CHAPTER 4:CHEMICAL

COMPOSITION OF THE CELL

• ELEMENT IN THE CELL1. There are about 92 element

occurring naturally in nature.2. From these 92 element, only about

25 element are needed to build living organisms.

3. Not all these element found in all living cell.

4. Main element (CHON) are the most frequently found elements in cells, forming about 96% of the human body mass.

5. Trace-elements are the elements are found in small quantity in cells, but are important in biological processes.

CHEMICAL COMPOUND IN THE CELL1. Chemical compounds in the cell can be divided into two

major group:• Organic• Inorganic2. Organic compounds are:• Chemical compounds contain carbon (exception are

carbon monoxide, carbon dioxide, carbides and carbonates which are typically considered as inorganic)

• Are usually found in and originate from living organism.• Usually consist of macromolecules (large molecules).3. Inorganic compounds are:• Chemical compounds that do not contain carbon• Usually a smaller and simpler than organic compounds• Founds in cells water, acids, alkalis and mineral salts

• There are 4 main group of organic compounds in cells:

I. CarbohydratesII. Lipids III. ProteinsIV. Nucleic acids

• CarbohydratesI. The carbohydrates are made up of carbon,

hydrogen and oxygen. The ratio of hydrogen to oxygen atoms in a molecule usually 2:1.

II. Many carbohydrates have the general formula CX(H2O)Y,where x is approximately equal to y.

III. Three basic types of carbohydrates are monosaccharide, disaccharides and polysaccharides

• Monosaccharide i. Monosaccharide also called simple sugarii. The common monosaccharide are six-

carbon sugar with a molecular formula of C6H12O6

iii.Example of monosaccharide are glucose, fructose (fruit sugar) and galactose

iv.Glucose is the most common monosaccharide and respiratory substrate

v. Monosaccharide are sweet-tasting crystalline substances which are soluble in water

• Disaccharidesi. Disaccharides are formed from two

monosaccharide molecules combining together with the elements of a molecule of water. The chemical reaction of the formation is known as condensation.

ii. The general formula of a disaccharides is C12H22O11

iii. Disaccharides also called double sugar.iv. Disaccharides can be broken down to their

constituent monosaccharide by a chemical reaction involving the addition of water. The reaction is know as hydrolysis.

v. Like monosaccharide, they are sweet-tasting crystalline substances that are soluble in water.

vi. The most common disaccharides are maltose, lactose and sucrose.

Hydrolysis

Condensation

C12H22O11

sucrose

+ H2 O

water C6H12O6

fructose

C6H12O6

glucose

+

Hydrolysis

Condensation

C12H22O11

maltose

+ H2 O

water C6H12O6

glucose

C6H12O6

glucose

+

Hydrolysis

Condensation

C12H22O11

sucrose

+ H2 O

water C6H12O6

fructose

C6H12O6

glucose

+

Hydrolysis

Condensation

C12H22O11

lactose

+ H2 O

water C6H12O6

galactose

C6H12O6

glucose

+

• Polysaccharidesi. Many monosaccharide molecules join

together in a condensation reaction (with the removal of water molecules) to form a large polysaccharides molecules.

ii. Polymerisation is the process of condensing many individual monosaccharide molecules to form a large polysaccharides molecules.

iii. In polymerisation, the individual monosaccharide molecule are called monomers.

iv. Polymerisation of monosaccharide forms:• Glycogen – in humans and animals• Starch and cellulose – in plants

glucose

Starch structureSub unit: GlucoseConsists of two components.a)Unbranched, helical chains of glucose unitsb)Branched chains of glucose units

Major storage of carbohydrate in plants

glucose

•Sub unit: Glucose

•Molecules with many side branches

•Major storage of carbohydrates in animals and fungi, for examples, in muscle cells and liver cells

glycogen

glucose

cellulose

Straight unbranched chain of glucose unitsPlant cell wall

• Reducing and non-reducing sugara) Some sugars act as mild reducing

agentsb) Two common test reagent to test for

reducing sugar are:i. Benedict’s reagent (alkaline solution of

CuSO4)ii. Fehling’s reagent (alkaline solution of

CuSO4)c) Reducing sugars reduce Cu²+ (blue

solution) to Cu+ (brick red precipitate) in both reagents.

