Cell Metabolism and Energy Pathways: Enzymes, REDOX, and Cellular Respiration

Metabolism

the total of all the chemical reactions and physical activities of the cell.

Catalyst

a substance that increases the rate of a chemical reaction.

Enzyme

protein molecules that increase the rate of a chemical reaction.

Activation Energy

the energy required to start a chemical reaction.

Enzyme-Substrate Complex

the intermediate formed when an enzyme binds to its substrate.

Factors Affecting Enzyme Activity

1) optimal temp 2) optimal pH 3) optimal amount of substrate.

Cofactors

ions or small molecules that help an enzyme work.

Examples of Cofactors

copper, iron, zinc.

Coenzymes

non-protein, organic molecules that help an enzyme work.

Examples of Coenzymes

NAD+, FAD+, coenzyme A.

REDOX Reactions

chemical reactions involving the transfer of electrons.

Oxidized Molecule

a molecule that loses electrons and H+.

Reduced Molecule

a molecule that gains electrons and H+.

Electron Acceptors in Catabolic Reactions

1. NAD+ (reduced to NADH) 2. FAD+ (reduced to FADH2).

Anabolic Chemical Pathways

chemical reactions in which smaller molecules are joined together to build larger molecules.

Catabolic Chemical Pathways

chemical reactions in which larger molecules are broken apart into smaller ones.

Dehydration Synthesis

the process of joining glucose molecules together to make a disaccharide.

Hydrolysis

the process of breaking down a disaccharide into monosaccharides.

Cellular Respiration

chemical reactions that convert food molecules (carbohydrates, lipids, proteins) into ATP.

ATP

Adenosine triphosphate, a modified RNA nucleotide with three phosphate groups.

High Energy Bond in ATP

the covalent bond attaching the last phosphate group.

Energy Released from ATP

used for cellular activities that require energy.

Energy Released from Breaking ATP

produces ADP + Pi.

Energy for Cellular Activities

used for active transport, cellular movement, some anabolic reactions, muscle contraction, nerve conduction, bioluminance.

Energy Amount Released from ATP

7.3 Kcal.

ATP Production Rate

~ 50g (1.8 oz) 8,000g (17lb)/hour.

Anaerobic cellular respiration

O2 is not required in the chemical reactions that convert food molecules into ATP.

Aerobic cellular respiration

O2 is required in the chemical reactions that convert food molecules into ATP.

Simplified balanced chemical reaction for aerobic cellular respiration of glucose

C6H12O6 + 6O2 6CO2 + 6H2O + 36-38 ATP

Glycolysis

Breakdown of glucose.

Energy produced in Glycolysis

Produced only 2 ATP net (~ 2% of all the energy found in glucose).

Energy lost in Glycolysis

Only 3% lost to heat at this point.

Energy in NADH from Glycolysis

The 2 NADH contain about 16% of the energy from glucose.

Energy in pyruvate from Glycolysis

The two pyruvate contain about 79% of the energy from glucose.

Transition Reaction

Converts the two pyruvate molecules from glycolysis into two molecules of acetyl Coenzyme A (acetyl-CoA).

Byproduct of Transition Reaction

2 NADH + by product - 2 CO2.

Krebs Cycle

Breakdown of the 2 acetyl-CoA molecules.

Energy produced in Krebs Cycle

2 ATP are produced.

NADH produced in Krebs Cycle

6 NADH are produced.

FADH2 produced in Krebs Cycle

2 FADH2 are produced.

Byproduct of Krebs Cycle

4 CO2.

Electron Transport Chain (ETC)

The energy stored in NADH and FADH2 is transferred into making ATP.

Final electron acceptor in ETC

The last molecule to accept the electrons is called the terminal (final) electron acceptor, which is O2.

Energy produced from NADH in ETC

Each NADH can produce 3 ATP in the ETC.

Energy produced from FADH2 in ETC

Each FADH2 can produce 2 ATP in the ETC.

Total ATP produced in Aerobic cellular respiration

38 ATP total are produced.

Efficiency of Aerobic cellular respiration

Aerobic cellular respiration of glucose is approximately 37% efficient.

Fermentation

Pyruvate is further oxidized without free oxygen (O2).

Purpose of fermentation

To convert NADH back into NAD+ during glycolysis, allowing the cell to continue to make 2 ATP from glycolysis without O2.

Acid fermentation in humans

Glycolysis → pyruvate + NADH → lactic acid (3C) + NAD+.

Alcohol fermentation in yeast

Glycolysis → pyruvate + NADH → ethanol (2C) + CO2 + NAD+.

Drawbacks to fermentation

1. Wastes large amounts of energy found in glucose. 2. The waste products of fermentation can impede or stop cell function.

Triglycerides in Glycolysis

Triglycerides must first be broken down into its three fatty acids and glycerol.

Energy from a single triglyceride

Approximately 458 ATP can be generated from a single triglyceride.

ATP generated per amino acid

12-16 ATP are generated per amino acid.