Chapter 8: Glycolysis and Cellular Respiration

What is Photosynthesis?

Glucose

A key energy-storing molecule:Nearly all cells metabolize glucose for energy

Other organic molecules are converted to glucose for energy harvesting

Overview of Glucose Breakdown

C6H12O6 + 6O2 6CO2 + 6H2O + ATP + (heat E)

Glucose Breakdown The main stages of glucose

metabolism are: Glycolysis

Cellular respiration

Glycolysis Glycolysis

Occurs in cytosol Does not require oxygen Breaks glucose into pyruvate Yields two molecules of ATP per molecule

of glucose

Fermentation If oxygen is absent fermentation

occurspyruvate is converted into either

lactate, or into ethanol and CO2

If oxygen is present, cellular respiration occurs

Cellular RespirationOccurs in mitochondria (in

eukaryotes) In cytosol (in prokaryotes)

Requires oxygenBreaks down pyruvate into carbon

dioxide and waterProduces an additional 32 or 34 ATP

molecules, depending on the cell type

Summary of Glycolysis

Each molecule of glucose is broken down to 2 molecules of pyruvate.

A net of 2 ATP and 2 NADH molecules are formed.

Fermentation Occurs under anaerobic conditions Pyruvate is converted into lactate or

ethanol and CO2

Fermentation does not directly produce more ATP

But is necessary to regenerate NAD+, which must be available for glycolysis to continue

Fermentation Some cells ferment

pyruvate to form acids Human muscle cells can

perform fermentation Anaerobic conditions

produced when muscles use up O2 faster than it can be delivered (e.g. while sprinting)

Lactate (lactic acid) produced from pyruvate

Fermentation Some microbes ferment pyruvate to other

acids (as seen in making of cheese, yogurt, sour cream)

Some microbes perform fermentation exclusively (instead of aerobic respiration)

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Fermentation Yeast cells perform

alcoholic fermentation

Glucose is fermented to ethanol and CO2

Cellular Respiration

Occurs within mitochondria in eukaryotic cells

Electron Transport Chain Most of energy in glucose is stored in

electron carriers NADH and FADH2 Only 4 total ATP produced per glucose after

complete breakdown in the Krebs Cycle NADH and FADH2 deposit electrons into

electron transport chains in the inner mitochondrial membrane

Electrons join with oxygen gas and hydrogen ions to make H2O at the end of the ETCs

Chemiosmosis1. Energy released from electrons as they are

passed down the ETC2. Released energy used to pump H+ across

inner membrane H+ accumulate in intermembrane space

3. H+ form a concentration gradient across the membrane (a form of stored energy)

4. H+ flow back into the matrix through an

ATP synthesizing enzyme

Chemiosmosis Flow of H+ provides energy to link 32-34

molecules of ADP with phosphate, forming 32-34 ATP

ATP then diffuses out of mitochondrion and used for energy-requiring activities in the cell

Influence on How Organisms Function

Metabolic processes in cells are heavily dependent on ATP generation

Muscle cells switch between fermentation and aerobic cell respiration depending on O2 availability

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The End