molecules
Water and Biomolecules
Water: The Ubiquitous Molecule
Approximately 65% of the human body is water.
Water (H2O) consists of two hydrogen atoms and one oxygen atom.
Water is a polar molecule.
The oxygen atom is electronegative, pulling electrons towards it.
This creates a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.
Water as a Solvent
Water is the universal solvent in animal biology.
Solute: Any substance suspended in water (the solvent).
Examples: glucose, sodium, potassium, and bicarbonate.
These solutes have specific roles in the body but function as solutes when in solution (within the solvent of H2O).
Osmolarity: Measuring Solute Concentration
Osmolarity: The measurement of solute concentration in a solution.
Applies within a cell, outside a cell, or within a tissue.
Based on the number of solutes relative to the volume of water.
Considers the total number of solutes, regardless of the type, in relation to the volume of water.
Hydrogen Bonding in Water
Water molecules engage in hydrogen bonding with each other.
The partial negative charge on an oxygen atom attracts the partial positive charge on a hydrogen atom of another water molecule.
Hydrogen bonding also occurs between hydrogen atoms (e.g., in hydroxide, , groups) and other molecules.
Influences the shape of proteins.
Polarity, Hydrophilic, and Hydrophobic Molecules
Water interacts well with other polar molecules or charged atoms (ions).
Ions: Charged atoms.
Cations: Positively charged atoms.
Anions: Negatively charged atoms.
Hydrophilic vs. Lipophilic
Hydrophilic: Water-loving; describes polar molecules that mix well with water.
Lipophobic: Describes polar molecules that do not mix well with lipid-based molecules.
Hydrophobic: Describes lipid-based molecules that do not mix well with water.
Lipophilic: Describes lipid-based molecules that mix well with other lipids.
Surface Tension
Hydrogen bonding creates surface tension, causing water molecules to stick together.
Example: difficult to separate wet glass slides due to surface tension.
Serous Membranes
Serous membranes exemplify surface tension in the body.
Example: Pleural membranes around the lungs.
Visceral pleura: Adheres directly to the lung.
Parietal pleura: Outer layer.
Pleural space: Space between parietal and visceral pleura containing pleural fluid.
Pleural fluid: Serous fluid causing the membranes to stick together due to surface tension.
The Role of Surface Tension in Breathing
Surface tension within the serous fluid is essential for breathing.
The lungs expand and contract with changes in the thoracic cavity.
As the thoracic cavity enlarges, the lungs enlarge, decreasing pressure and allowing air to flow in.
Our ribs, attached to the inner lining of the ribs, is the parietal pleura. When our muscles take our ribs and pull them outwards, it's going to take the parietal pleura with it. That's the outermost layer right here. And because the parietal pleura is physically stuck to the visceral pleura, the visceral pleura is directly adhering to the lung. When the ribs move outwards or the diaphragm moves down, those structures are pulling the lungs outward and inferior. And because the visceral pleura is directly attached to the parietal pleura, it makes the lungs larger, and this would not be able to happen without the surface tension created by the water molecules.
Biomolecules
Four main types: carbohydrates, proteins, fats (lipids), and nucleic acids (nucleotides).
Carbohydrates
Glucose (): Six carbons, twelve hydrogens, and six oxygens.
Each vertex in a carbohydrate molecule represents a carbon atom.
Carbon atoms prefer to have four bonds.
Monosaccharides: Single sugar molecules.
Glucose can exist in open-chain (acyclic) or ring (cyclic) form.
Examples: glucose, galactose, and fructose (all have the formula )
Galactose: Very similar to glucose with a slight structural difference.
Fructose: A five-carbon ring structure.
Disaccharides: Two monosaccharides covalently bonded.
Examples: sucrose, maltose, and lactose.
Sucrose: Glucose + Fructose.
Maltose: Glucose + Glucose.
Lactose: Galactose + Glucose.
Complex Sugars:
Glycogen: Storage form of glucose in animals (stored in the liver and skeletal muscle).
Starch: Storage form of glucose in plants.
Insulin and Glucagon
Insulin: Released from pancreatic beta cells during times of elevated blood glucose levels.
Stimulates glucose uptake from the blood into liver cells (hepatocytes) to form glycogen.
Lowers blood glucose concentrations.
Glucagon: Released from pancreatic alpha cells during times of low blood glucose levels.
Stimulates the breakdown (hydrolysis) of glycogen to release glucose into the blood.
Increases blood glucose levels.
Proteins
Proteins are the most ubiquitous biomolecule within the body.
Functions: Channels, enzymes, antibodies, receptors, and structural components.
Arise from DNA in the cell nucleus, which provides the genetic blueprint.
Protein Structure
Primary Structure: The amino acid sequence.
Amino acids are the building blocks of proteins (20 different amino acids).
Polypeptide chain: A sequence of amino acids.
Secondary Structure: Initial shape or morphology of the protein.
Alpha helices.
Beta-pleated sheets.
Held together by hydrogen bonds.
Tertiary Structure: The three-dimensional folding of the protein upon itself.
Influenced by hydrogen bonding.
Quaternary Structure: Combination of multiple polypeptide chains.
Example: Hemoglobin (four polypeptide chains).
Hemoglobin and Oxygen Transport
Hemoglobin contains four hem groups, each with an iron atom at the center.
Oxygen binds to the iron atom for delivery to tissues.
Binding of oxygen to one hem group causes a conformational change, facilitating binding to other groups.
Enzymes
Enzymes are proteins that catalyze (speed up) reactions in the body.
Example: An enzyme facilitates the covalent bonding of two glucose molecules to form maltose.
Denaturing Proteins
Denaturing: Unintended change in the shape of a protein, rendering it nonfunctional.
Causes: Changes in pH, elevated temperatures, or differing ion concentrations.
Genetic Mutations and Protein Structure
Mutations in DNA can disrupt protein structure and function.
Example: Sickle cell anemia.
A single amino acid substitution (e.g., valine to glutamate) in the hemoglobin molecule causes red blood cells to assume a sickle shape.
Sickle-shaped cells can get stuck in capillaries, impairing oxygen delivery.
Lipids (Fats)
Includes phospholipids and steroid molecules.
Steroid molecules are based on cholesterol.
Examples: estrogen, testosterone, and cortisol.
Triglycerides: Composed of one glycerol molecule and three fatty acids.
Non-polar molecules, primarily hydrocarbons.
ATP (Adenosine Triphosphate)
Composed of one ribose molecule, an adenosine molecule, and three negatively charged phosphate groups.
The negative charges of the phosphate groups create tension, making ATP an energy-rich molecule.
Breaking one of the phosphate bonds releases energy for the body to do work.
The Cell
Nucleus: A membrane-bound organelle housing DNA.
Mitochondria: Organelle responsible for ATP synthesis.
Ribosomes: Not membrane-bound, but essential for protein synthesis.
Microvilli: Surface appendages that increase the cell's surface area for more receptors, channels and metabolic activity.
Cilia: Surface appendages that propel substances away from the cell.
An epithelial tissue containing cilia, and also within that epithelial tissue, there's a bunch of mucus.
Those trapped pathogens or microorganisms are going to get propelled superiorly by the cilia, eventually into the oral cavity, which one can eliminate from their mouth, or they can even swallow it.
Cigarette smokers can get paralyzed cilia, so they're not functioning anymore, and as a result, they have to cough a lot to get that mucus up and out of their airway because the cilia are not functioning anymore.