• Proteins1. Proteins are compounds of these element:

carbon, hydrogen, oxygen, nitrogen sulphur and phosphorus.

2. Amino acids are the subunits of all proteins.3. Each amino acids carries two functional group:a) A carboxyl group (- COOH) which is acidic andb) An amino group (-NH2) which is basic. COOH carboxyl group

C NH2 amino group

• Two amino acids can combine together to form a dipeptide by a condensation reaction between the carboxyl group of one and the amino group of the other. The resulting a bond liking the two amino acids that is called a peptide bond.

cooh Hn c nC C c c NH2 hooc nh2 hooc

O h h

H2O

condensation

Peptide bond

• Long chains of amino acids are called polypeptides.

• A polypeptide is formed by the condensation reaction of many amino acids, with the removel of water.

• A polypeptide chain can also be hydrolysed, with the addition of water molecules to form individual amino acids.

PROTEIN STRUCTURE• Primary-linear sequence of amino acids • Secondary structure- forming ahelixor pleated

sheet.• Tertiary structure- compact structure• Quaternary structure- 2 or more tertiary

structure

LIPIDS• Lipids a diverse group of substance that

contain carbon, hydrogen and oxygen. The proportion of oxygen is lower than that in carbohydrates. For example, the general formula of stearic acid is C18H36O2.

• All lipids are insoluble in water• Lipids dissolve readily in other lipids and

in organic solvent such as ether and ethanol.

• The main types of lipids are:a) Fatsb) Oilsc) Waxesd) Phospholipidse) steroids

Fats and oils• Fats are solid at room temperature

(20°C), whereas oil are liquid• Each molecule of fats or oils is made up

of one glycerol combine with three fatty acids which may be the same or may be different. Three molecule of water are remove in this condensation reaction.

Hydrolysis (+ H2O)

Condensation (- H2O)+

glycerol 3 fatty acids molecules

Triglyceride + 3 water molecules

• These molecules of fats and oils are known as triglycerides.

• Fats often contain only saturated fatty acids.• Oils usually contain unsaturated fatty acids.• In a saturated fatty acids, the carbon

atoms are bonded to the maximum number of other atoms. Saturated fatty acid has only single bond and the hydrocarbon chain is relatively straight.

• Unsaturated fatty acids has double bond in the form of –CH=CH- in the hydrocarbon chain. Fatty acids; those with two or more double bond are called polyunsaturated fatty acids.

• Fats and oils function efficiently as energy storage material. Fats and oils provide 38kJ per gram, while carbohydrates can provide only 17 kJ per gram.

Type of fatty acids

Example

Structural formula

Saturated Stearic acid

CH3(CH2)16COOH

Unsaturated

Oleic acid

CH3(CH2)7CH=CH(CH2)7COOH

Waxes• Waxes are similar to triglycerides, but the

fatty acids are bonded to long-chain alcohols rather than glycerol

• Waxes are usually hard solids at room temperature

• Waxes are used to waterproof the external surface of plants and animal. The cuticle of a leaf and the protective covering on an insect’s body are made of waxes.

• Wax is also a constituent of the honeycomb of bees

Phospholipids• Phospholipids have a similar structure

to triglycerides but one of the fatty acids is replaced by a phosphate group

• The end of the phospholipids molecule containing the phosphate group is hydrophilic. The other end containing the hydrocarbon chain of the fatty acids is hydrophobic.

• The hydrophilic end is soluble in water while hydrophobic is insoluble in water.

• Phospholipids bilayer from the basis of all cell membrane.

Steroids• A steroid molecule has a complex ring

structure• Steroid occur in plants and animals• Examples of steroids are cholesterol,

testosterone, estrogen and progesterone.Steroid Functioncholesterol Strengthens the cell

membrane at high body temperature

testosterone Male reproductive hormoneestrogen and progesterone.

female reproductive hormone

• Saturated and and saturated fats• Animal fats such as lard, butter and

cream are example of saturated fats• Vegetable oil such as olive oil and

sunflower oil are example of unsaturated fats.

