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How is ATP produced and used in living organisms?
What is ATP?
Adenosine Triphosphate (ATP) is a molecule present in all living organisms
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It is used as a
source of energy in cells for a multitude of different processes, and is created in a phosphorylation
reaction between Adenosine Diphosphate (ADP) and an inorganic phosphate (Pi) which is catalysed
by the enzyme ATP synthase
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The
energy stored is in the form of a phosphate bond between two of the phosphate groups, which is
released through a hydrolysis reaction catalysed by the enzyme ATP hydrolase
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Production and use via photosynthesis
The production of ATP on a global scale starts with plants, which convert light energy from the sun
into chemical potential energy in the form of ATP
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In the light-dependent reaction, ADP is combined
with Pi to form ATP in the thylakoid membranes of the chloroplasts
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Energy from the
excited electrons then makes ATP, through transporting H⁺ ions (protons) into the thylakoid, causing
it to have a higher concentration of protons than the stroma
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In this stage of
photosynthesis NADPH is also produced and photolysis of water occurs
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CO₂ is combines with ribulose bisphosphate (RuBP) in a reaction catalysed by rubisco,
forming two GP molecules
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One more molecule of ATP is required to recycle most
of the TP back to RuBP, with only a small amount of carbon being utilised
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Production and use via respiration
The production of ATP in respiration occurs in two different ways – aerobic respiration and
anaerobic respiration
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The products of the first three stages are utilised
in the final stage to produce lots of ATP
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These
are then oxidised, producing two pyruvate molecules, along with four ATP molecules and two
reduced NAD (NADH)
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In anaerobic
respiration, no further stages occur
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The next three stages of aerobic respiration all occur in the matrix of the mitochondria
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They are decarboxylated and oxidised, before being combined with
coenzyme A to form acetyl coenzyme A
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Oxidative phosphorylation is the next step,
which is where the energy carried by electrons from NADH and FADH is used to make ATP
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When they travel back along their concentration gradient
through ATP synthase, they drive the synthesis of ATP from ADP and Pi
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Hence, respiration must occur to release
the energy they store in this form
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Active transport in
plants is essential, as it enables the root hair cells to take in minerals, such as nitrates, from the soil
against their concentration gradient
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This requires carrier molecules which
are proteins embedded in the cell-surface membranes of the cells
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It is an enzyme which moves one molecule against its
concentration gradient, whilst moving the other with theirs
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With glucose, this occurs because the concentration of glucose in the mammalian ileum is
too low for glucose to diffuse out and into the blood, so glucose is absorbed from the lumen of the
ileum by co-transport
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Sodium ions then diffuse
from the lumen of the ileum into the epithelial cell, down their concentration gradient, via a sodiumglucose co-transporter
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Without this system in
place, it would be impossible for mammals to get the glucose they need for respiration, so they
would be unable to produce the ATP required to function
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It is used in both transcription and
translation, with its use in translation revolving around the need for a transport RNA molecule to
bind to an amino acid
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The
tRNA molecule then attaches itself to a complementary anticodon, and once a second tRNA
molecule has done the same adjacent to it, a peptide bond forms between the amino acids, and the
first, and now empty, tRNA molecule leaves the ribosome
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Muscle contractions
These are a feature in many organisms which would be unable to occur if it were not for ATP
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Myosin filaments have globular
heads which can move back and forth, and have two binding sites: one for actin and one for ATP
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When an action potential arrives, calcium ions (Ca²⁺) are released and this
serves two purposes – it moves the tropomyosin to unblock the binding site, and it activates ATP
hydrolase which hydrolyses ATP into ADP and Pi, providing the required energy for the muscle
contraction
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When the muscle stops being stimulated,
ATP is used to actively transport the calcium ions back to the sarcoplasmic reticulum
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Tactic and kinetic responses to a stimulus occur when simple organisms detect a
certain stimulus, and the movement requires energy in the form of ATP
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Furthermore, in other synapses where ions are used, ATP us
important in the active transport of ions in order to remove Ca²⁺ ions from the synaptic knob after
an action potential has arrived
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It is a reduction reaction which gives off energy, and hence it
requires chemical energy, which is provided by ATP hydrolysis that allows the activation energy

barrier to be overcome
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Ultimately, nitrogen fixation results in the release of
energy, however like many other biological systems; it requires energy to active the reaction
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Rhizobium is an example of a bacteria which exhibits a mutualistic relationship,
living inside the root nodules of leguminous plants

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