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Biochem sheet( 6) Lipids & membranes

Made by: enas omar

corrected by laith sorour

date:6/10/2016

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Lipids & membranes

Lipids 00:47

• Lipids: a heterogeneous class of naturally occurring organic compounds classified together

on the basis of common solubility properties

• insoluble in water, but soluble in nonpolar organic solvents including diethyl ether,

chloroform, methylene chloride, and acetone

# Main characteristics of lipids:

• carboxyl group

• methyl group

• insoluble in water yet soluble in organic solvents

*because of that when you have fat(oil) on your hands you use soap with hot water

so emulsification occurs

• Amphipathic in nature

• Amphipathic = compounds that contain groups which are soluble in water & groups which

are insoluble in water

• These compounds are soluble in water because they contain oxygen & hydrogen

• The most common example of these compounds is cholesterol

*fatty acids contain hydrophilic head and hydrophobic tail

• Lipids include

Open Chain forms

• fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, glycolipids,

• lipid-soluble vitamins

• prostaglandins, leukotrienes, and thromboxanes

Cyclic forms

• cholesterol, steroid hormones, and bile acids

*األساس فيهم الكولسترول

*cholesterol gives steroid hormones and bile ducts and the active form of vitamin D

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Functions of lipids 3:25

• Source of energy

• Most of our energy is derived from lipids

• The primary role of lipids in your body is to provide energy for muscles and body processes

*carbohydrates are stored as glycogen

• Cellular membranes

the main elements of cell membrane are lipids (glycolipids, cholesterol….)

• All cells in our body are bordered by lipid bilayer

• Excellent insulators which protect the body

• Thermal insulators & protection

• Therefor fat people don’t feel the coldness in winter unlike thin people

• Besides, once a fat person enters a swimming pool he would float because the large

quantity of lipids.

• Lipids are also used to insulate and protect your body. You have a layer of fat just

below your skin that helps to keep your internal body temp regular despite the

external temp. Your vital organs such as kidneys and heart have a layer of fat around

them that acts like bubble wrap to protect them from injury.

• Electrical insulators (in membranes)

• Special roles:

• Signals

• Second messengers which are stimulated by extracellular hormones(protein

hormones) ( can't cross the cell membrane because they are insoluble in lipids)

• Hormones, Mediators, or growth factors.

• Hormones are divided into two main groups :

• 1-extracellular hormones: such as protein hormones(like insulin, growth

hormones, and adrenaline.) which work in the cell surface and stimulate a

second messenger to initiate a series of events like

• 2-intracellular hormones: such as steroid hormones which can cross the cell

membrane and change the formation of DNA.

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• Cholesterol is a type of lipid needed to produce important steroid hormones

in your body, such as: estrogen, testosterone, progesterone, and the active

form of vitamin D.

*steroid hormones end with –ol =two alcohol groups\ one =there is ketone

*protein hormones end with –ine \in

• Coenzymes

• Vitamins

Vitamins are absorbed by lipids, lipids serve as source of fat soluble vitamins like A,D,E,K.

Therefor when there are problems in absorption (problems in intestine), vitamins deficiency occurs.

-some vitamins like vitamin K are produced in intestine

Fatty acids 9:48

• Fatty acid: an unbranched-chain carboxylic acid, most commonly of 12 - 20 carbons,

derived from hydrolysis of animal fats, vegetable oils, or phospholipids of biological

membranes

• Usually contain even numbers of carbons (can contain odd, depending on how they are

biosynthesized)

•FA that contain C=C, are unsaturated: If they contain only C-C bonds, they are saturated

Unsaturated fatty acids can be trans with straight chains or cis with angles.

In most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare

• Length of fatty acid plays a role in its chemical character

• For instance, saturated fatty acids have higher melting points than unsaturated ones

• When the length of hydrophobic hydrocarbon chain of fatty acid increase, melting points

increase.

• When the number of double bonds in unsaturated fatty acids increase, melting points

decrease. the greater the degree of unsaturation, the lower the melting point

Examples of saturated fatty acids :

palmitic acid 16 c atoms ,,,,,,,,,,,, stearic acid 18 c atoms , found in beef

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ex of unsaturated fatty acids:

oleic acid1 double bond , in cholesterol

linoleic acid18 c atoms , 2 double bonds ,cis confirmation

look to slides 813 to see the structures of these fatty acids

This table show the fatty acid composition of three common fats, we can notice that olive oil is

liquid at room temp because it consists mainly of unsaturated C16-C18. Butter is soft solid because

it consists of equal quantities of saturated & unsaturated. Beef fat is hard solid because composed

of saturated and contains small amount of carbons C4-C14 .

