The Chemical Components Of Cells

LECTURE 2 The Chemical Components of Cells Campbell & Reece. 7th Edn. Ch 5, pp. 68-80, 86-89

By Dr Mohamed Abumaree Molecular Reproductive Biology & Immunology College of Medicine King Saud bin Abdulaziz University for Health Science Riyadh 2009

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Objectives 1.To know macromolecules in human cells 2.To recognize macromolecules

the

structures

of

3.To know the functions of macromolecules 2

Macromolecules  Four types of macromolecules: 1) Carbohydrates 2) Lipids 3) Proteins 4) Nucleic acids  NOT all macromolecules are polymers: a repeating units of monomers: building blocks linked by covalent bonds 3

 Polymers: made by a dehydration reaction: 2 monomers are covalently added to each other & H2O molecule is lost  Each monomer contributes to the lost of water molecule: One provides OH group & other provides H  Dehydration reaction is repeated to form a polymer with the help of energy & enzymes 4

Polymers are disassembled to monomers by hydrolysis reaction (bonds broken) 5

 The digestion process in humans is an example of hydrolysis 1. The hydrolysis of organic components in our food (polymers) releases monomers 2. Then monomers are absorbed into bloodstream and distributed to all body cells

the

1. Also, cells can assemble monomers into new polymers (differ from the digested ones) to perform specific functions required by the cell 6

Carbohydrates

Monosaccharides

Polysaccharides

Disaccharides

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Monosaccharides  Simple or single sugars. For example, glucose  Classification according to: 1.The carbon skeletons length or 2.The arrangement around asymmetric carbons, carbons a carbon attached to 4 different partners or 3.The location of carbonyl group 8

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 Monosaccharides, Monosaccharides particularly glucose, are major: 1.Nutrients for cells 2.Fuel for cellular work 3.Raw materials for amino & fatty acids synthesis Not used sugar molecules will be incorporated into disaccharides/polysaccharides 10

Disaccharide

 2 monosaccharides are joined covalently (a glycosidic linkage) to form a disaccharide (a dehydration reaction). Examples: 1. Lactose (milk) consists of glucose & galactose 2. Sucrose (sugar) consists of glucose & fructose 11

Polysaccharides Monosaccharides are joined together by glycosidic linkages to form polysaccharides

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Storage Polysaccharides  Example: 1. Starch in plant 2. Glycogen in animals (Humans)  Glycogen is hydrolyzed into glucose when there is a demand for sugar  In humans, glycogen stores are depleted in about a day unless they are replenished by food consumption 13

Structural Polysaccharides  Cellulose (insoluble fiber) (plant cell wall)  NOT all organisms can digest cellulose  Cellulose is an important part of a healthful diet  Humans cannot digest cellulose:  But cellulose aids in the smooth passage of food through the digestive tract in order to be eliminated with the feces 14

Lipids  Macromolecules but NOT polymers  Hydrophobic (Little or no affinity for water)  Have some polar bonds associated with oxygen,  But they consist mostly of hydrocarbons  Biologically important types of lipids: Fats, phospholipids, & steroids 15

Fat Constructed from a glycerol (alcohol) & fatty acids

 A fatty acid has a carboxyl (functional) group attached to a long nonpolar hydrocarbon chain (16/18 carbon atoms in length) 16

Triacylglycerol (triglyceride) Constructed from 3 fatty acids molecules, molecules each is joined to a glycerol by an ester linkage (a bond between –OH & a carboxyl group, one water molecule is released

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Saturated Fatty Acid  No double bonds between carbon atoms (so many hydrogen atoms are bonded to the carbon skeleton; so saturated with hydrogen) hydrogen  Most animal fats (such as butter) are solid at room temperature (RT)

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Unsaturated Fatty Acid  One/more cis double bonds  Example, plant & fish fats  Liquid at room temperature

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Cis Fat (Naturally found) H H | | -C = CHydrogen atoms are on the same side of the chain of carbon atoms at the carbon-carbon double bond 20

 Hydrogenated vegetable oils (trans double bonds):  Unsaturated fats are synthetically converted to saturated fats (Peanut butter, margarine…)

 Saturated fats may contribute to the cardiovascular disease (atherosclerosis)  But trans fat may contribute more than saturated fats to atherosclerosis & other problems 21

Trans Fat (Synthetically Made) Hydrogen atoms are on opposite sides of the chain of carbon atoms at the carbon-carbon double bond

H | -C = C| H 22

The major function of fats is energy storage A gram of fat stores more than twice as much energy as a gram of a polysaccharide, such as starch 23

Phospholipids  Composed of 2 fatty acids, glycerol, acids glycerol phosphate group & a small molecules, such as choline (charged/polar)  Phospholipid diversity is based on differences in fatty acids & polar groups

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 Phospholipids show ambivalent behavior toward water, because phospholipids have: 1. Hydrophilic (polar) head 2. Two hydrophobic (non-polar) tails 25

Steroids  Have a carbon skeleton consisting of 4 rings attached to different functional groups  Many hormones (sex hormones) are steroids produced from cholesterol  So, cholesterol is a essential in animals, although a high level of it in the blood may contribute to atherosclerosis 26

Nucleic acids (Polynucleotides)  Nucleic acids consist of nucleotide monomers 

Composed of nitrogenous base, pentose and phosphate group 

A nucleoside: nucleotide without phosphate group

a a 27

Nitrogenous Bases

NO oxygen atom on the second carbon in the ring of deoxyribose 28

• Because the atoms in both the nitrogenous base & the sugar are numbered, the sugar atoms have a prime (′) after the number to distinguish them

Deoxyribose in DNA

Ribose in RNA 29

Nucleotide Polymers 

The phosphate group is attached to the 5′ carbon of the sugar giving a nucleotide 

Nucleosides are joined covalently (phosphodiester linkages: linkages between the –OH group on the 3′ carbon of one nucleotide & the phosphate on the 5′ carbon of the next)

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 There are 2 free ends of the polymer: 1. One end has a phosphate attached to a 5′ carbon (5′ end ) 2. The other end has a hydroxyl group on a 3′ carbon (3′ end)  So, DNA strand has a built-in directionality along its sugarphosphate backbone, from 5′ to 3′ 31

 The sugar phosphate backbone are attached to the nitrogenous bases  The sequence of bases along a DNA polymer is unique for each gene  The of bases in a gene specifies the protein’s structure & function in the cell 32

DNA molecules have 2 polynucleotides (double helix)

The double helix run in opposite 5′ → 3′ directions from each other (antiparallel)

 The bases are held together by hydrogen bonds  Compatibility:  A pairs with T  G pairs with C