CHEMICAL COMPOSITION OF

THE CELL

4.4 LIPIDSBy: Rumaizah Muhamad

LIPIDS

• Elements of lipids:– Carbon– Hydrogen– Oxygen

• Some lipids contain:– Phosphorus– Nitrogen

• Insoluble in water.• Soluble in:– Other lipids and – Organic solvents (eg; alcohol & ether)

Types of Lipids1. Fats2. Oils3. Waxes

o found on cuticles of the epidermis of leaves, fruits and seeds of some plants

o Waterproof: prevent entry and evaporation of watero Eg: sebum

4. Phospholipidso Components of plasma membrane

5. Steroidso Complex organic compoundso Including cholesterol and hormoneso Eg: testosterone, estrogen and progesterone

Triglycerides

Fats & Oils

• Fats & oils are triglycerides

* Each fatty acid consists of a long hydrocarbon chain with a different number of carbon atoms for different fatty acids.

Fatty Acids

Saturated FATS

• Fats containing saturated fatty acids saturated fats

Unsaturated fats• Fats containing unsaturated

fatty acids unsaturated fats

Fatty Acids

Saturated fats• Cannot form any chemical

bond with other atoms.• All the bonds between the

carbon atoms have maximum number of H atoms.

• Eg: butter (solid at RT)

Unsaturated fats• Carbon atoms in

hydrocarbon chain are not bonded to the maximum number of H atoms.

• One double bond monounsaturated fats

• Two/ more double bond polyunsaturated fats.

• Eg: corn oil (liquid at RT)

TEST YOURSELF

A. Tick (√) if the statement is true.1) Lipids contain oxygen, hydrogen and carbon [ ]2) Fats and oils are triglycerides [ ]3) A triglyceride has one glycerol and three fatty acids

[ ]4) Saturated fats are liquid at room temperature [ ]5) Unsaturated fats are essential to good nutrition[ ]

4.5 ENZYMES

• Enzymes are biological catalyst that regulate almost all the cellular reactions.

• It is needed in life processes to regulate biochemical processes in the cells metabolism.

Characteristics of Enzymes

• Enzymes are proteins: synthesized by living organisms.

• In enzymatic reactions:

• Alter/ speed up the rates of chemical reactions but remain unchanged at the end of reactions.

Cont.

• Not destroyed by the reactions they catalyze.• Have specific sites called active sites to bind to

specific substrates.• Highly specific one enzyme can only catalyze one

kind of substrate.o Eg: starch molecules can only fit to active sites of amylase, not

sucrase.

• Only needed in small quantities.• Reversible: can catalyze reaction in either

direction.

Cont.

• Activity of enzymes can be slowed down or completely stopped by inhibitors.– Eg: Lead, mercury

• To function well, enzymes require helper molecules called cofactor.– Eg: • organic cofactor are derivatives of water-soluble

vitamins such as Vit.B.• Inorganic cofactors: ferum and copper

Naming of Enzymes

• Named according to the name of the substrate it catalyses.

• Adding suffix –ase at the end of the name of their substrate.

• Eg:

• Other enzymes were named before a systematic way of naming enzymes. Eg: pepsin, trypsin and rennin.

The Sites of Enzyme Synthesis

• Enzymes are proteins, therefore ribosomes are also the sites of enzyme synthesis.

• Information for enzyme synthesis is carried by DNA.– Different sequences of bases in the DNA are coded

to make different proteins.– During the process, messenger RNA is formed to

translate the codes into a sequence of a.acids.– These a.a are bonded together to form specific

enzymes according to DNA’s codes.

Intracellular Enzymes

• Intracellular enzymes: enzymes which are synthesized and retained in the cell for the use of the cell itself.– Found in cytoplasm, nucleus, mitochondria,

chloroplast– Eg: oxidoreductase catalyses biological oxidation

and reduction in mitochondria.

