Transcript Chapter 2

Chemistry for Biology
Why study chemistry in biology?
Think about what you are made of.
If we completely broke you down, you would end up a pile of
Elements (or atoms).
-elements are the simplest chemical units that exist.
They cannot be broken down by ordinary chemical
means like dissolving in water and melting in fire.
-gold is an element. What happens if you take a gold
bracelet and apply heat to it?
Your body is mainly Carbon, Hydrogen, Oxygen and Nitrogen.
-see Figure 2.3 on pg. 22 of your book.
You are approximately 96% these four elements.
Elements are composed of 3 parts:
Protons- located in the center of the atom. These
particles carry a POSITIVE charge.
Neutrons- also located in the center of the atom. These
particles carry NO charge.
Electrons- these particles
are located outside the
nucleus in orbitals.
Electrons carry a negative
charge. They are “held” in
their orbits by the opposite
charge of the protons in the
nucleus.
Elements are arranged on the Periodic chart. This is like a
dictionary for elements.
Large numbers represent the atomic number as well as the
number of protons in an element.
Smaller numbers are the atomic mass.
Symbols come from the element’s Latin name.
Many facts can be learned about an atom from the Periodic
Chart.
1. The number of protons is = to the atomic number.
example: Oxygen is #8 and has 8 protons.
2. The atomic mass minus the atomic number = the
number of neutrons.
example:
Oxygen atomic mass is 16 - 8(atomic number)
= 8 neutrons.
What happens if we change the number of protons??
(change the element entirely)
What happens if we change the number of neutrons??
(change the mass of the element)
Form an isotope of the element when we change the mass.
Isotopes have the same # of protons but different # of
neutrons and different atomic mass.
Isotopes are common in nature.
Called “radioactive” because they emit a charge.
They are used for many purposes.
Medical Uses:
Put in dyes to help with CAT and PET scans and MRI’s.
Dye is injected or put in a drink. (Barium is popular)
Other Uses:
Used to trace chemical pathways in organisms. Radioactive Oxygen used to study photosynthesis in plants.
Used to “date” fossils and bones…”carbon dating”.
Bad Isotopes cause problems:
Chernobyl nuclear meltdown…many people have cancer.
Cesium mimics elements that build bone, but breaks
bones down instead of building them up.
Different brain scans when
cocaine is present in blood and
not present in blood.
Three Mile Island
Nuclear Power Plant
Elements join to form Compounds.
-compounds are two or more elements joined in a
fixed ratio.
-most chemicals in nature are found in compounds
because elements alone are “unstable”.
-common compounds like H2O and Na+Cl- are part of
your everyday routines.
-the elements in salt are very dangerous alone…but
joined to form the compound, they are harmless.
http://www.etec.energy.gov/Ope
rations/Sodium/images/Sodium
Lump.jpg
http://www.amazingrust.co
m/Experiments/how_to/Im
ages/Chlorine_gas.jpg
Compounds are joined together by Bonds.
Two basic types of bonds are found in abundance in
biological systems.
Ionic Bonds– these bonds occur
when one element gives it’s
electrons to another element
creating a charge between
the two elements causing them
to bond.
http://lc.brooklyn.cuny.edu/smarttutor/corc1321/image
s/nature/9.a.Ionicbond-nacl.gif
“Opposites attract.”
Example: salt is made of
Na and Cl…
Na completely donates one
electron to Cl thus making Na +
and Cl – which bonds them
together. (Figure 2.8, pg. 25)
Covalent Bonds– these bonds occur when two or more
elements share electrons. Because the sharing is =,
there is no charge created.
Example: Oxygen that you breathe is really 2 O
atoms held together by a covalent bond. This is
drawn like O=O. The single bars represent one covalent
bond each. Thus, oxygen can be written as O2 .
(Figure 2.9, pg. 26)
http://www.sciencecontrol.com/wpcontent/uploads/2011/01/Covalent-Bond1.gif
Hydrogen Bonds are also important in biology…particularly
between adjacent water molecules. The positive charge of
the H+ has a special affinity for the negative charge of the Oand so the molecules have a very special arrangement.
