CHEMICAL COMPOSITION OF THE CELL

1. 4 major organic compounds of living systems:a. Carbohydratesb. Protein c. Lipidsd. Nucleic acid

2. Composed of C, H, O and N, additional elements: phosphorus (P), iron (Fe), magnesium (Mg), sodium (Na), potassium (K), iodine (I) and calcium (Cl).

Importance of organic compounds in the cell

1. 15% of protoplasm is made up of proteins.a. Building blocks of protein are amino acids

2. Carbohydrates are the major source of energy in cell.3. Lipids make up 15% of protoplasm 4. Nucleic acids are the complex macromolecules which store genetic information (DNA).

a. Nucleotide is the building blocks of nucleic acid

Importance of water in cell

1. Solvent a. Water is a polar molecule with an unequal distribution of charges b. Polar molecules attract one another plus ion c. Water dissolves many organic compounds

2. Transport medium a. Water is the main constituent of blood and body fluid b. Blood plasma contains and transport nutrients, respiratory gases and hormonesc. Waste products (urea, creatinine) are excreted from body through urine

3. Medium for biochemical reaction a. Digestive reaction such as hydrolysis of proteins, lipids and carbohydrates

4. Maintain stable internal environmenta. Concentration of water and inorganic salts that dissolve in water is important in

maintaining osmotic balance between blood and interstitial fluid 5. Lubrication

a. Mucus is composed of water, assists the movement of food substances in digestive tract

b. Synovial fluid in joint help to lubricate the joint when the joint is bend 6. High cohesion and adhesion force

a. Water molecules tend to stick to one another and move along in long unbroken columns through xylem vessel in plants

7. Maintain constant body temperaturea. High specific heat capacity

i. Water absorb a lot of heat from muscles or environment before temperature rises

ii. Prevent the body temperature rising too fast b. High latent heat vaporization

i. Helps to lower body temperature when sweating ii. When sweat is evaporating, it absorbs heat from skin and cools our body

CARBOHYDRATES

1. Common carbohydrates are starch and cellulose.2. Both are macromolecules with high molecular weights.3. Both are polymers (polysaccharides), built from repeating units of monomers (glucose).

A. Monosaccharides

C₆H₁₂O₆ (hexose)1. Simplest form of carbohydrates.

a. Glucose: immediate source of energy for cellular respiration b. Galactose: sugar in milk and yogurt

c. Fructose: sugar found in honey 2. Same molecular formula but different atoms arrangement.

a. Structural isomers: substances with identical molecular formulas but different structural formulas

B. Disaccharides 1. Made up of 2 monosaccharides combined together 2. 3 common disaccharides:

a. Maltosei. Product of partial digestion of starch

b. Sucrose i. Table sugar

ii. Found in sugar cane, sugar beet and sweet fruits c. Lactose

i. Sugar in milk 3. All sugars are soluble in water because of their hydroxyl group4. Glycosidic bond – linkage between sugar molecules 5. All monosaccharides and dissacharides are reducing sugar, except sucrose

C. Polysaccharides 1. Made up of chains of monosaccharides which are linked together by glycosidic bonds.2. Polysaccharides tend to be very large and branched.

a. Insoluble in water and amorphous (shapeless)3. General formula Cn(H₂O)n n is 200-25004. Most polysaccharides are starch, glycogen and cellulose. 5. Starch:

a. Glucose polymer b. Insoluble in waterc. Store as glucose in plant cell d. Digested by enzyme amylase e. 2 types of molecules

i. Amylose: linear, unbranched chains of several hundred glucose residues, coiled helically into compact shape

ii. Amylopectin: compact and highly branched

6. Glycogen:a. Store as glucose in animal cell b. Structure of glycogen is similar to that of amylopectin, branches in glycogen:

shorter and more frequent c. Glycogen is broken down into glucose when energy is needed d. Liver and skeletal muscle are major depots of glycogen

7. Cellulose a. Forms most structural components in plants b. Wood is largely cellulose while cotton and paper are pure cellulose c. Absence of side chains allow linear molecules to lie close together d. OH project out from each chain, forming hydrogen bonds with neighbouring

chains: creates rigid cross-linking between the chains, making cellulose a strong support material.

e. Fully permeable to water and solute

CONDENSATION AND HYDROLYSIS

1. Condensation of monosaccharides

2. Hydrolysis: chemical reaction that breaks up large molecules by adding water to them. Hydrolysis of dissacharides

REDUCING SUGAR AND NON-REDUCING SUGAR

1. Chemical test for disaccharides:a. Reducing sugar can be tested by Benedict’s solution b. When reducing sugar is boiled with benedict’s solution, brick red precipitate is

produced. c. Presence of sucrose can be detected by breaking down sucrose into glucose and

fructose via hydrolysis (heating sucrose with dilute HCl), followed by heating glucose/fructose with Benedict’s solution.

d. Brick red precipitate is formed indicates the presence of reducing sugar

2. Reducing sugars can act as reducing agentsa. Reducing sugar contain aldehyde groups are oxidised to carboxylic acids b. Reduce the Cu²⁺ to Cu⁺ which forms as red precipitate, copper (I) oxide

