Fermentation Respiration without Air

Glycolysis

Three Possible Pathways

Key Differences: Fermentation vs. Aerobic Respiration No oxygen is required for fermentation No oxygen is required for fermentation Fermentation involves no Krebs cycle or ETC Fermentation involves no Krebs cycle or ETC Reactions of fermentation occur completely in the cytosol Reactions of fermentation occur completely in the cytosol

1. No oxygen is required The oxygen for aerobic respiration is needed at the end of the ETC The oxygen for aerobic respiration is needed at the end of the ETC A lack of oxygen causes a traffic jam, blocking all the way up to the outer membrane of the mitochondria A lack of oxygen causes a traffic jam, blocking all the way up to the outer membrane of the mitochondria

1. No oxygen is required Without oxygen, the cell’s only way to produce ATP is through glycolysis Without oxygen, the cell’s only way to produce ATP is through glycolysis Fermentation allows a cell to continue producing ATP this way Fermentation allows a cell to continue producing ATP this way

2. No Krebs cycle or ETC Problem: how can the cell recycle the NAD+ without an ETC? Problem: how can the cell recycle the NAD+ without an ETC? NAD+ / NADH is required to move glycolysis forward NAD+ / NADH is required to move glycolysis forward Two ways to recycle NADH Two ways to recycle NADH

Alcohol Fermentation

Begin with pyruvate Begin with pyruvate One CO 2 is removed from pyruvate One CO 2 is removed from pyruvate Pyruvate becomes acetaldehyde Pyruvate becomes acetaldehyde

Alcohol Fermentation NADH oxidizes acetaldehyde NADH oxidizes acetaldehyde Acetaldehyde becomes ethanol Acetaldehyde becomes ethanol

Lactic Acid Fermentation

Pyruvate is oxidized by NADH Pyruvate is oxidized by NADH Pyruvate becomes lactic acid Pyruvate becomes lactic acid

3. Occur completely in the cytosol Require no organelle Require no organelle Probably the form of energy synthesis used before oxygen was present on Earth Probably the form of energy synthesis used before oxygen was present on Earth Used mostly by bacteria such as yeast Used mostly by bacteria such as yeast Eukaryotic cells sometimes go through fermentation Eukaryotic cells sometimes go through fermentation

Review What are the three possible energy- creating pathways a cell can use? What are the three possible energy- creating pathways a cell can use? When and where does fermentation take place? When and where does fermentation take place? What are three key differences between fermentation and aerobic respiration? What are three key differences between fermentation and aerobic respiration?