Download Biochemical Reactions

1
Types of Biochemical Reactions
During cellular processes macromolecules are continuously formed and
broken.
Anabolic reactions involve forming chemical bonds between small
molecular subunits in order to form a larger molecule. This occurs
during the formation of macromolecules.
Ex. amino acids form peptide bonds with each other to make a
polypeptide chain, making glucose during photosynthesis
Dehydration synthesis (or a condensation reaction)
• Results in the formation of macromolecules as covalent bonds are
formed between subunits (peptide bonds, ester bonds)
+
• involves the removal of H from subunit and OH from another
subunit resulting in the formation of water molecules
Catabolic reactions involve breaking the chemical bonds that exist
between subunits, within a large molecule.
Ex. peptide bonds are broken in order to release amino acids from a
polypeptide chain, breaking glucose during cell respiration
Hydrolysis reaction
• results in the breaking of macromolecules as covalent bonds are
broken between subunits
+
• involves the “splitting” of water molecules to create H and OH each
of which is added to one of the “freed” subunits
Redox Reactions
• involves the transfer of electrons from one atom to another
• the GAIN of electrons by an atom = REDUCTION
• the LOSS of electrons by an atom = OXIDATION
When electrons are transferred to a STRONGER electron acceptor (high
electronegativity value), energy is released because the electron ends up
in a more stable position.
2
Thermodynamics and Metabolism
Recall:
1st Law of Thermodynamics – E cannot be created or destroyed. It can
only be converted from one form to
another.
nd
2 Law of Thermodynamics – Energy conversion results in a loss of
energy, often in the form of HEAT.
In living systems, energy is converted from one form to another during
the chemical processes required for survival = METABOLISM. Some
of the energy is lost as HEAT. In order for these reactions to continue,
the lost energy must be replaced. Living things require a constant input
of energy to survive.
Chemical reactions usually require an initial input of energy to start the
reaction. This is called the ACTIVATION ENERGY (Ea).
•
Exothermic reactions
reactant molecules have MORE
potential E than products
= overall E OUTPUT
•
Endothermic reactions
reactant molecules have LESS
potential E than products
= overall E INPUT
Ea
Ex. The overall process of
cellular respiration
∆E
Ex. The overall process of
photosynthesis