Bio H – Biochemistry Unit
Intro to Biochemistry - Why we should love carbon so much
Biochemistry, as the name suggests, is the study of the chemistry going on inside living things. Much of this chemistry
centers around one element: Carbon. Carbon and its very special characteristics actually enable life to exist. Sure it has
some help from a handful of other atoms including oxygen, hydrogen, nitrogen, phosphorous and sulfur, but basically,
when we take these “legos” and combine them with a few rules we can create life!!! (which, by the way, is much cooler
than exploding test tubes, despite what your chemistry teachers will tell you)
Let’s begin by examining carbon and its “friends” in terms that we should already be familiar with. (in other words much
of this should be REVIEW)
Atomic structure: use the periodic table to complete the following table
Carbon
Hydrogen
Oxygen
Nitrogen
Phosphorous
Sulfur
Atomic
number
Atomic
Mass
# of
protons
# of
electrons
# of
neutrons
Common
isotopes
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While we’re at it lets review some of those terms. In your OWN words, describe what the follow mean.
o Atom
o
Proton
o
Electron
o
Neutron
o
Isotope
o
Ion
So now that we know a little about the atomic structure of our main elements, let’s talk about how we can bond these
atoms together to make chemical compounds. First a few basic rules:
Bio H – Biochemistry Unit
Only the electrons in the outer most shell participate in chemical bonding.
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What are these electrons called?
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How do we figure out how many of these electrons each element has?
Atoms that bond should fill each other’s outer shell
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How many electrons are needed to fill Shell 1, 2 and 3? (these are the only we care about!)
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Can you bond with multiple atoms to fill the shell?
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What happens if an atom’s outer shell is full all on its own?
o
What are these atoms collectively called?
Depending on the type of the bond, electrons can be either shared or transferred to fill shells.
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How do covalent bonds work? (Carbon’s favorite type of bond)
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How do ionic bonds work? (found in compounds like salt)
Compounds are formed when atoms are chemically bonded together.
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Examples: H2O, C6H12O6, CO
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The properties of the compound are different from the properties of each of the atoms by itself
o Na (explosive metal) + Cl (poisonous gas)  NaCl (tasty stuff on our fries!)
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The atoms that make up a compound are always in the same set proportion. Changing the proportion changes the
compound.
o H2O  Water, drink away!
H2O2  Hydrogen peroxide, not so much so!
Back to our friend Carbon – Carbon only forms covalent bonds, BUT its four valence electrons make it extremely
versatile. Remember when we said life is made of only a handful of legos? Well, when you only have a few building
blocks to work with, you better have at least one block that can do LOTS of stuff to make all the billions of compounds
that a living thing needs to survive. Carbon is that block!
I. Depending on the situation, carbon can share one, two or three of those electrons with another atom.
Examples: try to build then sketch each of the following.
CH4 – carbon shares one electron with each of four different hydrogen atoms
CO2 – carbon shares two electrons with each of two different oxygen atoms
CN- – One carbon shares three electrons with one nitrogen. BUT this doesn’t make a full octet. The leftover unpaired
electron gives the compound a negative charge.
Bio H – Biochemistry Unit
II. Carbon can bond with itself forming chains and rings of any size.
Notice all three structures below have 6 carbons but each one is unique. Build them to see for yourself.
III. Carbon compounds can have isomers
Isomers are compounds that have the same chemical formula but the atoms are arranged differently. Build the
following:
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Chemical formulas use numbers and the atomic symbols for elements to tell you three things:
1. Types of atoms bonded together
2. Number of each type atom bonded together
3. Number of molecules
5C6H12O6
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How many types of atoms? _________ List them: ___________________________________
How many of EACH type of atom in 1 molecule of the compound? ______________________________________
How many molecules ___________
You may have noticed that a common bonding partner of Carbon is Hydrogen. In fact, this pair is SO common that there
is an entire branch of chemistry dedicated to studying compounds containing carbon and hydrogen: organic chemistry.
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A compound consisting of only carbon and hydrogen is called a hydrocarbon. There are many of these but they
don’t come up a lot in biology. Most of the organic compounds that are relevant to biology contain some of those
other elements (O,N, P, S) as well as the carbon and hydrogen.