The Chemistry of Life - WCJCfacultyweb.wcjc.edu/users/kevind/documents/BIOL_1406_files/Lecture...

Biology – Kevin Dees

The Chemistry of LifeConcepts taken from chapters 2, 3 & 4


• Organisms are composed of matter• Anything that takes up space and has mass• Abiotic items are also composed of matter

• Matter is made up of elements• A substance that cannot be broken down into other

substances by chemical reactions• There are about 92 naturally occurring elements

– Oxygen, O– Carbon, C– Iron, Fe– Zinc, Zn– Etc…


Of the 92, naturally occurring elements, only 25 are known to be essential to life

• of these 25, only four (4) compose approx. 96% of living matter– Carbon, C– Oxygen, O– Hydrogen, H– Nitrogen, N


Trace elements

• Required by organisms in very small quantities

• Still very important despite their limited abundance– Fe, iron – required for oxygen transport– I, iodine – needed to produce a hormone in

the thyroid gland - goiter


Atoms

• The properties of elements depend on atoms

• Smallest unit of matter that retains the properties of an element

• Atoms are composed of subatomic particles

• Neutrons- no charge “neutral’• Electrons – negative charge• Proton – positive charge


Structure of atoms

• Nucleus– Protons– Neutrons

• Electrons orbit the nucleus


Atoms join to form molecules and compounds

• Two or more atoms join to form a molecule– i.e. H2 - hydrogen molecule

• A compound consists of two or more different atoms joining to form a molecule– i.e. H2 O – water molecule; also a compound


Chemical bonds hold atoms together in molecules and compounds

• Covalent bonds– Sharing of electrons by atoms– Very strong– Represented by dashed line in structural

formula• H-O-H

– May be single (one pair of electrons shared ) or double (2 pr. shared)

– May create polar molecules ( areas of charge)• H2O is polar


Water molecule – example of polar covalent bonding


• Ionic bonding – transfer (loss or gain) electrons

– Formation of ions – charged atom• Cation – positive charge – lost electron• Anion – negative charge – gained electron

– Bonds form due to attraction between anions and cations

– Very strong


• Hydrogen bonds– Very weak individually;

strength in numbers– Attractions between

partially positive H atoms and partially negative atoms

– Example: joins water molecules together


Fig. 2-UN2

Reactants Reaction Products

2 H2 O2 2 H2O


Water – special properties• Hydrogen bonding and polarity make

water very important to life’s processes

• Water is :Cohesive – hydrogen bonding holds

water molecules together


Water molecules pulled up the tissues of a plantor

creates surface tension on water’s surface


• Water is :–Able to absorb large quantities of

heat and only slightly change its own temperature – specific heat• Affect on climate – moderates coastal

climates• Insulation• Evaporative cooling – as water

absorbs energy and changes state (from liquid to gas), heat energy is taken away


• Water is:– Less dense as a solid than a liquid– “Ice floats”!!!!– This is important to water bodies

as they freeze in the winter. The ice floats and insulates the water beneath it!!!

Ice –stable crystals due to H bonds

Liquid water – H bonds break and reform


• Water is:– The universal solvent– The mixing of two or more substances is

known as a solution• The dissolving agent is the solvent• The substance dissolved is the solute

– Water dissolves polar or ionic compounds » Hydrophilic - water loving

– Water does not dissolve nonpolar compounds» Hydrophobic - water hating


• H2O H+ + OH-

• water hydrogen ion + hydroxide ion• These ions effect the pH (concentration of Hydrogen

ions)• pH scale:• Buffers - minimize change in hydrogen and hydroxide

ions

Water molecules may also dissociate – form ions

H+ > OH- = Acidic H+ < OH- = Basic

1470

Neu

tral


The importance of carbon• Water is the universal medium for life but all life

is made of chemical compounds that contain carbon

• These are known as organic compounds– Compounds that contain covalently bonded carbon– Inorganic compounds - non-organic (NaCl)– Hydrocarbons – organic molecules with only carbon

and hydrogen– Lots of stored energy!!!!!!– ATP (adenosine triphosphate) – energy currency of

the cell


Properties of organic molecules depend on the arrangement of the carbon skeleton and the

molecular attachments to that carbon skeleton

• Carbon skeleton

• Functional groups

• Properties – determine function

The Chemistry of Life - WCJCfacultyweb.wcjc.edu/users/kevind/documents/BIOL_1406_files/Lecture...

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