Chapter 2 text notes
Chapter 2 (review)
Chemical components of cell
Stable vs unstable elements. Unstable elements decay.
C,H,N,O : make up 96.5% of an organism’s weight
Outer most electrons determine how atoms interact
In living tissues, only e of an atom undergoes rearrangements.
Atoms with more than 4 shells are rare in biological molecules
2 types of bonds
Ionic: electrons are transferred from 1 atom to another
o Type of electrostatic attraction- force of attraction between 2 oppositely charged ions.
o i.e NaCl.
Covalent: sharing of electrons ( are shared unequally)
o A molecule is cluster of atoms
held together by covalent bond.
o Shared electrons form cloud of
o Nuclei held together by
opposing like charges.
o Attractive and repulsion forces
are in balance when nuclei are
Separated by bond length
Elements found with in human body.
Covalent bonds vary in strength
Bond strength is the amount of energy required to break a bond.
Making and breaking covalent bonds in living cells are controlled by enzymes.
There are different types of covalent bonds
Single bond vs double
Single bond allows rotation about axis
Double bond is shorter and more stronger than single
Intermediate bonds between double and single. i.e benzene
Polar structure: one with positive charge concentrated on one end and negative
charge concentrated on the other end.
Polar covalent bonds
Electrostatic attractions help bring molecules together in cell
Covalent bonds are very strong in aqueous solution
Strong vs weak electrostatic attraction
Strong: when atoms involved are fully charged i.e nacl
Weak: when polar covalent bonds occur Chapter 2 text notes
Importance of polar covalent bond in biology: they allow molecules to interact through
i.e Large molecules, such as proteins can bind to one another through complimentary
charges on their surface
The electrostatic attraction resembles ionic bond but is weaker than ionic.
Water is held together by H bonds
H2O: 70% of cells’s weight
H2O: highly polar covalent bond
Weaker than covalent bonds
When H binds to O or N or F
Hydrophilic: “water loving” molecules with + or – charges dissolve readily in water
i.e sugar, DNA, RNA and most of the proteins
Hydrophobic: Water fearing molecules
Are uncharged and form few or no H bonds. Don’t dissolve in water.
i.e hydrocarbons. They form hydrophobic thin membrane around the cell.
Some polar molecules form acids and bases in water
Strong vs weak acid
Strong acid lose their proton quickly
Weak acid holds on to the proton
Base: any molecule capa