Page 314 - Biology_F5

Gas exchange and respiration

Respiratory reactions cycle) in the mitochondria. Pyruvate can
There are two fundamental types of also be converted to ethanol and CO
2
reactions in cellular respiration, namely (fermentation) in anaerobic conditions
oxidation and decarboxylation. and allows cells to make small amounts
of ATP.
Oxidation. During respiration, oxidation
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can take place in three ways; through Some cells, such as yeast are unable
addition of oxygen, removal of hydrogen to carry out aerobic respiration and
(dehydrogenation) or removal of electrons. will automatically move into a type of
anaerobic respiration called alcoholic
Decarboxylation. Decarboxylation is fermentation. This occurs with the help of
the removal of carbon from a compound the enzyme pyruvate decarboxylase which
to form carbon dioxide. For a glucose removes a carbon dioxide molecule from
molecule which contains carbon, hydrogen the pyruvate to form an acetaldehyde.
and oxygen, it is the hydrogen which is The acetaldehyde is then reduced by the
required for respiration. Thus, carbon has enzyme alcohol dehydrogenase, which
to be removed by decarboxylation. transfers the hydrogen from NADH to the
acetaldehyde to form NAD and ethanol.
6.3.2 Glycolysis
Glycolysis process
Task 6.5 Normally, glycolysis is a determined
Search from the library and internet sequence of ten enzyme-catalysed
sources the simulations of glycolysis reactions and each step is facilitated by
process, and then prepare short notes a different enzyme. The intermediates
on what you have searched.
provide entry points to glycolysis, although,

Cellular respiration occurs in all living usually starts with glucose or glycogen
organisms. Glycolysis is the first stage to produce glucose-6-phosphate. The
of cellular respiration whereby glucose starting point for other monosaccharides
is oxidised into pyruvate. This process such as galactose and fructose can be
takes place in the cytoplasm of the cell converted into one of these intermediates.
and it does not require the presence All the reaction steps for the glycolysis
of oxygen. Physiologically, glycolysis take place in the cytoplasm. Glycolysis
produces energy at a high rate, but for a yields an overall of two molecules of
short duration. In anaerobic condition, ATP which are free energy-containing
pyruvate can be reduced to lactate molecules, two molecules of pyruvic acid
by lactate dehydrogenase. Anaerobic and two “high energy” electron carrying
glycolysis is also an effective means of molecules of Nicotinamide Adenine
energy production during short intense Dinucleotide (NADH). Glucose can also
exercise. Under aerobic condition be synthesised from non-carbohydrate
pyruvate is converted to Acetyl CoA and precursors by reactions referred to as
it continues to the citric acid cycle (Kreb’s gluconeogenesis. The pentose phosphate

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