Transcript Chemistry of Life

Water, acids, bases and buffers
What does it mean to be Alive?
 Remember Bio 11?
 1.
are made up of cells
 2. grow and maintain structure by taking in
chemicals and energy from their environment
 3. respond to the external environment
 4. reproduce and pass on their organization
(genetic information) to their offspring
 5. at the species level, evolve/change, and adapt to
the environment
The function of our body
systems:
 HOMEOSTASIS: all the things living organisms do
that cause it to maintain a relatively constant,
stable internal environment regardless of the
external environment. There are countless examples
in the human body: Guesses?
 blood pH =7.4
 body temp. = 37°C
 blood pressure = 120/80
 blood [glucose] = 0.1%

How is homeostasis controlled?
Positive/Negative Feedback
 It relies on FEEDBACK MECHANISMS.
 Brain control centers (e.g. in the hypothalamus)
monitor and control body conditions (e.g. pH,
temperature, blood pressure glucose levels)
 Sensors all over body detect unacceptable levels and
signal the appropriate brain center
 control center directs body to behave in such a way
that normal state is regained
 Once normal state is regained, the sensor stops
signaling the brain center (this the “negative
feedback part”), so adaptive response stops.
Negative Feedback Continued:
 results in a FLUCTUATION between two levels. e.g.
the concentration of glucose in your blood is almost
never exactly 0.1%. It’s usually a little bit above or a
little bit below. Over the course of a day, though, it
would average out to be exactly 0.1%.
The Essentials
 Life needs water!
 Organic vs. Inorganic
 Organic means it contains carbon.
Water molecules
 composed of two hydrogen (H) atoms and one larger oxygen (O)
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atom.
Each outside hydrogen atom is bonded to the middle oxygen
atom by a covalent bond. A sharing of electrons.
The oxygen atom attracts the electrons in these bonds more
strongly than the hydrogen atoms. This unequal sharing of
electrons causes each oxygen atom to be slightly negative in
charge (-) and each hydrogen atom to be slightly positive in
charge (+).
These partial charges make the water molecule polar in nature
with oxygen acting as a negative pole and hydrogens acting as
positive poles.
The oxygen atom also has two lone pair of electrons associated
with it that adds to its partial negative charge and results in the
bent nature of the water molecule.
A note about sharing: Electrons
 Covalent bond: sharing of electrons between atoms
 Polar Covalent bond: Unequal sharing (water)
 Ionic bond: when atoms donate (do not share)
electrons with each other.
 Hydrogen bonds: weak bond between hydrogen and
other molecules because of polarity.
 The Unequal sharing of electrons as well as hydrogen
bonds gives water its unique properties.
Covalent vs. Ionic
Models:
 Page 1 of text.
Waters Role
 Hydrogen bonding gives water a strong affinity for
itself and explains things like the formation of water
droplets, the movement of water to the tops of tall
trees, and the ability of water striders to get around.
 Water has many properties and functions useful to
living organisms. These include acting as a solvent,
temperature regulator and a lubricant. More on that
next.
 Water as a solvent
 A solvent is a fluid that makes up the majority of the volume in a
solution. The solvent will have other substances dissolved in it that are
called solutes. Water is an ideal solvent for many things that are found
in our bodies as solutes. These substances include salts like sodium
chloride that are ionic in nature and are attracted to the partial charges
in water. Once dissolved in water, these molecules are transported
throughout the body in blood and lymph (tissue fluid).
 Polar molecules like carbohydrates, proteins, and nucleic acids are
soluble in water and very important in the functioning of our cells.
Lipids or fats are non-polar molecules and do not dissolve readily in
water. This creates a hydrophobic effect due the hydrogen bonding in
water and is important for the formation of cell membranes. Water also
makes up the main component of our blood (92%) with many types of
cells and molecules dissolved in it. The fluid in our tissues is composed
mainly of water and exchanges materials with our blood. These ideas
will become important later in the course.
 Water as a temperature regulator
 Water in our bodies acts to moderate changes in our temperature much like
large bodies of water moderate temperature changes in coastal communities
(called the Lake Effect). The numerous hydrogen bonds in water help it resist
temperature changes as a lot of energy must be added to raise the temperature
of water. The opposite is also true as water tends to hold onto heat energy very
well resisting falling temperature. Water protects us from rapid temperature
changes and helps us maintain our normal body temperature. In situations
where we overheat, such as during strenuous exercise, sweating removes large
quantities of heat as water evaporates from our skin.
