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Lecture 2

MBB 231 Lecture Notes - Lecture 2: Phospholipid, Hydrophile, Heat Capacity

Molec Biol & Biochem
Course Code
MBB 231
Stephanie Vlachos

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Lecture 2
Understanding chemical bonding between atoms and molecules is fundamental to understanding
o Covalent bonds: strong bonds formed by the sharing of electrons between adjacent atoms
o Noncovalent interactions/bonds include
Van der waal interactions
Hydrogen bonds
Hydrophobic effect
Ionic bonds (electrostatic interactions)
The chemistry of living organisms is organized around carbon
o Carbon accounts for over half the dry weight of a cell
o Carbon atoms share electron pairs
o Single bond=single pair of electrons is shared and free rotation around the bound axis
o Double bond=two pairs of electrons shared and no free rotation around the axis
o Triple bond=three pairs of electrons shared and no free rotation around the axis
Energy required to break bonds varies
o A single bond is easier to break than a double bond due to the number of electrons bound in
a bond.
o What are the consequences of UV light to bonds?
UV light exposure has a high enough energy to break carbon-carbon and carbon-
hydrogen bonds which bonds found in our bodies and cells. These bonds can be
broken and affected by UV light.
o Covalent bonds are stronger and more stable than noncovalent bonds.
This is due to a higher amount of energy required to break covalent bonds as
compared to noncovalent bonds
More electrons are shared in double bonds, so more energy is required to break a
double bond than a single bond
o Noncovalent interactions are weak enough to continually reform at room temperature and
can come together to make one very strong interaction between parts of molecules.
o Chains or rings composed only of carbon and hydrogen
o Economically important
o Limited importance in biology due to the inability to be soluble in water
o The tedey of a ato’s aility to attract an electron. If an atom is more electronegative
than the other atom it is bound to, it will attract more electrons to itself and create a polar
covalent bond.
Hydrogen bonds
o Weak attractive interaction between an electronegative atom and hydrogen atom that is
covalently linked to a second electronegative atom.
o These interactions are generally weak, but very important in cells. For example, they are the
stabilizing forces in DNA helices, and proteins, and give water its many favorable
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