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Introduction
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Metabolism: The sum of all chemical reactions occurring in the body.
Cellular Metabolism: The sum of all chemical reactions occurring in a cell; metabolic reactions typically occur in pathways or cycles.
Types of Metabolic Reactions:
- Anabolism:
- Definition: The process in which small molecules are built into larger ones.
- Energy Requirement: Requires energy, specifically ATP produced during catabolism.
- Example: Dehydration synthesis:
  - Small molecules combine to form larger molecules, resulting in the production of water ( $H_2O$ ).
  - Used to create polysaccharides, proteins, and triglycerides.
- Catabolism:
- Definition: The process in which larger molecules are broken down into smaller ones.
- Energy Release: Releases energy in the form of ATP.
- Example: Hydrolysis:
  - Used to decompose carbohydrates, proteins, and lipids.
  - Involves the use of water to split these complex substances.
  - It acts as the reverse process of dehydration synthesis.

Overview: All cells perform both catabolic and anabolic reactions.
Importance of Regulation:
- Catabolic and anabolic processes must be carefully controlled to prevent imbalances that can damage or kill a cell.
Enzymes:
- Role: Control the rates of both anabolic and catabolic reactions, significantly increasing reaction rates.

Enzymes (Protein Catalysts):
- Description: Globular proteins that catalyze specific reactions.
- Functions:
- Increase the rate of chemical reactions.
- Lower the activation energy required to start reactions.
- Are not consumed in the reactions, allowing for repeated use.
- Specificity: Each enzyme is specific to a particular substrate based on the shape of its active site.
- Naming Convention: Many enzymes are named after their substrate with the suffix “-ase” (e.g., lipase breaks down lipids).

Metabolic Pathways:
- Definition: Series of enzyme-controlled reactions leading to the formation of a product.
- Characteristics: Each new substrate is the product of the previous reaction and each step is catalyzed by a different enzyme.
Rate-Limiting Enzyme:
- Definition: A regulatory enzyme that catalyzes one step of the pathway and typically sets the rate for the entire reaction sequence.
- Characteristics:
- The number of molecules of this enzyme is limited.
- Often is the first enzyme in the reaction sequence.
- In some pathways, the end product inhibits the rate-limiting enzyme, exemplifying negative feedback.

Cofactor:
- Definition: A non-protein substance that combines with an enzyme to activate it.
- Functions:
- Aids in folding the active site into the proper shape.
- Assists in binding the enzyme to its substrate.
- Types: Can be ions, elements, or small organic molecules (coenzymes).
Coenzyme:
- Definition: An organic molecule that acts as a cofactor, mostly derived from vitamins.
Denaturation:
- Definition: The inactivation of an enzyme or any other protein due to an irreversible change in its conformation, resulting in an inability to bind to its substrate.

Concept: A deficient or absent enzyme blocks the metabolic pathway that it catalyzes.
Consequence: Results in the accumulation of the enzyme's substrate and a deficiency of its product.
Example: Phenylketonuria (PKU):
- Condition: A missing or nonfunctional enzyme blocks the conversion of amino acid phenylalanine into tyrosine.
- Effect: Excess phenylalanine can poison the brain.
- Treatment: Managed with a special diet.

Energy:
- Definition: The capacity to change something or the ability to do work.
- Forms: Heat, light, sound, electrical energy, mechanical energy, and chemical energy.
- Principle: Energy cannot be created or destroyed but can be transformed from one form to another.
Cellular Respiration:
- Definition: Process that transfers energy from molecules and makes it available for cellular use.
- Note: Most metabolic reactions utilize chemical energy.

Chemical Energy Storage: Many metabolic processes require energy stored in ATP.
Energy Release:
- Energy is held in chemical bonds and is released when these bonds are broken.
Oxidation:
- Definition: The process through which energy is released from glucose and similar molecules via the loss of hydrogen atoms and their electrons.
- Enzyme Role: Enzymes lower the activation energy needed for oxidation in cellular respiration reactions.
Energy Transfer to ATP:
- Distribution: 40% as chemical energy and 60% as heat (maintains body temperature).

ATP (Adenosine Triphosphate):
- Definition: A molecule that carries energy in a form that the cell can use.
- Function: It is the main energy-carrying molecule in the cell. Energy from ATP breakdown is used for cellular work.
- Structure: Composed of 3 portions:
- Adenine
- Ribose (a sugar)
- 3 phosphate groups in a chain.
- The second and third phosphates are linked by high-energy bonds, allowing for quick energy transfer to other molecules.

ADP (Adenosine Diphosphate):
- Definition: Formed when ATP loses a terminal phosphate.
- Conversion: Can be converted back into ATP by attaching a third phosphate, a process called phosphorylation.
- Energy Source: Phosphorylation requires energy from cellular respiration.
- Energy Cycle: ATP and ADP continuously cycle between cellular respiration and energy-utilizing reactions.

Overview of Cellular Respiration:
- The cellular respiration of glucose occurs through 3 interconnected reaction sequences:
1. Glycolysis (Anaerobic):
  - First reaction sequence, breaking down glucose (6-carbon) into 2 pyruvic acid (3-carbon) molecules.
2. Citric Acid Cycle (Aerobic)
  - Series of aerobic reactions involved after glycolysis.
3. Electron Transport Chain/Oxidative Phosphorylation (Aerobic)
  - Final aerobic phase that produces a significant amount of ATP.
Characterization:
- Glycolysis and the Electron Transport Chain consist of stepwise reaction sequences.
- The Citric Acid Cycle involves a metabolic cycle where the final product reacts to replenish the original substrate.

Inputs Required: A supply of glucose and O2 are necessary for cellular respiration of glucose.
Final Products:
- Carbon dioxide (CO2)
- Water (H2O)
- ATP (40% chemical energy)
- Heat (60% as thermal energy).
Types of Reactions:
- Anaerobic reactions: Do not require O2 and yield little ATP.
  -