4.1.1 Respiration

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4.1.1 Respiration

• state that glycolysis takes place in the
  cytoplasm
• outline the process of glycolysis beginning with
  the phosphorylation of glucose to hexose
  bisphosphate, splitting of hexose bisphosphate
  into two triose phosphate molecules and further
  oxidation to pyruvate, producing a small yield of
  ATP and reduced NAD
• state that, during aerobic respiration in
  animals, pyruvate is actively transported into
  mitochondria

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Respiration The 4 Parts

• Respiration consists of 4 parts
• Glycolysis
• Link Reaction
• Krebs Cycle
• Oxidative Phosphorylation (the electron transport
  chain)

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Glycolysis

• Glycolysis is the first stage of respiration
• Glycolysis splits one molecule of glucose into
  two smaller molecules of pyruvate
• Glucose is a hexose (6-carbon) molecule
• Pyruvate is a triose (3-carbon) molecule.
• Pyruvate is also known as pyruvic acid.
• Glycolysis takes place in the cytoplasm of cells
• Its the first stage of both aerobic and
  anaerobic respiration, and doesnt need oxygen to
  take place. It is therefore an anaerobic process.

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6C
Number of carbons in the molecule
glucose
2Pi
Phosphorylation 2 phosphates are added
6C
Hexose bisphosphate
H2O
(Hydrolysis)
3C
2 x triose phosphate
4ADP 4Pi
2NAD
2H
Oxidation (as Hydrogen is lost)
4ATP
2NADH
2 x pyruvate
3C
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Stage 1 Phosphorylation

• Glucose is phosphorylated by adding 2 phosphates
  from 2 molecules of ATP to give a hexose
  bisphosphate.
• The hexose bisphosphate is split using water
  (hydrolysis)
• 2 molecules of triose phosphate and 2 molecules
  of ADP are created

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Stage 2 Oxidation

• The triose phosphates are oxidised (lose
  hydrogen) forming 2 molecules of pyruvate
• Coenzyme NAD (a co-enzyme is a helper molecule
  that carries chemical groups or ions around)
  collects the hydrogen ions forming 2 reduced NAD
  (NADH H)
• 4ATP are produced, but 2 were used up at the
  beginning so there is a net gain of 2ATP
• Overall, 2 molecules of pyruvate and a small
  yield of ATP and reduced NAD are produced

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What now?

• The pyruvate (pyruvic acid) is now moved by
  active transport from the cell cytoplasm into the
  mitochondrial matrix for the next stage of
  aerobic respiration

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Questions

1. Outline the role of co-enzymes in the glycolysis
   pathway
2. Explain why the net gain of ATP during
   glycolyisis is two and not four
3. Explain how oxidation occurs during glycolysis,
   although no oxygen is involved

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Questions

1. Outline the role of co-enzymes in the glycolysis
   pathway the coenzyme NAD accepts hydrogen atoms
   from the substrate molecules as triose phosphate
   is oxidised
2. Explain why the net gain of ATP during
   glycolyisis is two and not four because two
   molecules of ATP are used to activate hexose
   sugar at the beginning of the process, four ATP
   are made so the net gain is two
3. Explain how oxidation occurs during glycolysis,
   although no oxygen is involved hydrogen atoms are
   removed from triose phosphate and combine with
   NAD which is an oxidation reaction

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A
C
C
B
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Task

• Now (from memory only) on A3 paper, draw the
  process of glycolysis...
• Remember to leave space for the other 3 stages!!!

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6C
Number of carbons in the molecule
glucose
2Pi
Phosphorylation 2 phosphates are added
6C
Hexose bisphosphate
H2O
(Hydrolysis)
3C
2 x triose phosphate
4ADP 4Pi
2NAD
2H
Oxidation (as Hydrogen is lost)
4ATP
2NADH
2 x pyruvate
3C
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4.1.1 The Link Reaction

• state that the link reaction takes place in the
  mitochondrial matrix
• outline the link reaction, with reference to
  decarboxylation of pyruvate to acetate and the
  reduction of NAD
• explain that acetate is combined with coenzyme A
  to be carried to the next stage

