Biological molecules

  • Organic - compounds based on carbon + contain carbon bonded to hydrogen - proteins, lipids

  • Inorganic - compounds that do not contain carbon bonded to hydrogen - water, carbon dioxide

  • Micronutrients - inorganic nutrients needed in minute amounts

  • Macronutrients - inorganic ions needed in small amounts - magnesium, iron, phosphate, calcium

Importance of inorganic ions ( macronutrients ) :

Magnesium : chlorophyll → essential for photosynthesis = chlorosis

Iron : haemoglobin -→ transports oxygen inside red blood cells = anaemia

Phosphate : bones + teeth in mammals & in plant cells providing strength

Calcium : making nucleic acids & phospholipids, found in plasma membrane

Monomers + polymers:

  • polymers are made up of smaller molecules inked together called monomers -→ polymerisation

  • Condensation reaction - a molecule of water is eliminated and a chemical bond is created

Hydrolysis reaction - a molecule of water is inserted to the polymer and a chemical bond is broken

Carbohydrates :

  • storage + release of energy

  • Cellular structures - cellulose cell walls

Monosaccharides - monomers that form the building blocks for larger carbohydrates

  • General formula → Cn(H2O)n

  • Alpha glucose - OH on the bottom

  • Beta glucose - OH on the top - a + b are isomers as they are molecules with the same chemical formula but different arrangements

Properties of monosaccharides : soluble in water → easily dissolve inside the cell and are easily transported in the bloodstream

Disaccharides - formed when two hexose sugars combine in a condensation reaction + glycosidic bond is formed ( 1 - 4 glycosidic bond )

  • Maltose → alpha glucose + alpha glucose

  • Sucrose → glucose + fructose

  • Lactose → glucose + galactose

Polysaccharides - large complex carbohydrates formed from large numbers of monosaccharides joined by glycosidic bonds ( series of condensation reactions )

Properties of polysaccharides :

  • Due to the large size they are insoluble -→ does not affect osmosis

  • Compact → stored in small places in cell

  • Easily hydrolysed to release the glucose for respiration

Examples of polysaccharides :

Storage: Starch + glycogen

Structural: cellulose + chitin

Starch:

  • energy storage in plant cells , alpha glucose monomers

Amylose - straight chained helix held together by alpha 1 - 4 glycosidic bonds

Amylopectin - branched held together by 1 - 4 + 1 - 6 glycosidic bonds → quickly hydrolysed

Glycogen:

  • animal glucose energy storage found inside liver and muscle cells

  • 1-4 + 1-6 glycosidic bonds - highly branched allowing faster hydrolysis for glucose as animals have a higher metabolic rates→ release more energy

Cellulose:

  • gives plant cell rigidity → inelastic + high tensile strength to prevent the plant cells from bursting

  • Beta 1-4 glycosidic bond - straight chained

  • Beta glucose monomers joined by glycosidic bonds with adjacent beta glucose molecule rotated 180° to the previous

  • Hydrogen bonds form between OH groups of straight chains - forms a strong microfibril

Chitin:

  • in some of the OH groups of each of the beta glucose molecules of straight chain are replaced by nitrogen containing acetylamine groups

  • Lightweight, waterproof and very strong

  • Forms the exoskeleton of insects - also forms cell walls of fungi

Lipids:

  • carbon, hydrogen, oxygen - contain less 02 than carbohydrates

Triglycerides = glycerol (C3H803) and fatty acids ( methyl group, hydrocarbon chain, carboxyl group )

  • Not polymers as they are made up of two different types of subunits

saturated triglycerides: no carbon to carbon double bonds, solid → animal fats, straight chained

  • LDL contain and transport saturated fats that can block major arteries and cause heart attacks

unsaturated triglycerides : carbon to carbon double bond, liquid → oils, not straight chained - kinks

  • HDL contain and transport unsaturated fats and carry harmful fats away to the liver for disposal →lowers the risk of heart disease

Formation:

  • 1 Glycerol- organic alcohol, non polar -→hydrophobic - repels H2O, does not dissolve

  • 3 fatty acids-

  • Ester bond formed by a condensation reaction and 3 water molecules eliminated ( product )

Phospholipids :

  • 2 fatty acids +1 glycerol + phosphate group

  • Polar hydrophilic phosphate heads - attracted to water

  • non polar hydrophobic fatty acid tails - repel water

Properties of lipids:

  • insoluble in water but soluble in organic solvents → acetone/ethanol

  • fats are solid at room temp

  • Oils are liquid at room temp

Functions of lipids:

  • Energy storage - store in seeds and animals -→ release a lot more energy than carbohydrates

  • Protection of vital organs - used as shock absorption and prevents physical damage to internal organs

  • Thermal insulation - blubber in whales, seals, and polar bears reduces heat loss

  • Buoyancy - lipids are less dense than water they float → maintain buoyancy in organisms - fish

  • Metabolic water - production of metabolic water when lipids are oxidised by respiration - important in desert animals

  • Waterproofing - waxes are hydrophobic and cover the exoskeleton of insects and the cuticle of plant leaves → reduces water loss

Proteins:

  • amine group, carboxyl group, r group

  • R group varies due to the type, total number, sequence of amino acids

Dipeptide- two amino acids join to form a dipeptide - combine in a condensation reaction → peptide bond

Polypeptides : formed by many amino acids joining by peptide bonds
















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