Respiration 2011.doc

7/27/2019 Respiration 2011.doc

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ATP and respirationAll activities requiring energy are fuelled by a single molecule known as

A.T.P or Adenosine triphoshate.

These include :-

Muscle contraction

Active transport

Protein Synthesis

ATP is made up of one Adenosine and three phosphates

ATP is important as a means of transferring energy from energy releasing reactions such as respiration to energy requiring reactionssuch as active transport or protein synthesis

Hamilton Grammar School 1

3 PHOSPHATE GROUPS

ADENOSINE

High Energy

BondP P P

Glucose

+

Oxygen

Carbon

Dioxide

+

Water

Energy

EnergyATP

ADP

+

Pi

e.g. Amino

Acids

Protein

molecule

Energy

Energy

RESPIRATION ENERGY TRANSFER WORK


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ATP is continually synthesised and broken down within the cell asfollows

ADP + Pi ATP

This process of rapid breakdown and regeneration means that very

little ATP is present in a cell at any one timeATP is produced during respiration where a respiratory substrate suchas glucose is gradually oxidised by the removal of hydrogen (OILRIG)

Respiration should be seen as a series of reactions in which 6-carbonglucose is oxidised to form carbon dioxide. This is accompanied by thesynthesis of ATP from adenosine diphosphate (ADP) and inorganicphosphate (Pi).

Wordbank you will come across the following words during this topic and it important to know whatthey mean.

Regeneration to be made again Reduction molecules have hydrogen added to them Metabolism All body reactions (anabolic and catabolic) Anabolism Reactions which use energy to build complex molecules from simpler molecules

e.g. proteins and built from amino acids Catabolism - Reactions which release energy by breaking down complex molecules to simpler

molecules e.g. respiration.

Chemistry of Respiration

Respiration should be seen as a series ofenzyme controlledreactionsin which :-

6-carbon glucose is oxidisedto form carbon dioxide

this is accompanied by the synthesis ofATPfrom adenosine

diphosphate (ADP) and inorganic phosphate (Pi).

Respiration takes place in three main stages and we will look at each ofthese in turn.

Stage 1 Glycolysis

Stage 2 Krebs Cycle

Stage 3 Cytochrome system



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Stage 1 Glycolysis

The first stage of respiration is calledGlycolysis. This process

takes place within the cytoplasm. does notrequire oxygen involves the step by step breakdown of a 6-carbon sugar such as

glucose to form two 3-carbonpyruvic acidunits

Glycolysis results in a net gain of 2ATPas follows:-

energy from 2 ATP is required to trigger it

4 ATP are produced through energy released later in the process

The breakdown of glucose is an oxidation reaction involving theremoval of hydrogen

Hydrogen is removed by a dehydrogenase enzyme

The hydrogen removed temporarily binds to acoenzyme

moleculecalled NAD or nicotinamide adenine dinucleotide Glycolysis therefore yields hydrogen in the form of NADH

The NADH produced through glycolysis mayproduce further ATPmolecules at a later stage(cytochrome system) if oxygen becomesavailable

What happens next?

The pyruvic acid produced by glycolysis diffuses into an organelle calleda mitochondrion for further breakdown if oxygen becomes available see next page



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SUMMARY OF GLYCOLYSIS


OuterCrista

This is the site of stage 3The cytochrome system

Matrix Fluid

This is the site ofstage 2 KrebsC cle

Inner

Cytoplasm

This is the site of stage 1Glycolysis with the pyruvic acid

then diffusing into the matrix

2NAD+2H2

2NADPH2

4ADP +4Pi

4ATP

2ATP

2ADP+2Pi

Pyruvic Acid +Net

Gain of 2ATP

Glucose

Hydrogen is removed by a

dehydrogenase enzyme and passed

to a carrier co-enzyme molecule

called NAD

2 ATP are required to start the

process

Energy released

used to make ATP

2NADH2


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Stage 2 - Krebs cycle.

The aerobic phase, the Krebs cycle, can be considered as a processwhich begins when a 2-carbon acetyl group produced from pyruvic acidjoins with coenzyme A (CoA) to form acetyl CoA. see below

The convertion of the(3C) pyruvic acid to the (2C) acetyl groupinvolves the removal of carbon and the release of carbon dioxide.

The convertion of the(3C) pyruvic acid to the (2C) acetyl groupinvolves the removal of hydrogen which binds to NAD to form NADH

The Acetyl component of Acetyl CoA reacts with a 4-carbon compoundto form a 6-carbon compound (citric acid).

Citric acid is gradually oxidised, in a cyclic series of reactions, back tothe 4-carbon compound with carbons also being removed as carbondioxide.

During the Krebs cycle hydrogen molecules are continuously removedand bind to NAD to form NADH.

