Energy and Energy and RespirationRespiration

The need for energy in living The need for energy in living organismsorganisms

continuous supply of energy for:continuous supply of energy for: Synthesis of complex substances from Synthesis of complex substances from

simpler ones (anabolic reactions)simpler ones (anabolic reactions) Active transportActive transport Mechanical work – movementMechanical work – movement Maintenance of internal body Maintenance of internal body

temperaturetemperature

ATPATP

Adenosine triphosphateAdenosine triphosphate Energy released is not then directly Energy released is not then directly

used, it is passed on to ATP.used, it is passed on to ATP. ATP is made of:ATP is made of:

AdenineAdenine RiboseRibose 3 phosphate molecules3 phosphate molecules

When a phosphate group is removed When a phosphate group is removed from ATP, ADP is formed and energy from ATP, ADP is formed and energy is released.is released.

ATP + HATP + H22O O = ADP + H= ADP + H33POPO44 ± 30.5kJ ± 30.5kJ

ATP is the universal intermediary ATP is the universal intermediary molecule. It is known as the energy molecule. It is known as the energy currency.currency.

Synthesis of ATPSynthesis of ATP

Two ways: (see page 199)Two ways: (see page 199)

1. energy released by reorganising 1. energy released by reorganising chemical bonds.chemical bonds.

2. using electrical potential energy 2. using electrical potential energy when electrons are transferred by when electrons are transferred by electron carriers. This is called electron carriers. This is called chemiosmosis.chemiosmosis.

RespirationRespiration

Organic molecules are broken down to Organic molecules are broken down to release energy to make ATP.release energy to make ATP.

Two types:Two types:

A) Aerobic respiration – in the presence of A) Aerobic respiration – in the presence of oxygen.oxygen.

B) Anaerobic respiration – in the absence of B) Anaerobic respiration – in the absence of oxygen.oxygen.

Both start with glycolysis.Both start with glycolysis.

GlycolysisGlycolysis

Phosphorylation (adding phosphate) of Phosphorylation (adding phosphate) of glucose using ATPglucose using ATP

Occurs in the cytoplasm.Occurs in the cytoplasm.

Splitting hexose phosphate (6C) into two Splitting hexose phosphate (6C) into two triose phosphate molecules (3C)triose phosphate molecules (3C)

These are then oxidised, releasing ATP and These are then oxidised, releasing ATP and reducing NAD reducing NAD

Nicotinamide Adenine DiphosphateNAD

Consists of two nucleotides joined by their phosphate groups

Transfers electrons during respiration reactions

Glucose (hexose) (6C)

Hexose phosphate (6C) produced by phosphorylation using ATP

Hexose bisphosphate (6C) adding another phosphate using ATP

2 molecules of triose phosphate (3C)

A sequence of Intermediate molecules are formed, by reducing NAD and losing phosphates to produce 4 molecules of ATP

2 x Pyruvate (3C)

This splits into two

GLUCOSE (6C)

HEXOSE BIPHOSPHATE

TRIOSE PHOSPHATE (3C) TRIOSE PHOSPHATE (3C)

PYRUVATE 4 ATP PRODUCED PYRUVATE

2ATP

2ADP

NAD+

NADH

NAD+

NADH

2ADP

2ATP

2ADP

2ATP

2 ATP USED

Link reactionLink reaction

Occurs when oxygen availableOccurs when oxygen available

Pyruvate enters the mitochondrion by Pyruvate enters the mitochondrion by active transport.active transport.

It is decarboxylated (carbon removed)It is decarboxylated (carbon removed) Dehydrogenated (hydrogen removed)Dehydrogenated (hydrogen removed) As a result of this, COAs a result of this, CO22 is formed and is formed and

NAD is reducedNAD is reduced

Krebs cycleKrebs cycle Closed pathway of enzyme-controlled Closed pathway of enzyme-controlled

reactionsreactions

Occurs in matrix of mitochondriaOccurs in matrix of mitochondria

Acetyl CoA (2C) enters the cycle and joins Acetyl CoA (2C) enters the cycle and joins with a 4 carbon compound to make a 6 with a 4 carbon compound to make a 6 carbon compound.carbon compound.

A series of steps now transfer the 6C A series of steps now transfer the 6C (citrate) back to the 4C (oxaloacetate)(citrate) back to the 4C (oxaloacetate)

These steps include more decarboxylation These steps include more decarboxylation and dehydrogenation and dehydrogenation

Pg 203

LINK REACTION. Pyruvate molecules (3-carbon) from glycolysis are converted into another type of molecule called Acetyl-CoA in a process known as pyruvic oxidation. This conversion occurs when the pyruvate is broken down by a complex of 3 enzymes called pyruvate dehydrogenase, releasing a carbon atom which goes on to form carbon dioxide (CO2). The 2 remaining carbon molecules bond with coenzyme A forming Acetyl-CoA. During this process, electrons and a hydrogen ion are passed to NAD+, thus oxidizing the pyruvate, hence the name of the process.

