F214 RESPIRATION 3: ANAEROBIC RESPIRATION, THE
LINK REACTION AND THE KREBS CYCLE
Complete the notes sheets below. Where you see a blank
(…………………..), decide which word/phrase is most appropriate.
………………………. (which takes place in the ……………………) produces …… molecules
of pyruvate. The fate of the pyruvate depends on …………………… availability. In the
absence of oxygen, alcoholic fermentation or lactic fermentation takes place.
2 x PYRUVATE (….C)
1. Alcoholic fermentation:
When there is insufficient …………………….., it is important that the reduced NAD
(……………) is …………………….. back to NAD+ so that the energy yielding phase of
glycolysis can continue.
In yeast, pyruvate is decarboxylated to ETHANAL (…..C), releasing …………….. . The
enzyme alcohol dehydrogenase then ……………….. ETHANAL to ETHANOL (…..C), at
the same time ………………… NADH back to ……………. .
CH3CHO + NADH

C2H5OH +NAD+
Alcohol dehydrogenase
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The process is summarised below:
NADH
NAD+
Alcohol dehydrogenase
C2H5OH + CO2
What is the net production of ATP per molecule of glucose in anaerobic
respiration using alcoholic fermentation? …………… ATP molecules
2. Lactic fermentation:
The
main
aim
of
lactic
fermentation
is
to
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
Pyruvate is …………………… by NADH to form ………………………… acid. As this is a
redox reaction, NADH is ………………………… back to ……………. since an …… atom is
donated to the pyruvate. This reaction is catalysed by lactate dehydrogenase.
 1 molecule of NADH is ………………….. per pyruvate molecule.
 1 molecule of glucose will produce ………… molecules of ATP in using this
form of …………………………… respiration.
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The process is summarised below:
NADH
NAD+
Lactate dehydrogenase
C3H6O
The link reaction
In the presence of oxygen, pyruvate is ………………………. transported across the
inner and outer mitochondrial membranes into the …………………… . The purpose of
the link reaction is to convert ……C pyruvate into 2C acetate which can be oxidised
in the Krebs cycle.
 DECARBOXYLATION: PYRUVATE DECARBOXYLASE removes a ……………………..
group. This eventually becomes ……………………………. which …………………..
into the blood and is carried to the …………………… .
 DEHYDROGENATION: PYRUVATE DEHYDROGENASE removes ……………………..
atoms.
PYRUVATE (…..C)
NAD+
NADH
CO2
ACETATE (…..C)
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Coenzyme A accepts the …………………., forming ACETYL COENZYME A (Acetyl CoA).
The CoA carries the acetate to the next stage in aerobic respiration, the
…………………………….. . This stage also takes place in the mitochondrial matrix.
 Put the symbols below into the correct order to produce an equation
which summarises the link reaction:
+
2acetylCoA

2CoA
2pyruvate
2NADH
2CO2
2NAD+
+
………………………………………………………………………………………………………………………………
 During the link reaction, ………… molecules of ATP are produced.
 …………. molecules of …………….. NAD are produced.
So far, via glycolysis and the link reaction, the following have been produced:
Product
ATP
Reduced NAD (NADH)
Carbon Dioxide
Acetyl CoA
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Number of molecules produced per MOLECULE OF GLUCOSE:
The Krebs cycle
………………………… enters the Krebs cycle, which takes place in the ……………………… .
Acetyl (…..C) is transferred from CoA to join a 4C intermediate called
OXALOACETATE. CITRATE (…..C) is produced.
Acetyl CoA (…..C)
CoA
Citrate
(…..C)
Oxaloacetate
(…..C)
This is gradually dehydrogenated (……………………………) and decarboxylated
(…………………………….) over several steps until the 4C …………………………….. is reformed. ……………………….. and …………………………. are released. ………………… diffuses
into the blood while …… atoms are taken up by ……………., or an alternative carrier
called
FAD.
The
carriers
transport
H
atoms
………………………………………………………. for the final step in respiration.
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to
the
Acetyl CoA (…..C)
CoA
Oxaloacetate
(…..C)
Citrate
(…..C)
Intermediate compound (…..C)
Intermediate
compound (…..C)
Intermediate compound (…..C)
Intermediate compound (…..C)
 What 2 processes are occurring at the points marked with a
?
………………………………………….. and ……………………………………………..
 The process occurring at point
, where the first 4C intermediate is
changed to another 4C intermediate is called SUBSTRATE LEVEL
…………………………………… .
 At point
, the 2nd 4C intermediate is ……………… to a third 4C intermediate,
releasing ……….. hydrogen …………. . These are collected by ……………., which
is …………………. .
 At point
, the third …..C intermediate is …………………………. (oxidised) to
reform …………………………….. . Another NAD+ molecule is ………………………… .
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 There is 1 turn of the Krebs cycle for each molecule of acetate. For each
turn of the Krebs cycle, …... molecules of reduced NAD, …… molecules of
reduced FAD, …… molecules of CO2 and …… molecule(s) of ATP are
produced.
Per MOLECULE OF GLUCOSE, the following are produced by the Krebs cycle:
Product
ATP
Reduced NAD (NADH)
Reduced FAD (FADH)
Carbon Dioxide
Number of molecules produced per MOLECULE OF GLUCOSE:
***REMEMBER*** these reactions do not use oxygen, but they will not occur
without it. They are AEROBIC.
So far, via glycolysis, the link reaction and the Krebs cycle, the following have
been produced:
Product
ATP
Reduced NAD (NADH)
Reduced FAD (FADH)
Carbon Dioxide
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Number of molecules produced per MOLECULE OF GLUCOSE:
A summary of the processes so far:
NEXT
TIME!
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