Bio 121

The cells metabolize glucose for energy

The chemical equations for glucose formation during photosynthesis and glucose breakdown by glycolosis and cell respiration are symmetrical.

Cells are able to trap about 40% of the energy in glucose as ATP.

glycolysis in the cytoplasm breaks down 6-C glucose into two 3-C pyruvate molecules.

In the absense of oxygen, pyruvate is converted by fermentation in the cytoplasm to lactate or ethanol and carbon dioxide, generating a small amount of ATP energy.

In the presense of oxygen, pyruvate is completely broken down to carbon dioxide and water in the mitochondria, generating a large amount of ATP energy.

Glycolysis breaks down glucose to pyruvate, releasing chemical energy.

Steps: glucose activation steps of glycolysis are energy requiring.

* Glucose is converted to fructose bisphosphate, a 6-C hexose with two phosphate groups.

*Fructose bisphosphate is unstable and hish in energy.

* Glucose activation "costs" two ATP

Fructose bisphosphate splits into two 3-C molecules of G3P

Each G3P molecule undergoes a series of steps to be converted to pyruvate.

Energy-harvesting steps produce two NADH and four ATP.`

produces a net gain of 2 ATP and 2 high-energy electron carriers, NADH, for each molecule of glucose (6-C) converted to 2 pyruvate (3-C)

• 1. Under anaerobic conditions, NAD+ must be regenerated to allow glycolysis to continue.
• 2. Muscles cells undergo lactate fermentation during vigorous exercise when not enough oxygen is available to cells.
• 3. During fermentatioon, only 2 ATP are generated per molecule glucose.
• 4. As soon as oxygen is available, lactate will be converted back to pyruvate inthe liver, and cell respiration will resume.
• 5. Some microorganisms, such as the bacteria that make yogurt, sour crea, use lactate fermentation; produces distinctive acidic taste in these foods.

many microorganisms, including yeast, convert pyruvate to ethanol and CO2

Alcoholic fermentation is taken advantage of to produce alcoholic beverages and bread.

1. In the matrix, pyruvate reacts with a molecule of coenzume A (CoA) to produce acetyl-COA, one CO2 and one NADH

2. Each acetyle-COA combines with a molecule of oxalloacetate to produce 6-C citrate, releasing CoA.

3.Citric acid goes through a series of rearrangements in a cycle of reastions called the Krebs cycle.

4. End products of the Krebs cycle (per molecule of pyruvate): two CO2, one ATP, one FADHs, and three NADH; oxaloacetrate is regenerated

5. Final end products of mitochondrial matrix reactions: 6 CO2, 2 ATP, 8 NADH and 2 FADH2

1. From glycolosis and the mitochondrial matrix reactionPs, the cell has accumulated 4 ATP, 10 NADH, and 2 FADH2.

2. the electron carriers, NADH and FAHD2, donate their electrons to the lectron transport chains located in the inner mitochondrial membrance.

3. Energy released by these electrons is used to pump hydrogen ions from the matrix into the intermembrane compartment to produce ATP by chemismosis.

4. 02 is the final electron acceptor and combines with hydrogen ions to form water.

5. Without 02, electrons would pule up and ATP synthesis would stop.

captures energy stored in a hydrogen ion gradient and produces ATP.

1. During chemiosmosis, the flow of hydrogen ions provides enough energy to produce 32-34 ATP

2. The ATP diffuses out of themitochondria to the cytoplasm through the outer membrane, which is permeable to ATP, and is available to power cellular functions.

3. Chemiosmosis provides about 95% of the cell's ATP.

1. during a 100 meter dash, fermentation can supply enough ATP energy to keep up with ATP demand.

2. A longer race requires cell respiration to power muscles aequately; the runner must be taking in enough oxygen for cell repiration to continue.

3. Building up the capacity of the respiratory and circulatory systems is an important component of training for the marathon runner.