Biology unit 4 module 4.4

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Module 4.4
ATP is the immediate energy source. In respiration takes place in the cytoplasm, all the other steps in
the mitochondria. ATP synthesis is associated with electron transfer.
Know ATP is made from ADP + Pi (inorganic phosphate) when there is energy available.
List the uses of ATP in a cell.
Appreciate its role as a small, immediate energy source.
Know glycolysis takes place in the cytoplasm, starts with glucose and ends with pyruvate. A net
gain of ATP (substrate level phosphorylation) and reduced NAD coenzyme result.
Know the link reaction i.e. pyruvate to acetyl coenzyme A and that this 2 carbon molecule joins
with a 4 carbon molecule to make the first carbon molecule of the Krebs cycle.
Know the krebs cycle is a series of oxidation/reduction reactions, generates reduced NAD/FAD
coenzymes and ATP is made at substrate level phosphorylation. Carbon dioxide is lost.
Understanding how a cycle is energy efficient as it regenerates a substrate.
Know the synthesis of ATP is associated with the transfer of electrons and protons across
mitochondrial membranes at the oxidative phosphorylation level (ETC)
Know anaerobic respiration is glycolysis followed by the production of lactate or ethanol to
regenerate NAD. This allows further glycolysis and thus release of ATP
Appreciate the poor efficiency of aerobic and anaerobic respiration.
Key words:
ATP: adenosine triphosphate ­ an activated nucleotide found in all living cells that acts as an energy
carrier. The hydrolysis of ATP leads to the formation of adenosine diphosphate (ADP) and inorganic
phosphate, with the release of energy.
NAD: nicotinamide adenine dinucleotide ­ a molecule that carries electrons and hydrogen ions during
aerobic respiration.
Glycolysis: first part of cellular respiration in which glucose is broken down anaerobically in the
cytoplasm to two molecules of pyruvate.
Link reaction: the process linking glycolysis and the Krebs cycle in which hydrogen and carbon dioxide
are removed from pyruvate to form acetyl coenzyme A in the matrix of the mitochondria.
Krebs cycle: series of aerobic biochemical reactions in the matrix of the mitochondria of most
eukaryotic cells by which energy is obtained through the oxidation of acetyl coenzyme A produced
from the breakdown of glucose.
Oxidative phosphorylation: the formation of ATP in the electron transport system of aerobic
Substrate level phosphorylation: the formation of ATP by the direct transfer of a phosphate group
from a reactive intermediate to ADP.

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Aerobic respiration:
Cytoplasm of all living
2 ATP molecules are
added to glucose to form glucose
1.6. bisphosphate or
phosphrylated glucose.
This is unstable and
therefore splits into 2 x 3-carbon
compound triose phosphate (TP)
Hydrogen is removed
from each TP molecule and added
to NAD to form reduced NAD.
Enzyme controlled
reactions convert TP into
pyruvate. In the process 2
molecules of ATP are regenerated
from ADP.
Energy yields in glycolysis:
Two molecules of net ATP.
Two molecules of reduced NAD.…read more

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Pyruvate + NAD + CoA acetyl CoA + reduced NAD + CO2
The krebs cycle:
Oxidation/reduction reactions
Matrix of mitochondria
The 2 carbon acetyl A from the link reaction combines with a 4-carbon compound to produce
a 6-carbon compound.
This 6-carbon molecule loses carbon dioxide and hydrogens to give a 4-carbon molecule and
a single molecule of ATP produced as a result of substrate level phosphorylation.
The 4C molecule can now combine with a new acetyl CoA.…read more

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NADP ­ important in photosynthesis.
NAD works with dehydrogenase enzymes that catalyse the removal of hydrogen ions from
substrates and transfer them to other molecules such as the hydrogen carriers involved in
oxidative phosphorylation.…read more

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Anaerobic respiration:
In plants the pyruvate produced in glycolysis is converted to ethanol in anaerobic respiration.
In animals pyruvate is converted into lactate.
Pyruvate + reduced NAD ethanol + NAD
Pyruvate + reduced NAD lactate + NAD
Lactate can be oxidised back into pyruvate or converted to glycogen and stored.
Energy yields from anaerobic and aerobic respiration.
Energy from cellular respiration is derived in two ways:
Substrate level phosphorylation in glycolysis and the Krebs cycle.…read more


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