Respiration

The Stages of Respiration

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Anabolic and Catabolic Reactions

Anabolic Reactions

Biochemical reactions where large molecules are synthesised from smaller ones

Catabolic Reactions

Reactions were larger molecules are hydrolysed to produce smaller molecules

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What is Respiration?

It is the process whereby energy is stored in complex organic molecules such as; carbohydrates, lipids and proteins is used to make ATP. It occurs in living cells.

ATP

Is a phosphorylated nucleotide and is the universal energy curency

Energy

Is the abillity to do work

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What is ATP needed for?

  • Active Transport - moving ions and molecules against the concentration gradient
  • Secretion - large molecules made in some cells are exported by exocytosis
  • Endocytosis - bulk movement of large molecules into cell
  • Synthesis - of large molecules from smaller ones
  • Replication - of DNA and synthesis of organelles before the cell divides
  • Movement - such as movement of bacterial flagella and microtubule motors
  • Activation of Chemicals - glucose is phosphorylated at the beginning of respiration
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The Structure of ATP

A row of three phosphates joined to ribose and ribose joined to adenine, Phospahte(s) joined to carbon 5 and adenine joined to the first carbon.


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The Stages of Respiration

  • Glycolysis - Happens in the cytoplasm, aerobic or anerobic conditions. Glucose (6C) is broken down to 2x Pyruvate (3C)
  • Link Reaction - Happens in the matrix, Pyruvate is dehydrogenated and decarboxylated and converted to accetate
  • Krebs Cycle - Also takes place in the matrix, acetate is decarboxylated and dehydrogenated
  • Oxidative Phosphorylation - Takes place in the cristae of the mitochondria, ADP is phosphorylated to ATP
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Glycolysis

  • Glucose (6C) is phosphorylated to hexose phosphate (6C), using phosphate and energy from ATP
  • Hexose phosphate is phosphorylated to hexose bisphosphate (6C) using phosphate and energy from ATP
  • Hexose bisphosphate (6C) then splits into two molecules of triose phosphate (3C)
  • In a series of reactions, each molecule of triose phosphate is converted into pyruvate (or pyruvic acid) (3C)
  • During this series of reactions, enough energy is released to make 4 ATP molecules per triose phosphate. There is a net gain of 2 ATP molecules when one glucose molecule is split by glycolysis
  • During this series of reactions, hydrogen is removed from each triose phosphate molecule by dehydrogenation, this is catalysed by the enzyme dehydrigenase and is therefore affected by fluctuations in temperature, pH or concentration
  • The hydrogen is picked up by the hydrogen acceptor NAD, forming reduced NAD (NADH). Two molecules of reduced NAD are formed when one glucose molecule is split by glycolysis
  • At the end of glycolysis, the pyruvate molecules are activley transported into the matrix of the mitochondria
  • Products = 2x Pyruvate molecules , net gain of 2x ATP molecules, 2x reduced NAD
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Link Reaction

  • Takes place in the matrix of the mitochndria
  • Each pyruvate (3C) is decarboxylated (CO2 removed) and dehydrogenated (2H removed) to form acetyl (2C)
  • acetyl (2C) combines with coenzyme A to form acetly CoA
  • For each pyruvate, 1 molecule of CO2  and 1 reduced NAD are formed
  • the reduced NAD is used in the final stage of aerobic respiration - oxidative phosphorylation
  • the CO2  is given off as waste gas
  • Products = CO2 x2, Acetyl CoA x2, Reduced NAD x2
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Krebs Cycle

  • Acetyl CoA (2C) combines with a 4 carbon compound oxaloacetate to form a 6 carbon compound citrate. Coenzyme A is recycled back into the link reaction
  • The Citrate (6C) is dehydrogenated. 2H is removed and picked up by the carrier NAD, which becomes reduced to reduced NAD
  • The 6C citrate is decarboxylated, CO2 is removed to form a 5C compound
  • The 5C compound is dehydrogentaed and decarboxylated to form a 4C compound, at this stage there is enough energy released to form a molecule of ATP by substrate level phosphorylation
  • The 4C compound is dehydrogenated to form another 4C intermediate, this time the carrier FAD picks up the hydrogen and becomes reduced FAD
  • Finally the 4C compund is dehydrogenated to from 4C oxaloacetate, reduced NAD is formed
  • The regenerated oxaloacetate can now combine with another Acetyl CoA and the cycle turns again

THE CYCLE TURNS TWICE PER GLUCOSE MOLECULE

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Oxidative Phosphorylation

2H are accepted from reduced NAD by the FIRST carrier in the chain.  By this process, reduced NAD becomes REOXIDISED  to NAD and the first carrier becomes REDUCED.  This is an example of a REDOX reaction. 

Hydrogen atoms from the reduced NAD are split into PROTONS and ELECTRONS.

The electrons are passed via a series of electron carriers to oxygen, the protons go into solution in the matrix

Enough energy is released at three stages to make ATP from ADP & Pi. 

2H are accepted from reduced FAD to the SECOND carrier in the chain.  By this process, reduced FAD becomes REOXIDISED to FAD and the second carrier becomes REDUCED.  This is an example of a REDOX reaction. 

 Enough energy is released at 2 stages to make ATP from ADP & Pi.

 The final hydrogen acceptor is OXYGEN.  H2 & ½ O2 combine to form WATER. 

If oxygen is not available, the carriers in the electron transport chain all remain REDUCED and therefore red.NAD and red.FAD cannot offload their hydrogen. 

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Anaerobic Respiration

 Is the release of energy  from substrates , specifically GLUCOSE, in the absence of oxygen.

The ETC cannot function so:

Carriers cannot pass on their electrons and remain reduced

As they are already reduced  they can’t accept electrons from NAD and FAD

Reduced NAD and reduced FAD cannot be reconverted (reoxidised)  to NAD and FAD \

Krebs cycle and the link reaction stop because NAD and FAD are not available to accept electrons

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Lactate Fermentation

Reduced NAD is OXIDISED  to NAD

PYRUVATE  acts as the hydrogen acceptor

It accepts hydrogen from REDUCED NAD

NAD is now reoxidised and available to accept more HYDROGEN  from glucose

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Alcohol Fermentation

Each pyruvate molecule loses a CO2 molecule; pyruvate is decarboxylated and becomes ETHANAL.

This reaction is catalysed by PYRUVATE DECARBOXYLASE

Ethanal accepts hydrogen atoms from REDUCED NAD, which becomes reoxidised

Ethanal is reduced to ETHANOL; this reaction is catalysed by ALCOHOL DEHYDROGENASE

Reoxidised  NAD can now accept more hydrogen from GLUCOSE

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Alcohol Fermentation

Each pyruvate molecule loses a CO2 molecule; pyruvate is decarboxylated and becomes ETHANAL.

This reaction is catalysed by PYRUVATE DECARBOXYLASE

Ethanal accepts hydrogen atoms from REDUCED NAD, which becomes reoxidised

Ethanal is reduced to ETHANOL; this reaction is catalysed by ALCOHOL DEHYDROGENASE

Reoxidised  NAD can now accept more hydrogen from GLUCOSE

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Respiratory Substrate

A respiratory substrate is an organic substance that can be used by respiration.

  • RQ = CO2 out + O2 in
  • Carbohydrate = 1
  • Protein = 0.9
  • Lipid = 0.7
  • Protein and Lipid mix = 0.8
  • Anerobic Conditions = +1
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