Biol 1551 Sept 11^th  lecture notes

 

Chapter 2 Chemical basis of life

 

1) Essential chemical elements (Table in p19)

The four major elements O, C, H, N account for 96 % of all elements found in living organisms

 

elements	examples of molecule/structure containing the elements
O (oxygen)	carbohydrate, fat, protein
C (carbon)	carbohydrate, fat, protein
H (hydrogen)	carbohydrate, fat, protein
N (nitrogen)	protein
Ca (calcium)	bone, signal processing
P (phosphorus)	plasma membrane, nucleic acid
K (potassium)	generation of electric signals
S (sulphur)	protein
Na (sodium)	generation of electric signals
Cl (chlorine)	generation of electric signals
Mg (magnesium)	enzyme function

 

Trace elements are required only in small quantities (less than 0.01 %).  Examples of trace elements are:

·        Fe (iron) – needed for hemoglobin function (iron deficiency results in anemia. pregnant mother require more iron intake to provide blood supply for fetus).

·        I (iodine) – needed for thyroid function (table salts are often iodized to suppy iodine to our diet)

 

 

2) Structure of four major elements (Fig 2.6, p22)

 

 

3) Different chemical bonds

            a) ionic bonds – attraction of ions with opposite charges (Fig 2.7A, p23)

            b) covalent bonds – sharing of electrons between two atoms (table in p23)

                        non-polar covalent bonds – atoms attracts electrons with equal forces

                                                                        (equal electronegativity)

                                    ex. hydrogen gas (H₂), oxygen gas (O₂), methane gas (CH₄)

 

                        polar covalent bonds – unequal electronegativity between atoms, result in

                                                                        slight charges within molecule

                                    ex. water (H₂O) (Fig 2.9, p24)

 

 

c) hydrogen bonds – attraction between polar molecules (slightly positive part of

 molecule is attracted by slightly negative part of molecule)

                        ex. Water has strong cohesion and high surface tension because of

                                    hydrogen bonds between each water molecules. (Fig 2.10, p24)

 

Strength of bonds - covalent bonds > ionic bonds > hydrogen bonds

 

 

 

 

Chapter 3 Biological molecules

 

1) Living organisms are made mainly of organic compounds.

 

Organic compounds - compounds containing carbon

 

Unique feature of carbon – Carbon atom can form up to four covalent bonds with different atoms (four hands).  As a result, a wide variety of carbon-containing molecules (organic molecule) are found on earth, which perform a wide variety of functions.

 

a)      Hydrocarbons – molecules only consists of carbon and hydrogen, non-polar

b)      Functional groups – groups of atoms that normally participate in chemical reactios

Compounds containing functional groups are polar, hydrophilic (water soluble), readily participate in chemical reactions

 

            Four common functional groups (table in p35)

 

·        hydroxyl – alcohol – ethanol, sugar

·        carbonyl – ketone, aldehyde – sugar, formaldehyde (used as preservative)

·        carboxyl – carboxylic acid (acidic) – acetic acid (vinegar), protein

·        amino – amine (basic) – protein

 

2) Many biological molecules are large – macromolecules

a) Many macromolecules are made from smaller units called monomer.  Monomer units are combined to make polymer. 

 

b) Common mechanisms for synthesis of biological polymers (Fig 3.3 A and B, p36)

·        When monomers are combined to make polymer, water is lost from the product (dehydration synthesis).

·        When polymers break down, water is added to the product (hydrolyis).