Extracellular enzymes

• Extracellular enzymes: enzymes which are synthesized in the cell but secreted from the cell to work externally.• Eg: digestive enzymes produced by the pancreas but are

transported to the duodenum (the site for enzyme action).

• Production of extracellular enzymes. Refer to topic 2.3, appreciating the uniqueness of

the cell.

TEST YOURSELF!

1. List down 5 characteristics of enzyme operations.i. ____________________________________ii. ____________________________________iii. ____________________________________iv. ____________________________________v. ____________________________________

2. Define:i. Intracellular enzymesii. Extracellular enzymes

Mechanism of Enzyme Action

• Polypeptide chains of enzyme folded into a three-dimensional shape includes a ‘pocket’ called ACTIVE SITE.

• Active site complements its substrate (substrate must fit enzyme precisely).

• The mechanism of enzyme action can be explained by the ‘lock and key’ theory.

The ‘lock and key’ hypothesis of enzyme action

Key

Lock

Factors Affecting Enzyme Activity

1. Temperature2. pH3. Substrate concentration4. Enzyme concentration

Effects of TEMPERATURE

• Low temperature (T): enzyme-catalyzed reaction takes place slowly.

• Increase temperature: Reaction between substrate and enzyme accelerated.

• For every 10⁰C rise in T, rate of reaction is doubled.• Optimum T: temperature at which enzyme catalyses a

reaction at the maximum rate.– Human : 37⁰C– Plants : 25⁰C

• Beyond optimum T : enzymes lose their activities and denatured.

Beyond optimum T

• No longer increase rate of reaction.

• The bonds that hold enzyme molecules together begin to break at high T.

• Thus, destroying active site.

• Denaturation is irreversible.

TEST YOURSELF!Question 1 – 6. Tick (√) if the statement is true.1. All enzymes are proteins [ ]2. Most intracellular enzymes work best in neutral conditions. [ ]3. Extracellular enzymes work inside the cell [ ]4. The reaction of enzymes takes at the active site in the enzyme molecule.

[ ]5. The rate of enzyme reaction depends on the temperature and light

intensity. [ ]6. Enzymes are destroyed by heat because enzymes, being proteins, are

denatured at high temperature. [ ]7. The way a substrate’s molecule fits into an enzyme’s _________ is

explained by the lock and key hypothesis. The enzyme is the ____________ and the substrate is the _____________.

8. The enzyme activity is influenced by __________, ____________, ______________ concentration and enzyme concentration.

Effects pH on enzymes

• Sensitive to the changes of pH.• Optimum pH : pH at which the rate of reaction

is at the maximum/ fastest.• Eg: – Pepsin function in acidic condition (pH2) in

stomach– Trypsin function in alkaline condition (pH8.5) in

duodenum.

• A change in pH:– Alter the charges on active sites and substrate

surface– Reduce ability of both molecules to bind with each

other.• Effects of pH on enzymes : reversible.– When pH in environment reverts to optimum

level, the ionic charges on active sites are restored.– Thus, the enzymes resume their normal function.

Effects of substrate concentration

• Increase [substrate] : – More substrate available to bind to the active site.– Increase collisions between substrate and enzyme

molecules.– More products will be produced.

• Rate of reaction : directly proportional to [substrate] until reach a maximum rate.

Effects of enzyme concentration

• When [enzyme] increase: – more enzymes available.– more active sites for catalytic reaction.

• Rate of reaction: – increase if only there is abundant supply of

substrate and other factors (pH, T, pressure and constant).

– Proportional to [enzyme]

The Use of enzymes• Enzyme technology: the use of enzymes in industrial

processes.• By using your textbook and reference book, please find the

examples of enzymes used in industries.

Application Enzymes used Uses

1 Dairy industry Rennin Coagulate milk proteins in cheese manufacturing

Lipase Used in the ripening of cheese

2

3

4

5

The importance of Chemical Composition in Cells

Chemical Substances

Main Function Consequence of Deficiency

Carbohydrates

Proteins Impaired mental and physical development

Lipids Important source of energy

Enzymes