Cellular%20Respiration

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Cellular Respiration
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What you should know

• The role of ATP in the transfer of energy and the
  phosphorylation of molecules by ATP.
• Metabolic pathways of cellular respiration. The
  breakdown of glucose to pyruvate in the cytoplasm
  in glycolysis, and the progression pathways in
  the presence or absence of oxygen (fermentation).
  
• The role of the enzyme phosphofructokinase in
  this pathway.
• The formation of citrate.
• Pyruvate is broken down to an acetyl group that
  combines with coenzyme A to be transferred to the
  citric acid cycle as acetyl coenzyme A.
• Acetyl coenzyme A combines with oxaloacetate to
  form citrate followed by the enzyme mediated
  steps of the cycle.
• This cycle results in the generation of ATP, the
  release of carbon dioxide and the regeneration of
  oxaloacetate in the matrix of the mitochondria.
• Dehydrogenase enzymes remove hydrogen ions and
  electrons which are passed to the coenzymes NAD
  or FAD to form NADH or FADH2 in glycolysis and
  citric acid pathways.
• NADH and FADH2 release the high-energy electrons
  to the electron transport chain on the
  mitochondrial membrane and this results in the
  synthesis of ATP.
• ATP synthesis high-energy electrons are used to
  pump hydrogen ions across a membrane and flow of
  these ions back through the membrane synthesises
  ATP using the membrane protein ATP synthase. The
  final electron acceptor is oxygen, which combines
  with hydrogen ions and electrons to form water.

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Introduction to Cellular Respiration

• A series of metabolic pathways that brings about
  the release of energy from a foodstuff
• In doing so it also regenerates the high-energy
  compound Adenosine Triphosphate (ATP)

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ATP

• Adenosine Triphosphate
• Molecule able to provide energy immediately
• Consists of Adenosine 3 inorganic phosphate
  molecules
• Energy held within ATP is released when the
  terminal phosphate is broken off (by enzymes)

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ATP

• Adenosine Triphosphate
• This bond broken to release energy
• Adenosine Diphosphate (ADP) and an inorganic
  phosphate are produced
• Also, energy is required to regenerate ATP from
  ADP Pi

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• ATP acts as the link between catabolic (energy
  releasing reactions) and anabolic (energy
  requiring reactions)
• At any given moment some ATP molecules are
  undergoing breakdown (releasing energy), while
  others are being regenerated from ADP Pi (using
  energy)
• This means there is a
• relatively fixed quantity
• of ATP available

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PHOSPHORYLATION

• The addition of a phosphate group to a molecule,
  e.g. ADP Pi ATP
• Phosphates can also be transferred from ATP to
  reactants in the pathway to make them more
  reactive
• e.g. Glucose ------------gt Glucose- 6-
  Phosphate
• Often a step in a pathway can only proceed if a
  reactant becomes phosphorylated

ADP
ATP
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Importance of ATP formation

• We all need energy to function and we get this
  energy from the foods we eat
• The most efficient way for cells to harvest
  energy stored in food is through cellular
  respiration
• a catabolic pathway for the production of
  adenosine triphosphate (ATP)
• ATP, a high energy molecule, is expended by
  working cells
• Cellular respiration occurs in both eukaryotic
  and prokaryotic cells

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RESPIRATION

• Process by which energy is released from foods by
  oxidation.
• It involves the regeneration of ATP which is a
  high energy compound.
• Consists of 3 stages
• GLYCOLYSIS
• CITRIC ACID CYCLE (KREBS CYCLE)
• ELECTRON TRANSPORT CHAIN

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GLYCOLYSIS

• Takes place in the cytoplasm of the cell.
• Is a series of enzyme controlled steps
• Glucose (6C) is broken down into two molecules of
  Pyruvic Acid (3C) (Pyruvate)
• Does not require oxygen
• Net gain of 2 ATP

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Energy investment and payoff during glycolysis
Phosphorylation occurs twice. The 2nd time by
phosphofructokinase

• The first half of the chain makes up the energy
  investment phase- where 2 ATP are used per
  glucose molecule
• The second half of the chain makes up the energy
  payoff phase-where 4 ATP are produced per glucose
  molecule

