FermentationFermentationRespiration without AirRespiration without Air

GlycolysisGlycolysis

Three Possible PathwaysThree Possible Pathways

Key Differences: Fermentation Key Differences: Fermentation vs. Aerobic Respirationvs. Aerobic Respiration• No oxygen is required for fermentationNo oxygen is required for fermentation

• Fermentation involves no Krebs cycle Fermentation involves no Krebs cycle or ETCor ETC

• Reactions of fermentation occur Reactions of fermentation occur completely in the cytosolcompletely in the cytosol

1. No oxygen is required1. No oxygen is required• The oxygen for The oxygen for

aerobic respiration aerobic respiration is needed at the is needed at the end of the ETCend of the ETC

• A lack of oxygen A lack of oxygen causes a traffic causes a traffic jam, blocking all jam, blocking all the way up to the the way up to the outer membrane of outer membrane of the mitochondriathe mitochondria

1. No oxygen is required1. No oxygen is required• Without oxygen, the cell’s only way Without oxygen, the cell’s only way

to produce ATP is through glycolysisto produce ATP is through glycolysis• Fermentation allows a cell to Fermentation allows a cell to

continue producing ATP this waycontinue producing ATP this way

2. No Krebs cycle or ETC2. No Krebs cycle or ETC

• Problem: how can Problem: how can the cell recycle the the cell recycle the NAD+ without an NAD+ without an ETC?ETC?

• NAD+ / NADH is NAD+ / NADH is required to move required to move glycolysis forwardglycolysis forward

• Two ways to Two ways to recycle NADHrecycle NADH

Alcohol FermentationAlcohol Fermentation

Alcohol FermentationAlcohol Fermentation• Begin with pyruvateBegin with pyruvate• One COOne CO22 is removed from pyruvate is removed from pyruvate• Pyruvate becomes acetaldehydePyruvate becomes acetaldehyde

Alcohol FermentationAlcohol Fermentation• NADH oxidizes acetaldehydeNADH oxidizes acetaldehyde• Acetaldehyde becomes ethanol Acetaldehyde becomes ethanol

Lactic Acid FermentationLactic Acid Fermentation

Lactic Acid FermentationLactic Acid Fermentation• Pyruvate is oxidized by NADHPyruvate is oxidized by NADH• Pyruvate becomes lactic acidPyruvate becomes lactic acid

3. Occur completely in the 3. Occur completely in the cytosolcytosol• Require no organelleRequire no organelle• Probably the form of energy synthesis Probably the form of energy synthesis

used before oxygen was present on used before oxygen was present on EarthEarth

• Used mostly by bacteria such as yeastUsed mostly by bacteria such as yeast• Eukaryotic cells sometimes go through Eukaryotic cells sometimes go through

fermentationfermentation

ReviewReview• What are the three possible energy-What are the three possible energy-

creating pathways a cell can use?creating pathways a cell can use?• When and where does fermentation When and where does fermentation

take place?take place?• What are three key differences What are three key differences

between fermentation and aerobic between fermentation and aerobic respiration?respiration?