PROTEINS

1. Proteins are polymers. The monomers of proteins are amino acids. 2. All amino acids have same basic structure.

3. Essential amino acids can be found in meat. 4. Types of amino acids:

5. Amino acids can be joined together forming peptide bonds. 6. Condensation reaction forms covalent bond between monomers, amino group and acid

group of another. a. 2 amino acids join together to form dipeptide molecule

Protein structure

1. Primary structure i. Linear arrangement of amino acids in a protein

2. Secondary structure i. Polypeptides chains are folded into different shape ii. Example: α-helix and β-pleated sheets iii. Held together by hydrogen bonds: giving the shape and stability

3. Tertiary structure i. 3D structured protein ii. Large number of non-covalent interactions between amino acids

a. Disulphide bonds: strong double bond (S=S) is formed between sulphur and atoms

b. Ionic bonds: forms between 2 oppositely charged ‘R’ groupsc. Hydrogen bonds: hydrophobic and hydrophilic interactions

iii. Can be broken down by heat a. Increase of kinetic energy of protein molecules, vibrate more, bonds will

breakb. Protein loses its shape and denaturedc. Do not reform to original shape when cold

4. Proteins with 3D structure:i. Globular

a. Ball-like structures where hydrophobic parts are towards centre and hydrophilic parts towards the edge (water soluble)

b. Haemoglobin is water soluble globular protein 1. composed of 2 α-polypeptide chains, 2 β-polypeptide chains and

inorganic prosthetic group 2. haemoglobin carries oxygen around in blood 3. O₂ molecules bind to Fe²⁺ ion in heme group

ii. Fibrous a. Long fibres and insoluble in water b. Collagen in bone, cartilage, keratin (fingernails and hair)

5. Quaternary structure i. 2 or more polypeptide chains joined together

LIPIDS

1. Lipid consists of carbon, hydrogen and oxygen 2. Types of lipids:

a. Oilb. Fats c. Phospholipidd. Waxes e. Steroids

3. Fats and oils are triglyceride 4. Triglyceride is an ester that formed through condensation of one molecule of glycerol and 3

molecules of fatty acid.

5. Types and functions of lipids:

Lipids functions Triglycerides

- True fats - Good energy store - Cover many organs to provide physical

protection - Stored under skin as heat insulator - Transport fat-soluble vitamins (ADEK)

Phospholipids - Composed of diglyceride that bonded

to phosphate group

- Abundant lipids in plasma membrane - Control cell permeability

Waxes - Insoluble

Forms waterproof layer of cuticle on:- epidermis of plants (prevent water loss)- exoskeleton of insects (prevent water

loss)- feathers of birds (waterproof)- fur of mammals (waterproof)- sebum (oil, secreted by skin) to soften

the skin Steroids

- cholesterol - sex hormones - bile

- makes the plasma membrane more rigid and stable

- testosterone, oestrogen, progesterone: controls sexual development and body physiology

- emulsifies fat

6. Lipids are insoluble in water but soluble in organic solvents (alcohol, acetone).

Saturated fats Differences Unsaturated fats Only single bond present between carbon atoms

Presence of double bonds between carbon atoms and

fatty acids

At least double bond between carbon atoms

Difficult to react with additional hydrogen atom

Ability to react with an additional hydrogen atom

Easily react (double bond present)

Solid (high melting point) Condition at room temp Liquid (low melting point)Stearic acid (facial wash) Examples Oleic acid (vege oil)

ENZYMES

1. Enzymes are biological catalyst that increase the rate of metabolic reactions. 2. Enzymes are globular proteins with specific tertiary shape. 3. Reaction of enzymes are specific to specific reaction which depends on the shape of the

substrate. 4. Active site of enzyme acts as catalyst which the shape is complementary to the substrate. 5. In enzyme reaction, substrate is turned into product. 6. Example of enzymes:

a. Lactase: breaks down lactose into glucose and galactoseb. Catalase: breaks hydrogen peroxide into water and oxygen

Extracellular enzymes:

- Enzymes that have been secreted and used outside the cell - Cellulase: hydrolyses cellulose into glucose - Amylase: hydrolyses starch (amylose) into maltose

Intracellular enzymes:

- Enzymes that have been synthesized and used within the cell - DNA/RNA polymerase: synthesize DNA/RNA- Carbonic anhydrase: aids in the conversion of carbon dioxide to carbonic acid and

bicarbonate ions

7. Most reactions in cell require very high temperature to get going which destroy the cell. 8. Enzymes work by lowering the activation energy of reaction.

a. Activation energy: energy required to start a reaction

Explain the mechanism of lock and key hypothesis

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9. Characteristics of enzymes:a. Enzymes are protein b. Biological catalyst which speed up the rate of biochemical reactions c. Not destroyed at the end of reaction d. Enzyme controlled reaction is catalyst reversible reaction e. Sensitive to changes in temperature, very active at optimum temperature.

