Molecules in living organisms Life….Chapter TWO……Chapter THREE Principles of Biology Lecture 12 Molecules in living organisms Life….Chapter TWO……Chapter THREE

Primary Molecules in living organisms Water Carbohydrates Proteins Nucleic acids Lipids carbon-based molecules also called organic molecules This lecture is mainly on the discussion of water in organisms

Water in living organisms A molecule with simple composition and simple structure it is the most abundant molecule in organisms (accounts for more than 50% of the weight of every organism) Water has outstanding physical and chemical properties; It is formed through polar covalent bonding The Oxygen atom is more electronegative than the Hydrogen atom

Hydrogen bonding between water molecules

Hydrogen bonding and the properties of water…....... Hydrogen bonding:-between water molecules Charged region of polar water molecules are attracted to oppositely charged parts of neighboring molecules Each molecule can hydrogen bond to multiple partners

Hydrogen bonding and the properties of water Hydrogen bonding:-between water molecules is the basis of the cohesive property of water as well as the high surface tension of water hydrogen bonding is also responsible the for the outstanding temperature regulating ability of water water has high heat capacity it takes a lot of heat to change water from liquid to vapour So, H-bonding has significant influence on the propertiesof water! AND, it is important to living organisms!

Hydrogen bonding:-between water molecules Biological example : Insulation of Bodies of water by floating ice Ice is solid water , is less dense than water and floats in liquid In ice each molecule is hydrogen bonded to 4 neighbours in a 3- dimensional crystal Floating ice becomes a barrier that protects the liquid water below from colder air Life can exist under the frozen surface

Hydrogen bonding between water molecules Cohesion of water: Water molecules stay close because of hydrogen bonding between water molecules Because of properties of cohesion the tallest trees can transport water more than 100m upwards Surface tension: A measure of how difficult it is to stretch or break the surface of a liquid Biological example: some animals can walk, stand and run on water without breaking the surface

ii) between water molecules and other molecules found in organisms Solvation of polar molecules and ions due to their Hydrophilic (water loving) behaviour

Such behaviour is due to functional groups Hydroxyl (OH) groups Carboxyl (COOH) and Aldehyde (CHO) groups Keto (C=O) groups Amino (NH2) groups in alcohols, organic acids and Carbohydrates in organic acids and aldehydes in ketones and esters in amines and amides Please read refer to TABLE 3.1 in your textbook for further details

Aggregation for non-polar molecules a hydrophobic behaviour

Amphiphilic behaviour for molecules having both water-hating and water-loving parts CH3-(CH2)n – COOH We shall discuss molecules of this type under Carbon-based molecules in next series of lectures

More about the solvent properties of water Chemical reactions in organisms involve molecules in aqueous solutions So, concentration is a very important term even in Biology Concentration is always expressed in moles 1 mole = amount of the substance in grams equal to the atomic or molecular mass of that substance Example: 1 mole of glucose weighs 180g So, when 180g of glucose is dissolved in a 1L of water, we have a 1 molar (1M) solution of glucose .

In organisms, many dissolved substances have concentrations of nanomolar (nM = 10-9), micromolar (mM =10-6) or millimolar (mM = 10-3) Biologists are always interested in reactions between molecules but it is difficult to count molecules of any substance For this, we use a constant that relates the weight of any substance to the number of molecules of that This constant is Avogadro’s number, it informs us that there are 6.02 x 1023 molecules per mole of any

Another important property of water……… Water also has a tendency to form ions H2O H+ + OH- and this influences acid-base balance in organisms Also, some substances release H+ when they dissolve in water The hydrogen ion (H+) can attach to other molecules in organisms and change their properties This is very important in living organisms Acids donate H+ and bases accept H+ their relative proportions in any water environment determine the nature of chemical reactions that are possible This will be covered in detail under Bio 211 (semester 3)