BIOL2000 Lecture Notes - Lecture 2: Chemical Bond, Ionic Bonding, Electronegativity

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27 Jan 2016
Lecture 3: Chemical Bonds (TC) 01/25/2016
Covalent Bonds and Weak Chemical Interactions
Four elements that are 99% within the human body
oCarbon, Nitrogen, Hydrogen, and Oxygen
Cells contain four major families of small organic compunds
Sugars, Fatty acids, Amino acids, and Nucleotides
Sugars = energy for cells and subunits of energy storing (an
structural) polysaccharides
Fatty acids = components of cell membranes and source of energy
Amino acids = subunits of proteins
Nucleotides = subunits of RNA & DNA
Macromolecules = form building blocks for polymers
Monomers (two sugars) are condensed to form a bond to generate
oCovalent bonds
Covalent bonds are stable and are very strong
Abundant Biological Atoms
Individual components of molecule
96% mass of typical organism
Stable of chemically unreactive when the outer shell of electrons
are completely full
oIf not stable, they will try and share an electron or take an
electron (ionic bond)
Chemical bonding and electronegativity
Electronegativity = a measure of tendency of an atom to attract a
bonding pair of electrons
Increases as you go up/ further to the right of periodic table
Polar bond: when atoms are partially positively/negatively charge;
one atom is slightly more electronegative than the other
oEx: water
If one atom is a lot more electronegative than the other
oAtom B is more in control of electrons than atom A
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oEx: NaCl
Covalent Bonds
Sharing of electrons between atoms
Stability – takes a lot of energy to break
Strength – makes biological molecules stable
Bond number/type
Single bonds – allow atom free rotation
Double bonds – no rotation
Polar and Non-Polar Covalent Bonds
Nonpolar bonds
oElectrons share equally
oEqual/very little electronegative atoms
oEx: fats
oUnequal sharing results in dipole
oElectrons pulled to more electronegative molecule
oEx: water
Non-covalent Bonds
Binding b/t di?erent parts of single macromolecule molecule
Binding b/t biological molecules
Lower energy than covalent bonds = allows for rapid transient
oEx: DNA molecule binding-transcription factor protein binding
Rely on attractive force b/t opposite charges, not sharing of
Number of bonds contribute to stability of complex
3 Types of Interactions
Salt bridges: ionic intereaction b/t charged chemical groups
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