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Glycolysis True or False

1. Glycolysis produces a net gain of 4 ATP molecules
2. The co-enzyme NADH is oxidised during glycolysis
3. When coenzymes become reduced, they carry
   hydrogen molecules
4. Glycolysis takes place in the matrix of the
   mitochondrion
5. In glycolysis, glucose is converted in this
   order glucose, triose phosphate, hexose
   bisphosphate then pyruvate
6. Hydrolysis occurs when triose phosphate is
   converted to pyruvate

If you think they are false, you must write the
correct version- and there are false ones!!!
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Glycolysis True or False

1. Glycolysis produces a net gain of 4 ATP
   molecules- False the net gain is 2 ATPs as 2 are
   used up
2. The co-enzyme NADH is oxidised during glycolysis-
   False NAD is reduced during glycolysis to form
   NADH
3. When coenzymes become reduced, they carry
   hydrogen molecules- False they carry hydrogen
   atoms, not molecules or ions
4. Glycolysis takes place in the matrix of the
   mitochondrion- False it takes place in the
   cytoplasm
5. In glycolysis, glucose is converted in this
   order glucose, triose phosphate, hexose
   bisphosphate then pyruvate- False the correct
   order is glucose, hexose bisphosphate, triose
   phosphate, pyruvate
6. Hydrolysis occurs when triose phosphate is
   converted to pyruvate- False hydrolysis occurs
   when hexose bisphosphate is converted to triose
   phosphate

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Respiration The 4 Parts

• Respiration consists of 4 parts
• Glycolysis
• Link Reaction
• Krebs Cycle
• Oxidative Phosphorylation (the electron transport
  chain)

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The Link Reaction

• The link reaction happens when oxygen is
  available
• For each glucose molecule used in glycolysis, two
  pyruvate molecules are made
• But the link reaction uses only one pyruvate
  molecule, so the link reaction and the krebs
  cycle happen twice for every glucose molecule
  which goes through glycolysis
• The link reaction happens in the matrix of the
  mitochondrion

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3C
Number of carbons in the molecule
pyruvate
Decarboxylation- removal of a carboxyl group
(which becomes CO2) by the enzyme pyruvate
decarboxylase
CO2
1C
2C
acetate
NAD
Dehydrogenation- the enzyme pyruvate
dehydrogenase removes hydrogen atoms from
pyruvate and NAD accepts it
Coenzyme A (CoA)
NADH
2C
Acetyl CoA
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The Link Reaction Converts Pyruvate to Acetyl
Coenzyme A

• One carbon atom is removed from pyruvate in the
  form of CO2
• The remaining 2-carbon molecule (acetate)
  combines with coenzyme A to produce acetyl
  coenzyme A (acetyl CoA)
• Another oxidation reaction happens when NAD
  collects more hydrogen ions. This forms reduced
  NAD (NADH)
• No ATP is produced in this reaction

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The Products of the Link Reaction go to the Krebs
Cycle and the ETC

• So for each glucose molecule
• Two molecules of acetyl co enzyme A go into the
  Krebs cycle
• Two carbon dioxide molecules are released as a
  waste product of respiration (decarboxylation)
• Two molecules of reduced NAD are formed and go
  into the electron transport chain
  (dehydrogenation)

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Exam Questions

1. Describe simply how a 6-carbon molecule of
   glucose can be changed to pyruvate (5)
2. Describe what happens in the link reaction (4)

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Answers

• 1. The 6 carbon glucose molecule is
  phosphorylated using phosphate from 2 molecules
  of ATP (1) and hydrolysed/ split using water (1),
  to give 2 molecules of the 3-carbon molecule
  triose phosphate (1). This is then oxidised by
  removing hydrogen ions (1) to give 2 molecules of
  3-carbon pyruvate (1)

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Answers

• 2. The 3-carbon pyruvate is combined with
  coenzyme A (1) to form a 2-carbon molecule,
  acetyl coenzyme A (1). The extra carbon is
  released as carbon dioxide (decarboxylation of
  pyruvate) (1). The coenzyme NAD is converted into
  reduced NAD in this reaction by accepting
  hydrogen ions (dehydrogenation of pyruvate)

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The Challenge

• Can you draw glycolysis and the link reaction.?

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