 Water as a lubricant
 Water molecules cling together due to hydrogen bonding yet flow freely as a
fluid. These characteristics allow water to act as a transport medium and to
keep many of our internal structures moving. Water dissolves numerous
chemicals and allows them to be transported effectively in our bodies by our
circulatory system. The role of water as a lubricant is seen in sites where our
body surfaces interact with the dry environment we live in. Examples include
tears, mucus in the lungs, throat, and nose, and sinovial fluid in the joints.
Water in different states: Big Q
 One very cool thing about water is that it floats as a
solid (Ice!)
 Think about how important this property is to life on
earth.
 What would happen if it sunk?
 How do you think the future of fresh water will shape
economies of the future?
Must check-outs!
 http://environment.nationalgeographic.com/environ
ment/freshwater/
 http://www.unwater.org/statistics.html
Acids Bases and Buffers….and pH
 The pH scale is used to describe the relative acidity or
alkalinity (‘Basic-ness’) of solutions. The number scale
is from 0 to 14 and represents the number of H+ ions in
a solution
 A pH of 0 represents an extremely acidic solution such
as concentrated hydrochloric acid.
 A pH of 14 represents an extremely basic solution like
concentrated sodium hydroxide found in oven cleaner.
A pH of 7 describes a neutral solution like pure water
that contains an equal concentration of hydronium
(H+) and hydroxide (OH-) ions.
Acids
 are molecules that produce Hydronium Ions (H+)
when added to water. Strong acids, like hydrochloric
acid (HCl -> H+ and Cl-), produce large
concentrations of H+ ions, while weak acids, like acetic
acid found in vinegar, produce low concentrations of
H+ ions.
 Acidic solutions contain more acid (H+) than base
(OH-) and have a pH less than 7.
Bases
 Bases are molecules that produce Hydroxide Ions
(OH-) when added to water. Strong bases, like sodium
hydroxide (NaOH -> Na+ and OH-), produce large
concentrations of OH- ions, while weak bases like
sodium bicarbonate (baking soda), produce small
concentrations of OH- ions.
 Basic or alkaline solutions contain more OH- ions than
H+ ions and have a pH greater than 7. Basic solutions
are often called alkaline solutions.
Buffers
 compound or combination of compounds (often a weak
acid or base and a related salt) that keeps the pH of a
solution constant.
 Buffers resist changes in pH by reacting with any added
acids (H+) or bases (OH-). A common buffer system in
our bodies that keeps our blood pH at about 7.4
involves the weak acid, carbonic acid (H2CO3) and
bicarbonate ion (HCO3-).
 Carbonic acid and bicarbonate ion are both in the blood
creating an equilibrium system.
Why do we need buffers?
 All living things need to maintain a constant pH
(e.g. human blood pH = 7.4).
 Why is pH so important?
If pH changes, it can
cause enzymes – the chemical helpers that run the
chemical reactions essential to life - to “denature”
(i.e. change shape - more on this later!).
potential Hydrogen!
 The numbers in the pH scale can seem misleading,
because the pH scale is a logarithmic scale. That
means each number on the pH scale represents a
difference in magnitude of 10.
 For example, a pH of 2 is ten times more acidic than a
pH of 3.
 A pH of 2 is 100 times more acidic than a pH of 4.
 A pH of 13 is 1000 times more basic than a pH of 10, and
so on.
Macromolecules.
 There are a few basic molecules that help make up life
in general. These four basic components are:
 Carbohydrates, Proteins, Lipids and Nucleic Acids.
Vocab
 Acid, acid (carboxyl) group, adenine, adenosine triphosphate
(ATP), alpha helix, amine group, amino acid, base, beta pleated
sheet, bonding, buffer, carbohydrate, cellulose, complementary
base pairing, cytosine, dehydration synthesis, deoxyribonucleic
acid (DNA), deoxyribose, dipeptide, disaccharide, double helix,
glucose, glycerol, guanine, glycogen, hemoglobin, hydrogen
bonding, hydrolysis, lipid, lubricant, maltose, monomer,
monosaccharide, neutral fat, nitrogenous base, nucleic acids,
nucleotide, organic, peptide bond, pH, phosphate,
phospholipid, polarity, polymer, polypeptide, polysaccharide,
primary structure, protein, quaternary structure, R-group,
ribonucleic acid (RNA), ribose, saturated fatty acid, secondary
structure, solvent, starch, steroid, sugar-phosphate backbone,
temperature regulator, tertiary structure, thymine,
unsaturated fatty acid, uracil