Understanding Metabolism: A Comprehensive Guide to Cellular Processes

Posted on Apr 27, 2024 in Biology

Metabolism: Building and Breaking Down Molecules

Anabolism and Catabolism

Anabolism is the process of building complex molecules from simpler ones, like constructing a protein from amino acids. This involves condensation reactions, where molecules join together and water is released.

Catabolism is the opposite, breaking down complex molecules into simpler ones, like digesting food. This involves hydrolysis reactions, where water is used to break bonds between molecules.

The Molecules of Life

Life relies on carbon-based compounds, including:

• Carbohydrates: Sugars and starches used for energy.
• Lipids: Fats and oils used for energy storage and insulation.
• Proteins: Building blocks of cells and enzymes.
• Nucleic acids: DNA and RNA, carriers of genetic information.

Water: The Essential Solvent

Water is a polar molecule, meaning it has a slight positive and negative charge. This allows water molecules to form hydrogen bonds with each other and with other polar molecules.

Hydrophilic substances, like glucose, dissolve in water. Hydrophobic substances, like fats, do not.

Transport in Blood

Different molecules are transported in the blood in different ways:

• Polar molecules (e.g., glucose, amino acids) dissolve in plasma.
• Non-polar molecules (e.g., oxygen, fats) require carriers like red blood cells or lipoproteins.

Properties of Water

Water has unique properties that make it essential for life:

• Cohesion: Water molecules stick together, creating surface tension.
• Adhesion: Water molecules stick to other polar surfaces.
• Thermal properties: Water resists temperature changes, helping regulate body temperature.
• Solvent properties: Water dissolves many substances, facilitating chemical reactions.

Carbohydrates

Carbohydrates are classified based on their structure:

• Monosaccharides: Simple sugars like glucose and fructose.
• Disaccharides: Two monosaccharides joined together, like sucrose and lactose.
• Polysaccharides: Long chains of monosaccharides, like starch, glycogen, and cellulose.

Starch, Cellulose, and Glycogen

These are all polysaccharides with different functions:

• Starch: Energy storage in plants.
• Cellulose: Structural component of plant cell walls.
• Glycogen: Energy storage in animals.

Lipids as Energy Storage

Lipids are a more efficient way to store energy than carbohydrates because they provide more energy per gram and do not require water for storage.

Proteins

Proteins are made up of amino acids linked together in a specific sequence. The structure of a protein determines its function.

Protein Structure

• Primary structure: Sequence of amino acids.
• Secondary structure: Folding of the amino acid chain into alpha helices or beta sheets.
• Tertiary structure: 3D folding of the protein.
• Quaternary structure: Multiple protein subunits coming together.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy.

Enzymes are specific to their substrates and have an active site where the reaction takes place.

Enzyme Models

• Lock and key model: The substrate fits perfectly into the active site.
• Induced fit model: The active site changes shape slightly to accommodate the substrate.

Lactose Intolerance

People with lactose intolerance lack the enzyme lactase, which breaks down lactose. This can lead to digestive problems.

Lactose-free milk is produced by treating milk with lactase to break down lactose.

Cellular Respiration

Cellular respiration is the process of releasing energy from glucose to produce ATP, the cell’s energy currency.

Types of Cellular Respiration

• Aerobic respiration: Requires oxygen and produces a large amount of ATP.
• Anaerobic respiration: Does not require oxygen and produces a small amount of ATP.

Stages of Aerobic Respiration

1. Glycolysis: Glucose is broken down into pyruvate in the cytoplasm.
2. Link reaction: Pyruvate is converted to acetyl-CoA and enters the mitochondria.
3. Krebs cycle: Acetyl-CoA is further broken down, producing ATP, NADH, and FADH2.
4. Electron transport chain (ETC) and chemiosmosis: NADH and FADH2 donate electrons to the ETC, creating a proton gradient that drives ATP synthesis.

The Circulatory System

The circulatory system transports oxygen, nutrients, and waste products throughout the body.

Blood Vessels

• Arteries: Carry oxygenated blood away from the heart.
• Veins: Carry deoxygenated blood back to the heart.
• Capillaries: Connect arteries and veins, allowing for exchange of materials with tissues.

The Heart

The heart pumps blood throughout the body. The right side pumps blood to the lungs, and the left side pumps blood to the rest of the body.

The Respiratory System

The respiratory system exchanges oxygen and carbon dioxide between the body and the environment.

Breathing

Breathing involves the inhalation and exhalation of air.

• Inhalation: The diaphragm contracts and the rib cage expands, increasing the volume of the chest cavity and drawing air in.
• Exhalation: The diaphragm relaxes and the rib cage contracts, decreasing the volume of the chest cavity and pushing air out.

Alveoli

Alveoli are tiny air sacs in the lungs where gas exchange takes place. They have a large surface area and a thin lining to facilitate diffusion of gases.

Metabolic Pathways

Metabolic pathways are series of enzyme-catalyzed reactions that convert one molecule to another.

Enzyme Inhibition

Enzyme inhibitors can slow down or stop metabolic reactions.

• Competitive inhibitors: Compete with the substrate for the active site.
• Non-competitive inhibitors: Bind to a different site on the enzyme, changing its shape and preventing substrate binding.

End Product Inhibition

The end product of a metabolic pathway can inhibit the enzyme that catalyzes the first reaction, regulating the pathway.

ETC and Chemiosmosis

The ETC and chemiosmosis are the final stages of aerobic respiration, where most of the ATP is produced.

The ETC uses energy from electrons to pump protons across the inner mitochondrial membrane, creating a proton gradient.

ATP synthase uses the energy of the proton gradient to produce ATP.

Oxygen is the final electron acceptor in the ETC, combining with electrons and protons to form water.