((**Fatty acids start with carboxyl group and end with Methyl group

*omega-3\6 according to methyl group

*alpha\beta\gamma according to carboxyl ))

**linolenic acid (18:3 Δ 9, 12, 15) ===18 means there are 18 carbons *:3 there are 3 double bonds

* Δ 9,12 ,15 =double bonds are on carbon 9,12,15

In the shorthand notation for fatty acids

saturated FA: the number of carbons then (:) then (0) are shown

unsaturated FA: the number of carbons then (:) then the number and location of double bonds in

the chain raised above delta symbol (Δ) are shown, separated by a colon

Note: Counting starts from C of COOH

Examples: palmitic (16:0), stearic (18:0), and oleic acids (18:1Δ9) = double bond between C9 and

C10

Essential fatty acids 17:00

Which the body can't synthesize, in fatty acids synthesis our body can synthesize one double bond

only, y3ny two or more double bonds can’t be synthesized.

• They have to be supplied in the diet without exception.

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• They are all polyunsaturated fatty acids: the C20 fatty acid arachidonic acid (20:4 Δ 5,8,11,14)

and the two C18 acids linoleic acid (18:2 Δ 9,12) and linolenic acid (18:3 Δ 9,12 ,15 ).

• Linoleic acid , the precursor of w-6 arachidonic acid , which is the substrate for

prostaglandin

• Synthesis, and a-linolenic acid, the precursor of w-3 fatty acids that are important for

growth and development. Are dietary essentials in humans because we lack the enzymes

needed to synthesize them, Plants provide us with these essential fatty acids.

• Ps: arachidonic acid becomes essential if linoleic acid is deficient in the diet.

The animal organism requires arachidonic acid to synthesize eicosanoids

• Nutritional fats contain palmitic, stearic, oleic acid, and linoleic acid particularly often.

Unsaturated fatty acids are usually found at the central C atom of glycerol.

• Tryacylglycerols 18:45

• Triglycerides=glycerol + 3 fatty acids

• It’s the storage form of lipids

• The superficial fats under the skin

• More than 100000 kcal of energy is stored as triglyceride

• It remains at the last after consuming carbohydrates & proteins

*triglycerides is the storage form of lipids

• Triacylglycerol (triglyceride): an ester of glycerol with three fatty acids

• natural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with

NaOH, in a hydrolysis reaction called saponification (Latin, sapo, soap)

•

• Saponification : is the alkaline hydrolysis of the fatty acid esters

A triacylglycerol(a triglyceride)

CH2 O- CR

O

O

O

CH2 O- CR''

NaOH, H2 O

CH2 OH

CH2 OH

1,2,3-Propanetriol(Glycerol, glycerin)

+

RCOO-Na+

SodiumSoaps

HOCH

R' CO-CH

R' COO- Na+

R' ' COO-Na+

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• Ex: the chemical reaction btw any fat & NaOH is a saponification.

• Triglyceride + naoh + h2o glycerol + 3 soaps molecule

• Triglycerides can be either simple or mixed. In a simple triglyceride such as palmitin or

stearin all 3 fatty acid groups are identical. In a mixed triglyceride 2 or even 3 different fatty

acid groups are present, most fat & oils contain mixed triglyceride.

• Soaps :

• Soaps form water-insoluble salts when used in water containing Ca(II), Mg(II), and Fe(III)

ions (hard water)

•

• To get hard soaps Na should be used, but if soft soap is wanted such as (cream, hygiene) K

should be used.

• Hydrolysis of triglycerides 21:52

• Chemical hydrolysis, by saponification as mentioned earlier

• Enzymatic digestion by lipase enzyme

• Lipase which is located in pancreas, is an enzyme that hydrolysis the ester bonds in

triglycerides, to form fatty acids and glycerol.

• The pancreas is the most important organ in digestion.

*(pancreas releases pancreatic amylase for carbohydrates which digest starch into small

oligosaccharides ,lipases for lipids ,and enzymes for protein digestion like trypsin)

(pancreatic juice contains enzymes)

glycerol---fatty acids then bile comes and emullcificates and continues digestion

• Phospholipids 23:45

• Phosphoacylglycerols (= phospholipids) are the second most abundant group of naturally

occurring lipids

*neutral lipids= triglycerides = triacylglyceridesols =simple lipids

*fats group includes more

+

+

A sodium soap(soluble in water as micelles)

Calcium salt of a fatty acid(insoluble in water)

