The Chemical Context of Life
Chemistry is extremely crucial to understanding modern biology
If you hated chemistry – that's alright (sort of), but these are the things you really need to remember

Elements Required by Life

About 25 of the 92 natural elements are essential

C,O,H,N make up 96% of living matter

P,S,Ca,K and a few others make up most of the remaining 4%

Trace elements are required only in minute quantities

Atomic Numbers and Weights

# of protons determines what element an atom is

An element can have different numbers of neutrons, creating different isotopes

An atom can gain or lose electrons, which changes the charge on the atom

(i.e. H + has one fewer electron than H)

Cl has 1 more electron than Cl

Ca 2+ has 2 fewer electrons than Ca

Chemistry Terms

Chemical bond – the attraction of two atoms to each other, often by the sharing of electrons

Electronegativity – how badly an atom “wants” electrons
 Fluorine is the most electronegative atom, the closer an atom is on the periodic table, the more electronegative (worry about F, O, N, Cl)

Charge – protons carry + charge, electrons carry – charge. If an atom has more protons than electrons, it will have a + charge

Chemical Bonding

3 main types of bonds:



Covalent
Ionic: Attraction between + and molecules
Weak: Two molecules adhere temporarily

Covalent Bonds
O=O •
•
• Two or more atoms share 2 electrons, tightly holding the two atoms together
This is the strongest form of chemical bonds
A double covalent bond is the sharing of
4 electrons

Polar Covalent Bonds

Sometimes one atom pulls “harder” than the other
Most electronegative atoms
– F, O, N, Cl

This causes the electronegative atom to have more – charge, or what is called a partial – charge

Ionic Bonds

Attraction between a fully positively charged molecule and a fully negatively charged molecule

Often because one molecule “steals” an electron from the other

More About Ionic Bonds

Called salts

The positively charged atom (or compound) is called a cation (cats are positive!)

The negatively charged atom is called the anion

Like a magnetic attraction

MUCH, MUCH weaker than covalent bonds, but stronger than most other weak bonds

Weak Bonds – The Hydrogen Bond
•
In polar atoms such as water, one atom has a partial + charge, the other has a partial -

The + charge on one molecule is attracted to the
– charge on another molecule

This is a very weak attraction

Why Are H-Bonds So Important if
They're Weak?




Chemical Reactions
•
Involve breaking bonds and forming new ones
•
It always take a little bit of energy to break the initial bond in a reaction (Ea)

pH
HCl → H + + Cl -
HCl + H
2
Or
O → H
3
O + + Cl -
NaOH + H + → Na + + H
2
O
NH
3
+ H + ↔ NH
4
+
 pH measures the amount of H+ (or H
3
O+) in a solution
 pH = - log [H+]

The more acid there is, the lower the pH

The more basic the solution, the higher the pH

pH Scale
Remember each pH unit represents a tenfold difference!

If blood is too basic...
H
2
CO
3
→ H + + HCO
3
-
Buffers

Internal pH of cells is tightly regulated
If blood is too acidic...
H + + HCO
3
→ H
2
CO
3

Buffers help keep pH stable

Diffusion
•
Molecules are always moving around and bouncing off of each other
•
This causes them to spread apart

Diffusion Across a Membrane
•
Wherever it is more concentrated, more collisions will occur
•
Thus more molecules will get knocked across the membrane, if possible

Heat vs. Temperature
Kinetic energy is the energy of motion. Atoms and molecules are always moving, and thus always have kinetic energy. The faster the atom moves, the greater its kinetic energy

Heat is the total quantity of kinetic energy in matter

Temperature measures the average kinetic energy of a molecule
A calorie = the amount of heat energy it takes to raise 1g of water 1 degree celsius

Affects of High Temperature
•
More collisions= more diffusion
•
Easier to get bonds to break
•
Heat will cause most things to expand because the molecules move more and take up more space
•
Or in a confined space will increase the pressure as molecules collide more