CHEMICAL COMPOSITION OF THE CELL

CHAPTER 4

ElementsElements-made up all living and non-living things

- is a substance, composed of a kind of atom

-cannot broken down into simpler substances by chemical reaction

-There are 25 most common elements

carbon (C)hydrogen (H)oxygen (O)nitrogen (N)

-Most Essential elements 96% of the body mass

calcium (Ca)potassium (K)phosphorus (P)sulphur (S)sodium (Na)magnesium (Mg)chlorine (Cl)

-Other essential elements 4% of the body mass

-Trace elements 0.01% of the body mass

Compound -is formed from elements- two types:a)Organic compound - contain the carbon element - examples: carbohydrates, proteins, lipids, nucleic acids, vitaminsb) Inorganic compound - example: H20

Organic compounds & its importancea)Made up 15% of protoplasm – proteins & lipidsb)Building blocks of proteins - amino acidsc)Major source of energy in the cell – carbohydratesd) store genetic information – nucleic acids

Importance of Water to cell•Universal solvent•Medium for metabolic reaction•Maintain stable internal environment•Helps in lubrication•Supporting plant cell & soft body tissues•Has very high cohesion

Importance of Water to cell•Provide moist surface for gaseous exchange•Provide H atom for photosynthesis•Maintain thermal balance•Facilitate transportation of nutrients

Water as Universal solvent-water is a polar molecule with unequal distribution of charges-polar molecules attract one another and ions-water can dissolve many i) ionic compounds, such as salt ii) polar molecules such as sugar

Water as Medium for Biochemical reaction-biochemical reactions can only take place when there is water-Example: In digestion, the breakdown of proteins, lipids & carbohydrates needs water

Water maintain Stable Internal Environment-Water maintains the osmotic balance between the blood and interstitial fluid-This enable all activities and life processes in cell.

Water helps in Lubrication-Mucus composes mostly water which assists the movement of food substances in the intestinal tract

Water support plant cell & soft body tissues-Cell sap in plant contains water, glucose, mineral salt, toxic substances and mineral-This made tha concentration of cell sap higher and encourage water to diffuse in by osmosis-Plant cell becomes turgid

High cohesion property-cohesion force exist between molecules of the same type-Water molecules tend to stick to each other and move in long unbroken columns through the vascular tissues in plants.

Nucleic acids-organic compound-store genetic infomation in the form of code-building blocks of nucleic acids are called nucleotides

Nitrogenous base

Pentose sugar

Phosphate group

Nucleic acids-Two types:a)deoxyribonucleic acid (DNA)•double strand of polynucleotides which forma a double helix•is found in nucleus, chloroplast, mitochondrion•contains genetic infomation of organism

Nucleic acids-Two types:b) ribonucleic acid (RNA)•single strand of polynucleotides•is found in nucleus, cytoplasm, ribosome•copies genetic infomation carry by DNA for the use in protein synthesis

CarbohydrateElements in carbohydrates – C, H, O Monomer of carbohydrates -monosaccharidesTypes of carbohydrates:a)Monosaccharidesb)Disaccharidesc)Polysaccharides

- Examples: glucose, fructose, galactose

- is known as simple sugar- main source of energy for many

cells- combine with protein to form

glycoprotein- combine with lipids to form

glycolipid

Monosaccharides

- can be found in •plants and fruits (glucose) formula: •fruit and honey (fructose)•milk (galactose)

- are reducing sugars which act as a reducing agent

- Examples: maltose (malt sugar) sucrose (cane sugar) lactose (milk sugar)- is formed by two combination of

monosaccharides- involved two processesa) formation of disaccharides: condensationb) breakdown of disaccharides: hydrolysis

Disaccharides

Elements Carbon, Hydrogen, OxygenFormula (CH2O)n C6H12O6

General structure

- maltose and lactose are reducing sugar

- sucrose is non-reducing sugar

glucose + glucose Maltose

glucose + fructose Sucrose

glucose + galactose Lactose

Test for reducing sugar1)2ml of Benedict’s solution are added to glucose solution in a test tube

2)Test tube is placed in water bath of boiling water for 5 min.

Positive result Brick red precipitate is formed.