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Phosphorylation during energy investment stage

• The first phosphorylation of intermediates leads
  to a product that can continue to a number of
  other pathways
• (E.g. fermentation in the absence of oxygen)
• The second phosphorylation catalysed by
  phosphofructokinase is irreversible and leads
  only to the glycolytic pathway

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Energy payoff stage

• Hydrogen ions are released by the action of a
  dehydrogenase enzyme
• Co-enzymes NAD and FAD pick up the H ions to
  form NADH or FADH in glycolysis and the citric
  acid pathways
• NADH and FADH release high energy electrons to
  the electron transport chain on the mitochondrial
  membrane
• Resulting in the synthesis of ATP

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GLYCOLYSIS
GLUCOSE
2 ATP
2 ADPPi
2 NAD
2 NADH2
4 ADPPi
4 ATP
PYRUVIC ACID
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MITOCHONDRIA

• Citric Acid Cycle takes place in the matrix
• Electron Transport Chain takes place on the
  cristae

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CITRIC ACID CYCLE

• Takes place in the matrix of the mitochondria.
• Requires oxygen
• Pyruvate/Pyruvic acid converted to Acetyl which
  then combines with Coenzyme A (2C)
• Further Hydrogen ions are released and bind to
  NAD, forming NADH
• Acetyl CoA combines with oxaloacetate a 4C
  compound to form 6C citrate
• This stage involves the regeneration of
  oxaloacetate

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CITRIC ACID CYCLE

• Citrate is converted back to oxaloacetate by a
  series of enzyme controlled reactions.
• During the cycle, carbon is released in the form
  of carbon dioxide, hydrogen is released and binds
  to NAD/FAD and ATP is formed.

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CITRIC ACID CYCLE
CO2
2NAD
2NADH2
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ELECTRON TRANSPORT CHAIN

• Takes place on the cristae of the mitochondria.
• The reduced NAD/FAD transfer the high energy
  electrons to a chain of carriers called the
  cytochrome system
• Energy from the electrons is used to pump H from
  the inner matrix to the intermembrane space
• This maintains a higher conc of hydrogen ions in
  the intermembrane space, so..
• The return flow of H ions rotates part of the
  membrane protein ATP synthase and ATP is
  generated
• The final electron acceptor is oxygen which
  combines with hydrogen ions and low energy
  electron to form water

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ELECTRON TRANSPORT CHAIN

• The transfer of one H molecule releases 3 ATP
  molecules
• This is called oxidative phosphorylation

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ELECTRON TRANSFER SYSTEM
ADP Pi
ADP Pi
ADP Pi
NADH2
WATER
SERIES OF HYDROGEN CARRIERS
NAD
OXYGEN
ATP
ATP
ATP
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ATP PRODUCTION SUMMARY

• Each NADH2 molecule produces 3 ATP
• 12 NADH2 36ATP from Krebs cycle
• 2 ATP from glycolysis
• 38 ATP in total

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What you should know

• Substrates for respiration. Starch and glycogen,
  other sugar molecules, amino acids and fats.
• Regulation of the pathways of cellular
  respiration by feedback inhibition regulation
  of ATP production, by inhibition of
  phosphofructokinase by ATP and citrate,
• synchronisation of rates of glycolysis and citric
  acid cycle.
• Energy systems in muscle cells.
• Creatine phosphate breaks down to release energy
  and phosphate that is used to convert ADP to ATP
  at a fast rate. This system can only support
  strenuous muscle activity for around 10 seconds,
  when the creatine phosphate supply runs out. It
  is restored when energy demands are low.
• Lactic acid metabolism. Oxygen deficiency,
  conversion of pyruvate to lactic acid, muscle
  fatigue, oxygen debt.
• Types of skeletal muscle fibres
• Slow twitch (Type 1) muscle fibres contract more
  slowly, but can sustain contractions for longer
  and so are good for endurance activities. Fast
  twitch (Type 2) muscle fibres contract more
  quickly, over short periods, so are good for
  bursts of activity.

