Anaerobic Respiration

How cells make ATP in the absence of oxygen

Fermentation Allows Cells to Make ATP Without Using Oxygen

Glucose

Glycolysis

Oxygen Present Oxygen Absent

Citric Acid Cycle

Oxidative Phosphorylation

Fermentation

Alcohol Lactic Acid

Remember…

Glycolysis happens in the cytosol

It does not require the presence of oxygen

NAD+ acts as the electron acceptor

2 ATP are generated 2 NADH are

generated

Fermentation

An extension of glycolysis

Cells can use this step of respiration to keep up the ATP supply

But…must have a steady supply of NAD+ to act as the electron acceptor

•Unlike aerobic respiration, fermentation generates ATP through substrate-level phosphorylation

•Fermentation can only continue if there’s a supply of the oxidizing agent NAD+ to be used in glycolysis

After NADH is produced from glycolysis,its electrons are transferred to pyruvate. This regenerates the NAD+ that can again be used for another round of glycolysis.

In contrast…

In aerobic respiration - the supply of NAD+ is continually renewed as the NADH molecules deliver their electrons to the electron transport chain

Fermentation

In anaerobic respiration, we need another way to recycle NAD+

Instead, the electrons in NADH are transferred to pyruvate, the end product of glycolysis

LE 9-18

Pyruvate

Glucose

CYTOSOL

No O2 presentFermentation

Ethanolor

lactate

Acetyl CoA

MITOCHONDRION

O2 present Cellular respiration

Citricacidcycle

So fermentation is…

Glycolysis (2 ATP, 2 NADH, pyruvate)

PLUSExtra reactions that oxidize the NADH to

NAD+ by transferring electrons to pyruvate

2 main types of fermentation

Alcohol fermentation

Lactic acid fermentation

There Are 2 Types of Fermentation

Alcohol Fermentation•Glycolysis makes pyruvate•CO2 is released from pyruvate.

Alcohol fermentation

Occurs in yeast and many bacteria

Pyruvate (3 carbons) converted to acetaldehyde (2 carbons) and CO2 is

released (used in baking to make bread rise)

Acetaldehyde is reduced by NADH to ethanol, thus regenerating the supply of NAD+

Lactic Acid Fermentation

Occurs in muscle cells, some bacteria, some fungi

Pyruvate is reduced by NADH to lactic acid, thus regenerating the supply of NAD+

Muscle Cells

When muscles are working hard, they quickly exhaust the supply of oxygen to the cell

The cell launches into fermentation to keep up

Lactic acid accumulates in cells leading to cramps

Facultative Anaerobes

Organisms that can survive using either anaerobic or aerobic respiration

Yeast

Bacteria

Main differences between aerobic and anaerobic respiration Aerobic

Final electron acceptor - oxygenNAD+ regenerated

when electrons delivered to ETCHuge energy payoff -

38 ATP, glucose fully broken down through Citric Acid cycle

AnaerobicFinal electron acceptor

- pyruvate or acetaldehydeNAD+ regenerated

when electrons given to pyruvate or acetaldehydeLess energy payoff - 2

ATP, energy still trapped in pyruvate or ethanol

Ancient prokaryotes probably used glycolysis to make ATP

What is the basis for this statement??

•The oldest prokaryotes were around before there was sufficient oxygen in the atmosphere

•Glycolysis is the most widespread metabolic pathway among organisms

•Glycolysis occurs in the cytosol…..prokaryotes don’t have organelles

Glycolysis and the Citric Acid Cycle Connect to Many Other Metabolic Pathways

Many molecules aside from glucose can be used in cellular respiration to make ATP:

The monomers of different molecules begin the process at different steps

The energy in organic molecules, which is used to power the cell, is released, but not produced during cellular respiration.