Test for non-reducing sugar1)2ml of sucrose solution and 1ml of dilute hydrochloric acid are added to a test tube. 2)Test tube is placed in water bath of boiling water for 5 min.3)The test tube is then cooled under a running tap and sodium hydrogen carbonate is added to neutralise excess acid.

Test for non-reducing sugar4) When it stops fizzing, 2ml of Benedict’s solution are added to the mixture in the test tube5) The test tube is placed in water bath of boiling water again for 5 min.

Postive resultBrick-red precipitate is formed

- Examples: starch, cellulose, glycogen- is formed by combination of many

monosaccharides- insoluble in water due to large

molecular size- do not taste sweet and do not

crystallise

Polysaccharides

- are stored in the form of a) glycogen in animals (liver and

muscle cells) and yeastb) starch in plant- involved two processesa) formation of polysaccharides:

condensation

b) breakdown of polysaccharides: hydrolysis

glucose

Starch/cellulose/glycogen

Test for starch1ml of iodine solution is added to starch suspension.

Positive resultThe iodine solution changed from brown to blue black.

Elements in protein: C, H, O, N, P, SMonomer of proteins: amino acidTypes of proteins:a) Essential amino acids (1st class protein)- cannot be synthesised by vertebrate cells- only obtain from the diet- animal protein contains all essential amino acids- example: leucine

ProteinProtein

b) Non-essential amino acids (2nd class protein)- can be synthesised- derived from other amino acids- plant protein

Formation of Dipeptides

Breakdown of Polypeptides

Formation and Breakdown of dipeptides and polypeptides

Protein Structurea) Primary structure

a) Primary structure Peptidebond

aminoacid

- Linear sequence of amino acids in a polypeptide chain

- Example: hormone insulin

b) Secondary structure

- Polypeptide chains coil to form α-helix chains or pleat to form β-pleated sheets

- Example: keratin, collagen

c) Tertiary structure

- Helix chains and pleated sheets are folded into a 3-dimentional shape

- Example: plasma proteins, enzymes, myoglobin,

antibodies, many hormones

d) Quarternary structure- Many

polypeptide chains combine with non-protein groups to form a large complex protein molecule

- Example: haemoglobin,

chlorophyll

Protein Testa)Millon testA few drops of Millon’s reagent are added

to food sampleThe sample is boiled for 5 minAfter cooling, a few drops of 1% sodium

nitrite is added.

Observation (positive)Brick-red precipitate appears on the

surface of the solution.

Protein Testb) Biuret test20% of NaOH solution is added in excess to food sample.A few drops of Cu(II)SO4 are added slowly to the mixture.The mixture is shaken gently and allowed to stand

Observation (positive)Solution turns purple.

LipidsElements Carbon, Hydrogen,

OxygenFormula CnH2nOn

Sources butter, margarine, olive oil

Types fats, oils, waxes, steroidsphospholipids

Fats and Oils•they are triglycerides triglyceride is an ester formed through condensation of glycerol and three molecules of fatty acids

•triglycerides can also be broken down into fatty acids and glycerol by hydrolysis reactions

• Each molecule of fat or oil consists of one molecule of glycerol and three molecules of fatty acids.

• Fatty acids consists of a long chain of

hydrocarbon chain with a different number of carbon atoms

are either saturated or unsaturated

Saturated fats Unsaturated fatsFats containing saturated fatty acids

Fats containing unsaturated fatty acids

Saturated fats Unsaturated fatsDo not have double bond between the C atom (All the bond between the carbon have maximum number of H atom cannot form any chemical bonds with other atom)

Have at least one double bond between C atoms(the C atoms are not bonded to the maximum number of H atoms)Unsaturated fat with one double bond → monounsaturated fatUnsaturated fat with more than one double bond → polyunsaturated fat

Saturated fats Unsaturated fatsSolid at room temperature

Liquid at room temperature

Example: butter (mostly animal fats)

Example: corn oil (mostly plant oil)

Wax•Found on the cuticles of the epidermis of leaves, fruits and seeds•Are waterproof, thus preventing the entry and evaporation of water

Sebum•Excreted from oil glands contain wax that soften our skin

Phospholipid• Important component of plasma

membrane

Steroids• organic compounds which

include cholesterol and hormones such as testosterone, oestrogen, progesterone