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Substrates for respiration

• Starch and glycogen (carbohydrates) are broken
  down to glucose
• Maltose and sucrose (carbohydrates) can be
  converted to glucose or glycolysis intermediates
• Proteins can be broken down to amino acids and
  converted to intermediates of glycolysis and the
  citric acid cycle
• Fats can be broken down into fatty acids and
  glycerol. Glycerol is converted to a glycolytic
  intermediate and fatty acids converted for use in
  the citric acid cycle

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Regulation of Cellular Respiration

• The cell conserves its resources by only
  producing ATP when required
• Feedback inhibition regulates and synchronises
  the rates of the glycolytic and citric acid cycle
  pathways

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• If more ATP than the cell needs is produced the
  ATP inhibits phosphofructokinase slowing
  glycolysis
• High concentrations of citrate also inhibit
  phosphofructokinase
• When citrate concentration drops the enzyme is no
  longer inhibited

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Energy systems in muscle cells

• During strenuous muscle activity the cell breaks
  down its reserves of ATP and releases energy
• Muscle cells can only store enough ATP for a few
  muscle contractions
• Muscle cells have an additional source of energy

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Energy systems in muscle cells

• Creatine phosphate acts as a high energy reserve
  available to muscle cells during strenuous
  exercise
• During strenuous exercise creatine phosphate
  breaks down releasing energy and phosphate which
  are used to convert ADP to ATP by phosphorylation

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• This system can only support strenuous muscle
  activity for around 10 seconds before the supply
  of creatine phosphate runs out
• When ATP demand is low, ATP from cellular
  respiration restores the levels of creatine
  phosphate

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Lactic acid metabolism

• If strenuous exercise continues the cells respire
  anaerobically as they do not get enough oxygen
• Neither the citric acid cycle nor electron
  transport system can generate the ATP required
• Only glycolysis is able to provide more ATP
• This results in pyruvate being converted to
  lactic acid
• It involves the transfer of hydrogen from NADH
  produced during glycolysis to pyruvic acid to
  produce lactic acid
• NAD is regenerated to maintain ATP production
  during glycolysis
• Only 2 molecules of ATP are produced from each
  molecule of glucose

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• As lactic acid builds in the muscles it causes
  fatigue
• An oxygen debt builds up
• When the oxygen debt is repaid, the lactic acid
  is converted back to pyruvic acid which then
  enters the aerobic pathway

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ANAEROBIC RESPIRATION
Oxygen debt builds up
Glucose (6C)
Pyruvic Acid (2 X 3C)
Lactic Acid (2 X 3C)
Oxygen debt repaid
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AEROBIC V ANAEROBIC
Aerobic Respiration Anaerobic Respiration
Number of ATP molecules per glucose molecule 38 2
Products of reaction (other than ATP) Carbon dioxide and water Lactic acid
Location in cell mitochondrion cytoplasm
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Types of skeletal muscle

• Skeletal muscles bring about movement of the body
• Two types of skeletal muscle fibres
• Type 1- Slow Twitch Muscle Fibres
• These contract slowly, but sustain contractions
  for longer
• Good for endurance activities
• Rely on aerobic respiration to generate ATP
• Have many mitochondria
• Have a large blood supply
• Have a high concentration of myoglobin which is
  good at storing oxygen (myoglobin also extracts
  oxygen from the blood)
• Major storage fuel is fats

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• Type 2- Fast Twitch Muscle Fibres
• Muscle fibres contract quickly
• Over short periods of time
• Good for bursts of activity
• Generates ATP through glycolysis
• Have only a few mitochondria
• Lower blood supply
• Major storage fuels are glycogen and creatine
  phosphate

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• Most human muscle tissue contains both slow and
  fast twitch fibres
• Athletes show distinct patterns of muscle fibres
  that reflect their sporting activities

• Fast twitch fibres are responsible for strength.
  Sports requiring sudden bursts of maximum
  activity, such as in sprinting, throwing, jumping
  and lifting rely on fast twitch fibres.

• Slow twitch fibres are responsible for stamina
  and suppleness. The action of slow twitch fibres
  is dependent on aerobic respiration. So, the
  supply of oxygen is important. The presence of
  large quantity of myoglobin is necessary.
  Therefore, slow twitch fibres give the
  characteristic red colour.