Not very strong alone, but when combined with many other H
bonds in a sheet of water make for a very strong compound.
http://www.doctortee.com/dsu/tiftickjian/cseimg/biology/chemistry/hydrogen-bonds.jpg
http://water.me.vccs.edu/courses/ENV211/changes/
hydrogenbond.gif
Water is the single most important compound on the planet.
Your cells are 70-95% water.
Life began in the water…and evolved there for ~3 billion ybp
before moving on to land.
Earth is 75% water…one of the reasons we can live here.
Chemical structure of water is simple: 2 atoms of Hydrogen
covalently bonded to one atom of Oxygen.
Water is slightly charged…thus we say it is a polar molecule.
The hydrogen end is slightly + in charge, the oxygen end is
slightly – in charge.
This charge creates hydrogen bonds between two water
molecules creating “sheets” of water with cool properties.
Water has 4 unique properties that make it essential for life.
1. Water molecules are cohesive. They stick to each other.
They also take different shapes according to the container
they are in.
--think about all the times water changes shape before it
finally ends up in your cells.
--cohesion of water molecules allows insects to walk on water.
--water molecules move from the
roots of plants up through the
stem and finally evaporate out the
leaves by cohesion.
(see Fig. 2.12, pg. 29)
2. Water can help moderate temperatures.
--since water has the ability to soak up large amounts of
heat and then slowly release it during periods of cold,
water can help keep the temperature of an area within a
reasonable set of limits.
--water is also responsible for moderating body temperature
during overheating. How does it do this?
http://www.konalaniyoga.org/wp-content/uploads/2010/09/Hawaii-beachwater1.jpg
3. Ice is less dense than
liquid water. In other words
…ICE FLOATS!!...
http://images.pictureshunt.com/pics/i/iceberg-12482.jpg
--when water starts to get cooler, individual molecules move
apart, creating “pockets” of air in a crystal that weighs less
than the liquid it forms from…so it can float!!
Why is this important to life?
What would happen if all the oceans, rivers, ponds and lakes
froze from the bottom up? Would they ever thaw completely
out? What about organisms that live in them?
Ice also creates an insulating layer to keep water below it warm.
4. Water is a Universal Solvent.
--water will mix with just about anything.
--creates an Aqueous Solution.
--examples are numerous…blood, tea, soda (polar)
Water won’t mix with petrols…oil containing products.
--paint that is oil based, gasoline, grease on your dishes or
clothing, vinegar/salad oil (non-polar)
**SOAP DOES NOT DISSOLVE OIL**
Soap is an important additive to water in order to remove oil.
Soap has unique properties because it has both a polar and
non-polar end to its molecule.
The polar end will attach to
water, the non-polar end to
oil, forming a micelle of
water and oil just long
enough to remove
oil from the object.
Life is constantly changing it’s chemical composition.
This is largely due to chemical reactions taking place.
In a reaction, there are reactants and products.
Reactants are what enter the process and products are what
come out at the end.
Think of it like baking a cake…what goes in is very different from
what comes out!! But it is all still there at the end!!
Water is formed by combining Hydrogen and Oxygen…
2 H2 + O2 = 2 H2O.
This equation is also balanced meaning that the ingredients are
equal on both sides of the equation. Nothing is lost and nothing
is created.
Water monitors pH of many living things.
pH is the measure of potential Hydrogen…or the number
of hydrogen atoms present in a solution.
When water breaks apart it produces an H+ and an OHSolutions are rated on a pH scale ranging from 0-14.
Acids go from 0-6.9
Pure water is neutral at 7.0
Bases go from 7.1-14.0
These numbers are determined by the amount of hydrogen
the solution has. Lots of hydrogen means an acid is formed,
Lots of OH means a base is formed. Neutral substances have
equal amounts of H and OH.
pH Scale ranks common substances according to their acid and
base content. Each jump on the scale represents 10 x more or
less hydrogen atoms than the previous substance.
Acid rains cause many problems for the environment.
Many plants are acid intolerant, so a build-up of acid in
the soil can cause them to die. Plants that are acid
tolerant will take over the soil and may limit the food
supply for other organisms.
Acid rain run-off can raise the pH of lakes, rivers, and
streams in an ecosystem, effecting the entire aquatic
food chain.
Recreation can also be affected by acid rain.
Car paint peels off, marble statues erode.