Step 1. The Acetyl-CoA then enters the Krebs cycle. It initially combines with a 4-carbon molecule called oxoaloacetic acid, forming a 6-carbon molecule of citric acid (citrate). This reaction is catalyzed by the enzyme citrate synthase.  Upon this formation, the coenzyme A is released, returning to the link reaction.

Step 2. The citrate molecule is then dehydrated (H20 molecule is removed) and then rehydrated by the enzyme aconitase. The resulting molecule is just a rearranged form of citrate known as isocitrate.

Step 3. Next, isocitrate undergoes what is known as a oxidative carboxylation, which simply means that a carbon and hydrogen are given off. The result of this is a 5-carbon molecule called alpha-ketoglutarate. This process is catalyzed by the enzyme isocitrate dehydrogenase. Additionally, the carbon that broke off forms CO2, while the hydrogen reduces NAD+ to form NADH.

Step 4. In the next reaction, alpha-ketoglutarate has yet another carbon molecule removed and is then transferred to a CoA molecule by the enzyme alpha-ketoglutarate dehydrogenase. The resulting product is a 4-carbon molecule of Succinyl-CoA. Additionally, CO2 and NADH is formed.

Step 5. After succinyl-CoA is formed, the molecule then undergoes the removal of the CoA carrier, resulting in the production of succinate. Additionally, the enzyme succinyl-CoA synthetase that removes the CoA also produces GTP (Guanosine Triphosphate) through substrate level phosphorylation (phosphate molecule directly added to another molecule). (GTP is a high energy molecule similar to ATP, and later an ADP molecule takes the phosphate from GTP and makes ATP)

Step 6. Next, succinate is dehydrated by the enzyme succinate dehydrogenase. The resulting product is furmate.

Step 7. Furmate is then hydrated (water added) by enzyme furmase to form malate

Step 8. Lastly, the malate is dehydrogenated by the enzyme malate dehydrogenase, forming the original molecule oxaloacetate. From this reaction, NADH and H+ are also produced.

SUMMARYEvery pyruvate molecule that enters the Krebs cycle generates 3 molecules of CO2, one molecule of ATP, one molecule of FADH and 4 molecules of NADH

ADP+P ATP

Pyruvate 3CO2

4NAD+ 4NADH FAD+ FADH The reduced NAD and FAD molecules enter the electron transfer chain, and result in a large number of ATP molecules being produced.

Electron Transport ChainElectron Transport Chain NADH and FADHNADH and FADH22 oxidised - electron and oxidised - electron and

proton releasedproton released1.1. electron picked up by an electron carrier electron picked up by an electron carrier

on the inner membraneon the inner membrane2.2. It is passed from one acceptor to another It is passed from one acceptor to another

along a chain.along a chain.3.3. electron has a high potential energy at electron has a high potential energy at

beginning of chain but as it is passed beginning of chain but as it is passed along the electron falls to a lower energy along the electron falls to a lower energy state.state.

energy released actively pumps the energy released actively pumps the hydrogen ion (proton) into the hydrogen ion (proton) into the intermembrane space.intermembrane space.

electron reaches the end of the chain electron reaches the end of the chain it rejoins to the hydrogen ion to it rejoins to the hydrogen ion to make a hydrogen atom.make a hydrogen atom.

These hydrogen atoms then join to These hydrogen atoms then join to oxygen to form water.oxygen to form water.

ChemiosmosisChemiosmosis hydrogen ions actively transported into hydrogen ions actively transported into

the intermembrane space.the intermembrane space.

ChemiosmosisChemiosmosis is the movement of ions  is the movement of ions across a selectively-permeable membrane, across a selectively-permeable membrane, down their electrochemical gradient.down their electrochemical gradient.

concentration of hydrogen ions in the concentration of hydrogen ions in the intermembrane space builds up so intermembrane space builds up so diffusion occurs.diffusion occurs.

The hydrogen ions move through a protein The hydrogen ions move through a protein channel and as they move they provide channel and as they move they provide energy for ATP synthase to join ADP and P energy for ATP synthase to join ADP and P to make ATP.to make ATP.

- If there is no oxygen there is no - If there is no oxygen there is no where for the hydrogen to gowhere for the hydrogen to go

- which then blocks the electron - which then blocks the electron transport chain transport chain

- which stops the NAD from being - which stops the NAD from being regenerated regenerated

- so the krebs cycle is blocked - so the krebs cycle is blocked - so the link reaction is blocked - so the link reaction is blocked - and only glycolysis can occur – - and only glycolysis can occur –

anaerobic respiration.anaerobic respiration.

Anaerobic RespirationAnaerobic Respiration

To regenerate NAD to be able to continue To regenerate NAD to be able to continue glycolysis, pyruvate becomes the glycolysis, pyruvate becomes the hydrogen acceptor.hydrogen acceptor.

This either forms lactic acid or ethanol.This either forms lactic acid or ethanol.