TOP TIP - Note - Intermediate molecules need not be named, but thenumber of C atoms in compounds should be accounted for. see p6



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SUMMARY OF THE KREBS CYCLE


2NADH to

cytochrome system

2NADH to

cytochrome system

2Pyruvic Acid

- 3 carbon molecule

Acetyl co-A

Citric Acid

6 carbon molecule

Intermediate

4 carbon molecule

2NADH to

cytochrome system

Intermediate4 carbon molecules

5 carbon molecule

KREBSCYCLE

2 Acetyl- 2 carbon molecule

2CO2

Co-enzyme A (co-A)

binds to Acetyl

2CO2

2CO2

2NADH to

cytochrome system

Intermediate

4 carbon molecules

2NADH to

cytochrome system

op Tip The Acetyl produced after glycolysis is a 2C compound. This is carried for a

hort while by Co-A (acetyl co-A). The 2C acetyl then reacts with the 4C compound to

ve 6C citric acid releasing the carrier Co-A.


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STAGE 3 CYTOCHROME SYSTEM

The final stage of respiration is known as the cytochrome system. see below

This system of hydrogen carriers is the most important means of

releasing energy in respiration.

This is a system of carrier molecules is found on the cristae of themitochondria

Hydrogen bound to the carrier molecule NAD is passed down a seriesof molecules successively reducing (gain) and oxidising (loss) eachcarrier in turn. Top Tip Learn this phrase off by heart as it is difficult to describe any otherway!

The final hydrogen acceptoris oxygen which forms wateras aresult.

If oxygen is not present to act as the final accceptor, the hydrogencannot pass through the system andcomplete oxidation cannot takeplace.


What happens next?

All NADH resulting from the continuous removal of hydrogen aretransferred to the cytochrome system resulting in formation of ATP and

eventual formation of water

OxygenReduced Carrier

e.g. NADH2

WaterOxidised Carrier

e.g. NAD

PiADP

ATP

PiADP

ATP

PiADP

ATP

Carrier4 -

Cytochrome

OxidaseCarrier3Carrier2Carrier1


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Adding up all the ATPs

OTHER RESPIRATORY SUBSTRATES

TOP TIP


This bit is pretty tricky and you should only spend time on it if you are aimingfor an A pass.

Each molecule of NADH which passes its hydrogen into the cytochromesystem gives releases enough energy to synthesise 3 A.T.P molecules

The process of respiration has released 12 NADH( look back to see if youcan find them all) which after passing the hydrogen into the cytochromesystem results in 36 ATP

Glycolysis released a further net gain of 2ATP

1 molecule of lucose therefore ives rise to 38 ATP

Carbohydrates such as glucose are the main respiratory substrate butif they are not available fats and proteins may be used as analternative.

The Fatty acids from fats are converted to Acetyl Co-A and enterthe Krebs cycle. Fats release twice the energy/gram compared tocarbohydrates but the energy is released much more slowly.

The amino acids from proteins may also be used but only duringperiods of starvation

The following page shows a summary of the whole process which willscare you at first. Try to learn it in steps as follows

Step 1 Draw the main backbone with the main molecules and theircarbons.

Step 2 If you notice the number of carbons reducing ( e.g. 3C 2C)put an arrow in showing the CO2 has been removed

Step 3 At all stages other than build up stages ( e.g. 4C2C) youcan assume than hydrogen is removed


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RESPIRATION THE WHOLE PROCESS ON ONE DIAGRAM


36 ATP + 2 net gain in glycolysis = 38 ATP in total

36 ATP

Acetyl (2C)

CO2

Co- enzyme A

NADH2


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ANAEROBIC RESPIRATION


This is respiration without oxygen present. If this happens onlythe first stage called glycolysis can take place.

Once pyruvic acid has been formed the cell must convert this to

other compounds.

In yeast

Pyruvic acid is converted to ethanol ( 2C) and carbon dioxide ( 1C).The ethanol cannot be changed back as a carbon has been lost.

In animals and bacteria

Pyruvic acid is converted to lactic acid ( 3C) . This can be changed

back to pyruvic acid as soon as oxygen becomes available again

Anaerobic respiration only gives a total of 2ATP


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Respirometers

Measuring the rate of respiration

Respirometers measure respiration as oxygen uptake/minute

Carbon dioxide released is absorbed by sodium hydroxide

Cold blooded animals are used as heat released by warm bloodedanimals affects volume of gas in test tube

Temperature must be kept at a constant during experiment byplacing in water bath

Control tube contains glass beads or non respiring (dead) organism

Top Tip Peas are often used be careful not to assume they are

photosynthesising

Hamilton Grammar School

Filter paper

Sodium

Hydroxide

Solution

Respiratory

Chamber

Scale

Coloured

dye

Tap

Respiring

material

e.g. germinatingsunflower seeds

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