Some notes I wrote on respiration.

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  • Created on: 08-03-13 12:35
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Cellular respiration is a process by which organisms produce ATP in a complex series of
reactions. ATP is the energy source for all metabolic reactions which occur in the cell. Energy
is needed for many bodily functions, including, muscle contraction, protein synthesis, active
transport, maintaining body temperature and nerve conduction.
GLYCOLYSIS: This process takes place in the cytoplasm
of the cell. A 6-carbon (6C) sugar, namely glucose, is
split by a series of reactions into two molecules of
pyruvic acid, a 3-carbon (3C) molecule. Initially, glucose is
converted into glucose phosphate (6C) by
phosphorylation in which a molecule of ATP is used up.
This glucose phosphate is converted into fructose
phosphate by isomerisation and another molecule of
ATP is used. The phosphorylated sugar splits to give two
molecules of triose phosphate (3C). Two hydrogen
atoms are removed from the 3C sugars, catalysed by
the enzyme dehydrogenase, and are picked up by NAD
(which acts as a hydrogen acceptor) to form reduced
NAD. ATP is made when the 3C sugar is converted into
pyruvic acid.
THE LINK REACTION: If there is plenty of oxygen
available then the pyruvic acid formed during
glycolysis is taken into the mitochondria. It joins
with the molecule coenzyme A to form acetyl
coenzyme A (2C), releasing a molecule of carbon
dioxide as well as a molecule of hydrogen to reduce
KREBS CYCLE: Acetyl coenzyme A combines with a
4C compound to form citric acid (6C). This is
converted into succinate (4C), releasing two
molecules of carbon dioxide and two hydrogen
atoms which are picked up by NAD. 3 molecules of
ATP are synthesised. Succinate or (succinic acid) is
converted into malate (4C) or malic acid, and then converted into oxalo-acetic acid (4C),
which in turn combines with acetyl coenzyme A and the cycle begins again. As a result of

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NAD, one of reduced FAD and one of ATP are
produced. ATP is produced in the stalked particles on the inner mitochondrial membrane. For
each molecule of glucose that enters the glycolytic pathway, two molecules of pyruvic acid
are formed and so the Krebs cycle turns twice.
ELECTRON TRANSPORT CHAIN: This process is known as oxidative phosphorylation
because ADP is phosphorylated in a process which requires oxygen. Hydrogen atoms from
the Krebs cycle are picked up by NAD.…read more

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C sugar. It is affected by the concentration of ATP and citrate form the Krebs cycle.
When there is plenty of ATP or the components of the Krebs cycle, glycolysis slows down
and vice versa. By changing the rate of glycolysis, the rate of the whole process of cellular
respiration is controlled.…read more


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