summary of respiration

summary of respiration

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LINK REACTION AND KREBS CYCLE
Communication, homeostasis and energy
F214 Unit 4: Respiration
The next stage involved only in aerobic respiration begins with the pyruvate molecules produced from glycolysis. This part of aerobic respiration
happens in the mitochondrial matrix and the pyruvate is transported there from the cytoplasm
pyruvate
(3C) In the link reaction, named so as it links glycolysis to Krebs, a molecule of pyruvate
ATP is first decarboxylated (has carbon dioxide removed) using decarboxylase enzymes
NAD (ox) and dehydrogenated (has hydrogen removed) using dehydrogenase enzymes. The
The process of respiration releases energy from food molecules, mainly glucose. Energy is released in the form of CO2
hydrogen atoms are accepted by a molecule of NAD. The result is an acetyl group
ATP (adenosine triphosphate), a molecule which is often described as the universal energy currency of cells, because NADH2 (red)
which binds with coenzyme-A to form acetyl coenzyme A. The coenzyme-A leaves
it can be used to fuel all metabolic reactions which require energy and is immediately available wherever there is Link
(2C) the molecule (leaving it as acetate) and is recycled to be used again
acetyl coenzyme A reaction
ATP. It is formed from one molecule of ADP (adenosine diphosphate) and one extra inorganic phosphate group (Pi)
The acetate is a 2-carbon molecule which then joins a molecule of oxaloacetate (a
Aerobic respiration takes place under aerobic conditions ­ where oxygen is present ­ and has a higher overall yield
Coenzyme A 4-carbon compound) to form citrate (a 6-carbon compound). Citrate is then
of ATP. Anaerobic respiration occurs where oxygen is not readily available, and is much less efficient
decarboxylated and dehydrogenated to form a 5-carbon acid, which also has
(2C)
Whilst the common respiratory pathway for both types of respiration occurs in the cytoplasm, the bulk of aerobic acetate hydrogen and carbon dioxide removed, forming a 4-carbon acid. At this stage,
respiration actually occurs in the mitochondrion, an organelle with a double membrane. Processes within aerobic substrate-level phosphorylation occurs as in glycolysis ­ an inorganic phosphate is
respiration occur in the matrix and the inter-membrane space between the two surrounding membranes removed from the compound and attached to a molecule of ADP to form ATP
A molecule of FAD is then reduced, as is a molecule of FAD, and the
(6C)
THE MITOCHONDRION oxaloacetate
(4C) citrate removal of these four hydrogen atoms forms oxaloacetate, and so the
cycle continues
The mitochondrion consists of the mitochondrial matrix where the link reaction and Krebs cycle occur. This is the CO2 NAD (ox)
interstitial fluid within the organelle. The matrix is readily equipped with all the substances required for the cell to NADH2 There is one complete turn of the cycle for each molecule of pyruvate. The
NADH2
undergo aerobic respiration (including the coenzyme NAD and the cofactor FAD, and compounds such as co-A and NAD
(red) (ox) end products of Krebs cycle for each glucose include two molecules of ATP
Krebs (red)
oxaloacetate) 5C acid produced directly during Krebs, six lots of reduced NAD and two reduced
FADH2 cycle
FAD, as well as four molecules of carbon dioxide, a waste by-product. The
The inner membrane is lined with huge numbers of cytochromes to allow for the electron transport chain, so that FAD (ox)
(red) CO2 link reaction produces a further two reduced NAD and two carbon dioxide
chemiosmosis can occur. There are also stalked particles in this membrane (which are ATPase)
4C acid NAD (ox) molecules added on to this total
NADH2
The molecules of reduced NAD and FAD will enter the electron transport
4C acid (red)
GLYCOLYSIS chain and donate their accepted hydrogen atoms so that ATP can be
synthesised via oxidative phosphorylation. Generally, one NADH2 yields
The first stage of respiration common to both types (6C)
glucose ATP 2.5 ATP and one FADH2 yields 1.5 ATP
is glycolysis. This first series of metabolic reactions ADP + Pi
occurs in the cytoplasm not the mitochondrion ATP
Glucose undergoes phosphorylation, taking up a ADP ELECTRON TRANSPORT CHAIN
phosphate group from a molecule of ATP (reducing (6C) This process involves various electron carriers embedded in the inner mitochondrial membrane, called cytochromes. These membranes are folded
fructose phosphate
it to ADP) and becoming glucose phosphate. This is into cristae to give a large area for many of these electron transport systems
then rearranged into another molecule ­ fructose ATP
phosphate, which is again phosphorylated to intermembrane
ADP space
become fructose biphosphate. This six carbon sugar
(6C)
is then split into two smaller molecules which are fructose biphosphate
each called triose phosphate (3-carbon) inner inner
mitochondrial mitochondrial
Finally, two molecules of membrane membrane
ADP are phosphorylated for (3C) (3C)
triose phosphate triose phosphate
each triose phosphate to
become ATP, and the sugar 2ADP + 2Pi 2ADP + 2Pi electron carriers
then has two hydrogen NAD (ox) NAD (ox) mitochondrial (cytochromes)
2ATP 2ATP matrix stalked particle
atoms removed using NADH2 (red) NADH2 (red) (ATP synthase)
dehydrogenase enzymes to
become a molecule known (3C) (3C)
pyruvate pyruvate
as pyruvate Molecules of reduced NAD and reduced FAD arrive at the electron transport chain and offload the hydrogen atoms they are carrying. Each hydrogen
The hydrogen atoms are accepted by a coenzyme called NAD (nicotinamide adenine dinucleotide), reducing the atom can be split into a proton and an electron, and since each molecule donates two hydrogen atoms, either donates two protons and two
coenzyme to reduced NAD (or NADH2). Overall, as two ATP were used to phosphorylate the sugar and four were electrons at one time. The electrons are accepted by the first cytochrome (only NAD can donate to this cytochrome) and are passed along the chain
eventually made, it is said that the net ATP production per glucose molecule in glycolysis is 2 ATP. Two molecules of to the next carrier, cytochrome II. Further electrons will be accepted by this second cytochrome (FAD can only donate to this carrier), and again
pyruvate and two molecules of reduced NAD were also produced electrons are passed along to the third, and finally the fourth carrier, until leaving the chain at the end to help produce the by-product water

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CHEMIOSMOSIS AND OXIDATIVE PHOSPHORYLATION ANAEROBIC RESPIRATION
The movement of electrons from carrier-to-carrier releases energy, and at the first, third and fourth cytochromes this energy is used The majority of anaerobic respiration is the simple glycolysis pathway.…read more

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