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

2. 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

3. 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

4. Hydrogen bonding between water molecules

5. 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

6. 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!

7. 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

8. 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

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

10. 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

11. Aggregation for non-polar molecules a hydrophobic behaviour

12. 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

13. 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 .

14. 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

15. 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)