Biological Molecules

Nutrients

Chemical substances in food that provide energy and materials needed by the body

Condensation Reaction

Condensation is a chemical reaction whereby 2 or more simple molecules are joined together to form a larger biological molecule with the removal of water

Hydrolysis

Hydrolysis is the splitting up of a complex biological molecule into its component units with the addition of water molecules

Carbohydrates

• Made up of the elements carbon, hydrogen and oxygen

• General formula Cm(H2O)n

• Hydrogen and oxygen atoms are present in the ratio 2:1

Monosaccharides

Glucose, fructose, galactose

• sweet tasting

• soluble in water

• able to lower water potential of solutions

Disaccharides

maltose, lactose, sucrose

Maltose	Glucose + Glucose
Lactose	Glucose + Galactose
Sucrose	Glucose + Fructose

Glycosidic bond

Polysaccharides

Storage polysaccharides:

1. Starch (plants)

   • Formed from the condensation reaction of large number of glucose molecules

   • Can be in long straight chains or branched chains

2. Glycogen (animals)

   • Formed from the condensation reaction of large number of glucose molecules

   • glucose molecules joined up in highly branched chains

Structural Polysaccharides:

1. Cellulose

   • Formed from the condensation reaction of large number of glucose molecules

   • glucose molecules that forms cellulose are bonded differently as compared to starch, hence giving cellulose a different property

   • Insoluble in water

Starch and glycogen are suitable storage materials because:

• insoluble in water so they do not affect water potential in cells

• too large to diffuse through the cell membranes, so they stay in the cells

• compact shapes which occupy lesser space than all the individual glucose molecules that make up a glycogen or starch molecule

• can be easily hydrolysed to glucose when needed

Function of cellulose cell wall

• provide mechanical support for plant cell and to the plant, especially for herbaceous (soft stem) plants

• resist expansion when water enters by osmosis, ensuring integrity of plant cell and to provide turgidity

General functions of carbohydrates

• Glucose- as a substrate for respiration to release energy for all cellular activity

• Deoxyribose sugars- Used for the formation of nucleic acids

• Forms lubricants

• Forms nectar in some flowers

• Cellulose- To form supporting structure

Lipids

• contains carbon, hydrogen and oxygen with much lesser oxygen as compared to carbon and hydrogen

  • insoluble in water but soluble in organic solvent

Triglyceride

consists of 3 molecules of fatty acids and one molecule of glycerol

Fatty acid

• is a long hydrocarbon chain with a carboxyl function group

• hydrocarbon chain can be unsaturated (contains carbon carbon double bond) or saturated (no carbon carbon double bond)

• hydrophobic

Ester bond

Properties of triglycerides

• Oil

  • at least one carbon-carbon double bond

  • lower melting point and molecular weight

• Fats

  • absence of carbon-carbon double bond

  • higher melting point and molecular weight

• Insoluble in water

• Stored as droplets inside of specialised fat cells, known as adipose cells, because they are insoluble and do not affect water potential in cells

Functions of triglycerides

• Energy storage

  • one gram of triglyceride yields about twice as much energy than one gram of carbohydrates

• Heat insulator

• Buoyancy in animals

  • Less dense than water

• Protective layer

  • Ability to absorb shock

• Important component of the myelin sheath

  • Acts as electrical insulator

• Provides metabolic water

  • Oxidation of triglycerides produce metabolic water

  • Triglycerides release twice as much water as carbohydrates when oxidised during respiration

• As a solvent

Phospholipids

Phospholipids are a group of compound lipids that contain two molecules of fatty acid, one molecule of glycerol and a phosphate group

hydrophilic phosphate group attracted to water molecules and hydrophobic fatty acid tail repelled by the water molecules

Function: major component of biological membranes

Proteins

• Made up of carbon, oxygen, hydrogen and nitrogen

• unique 3 dimensional shape

• denatured when heated

Amino acid

• NH3-amino group

• COOH- carboxyl group

• hydrogen atom

• R group

Peptide bond

Bonds in protein structure

Peptide bonds join amino acids to form a polypeptide chain

Polypeptide chain folds into a particular 3 dimensional shape

Functions of Proteins

• synthesis of new cells, for growth and repair of worn-out cells

• Biological catalysts

• Chemical messenger

• Transport proteins

• Structural proteins

• Defence of the body

Kwashiokor

form of protein deficiency disease

• caused by malnutrition, children have swollen stomachs

• skin crack and become scaly