2 CH3 ( CH2 ) 1 4 COO-Na

+Ca

2 +

[ CH3 ( CH2 ) 1 4 COO-] 2 Ca

2 +2 Na

+

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• found almost exclusively in plant and animal cell membranes, which typically consist of

40% -50% phosphoacylglycerols and 50% - 60% proteins

• the most abundant phosphoacylglycerols are derived from phosphatidic acid, a molecule

in which glycerol is esterified with two molecules of fatty acid and one of phosphoric acid

• the three most abundant fatty acids in phosphatidic acids are palmitic (16:0), stearic

(18:0), and linoleic (18:1)

• phospholipids are the main structure of membrane

• phospholipids consist of glycerol backbone 2 fatty acids & phosphate group

• phosphatidyl esters :

• further esterification with a low-molecular-weight alcohol with phosphate group gives a

phosphoacylglycerol or phosphatidyl ester

• phosphatidyl esters consist of : glycerol backbone & 2 fatty acids & special group such as (

choline & serine )

• ethanolamine & choline are the most common phosphatidyl esters in the body(membranes)

.

• pulmonary surfactant 28:00

• DPPC (dipalmitoylphophatidylcholine) ( الدكتور حكى االسم فشكلة مطلوب ) nrja3 l mwdo3na

,,,,,, DPPC is made and secreted by type ll pneumocytes , is a major lipid component of lung

surfactant , which is the extracellular fluid layer lining the alveoli .surfactant serves to

decrease the surface tension of this fluid layer , reducing the pressure needed to reinflate

alveoli, thereby preventing alveolar collapse .

• Ps : surfactant = a complex mixture of 90% lipids + 10% proteins ( with DPPC being the major

component for reducing surface tension).

• A deficiency in DPPC causes Respiratory Distress Syndrome RDS.

*first thing must happen when baby is born he must cry (if he cries everything is good)

• Waxes 30:00

• A complex mixture of esters of long-chain carboxylic acids and alcohols

• Found as protective coatings for plants and animals

• Most animals are surrounded by wax to protect them from coldness in winter.

*biological wax is bee wax which is an ester of palmitic acid with the alcohol triacontanol

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• Sphingolipids 31:10

• contain sphingosine, a long-chain (18 C) aminoalcohol from which this class is named

• Found in plants and animals

• Abundant in nervous system

• Ends with ine so it contains amino group

• Contains long chain & amino group & alcohol (oh)

• Ex: sphingomyelin (sphingolipid + myelin) , which is a major structural lipids in the membranes of

nerve tissue.

Glycolipids 32:34

• Glycolipid: a compound in which a carbohydrate is bound to an -OH of the lipid

• many glycolipids are derived from ceramides

• Ceramide + simple sugar= cerebroside (found in nerve and brain cells)

Glucocerebroside is a lipid consisting of three components. The first of these is a

long chain alcohol called sphingosine A long chain fatty acid is linked to the nitrogen

atom (N) on carbon atom 2 of sphingosine creating a structure known as ceramide

• Multiple sclerosis :

• It is the most common autoimmune disorder affecting the central nervous system.

• The insulating covers of nerve cells in the brain and spinal cord are damaged.

•

• Nystagmus: rapid involuntary movements of the eyes.

• Dysarthria: difficult or unclear articulation of speech.

• Dysphagia: difficulty in swallowing.

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• Ataxia: the loss of full control of bodily movements

• Ps: these definitions were NOT mentioned by the doctor,, just to clarify the terms .

• Steroids 34:47

• Steroids: a group of plant and animal lipids that have this tetracyclic ring (four fused

rings) structure

• Composed from three six-membered rings (A, B and C) and one five-membered ring (D)

• The features common to the ring system of most naturally occurring steroids are

illustrated here

• The name of cyclic structure is ( cyclopentanoperhydrophenanthrene) 32 letters

• Elly 3dhom y9of 3 janeb :p

• Cholesterol

• The steroid of most interest is cholesterol

• Cholesterol is the major component of biological membranes (especially animal

membranes)

• The precursor of other steroids (sex hormones and vitamin D)

• Consist of 27 c atoms & hydroxyl group on C3 & methyl group

• Androgens

• Androgens: male sex hormones

• synthesized in the testes

• responsible for the development of male secondary sex characteristics

• estrogens

• Estrogens: female sex hormones

• synthesized in the ovaries

• responsible for the development of female secondary sex characteristics and control of

the menstrual cycle

*الزم تعرف من ايش بتكون كل نوع بدون حفظ البنية)اسماء و ايش بعمل( و انتبهوا على المعلومات اللي بالجداول و الرسمات

امينو اسيدز الزم تعرف البني*

• sorry in advance for any mistake you would find

Best wishes