Saturated fats Unsaturated fatsSimilarities

1. Both are triglycerides2. They yield 38 kJ per gram3. Their molecules congregate into globule

because of their hydrophobic propertiesDifferences

Saturated fats Unsaturated fatsHigher melting point Lower melting pointMost are solid at room temperature

Most are liquid at room temperature

More likely to cause disease of the heart and arteries

Less likely to cause disease of the heart and arteries

More stable at room temperature and less readily become rancid

Unstable at room temperature and less readily become rancid

ENZYMES• Enzymes are protein molecules

act as biological catalysts. They speed up the rate of metabolic reactions and do not chemically changed at the end of the reaction

• The substance whose reactivity is increased by an enzymes is knowing as a substrate

THE GENERAL CHARACTERISTICS OF ENZYMES• Enzymes speed up the rates of biochemical reactions in cells.• Only a small amount of enzymes is needed to catalyse a lot of substrate.• Enzymes are very specific – each class of enzymes will catalyse only one particular reaction.• Enzymes are not used up or destroyed in the reactions that they catalyse, but can be reused again.• Enzymes catalyse reversible reactions• Many enzymes are only able to work with in presence of a coenzymes (or cofactor).• Enzymes are effected by changes in temperature and pH

NAMING OF ENZYMES• An emzyme is named by taking its substrate

name and adding the suffix ‘-ase’• Example, protease catalyses the hydrolysis

of protein.• The ‘-ase’ rule does not apply to enzymes

discover before the ‘-ase’ idea was introduced. For example, pepsin, rennin, ptyalin and tripsin.

• The modern classification of enzymes was decided by the International Union of Biochemistry (IUB) in 1961

INTRACELLULAR AND EXTRACELLULAR ENZYMES

• Intracellular emzyme that catalyses reaction within a cell and formed by the free ribosome in the cytoplasm.

• Extracellular emzyme that leaves the cell and catalyses reaction outside the cell and synthesised by ribosome attached to the rough endoplasmic recticulum.

MECHANISM OF ENZYMES ACTION

• Each enzyme molecule has a region with very precise shape called active site.

• The substrate molecule fit into the active site of the enzymes like a key into a lock, forming an enzyme-substrate complex, a temporary structure.

• Reaction take place at active site to form a product.

• The product have a different shape from the substrate and therefore repelled from a active site.

• THERE ARE 4 FACTORS AFFECT THE ACTIVITY OF ENZYMES

1. pH2. Temperature3. Concentration of enzyme4. Concentration of substrate

The effect of pH on enzyme activity

• Each enzyme has a optimum pH at which its rate of reaction is the fastest. i.e. pepsin at pH 2,(acidic) amylase pH 7 (neutral) and trypsin at pH 8-9 (alkaline)

The effect of temperature on enzyme activity

•The rate of reaction will increase up to maximum, known as optimum temperature.

•After the optimum temperature around 37ºC-40ºC, the rate of reaction falls quickly because of the bonds maintaining the structure of the enzyme start to break and the active site loses its shape.

•At 60ºC, enzyme activity will stop altogether because the enzyme is denatured

The effect of substrate concentration on enzyme activity

1. Increase the substrate concentration will increase the chance of enzyme-substrate collision, and the rate of reaction will increase.

2. Addition of substrate will not increase the rate of reaction anymore because the constant enzyme concentration becomes the limiting factor.

The effect of enzym concentration on enzyme activity

1. When the concentration of enzyme increase, there are more chance enzyme-substrate collision. The rate of reaction increase linearly as long as no other factors are limiting.THE USES OF ENZYMES

1.Enzyme can extracted from any living organism, and used either at home or in industry2.Enzymes that are commonly used in daily life are:a.Papain-found in papaya used to tenderise meatb.Protease-used to tenderise meat and remove hair from the skin etc.

CHEMICAL COMPOSITION OF THE CELL

Compound Element

Water

LipidCarbohydrate

Enzymes

Protein

Factors

Why

What

How

Affected by

Importance

Definition

Mechanism

Simpler molecules

FormBreak down into

Health problems

Deficiency

Leads to

Consists of

Can be classified

Includes

Forms