Chemistry of Life Topic 3

The most frequently occurring chemical elements in living things are Carbon, Hydrogen, Oxygen and Nitrogen - found in all carbohydrates, proteins, lipids, and nucleic acids

A variety of other elements are needed by living organisms but are less common, including: ·Sulfur ·Calcium ·Phosphorus ·Iron ·Sodium ·Potassium

Element Example role in plants Example role in animals Example role in prokaryotes Sulfur in some amino acids Calcium co-factor in some enzymes co-factor in some enzymes & component of bones Phosphorous phosphate groups in ATP Iron in cytochromes in cytochromes & haemoglobin Sodium in membrane function in membrane function & sending nerve impulses

H2O

POLARITY – Polar Bear!!!

·The H - O bond in water is a polar covalent bond. Structure of water ·The H - O bond in water is a polar covalent bond. ·The nuclei of oxygen is significantly larger and has a greater charge than the nuclei of hydrogen ·Consequently the electron pair in the covalent bond is found ‘closer’ to the oxygen than the hydrogen nuclei ·This creates a polar molecule in which oxygen carries a small negative dipole and hydrogen carries a small positive dipole

Hydrogen Bond Formation ·Because of the partial charges, Oxygen atoms of each molecule are attracted to the hydrogen atoms of other molecules ·H-bonds are key to many of water's properties ·H-bonds are essential for many biological molecules to form, nucleic acids being the most important O H O H O H O H

Properties of Water Cohesive: water molecules tend to attract each other and stick together · Causes water to have a high surface tension - forms droplets - vascular tissue in plants can draw water up to great heights against gravity - helpful to organisms such as water bugs who walk on water ·Causes many of water's thermal properties

Thermal: water has a high specific heat capacity (or simply specific heat) ·Heat capacity is defined by the amount of energy needed cause a rise in temperature ·Water can absorb or release a lot of heat before changing temperature ·It takes energy to break the H bonds and get water molecules to increase in kinetic energy ·e.g. the water in blood keeps your body temperature fairly stable

·This is also why water provides such a great living environment for many organisms Ocean temperatures only fluctuate by +/- 1.5 degrees throughout the year.

Coolant ·Heat generated by the metabolic process of the body must be removed in order to prevent enzyme denaturation ·Water in the blood helps to carry this heat to your skin where it can be transferred to the air ·Sweat also helps to carry heat away from your body

Water also has a high heat of vaporization ·Because it takes a lot of energy (heat) to get water to change state, evaporating water takes a lot of heat with it. ·e.g. sweating: heat from the body causes sweat to evaporate, which removes heat and cools the body.

Ecological effects ·high specific heat capacity of water allows it to maintain stable temperatures, excellent living environment for many organisms ·moderates the environmental temperature

Solvent: The polarity of water gives it strong solvent properties for polar or ionic solutes ·Majority of molecules found in and around cells are polar or ionic: carbohydrates, protein, nucleic acids (DNA, RNA) ·"Like dissolves like" ·The polar water molecules are attracted to the charges in the solute (e.g. sodium)

Transport Medium ·Blood is mostly water - Transports blood cells and dissolved molecules -Common solutes in blood: glucose (blood sugar) amino acids, fibrinogen (protein for blood clotting), hydrogencarbonate ions (a means of transporting CO2) · Vascular tissue in plants - Xylem carries water and dissolved minerals up from roots - Phloem carries dissolved sugars down from leaves

Metabolic Medium ·Being a good solvent for biochemicals means water is also a good medium for biochemical reactions Aqueous Solution Location Common Reactions cytoplasm fluid inside cell but outside organelles glycolysis / protein synthesis reactions nucleoplasm fluid inside nuclear membrane DNA replication / transcription stroma fluid inside chloroplast membrane light-independent reactions of photosynthesis blood plasma fluid in arteries, veins and capillaries loading and unloading of respiratory gases / clotting