Chapter all: Cell Chemistry

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1 Dec 2016
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2. CELL CHEMISTRY AND BIOENERGETICS
Carbon, hydrogen, nitrogen and oxygen constitute about 96.5 % of an
organism’s weight.
Cells, which are the basic unit of life, are composed of 70% water.
The atoms of the elements are help together by covalent bonds, which are
about 100 times stronger than the thermal energies present within the cell.
Two different molecules are held together by weak bonds termed as
noncovalent bonds.
The attraction between a positively charged region of one water molecule
(one of its H atoms) approaches a negatively charged region (the O) of a
second water molecule, results information of a hydrogen bond.
Hydrogen bond is a special form of polar interaction in which an
electropositive hydrogen atom is shared by two electronegative atoms.
Hydrogen bonds are much weaker than covalent bonds and are easily
broken by the random thermal motions that reflect the heat energy of the
molecules.
Many hydrogen bonds that link water molecules together, make water liquid
at room temperature, with a high boiling point and high surface tension,
rather than a gas.
Molecules that carry charge interact favorably with water and are considered
as water loving. Such molecules are termed hydrophilic. They include
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sugars, DNA, RNA, and most proteins.
Molecules that are uncharged form few or no hydrogen bonds, and so do
not dissolve in water. They are termed hydrophobic. Hydrocarbons are an
important example.
There are four types of non-covalent attractions that help bring molecules
together in cells. They are
Ionic bonds (Electrostatic attractions)
Hydrogen bonds
van der Waals attractions
Hydrophobic force
H+ (proton) can easily dissociate from its original water molecule and
associate with the oxygen atom of another water molecule, generating a
hydronium ion (H3O+) and hydroxyl ion.
The concentration of H3O+ is expressed using a logarithmic scale called the
pH scale.
Pure water has a pH of 7.0 and is said to be neutral. It is neither acidic (pH
<7) nor basic (pH >7).
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Weak acids and bases release or take up protons near pH 7, keeping the
environment of the cell relatively constant under a variety of conditions. Such
solutions are called buffers.
The backbone of cell is organic as it is mainly made of carbon compounds.
There are four major families of small organic molecules in the cell. They
are:
sugars
fatty acids
nucleotides
amino acids (Figure 2–6)
The most abundant carbon containing molecules in the living cells are
termed as the macromolecules.
The macromolecules in cells are polymers that are constructed by
covalently linking small organic molecules called monomers, into long
chains (Figure 2-8).
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