Denatured at high temperature. f. Sensitive to change in pHg. Specific, one type of enzyme can catalysed only one type of substrate

Factors affecting enzyme activity

A) Temperature 1. Increase in temperature increases kinetic energy of molecules. Increase in random collisions

between enzyme molecules and substrate molecules. Increase the rate of reaction, forming more product.

2. As temperature increases, weaker hydrogen and ionic bonds will break. Breaking of bonds within enzyme caused the change in shape of active site. Enzymes are denatured and no longer function. Rate of reaction decreases.

B) pH1. Lower pH means higher [H⁺] and lower [OH⁻].2. H⁺ and OH⁻ interfere with hydrogen and ionic bods that hold an enzyme. Change in shape of

enzyme, especially the active site. 3. Different enzymes have optimum rate of reaction at different pH values4. Extreme changes in pH causes the enzyme to denature.

C) Substrate concentration 1. Limiting factor: stops a reaction from proceeding at higher rate. 2. Rate of reaction of enzymes increase with the increase of substrate which any further

increase produces no significant change in reaction rate. 3. Active sites of enzymes are saturated with substrate. 4. Enzyme-substrate complex has to dissociate before the active sites are free to

accommodate more substrate. 5. Substrate is high and temperature and pH are constant, rate of reaction is proportional to

enzyme.

D) Enzyme concentration 1. At low enzyme concentrations, adding more enzyme increases rate of reaction. More

enzymes is more likely to bind with substrate. 2. At high enzyme concentrations, adding more enzymes has no effect on reaction rate. Rate of

reaction becomes constant and enzyme concentration is no longer a limiting factor.

Uses of enzyme in daily life and industry

Enzymes Uses Type of industry/application α-Amylase Converts starch flour into

sugar in making of bread or dough

Baking industry

Amylase Removes starch that is used as stiffeners in fabrics

Textile products

Amylase and amyloglucoxidase Change starch to sugar in the making of syrup

Starch products

Protease, lipase and amylase Dissolve protein, oil, starch stains on clothes

Biological washing powder or detergents

Protease and protease papain Tenderises meat Food processing and meat industry

Protease Removes the skin of fish Remove cloudiness during storage of beer

Fish productsBrewing industry

Zymase (produced by yeast) Converts sugar into ethanol Alcoholic beverages (brewing industry)

Lipase Ripening of cheese Dairy industry Rennin Coagulate milk protein Dairy industry (making yogurt)Lactase Hydrolyses lactose to glucose

and galactoseMaking of ice cream

Cellulose Breaks down cellulose and remove seed coat from cereal grains Extracts agar from seaweed

Cereal grain products Seaweed products

Trypsin Removal of hair from animal hides Removes blood clots and clean wounds

Leather products Medical analysis

Pancreatic trypsin Microbial trypsin

Treats inflammation Dissolves blood clots

Medical/pharmaceutical products

Glucose isomerase Production of high fructose syrup:Glucose is converted into fructose. Fructose is sweeter than glucose which widely used in slimming products

Explain how enzymes act in:

1. Helping to cook meat 2. Extracting agar from seweed3. Making fresh yogurt 4. Production of variety of cheese

Importance of chemical composition in cells

1. Carbohydratesa. Glucose is oxidised to produce energy in cell metabolism

b. Starch is the food stored in plant cellsc. Glycogen is the food stored in animal cells d. Cellulose makes up the cell wall of plant cells

2. Proteins a. Enzymes act as biological catalyst which increase the rates of reactions in cellsb. Antibodies are produced by WBC to destroy foreign bodies c. Some hormones are protein: insulin which produced in pancreas, oestrogen and

testosterone. Stimulate functions of certain organs d. Respiratory pigment: Hb, carries oxygen in the red blood cells

3. Lipids a. Provide the most energy b. Fat stored in adipose tissues under the skin keeps body heat: heat insulator,

protection to organs c. Acts as solvent for vitamins ADEKd. Phospholipid is the main component of cell membrane e. Cuticle on leaves surface and stems prevents excessive water loss from plants f. Steroid: cholesterol maintains the structure of plasma membrane

4. Watera. Acts as transport medium b. Medium for biochemical reaction c. Solvent d. Supplies hydrogen and oxygen for reaction in cell e. Gives support in herbs f. Helps to control the temperatures of animal bodies

5. Nucleic acid a. Deoxyribonucleic acids (DNA) is the main part of chromosomes b. DNA forms genetic material of the cellc. Ribonucleic acids (RNA) plays important role in protein synthesis d. RNA forms genetic material in some virus

6. Nucleotides are small organic molecules 7. Each nucleotide has 5-carbon sugar (ribose or deoxyribose), nitrogen-containing base (single

or double ringed) and phosphate group.

8. Nucleic acids DNA and RNA a. Four different types of nucleotides are bonded together in large macromolecule b. RNA is single-stranded: functions in assembly of proteins c. DNA is double stranded (polynucleotides): genetic messages are encoded in its base

sequence