What is the aqueous environment inside our cells like? Importance of Diffusion Importance of Water pH Body Systems, Homeostasis and Feedback Mechanisms Larry Frolich, Water Chemistry and Diffusion Water Chemistry, Diffusion and Ions

Larry Frolich, Water Chemistry and Diffusion Common Elements Composing the Human Body

Larry Frolich, Water Chemistry and Diffusion Common Elements Composing the Human Body Besides Water (H,O) and Molecules of Life (C,H,O,N), dissolved ions are crucial to creating cellular aqueous environment

Larry Frolich, Molecules and Diffusion The importance of Diffusion Diffusion is fast and effective across microscopic distance Virtually all living processes involve diffusion and/or osmosis Cell membranes control diffusion and allow for life chemical reactions to take place Diffusion lets tissues do job and permits organ systems to function Examples: –Oxygen in circulatory system –Food in digestive system –Calcium in muscular function –Nerve impulses Cell membranes and Diffusion

Larry Frolich, Water Chemistry and Diffusion The importance of water Water is the single most abundant component of cells and organisms % of a cell is water (10-20 in spores and dry seeds) The polarity of water molecules are caused by the angles that hydrogen atom bond to the oxygen atom ( ), making the oxygen atom electronegative (  - ). This property accounts for the cohesiveness, the temperature- stabilizing capacity and the solvent properties of water. Hydrogen bonding between water molecules

Larry Frolich, Water Chemistry and Diffusion Water molecules are cohesive -- Hydrogen bonds form between the hydrogen atoms and the oxygen atoms of water molecules and are responsible for its high boiling point, high specific heat, and high heat of vaporization. Water has a high temperature- stabilizing capacity -- Specific heat is the amount of heat a substance absorb per gram to increase its temperature 1 0 C. The specific heat of water is 1.0 calorie per gram. Water has a high heat of vaporization, the amount of energy required to convert one gram of a liquid into vapor. Water is an excellent solvent. A solvent is a fluid in which another substance, called the solute, can be dissolved. Hydrophobic: “water fearing” Hydrophilic: “water loving” The solubilization of sodium chloride because water molecules form spheres of hydration More properties of water originated from its polarity

pH and lungs and kidneys Concentration of free H+ ions is kept very constant by bicarbonate buffering Kidneys and lungs are crucial in keeping this balance Larry Frolich, Water Chemistry and Diffusion

The importance of selectively permeable membranes Membranes are physical barriers of cells and subcellular compartments controlling material exchange between the internal environment and the extracellular environment A membrane is essentially a hydrophobic permeability barrier consisting of phospholipids, glycolipids, and membrane proteins Membranes contain amphipathic molecules such as phosphatidyl ethanolamine, an example of phosphoglycerides, the major class of membrane phospholipids in most cells. Polar head Nonpolar tail

Larry Frolich, Water Chemistry and Diffusion The properties of membranes A membrane is a lipid bilayer with proteins embedded in it. Each layer is about 3-4 nm thick, with the hydrophobic tails facing each other in the middle. Functions of the associated proteins: transport proteins; enzymes, receptors, electron transport intermediates (mitochondria), or chlorophyll-binding proteins (chloroplast) Membranes are selectively permeable. Freely diffusing molecules: H2O, CO2 or MW < 100 Dalton However, ions like Na + and K + are effectively excluded (10 8 times less efficient). They need either hydrophilic channels or carriers for their crossing of the membrane

Ions and dissolved substances move across cell membrane It is crucial to keep the right concentrations of salts and other dissolved substances, especially glucose, inside the cell Diffusion and active transport across cell membrane are involved Larry Frolich, Water Chemistry and Diffusion

Larry Frolich, Molecules and Diffusion Body Systems and Diffusion Understand path through body of: Food/Nutrients (glucose) Oxygen Carbon Dioxide Nitrogen

Larry Frolich, Molecules and Diffusion Homeostasis “…the ability to maintain relatively constant internal conditions even though the outside world changes continuously…” