * the number of isoprene units determine the form of vit.k * Vitamin K has an important role in blood clotting(Pro-Thrombin activation * it adds COO- to glutamate forming carboxyglutamate ,then forms bidentate”two teeth” ligand which binds Ca++



Arachidonic acid metabolites :

Arachidonic acid is a polyunsaturated fatty acid contain 20 carbons and 4

double bonds .

The derivative of arachidonic acid is called Eicosinoids (eico means 20)

1- prostaglandins :

Derived from AA , the different types are determined by number and location of double bond and the presence or absence of oxygen containing functional group



*contain five membered ring

•Function •Smooth muscle contraction

•Control of blood pressure

•Induce inflammation

•Aggregation of platelets Inhibited by Aspiri , Cortisone

2-Leukotrienes:

derived from arachidonic acid



Found in WBC (White Blood Cells, Leukocytes)

Contain 3 conjugated double bonds

Functions :

cause constriction of smooth muscle cells, especially in the lungs (Asthma)

Synthesis stimulated by allergic reactions(pollen)

3-Thromboxanes contain cyclic ethers • TxA2 induce platelet aggregation and smooth muscle cell contraction

chapter 8 summary

Documents

ester bonds

fat unsaturated fatty

university street

nonpolar groups

days hotel tel

alcohol groups

ester linkage

polar head groups