In animals end product is lactic acidIn animals end product is lactic acid

CC66HH1212OO66 → 2CH→ 2CH33CH(OH)COOH + 2 ATPCH(OH)COOH + 2 ATP

In plants and yeast end product is ethanol In plants and yeast end product is ethanol and carbon dioxideand carbon dioxide

CC66HH1212OO66 → 2CH→ 2CH33CHCH22OH + COOH + CO22 + 2ATP + 2ATP

Lactic acid is produced just by adding Lactic acid is produced just by adding 2 hydrogen molecules to pyruvate.2 hydrogen molecules to pyruvate.

Ethanol is produced by first removing Ethanol is produced by first removing a carbon molecule (releasing carbon a carbon molecule (releasing carbon dioxide) and then adding the 2 dioxide) and then adding the 2 hydrogen molecules. That is why hydrogen molecules. That is why alcoholic fermentation is alcoholic fermentation is accompanied by evolution of carbon accompanied by evolution of carbon dioxide.dioxide.

What happens to the products What happens to the products of anaerobic respiration?of anaerobic respiration?

Both lactic acid and ethanol contain a lot Both lactic acid and ethanol contain a lot of energy.of energy.

In animals this energy can be released by In animals this energy can be released by changing lactic acid back to pyruvate and changing lactic acid back to pyruvate and then pyruvate continuing on the rest of then pyruvate continuing on the rest of the aerobic respiration pathways.the aerobic respiration pathways.

This requires oxygen to unblock the ETC This requires oxygen to unblock the ETC and Krebs cycleand Krebs cycle

The amount of oxygen required to do this The amount of oxygen required to do this is called the oxygen debt.is called the oxygen debt.

Plants cannot use the ethanol.Plants cannot use the ethanol. It cannot be converted back into It cannot be converted back into

pyruvate and it cannot be oxidisedpyruvate and it cannot be oxidised The ethanol is toxic and if anaerobic The ethanol is toxic and if anaerobic

respiration continues for too long the respiration continues for too long the plant will be poisoned and die.plant will be poisoned and die.

Seeds and plants growing in Seeds and plants growing in waterlogged conditions can respire waterlogged conditions can respire anaerobically for a short time.anaerobically for a short time.

Respiratory QuotientRespiratory Quotient

It is a unitless number used in It is a unitless number used in calculations of basal metabolic rate calculations of basal metabolic rate (BMR)(BMR)

It is the ratio of the volume of carbon It is the ratio of the volume of carbon dioxide released to the volume of dioxide released to the volume of oxygen consumed by a body tissue or oxygen consumed by a body tissue or an organism in a given period.an organism in a given period.

The respiratory quotient (The respiratory quotient (RQRQ) is ) is calculated from the ratio:calculated from the ratio:

RQ = CO2 eliminated / O2 consumedRQ = CO2 eliminated / O2 consumed

The range of respiratory coefficients The range of respiratory coefficients for organisms in metabolic balance for organisms in metabolic balance usually ranges from 1.0 usually ranges from 1.0 (representing the value expected for (representing the value expected for pure carbohydrate oxidation) to ~0.7 pure carbohydrate oxidation) to ~0.7 (the value expected for pure fat (the value expected for pure fat oxidation). oxidation). 

CarbohydratesCarbohydrates The value of RQ is equal to 1 if carbohydrates are the The value of RQ is equal to 1 if carbohydrates are the

respiratory substrates in aerobic respiration.respiratory substrates in aerobic respiration.

FatsFats When the respiratory substrate is fat, the RQ is about 0.7.When the respiratory substrate is fat, the RQ is about 0.7. Example: TripalmitinExample: Tripalmitin

Fats contain less oxygen than carbohydrates and so they Fats contain less oxygen than carbohydrates and so they require more oxygen for oxidation.require more oxygen for oxidation.

Anaerobic respirationAnaerobic respiration The value of RQ is infinity during anaerobic respiration The value of RQ is infinity during anaerobic respiration

because CO2 is produced but O2 is not utilised.because CO2 is produced but O2 is not utilised.

Measuring RQMeasuring RQ This is done by measuring the change in the This is done by measuring the change in the

volume of gas surrounding the material as it volume of gas surrounding the material as it respires – respires – first as carbon dioxide is absorbed (to measure the rate first as carbon dioxide is absorbed (to measure the rate

of oxygen consumption) of oxygen consumption) and then without absorbing the carbon dioxide (from and then without absorbing the carbon dioxide (from

which you can calculate the rate of production of carbon which you can calculate the rate of production of carbon dioxide by comparison with the first measurment).dioxide by comparison with the first measurment).

The apparatus consists of two vessels. One vessel The apparatus consists of two vessels. One vessel contains the organisms and the other acts as contains the organisms and the other acts as a a thermobarometerthermobarometer – small changes in  – small changes in temperature or pressure cause air in this vessel temperature or pressure cause air in this vessel to expand or contract, compensating for similar to expand or contract, compensating for similar changes in the first vessel. Changes in the changes in the first vessel. Changes in the manometer level are thus due only to the manometer level are thus due only to the activities of the respiring material.activities of the respiring material.