Chapter 9 Cellular Respiration

Chapter 9 Cellular Respiration

Section 9-1 An Overview

Be Able To

• Explain where organisms get their energy.

• Define cellular respiration.

• Explain the relationship between

photosynthesis and cellular respiration.

Key Terms^{: Pg 250.}

Overview of Cellular Respiration

• The energy of organic

compounds is transferred to ATP through cellular

respiration.

• Aerobic processes require oxygen, whereas anaerobic processes do not.

• Cellular respiration occurs in mitochondria in 2 stages:

glycolysis and aerobic respiration.

• The aerobic stage produces most of the ATP

Overview of Cellular Respiration

• The structure of mitochondria and chloroplasts are similar.

• The two parts of a mitochondrion are the matrix and the inner

mitochondrial membrane.

• The Krebs Cycle produces ATP from the breakdown of glucose for the 2^nd part of cellular respiration.

• Large amounts of ATP are created with the help of O₂ during the 2^nd stage known as Electron Transport.

• C₆H₁₂O₆ + 6O₂ 6C0₂ + 6H₂O + energy

• The products of photosynthesis are the reactants of cellular respiration.

Chapter 9 Cellular Respiration & Fermentation

Section 2 The Process of Cellular Respiration Be Able To

• Relate aerobic respiration to the structure of a mitochondrion.

• Summarize the events of Glycolysis and the Krebs Cycle.

• Summarize the events of the electron transport chain and chemiosmosis.

• Contrast the roles of glycolysis and aerobic respiration in cellular respiration.

Key Terms: Pg 254

Glycolysis

• Glycolysis consists of a series of chemical reactions catalyzed by specific enzymes that occur in the cytosol of the cell and can be

summarized into 4 steps:

1) 2 ATP molecules supply 2 phosphates groups to glucose.

2) 6-carbon compound of step 1 splits into 2 PGAL molecules.

3) Both PGAL molecules donate electrons to NAD+ and gain 2 phosphate groups to form 2 new 3-carbon compounds.

4) 4 phosphate groups are stripped from the 3-carbon compounds to produce pyruvic acid and ATP.

• Glycolysis has a net yield of 2 ATP molecules.

Glycolysis

Overview of Aerobic Respiration

• Aerobic respiration occurs in the Krebs cycle and in the electron transport chain.

• The electron transport chain uses the NADH produced by the Krebs cycle to produce large amounts of ATP.

• In prokaryotic cells, the Krebs cycle and electron transport chain occur in the cytosol.

• In eukaryotic cells, the Krebs cycle and electron transport chain occur inside the mitochondrial matrix or the space inside the inner membrane or the cristae of

mitochondria.

• An intermediate step occurs before the Krebs cycle during which each pyruvic acid joins with coenzyme A, donates electrons to NAD+, and loses a CO₂ molecule to form a 2-carbon compound called acetyl coenzyme A or acetyl CoA.

Before the Krebs cycle the intermediate step occurs in the

mitochondrial matrix.

The Krebs Cycle

• The reactions of the Krebs cycle that take place in the mitochondrial matrix can be summarized in 5 steps:

1) Acetyl CoA joins with the 4-carbon compound oxaloacetic acid to produce the 6-carbon compound citric acid and releases coenzyme A.

2) Citric acid releases a CO₂ molecule to become a 5-carbon compound and donates a hydrogen atom to NAD+.

3) 5-carbon compound releases a CO₂ molecule to become a 4-carbon

compound, donates a hydrogen atom to NAD+, and produces 1 ATP molecule.

4) 4-carbon compound donates a

hydrogen atom to FAD to form FADH₂. 5) 4-carbon compound regenerates

oxaloacetic acid by donating a hydrogen atom to NAD+.

• 1 glucose molecule produces 6 NADH, 2 FADH₂, 2 ATPs, and 4 CO₂ molecules.

The Krebs Cycle

Electron Transport Chain & Chemiosmosis

• The electron transport chain lines the inner membrane of the mitochondrion.

• The high energy electrons in NADH and FADH₂ are passed along the molecules of the electron transport chain.

• Each time an electron is passed it loses energy which is then used to pump H+

out of the mitochondrial matrix.

• The pumping of H+ creates a concentration gradient.

• ATP is generated when H+ diffuse back into the mitochondrial matrix through ATP synthase.

• ATP cannot be synthesized if oxygen is not available to serve as the final acceptor of electrons.

• Oxygen also combines with hydrogen atoms supplied by NADH and FADH₂ to form water.

Oxidative Respiration via the Electron Transport Chain

Efficiency of Cellular Respiration

• Glycolysis and the Krebs cycle supply 10 NADH and 2 FADH₂ molecules to the electron transport chain.

• For each NADH molecule 3 ATP

molecules are generated and for each FADH₂ molecule 2 ATP molecules are generated.

• Therefore 10 NADH and 2 FADH₂ molecules can be used in aerobic respiration to generate up to 38 molecules of ATP per molecule of glucose.

• As it turns out aerobic respiration is nearly 20 times more efficient than glycolysis.

Which step produces the most ATP molecules?

Section 9.3 Fermentation

Be Able To

• Explain how fermentation allows glycolysis to continue.

• Identify different ways that fermentation is important.

• Key Terms: Pg 262.

Fermentation

• Fermentation is a process in which cells make a limited amount of ATP in the absence of oxygen.

• Fermentation pathways regenerate NAD+.

• In lactic acid fermentation an enzyme converts pyruvic acid into lactic acid.

• In alcoholic fermentation pyruvic acid is converted to ethyl alcohol in 2 steps:

1) A CO₂ molecule is removed.

2) 2 hydrogen atoms are added to form ethyl alcohol

• Fermentation is inhibited by ethyl alcohol concentration.

Fermentation at Work: Saki

Energy and Exercise

• Humans have three main energy systems:

1) ATP is our quick energy source on

hand but our supply is rather limited ~10

seconds

2) ATP via lactic acid fermentation which can supply about 90 seconds of activity.

3) ATP via aerobic

respiration which can produce ATP for hours of low level aerobic activities.