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Topic 3: Chemistry of Life
Anaerobic Respiration
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Anaerobic Respiration
Glycolysis allows organisms to obtain
energy in the absence of oxygen
Glycolysis yields 2 AT and 2 !A"# Cells possess a limited s$pply of !A"%
&f glycolysis contin$es witho$t a
mechanism to oxidi'e !A"# bac( into!A"%) that step will be halted in glycolysis
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*rganisms ha+e e+ol+ed se+eral ways of
recycling !A"% to allow glycolysis to
contin$e when oxygen is not present
,$(aryotes primarily $se two main methods:
-. ,thanol /ermentation2. Lactic Acid /ermentation
Anaerobic Respiration
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/ermentation: transferring the hydrogen
atoms of !A"# are transferred to certain
organic molec$les instead of the electrontransport chain
/ermentation
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!A"# is oxidi'ed by acetaldehyde to form
!A"%
This forms ethanol 0the alcohol $sed in
alcoholic be+erages1
This process allows !A"% to be recycled
and glycolysis to contin$e
,thanol /ermentation
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The prod$cts are 2 AT) 2 !A"%) ethanol
and C*2
,thanol and C*2are released from the cell
as waste prod$cts
,thanol /ermentation
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ractical ses:
,thanol fermentation is carried o$t byyeast to lea+en bread
east cells ferment gl$cose from starchand release C*
2and ethanol
The C*2gas b$bbles ca$se
the bread to rise and the
ethanol e+aporates away
when the bread is ba(ed
,thanol /ermentation
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ractical ses:
&n wine ma(ing) yeast cells
ferment s$gars fo$nd incarbohydrate4rich fr$it 5$ices)
s$ch as grape 5$ice
east cells die as a res$ltof ethanol acc$m$lation
,thanol /ermentation
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/looded plants $ndergo ethanol
fermentation in the roots and may die if
oxygen is not ret$rned to the roots
This is why it is important not to o+erwater
ho$se plants
,thanol /ermentation
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nder normal conditions) animals) s$ch ash$mans) cataboli'e gl$cose by aerobicrespiration
"$ring stren$o$s exercise) m$scle cellsbrea(down gl$cose molec$les faster thanthey can be s$pplied with oxygen
nder these conditions) aerobicrespiration slows down and lactatefermentation begins
Lactic Acid /ermentation
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!A"# prod$ced d$ring glycolysis
transfers its hydrogen atoms to pyr$+ate
This regenerates !A"% and allows
glycolysis to contin$e
This res$lts in a change of pyr$+ate to
lactic acid or lactate
Lactic Acid /ermentation
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The acc$m$lation of lactic acid in m$scletiss$e ca$ses stiffness) soreness) andfatig$e
Lactic acid is transported thro$gh thebloodstream from the m$scles to the li+erto be bro(en down
6hen +igoro$s exercise ceases) lacticacid is oxidi'ed bac( to pyr$+ate tocontin$e thro$gh the 7rebs Cycle ifoxygen is present
Lactic Acid /ermentation
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,xtra oxygen is re8$ired to cataboli'e
lactate to C*2and #
2*
!eeding extra oxygen to do so is calledoxygen debt
anting after stren$o$s acti+ity is the
body9s way of paying; the oxygen debt
Lactic Acid /ermentation
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"id o$ 7now