Biological Chemistry
Review
The understanding the basic chemistry of life
is vital to a full comprehension of biology.
• Atom:
smallest part of an element that
displays the properties of that element
– made up of 3 subatomic particles.
• Protons (positively charged)
• Neutrons (uncharged)
in nucleus
• Electrons (negatively charged) Outside of
nucleus
• Ions are atoms that have gained
or lost electrons
–Signified by either (+) or (–)
–ex. Na+ K+ Cl- Ca2+
1. Ionic Bonds
• Transfer of electrons from a metal
(positive ion) to a non-metal (negative ion)
Ionic Bonding
2. Covalent Bonds
• Atoms share e-s
• Between 2 non-metals
• http://www.bbc.co.uk/schools/gcsebitesize/science/add_gatew
ay/periodictable/covalentbond.shtml - covalent bonds
• http://www.youtube.com/watch?v=_mE6TkczxjE – Water
Story (1:36)
Covalent Bonding
• single covalent bond
(sharing 2 e-)
• double covalent bond
(sharing 4 e-)
• Can have triple covalent
bond (share 6 e-)
Nonpolar covalent bonds
• electrons shared fairly
equally between
atoms
Polar Covalent Bonds
= Unequal sharing of electrons
• Creates a dipole (slight positive end & slight
negative end)
Compound formulas
Shape of Molecules
= when H covalently bonds with one atom, which is also
attracted to another atom (usually O, N or F) of a different
molecule
•Always represented by dotted lines
If you need more…
• www.KhanAcademy.org
– Chemistry section
• MIT courseware → Highlights for High
School → Biology → Chemistry of Life →
Organic Molecules in Organisms
– http://ocw.mit.edu/highschool/biology/chemistry-of-life/organicmolecules-in-organisms
Goal (PLO B2 & B3)
Inorganic Compounds
1. Salts
2. Water
3. Acids/bases, pH, buffers
Inorganic compounds
Organic Compound
Usually metal + non-metal
Always contain carbon and
hydrogen
Usually ionic bonding
Always covalent bonding
Associated with non-living
Associated with living things
Ex. salts, water, acids, bases, Ex. carbohydrates, lipids,
buffers
nucleic acids, and proteins
1. Salts
– Needed for survival
– Too little → fatigue, exhaustion, cramps,
nausea, thirst, decreases blood pressure and
even death
– Too much → dehydration of cells and
hypertension; can lead to heart attack
Water (cont’d)
Structure of water:
• Biological function/importance is due to its
chemical structure
• Water is a polar molecule
– How does polarity of H2O produce H-bonding?
• Oxygen is bigger & negatively charged
• H is smaller & positively charged
• oxygen pulls the electrons toward it creating
a dipole
– O slightly more negative (↑ e- time)
– H slightly more positive (↓ e- time)
= POLAR COMPOUND
• In a H-bond:
– H (positive dipole) of one H2O attracted to O
(negative dipole) of different H2O molecules**
– H-bonding can occur between the H and other
polar compounds
Special properties of H2O
1. temperature regulator
– H2O has a high specific heat capacity
•
Means takes a lot of energy to increase temp of
H2O and loses energy slowly
– Keeps our body temp constant
•
Water vaporization → much heat energy released
(sweating)
– High melting & boiling points
2. Acts as a solvent
• When Polar substances (ie salts, sugars, some proteins)
are added to water, oxygen (-) attracts positive end of
solute & H (+) attracts negative of solute thus pulling the
substances apart
– H2O acts as a solvent
– e.g. NaCl dissolves into Na+ & Cl- in water
3. Acts as a lubricant
• In mouth, joints, lungs, etc.
– In lungs CO2 & O2 only diffuse across moist
membranes
4. Water has a high surface tension
– This allows some insects to walk on the
surface of a pond or lake.
Use p. 28-29 (9 ed.)
th
1.
2.
3.
4.
What is an acid? Write the equation.
What is a base? Write the equation.
What does water dissociate into?
Give a definition for a neutral substance?
(think about this one it is not in the text)
5. What is meant by pH?
6. What is the pH scale?
Acids and Bases
• When water ionizes, it releases an equal number
of hydrogen ions (H+) and hydroxide ions (OH-).
H 2O
H+ and OH-
• Neutral solutions:
– Equal amounts of H+ and OH– acid + base → water + salt
– e.g. HCl + NaOH → H2O + NaCl
• The pH Scale (proportion of H ions)
– Measures acidity & alkalinity (basicity) of a solution
– Ranges from 0 - 14
– A pH below 7 is acidic
[H+] > [OH-]
– A pH above 7 is alkaline
[OH-] > [H+]
– A pH of 7 is neutral
[H+] = [OH-]
[ H+ ]
pH is the concentration of ____ expressed as a
logarithm. Every change in the pH scale of one unit
10
is a change in ______
times the concentration of H+.
• To determine pH from a diagram, only pay
attention to the OH- and H+
– if there are more H+ = acidic
– if there are more OH- = basic
– if there is an equal number of OH- and H+ =
neutral
Buffers
• A buffer is a chemical(s) that can resist changes
in pH
• living organisms need to maintain a constant pH
level because the chemical processes are sensitive
to changes in H+ and OH• We have a built in system to maintain our internal
pH (homeostasis)
• Buffers function by taking up excess H+ or
OH- to help keep pH constant
In a strong acid solution, there are too many hydrogen ions.
ions
So, if we add a strong acid to a solution with a buffer, the
buffer is attracted to the hydrogen ions.
So the buffer (example: CO32-) will react with the H+ to form
(in this case) HCO3- .
H+ + CO32-
HCO3-
Therefore, the H+ gets absorbed by the buffer and the pH of
the solution does not change.
change
When it is in an ACIDIC solution, a buffer will absorb H+ ions.
In a strong base solution, there are too many hydroxide ions.
ions
So if we add a strong base to a solution with a buffer, the buffer
(example: H2CO3) will give up its H+ in order to transform the
base (OH-) into water (H2O), also written as H(OH).
Because the buffer has lost a H+, it will become HCO31-.
OH- + H2CO3
H(OH) + HCO31-
Therefore, the OH- gets turned into water and the pH of the
solution does not change.
change
When it is in an BASIC solution, a buffer will donate/release H+ ions.
A buffer usually has 3 (or more) ‘versions’ of itself.
In the case we just looked at, the buffer could either be :
H2CO3
HCO31-
Buffers (cont’d)
• buffers only work until all the ions are
gone
• They are not permanent
• Why do we talk about this?
• Important in our cells and blood
• E.g bicarbonate in blood – most important buffer