Metabolism Overview

Study Notes

Metabolism is the ability to acquire and use energy from the environment, encompassing all chemical reactions in cells, tissues, organs, and organ systems. All living things, from bacteria to humans, conduct metabolism.
Two main types of metabolic reactions are catabolism (breaking down large molecules into simpler ones, releasing energy) and anabolism (building large molecules from simpler ones, requiring energy input).

The energy powering most biological systems on Earth originates from solar energy.
Plants capture solar energy for photosynthesis, producing their food.
Food (carbohydrates, lipids, proteins, and nucleic acids) provides the energy for cellular processes.
All molecules, including nutrients, store potential energy in the bonds between their atoms.

Nutrients are absorbed from the digestive tract and distributed in the bloodstream.
Lipids are stored as triglycerides in adipose tissue, stimulated by insulin.
Skeletal muscle utilizes absorbed nutrients for ATP production, also stimulated by insulin.
All tissues (except skeletal muscle) use absorbed nutrients for ATP production, stimulated by insulin, growth hormone, and sex hormones.
The liver and skeletal muscle store glycogen, stimulated by insulin.
Absorbed nutrients are used for:
- Providing immediate energy for cellular processes like muscle contraction, secretion, and active transport.
- Synthesizing structural or functional molecules for cell repair and replacement.
- Storing energy as glycogen or fat for later use.

Aerobic cellular respiration, using oxygen, produces carbon dioxide, water, and energy.
A portion of the generated energy is used to create ATP.
The overall reaction is: Fuel Nutrient + O2 → CO2 + H2O + energy

Catabolic reactions liberate energy stored in phosphate bonds of ADP, producing high-energy ATP molecules.
ATP (adenosine triphosphate) is the universal energy carrier in cells.
The reaction is: ADP + Pi + energy → ATP

Coenzymes NAD (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) carry energy and hydrogen.
NAD is derived from niacin (B3), and FAD from riboflavin (B2).
FAD accepts two hydrogen atoms (2H) to become FADH2.
NAD accepts two electrons (2e) and one proton (H+) to become NADH + H+.

Glycolysis:
- Breaks down glucose (C6) into two pyruvic acid molecules.
- A metabolic pathway in the cytoplasm involving many enzymatically controlled steps.

Acetyl-CoA enters a cycle of 9 reactions, also known as the Citric Acid Cycle.
The cycle is crucial for metabolizing glucose and requires 2 cycles.
The cycle involves an initial reaction with oxaloacetic acid, producing citric acid.
The cycle releases: CO2, free H+, & e- and forming ketoglutaric acid
The process generates 3 NADH, 1 FADH2, and 1 ATP for each cycle of acetyl-COA.

Located in the inner mitochondrial membrane.
Includes four large protein complexes and ATP synthase.
Flavoprotein (from riboflavin), Coenzyme Q (from Vitamin E), and Cytochromes (last: cytochrome a3) are components of the system.
Electrons and hydrogen atoms from NADH and FADH2 are passed down a chain, creating a proton gradient.
This gradient drives ATP synthesis by ATP synthase.

Beta-oxidation:
- The pathway for breaking down fatty acids, occurring in the mitochondrial matrix.
- Fatty acids are broken down by breaking and rearranging connections in 2 carbon segments.
Triglycerides:
- Major dietary lipids.
- Consist of a glycerol backbone and three fatty acids.
- Hydrolyzed (broken down) by lipase enzymes into glycerol and three individual fatty acids