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Summary Energy and respiration
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Biology A level revision notes on energy and respiration
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Energy and respirationWork in all living organisms requires energy and includes:
The synthesis of complex from simpler ones (anabolic ones), such as the
synthesis of polysaccharides from monosaccharides, lipids from glycerol and
fatty acids, polypeptides from amino acids and nucleic acids from nucleotides
The active transport of substances against the diffusion gradient, such as the
sodium potassium pump
Mechanical work such as muscle contraction and other cellular movement like
cilia and flagella
In a few organisms, bioluminescence and electrical discharge
Mammals use thermal energy that is released from metabolic reactions to
maintain body temperature
ATP is a suitable energy currency as it is readily hydrolysed to release large amounts
of energy. It is also small and water-soluble, which allows it to be easily transported
round the cell. Any excess energy is converted into thermal energy.
Short-term energy storage molecules – glucose and sucrose
Long-term energy storage molecules – glycogen, starch and triglycerides
(Store chemical potential energy)
Synthesis of ATP
Generated by using electrical potential energy:
Transfer of electrons by electron carriers in mitochondria and chloroplasts
Phospholipid membranes in mitochondria and chloroplasts are impermeable to
protons, so there is a difference in proton gradient
Protons are then allowed to flow down the gradient (by facilitated diffusion)
through a protein that spans the bilayer
Part of this protein synthesises ATP and is called ATP synthase
The transfer of 3 protons allows the production of 1 ATP molecule
This is called CHEMIOSMOSIS
Generated in glycolysis and link reaction
Role of ATP in active transport
Active transport is the movement of molecules or ions across a partially permeable
membrane against a concentration gradient. Energy is needed, ATP, to counteract the
tendency of the particles to move by diffusion down the gradient.
The sodium-potassium pump is a protein that spans the cell membrane and has
binding sites for sodium ions and for ATP on the inner side, and for potassium ions on
the outer side. The protein acts as an ATPase and catalyses the hydrolysis of ADP to
ATP and inorganic phosphate, releasing energy to drive the pump. Changes in the
shape of the protein move sodium and potassium ions across the membrane in
opposite directions. For every ATP, 2 potassium ions move into the cell and 3 sodium
out of the cell. This creates a negative gradient inside the cell.
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