Cambridge A Levels A2 Biology Chapter 12 Energy and Respiration
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Cambridge A Levels A2 Biology
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Chapter 12 Energy and Respiration: 31 pages
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Chapter 12 Energy and Respiration
12.1 Energy
12.2 Respiration
12.1 Energy Part 1
The Need for Energy
Metabolic Pathway
A metabolic pathway consists of a series of chemical reactions whereby each chemical reaction
is catalysed by a specific enzyme.
The product of each chemical reaction becomes the substrate for the next chemical reaction.
Catabolism
the breakdown of complex molecules into smaller molecules with the release of energy.
Eg: oxidation of glucose during respiration with the realease of CO2, water and ATP.
Anabolism
the synthesis of complex molecules from simple molecules and requires energy.
Eg: the synthesis of protein from amino acids
the synthesis of glycogen from glucose
,ATP
Structure of ATP
ATP is the universal energy currency of cells of all living organisms.
ATP molecule is a phosphorylated nucleotide.
ATP molecule consists of:
▪ A nitrogenous base (adenine)
▪ A pentose sugar (ribose)
▪ Three phosphate group
The phosphate group are inter-linked by phosphoanhydride bonds.
When one phosphate group is removed from ATP,
▪ ADP (adenosine diphosphate) is formed.
▪ 30.5kJmol^–1of energy is released.
Removal of a second phosphate
▪ AMP (adenosine monophosphate) is formed.
▪ 30.5kmol^–1 of energy is released.
Removal of the last phosphate,
▪ Adenosine is formed.
▪ 14.2kJmol^–1 of energy is released.
,The reaction is:
▪ exergonic, energy is released.
▪ catalysed by enzyme ATP synthase.
ATP is an intermediate source of energy in living cells rather than a long-term energy store.
In a typical animal cell, one ATP molecule is used within one minute of its formation (rapid
turnover)
ATP can release energy quickly, which only requires hydrolysis.
ATP is small and water soluble, so ATP can move around in cell easily.
ATP is a link between energy yielding and energy requiring reactions.
Features of ATP that make it suitable as the universal energy currency
, Uses of ATP
▪ Muscle contraction for movement.
▪ Cell motility (ability to move).
▪ Active transport of molecules/ions across the membrane.
▪ Synthesis of macromolecules.
▪ Cell division.
▪ Urea synthesis in the liver.
▪ Phosphorylation of sugars in the initial stage of glycolysis.
▪ Maintenance of body temperature.
Ways to Synthesise ATP
▪ Transfer of phosphate in substrate-linked reaction
Using energy provided directly by another chemical reaction.
Takes place in the cytoplasm.
Occurs in glycolysis and in Krebs cycle.
Less ATP is generated.
▪ Chemiosmosis
A process that takes place across the inner membranes of mitochondria and
chloroplasts.
Using energy released by the movement of hydrogen ions down their concentration
gradient.
More ATP is generated.
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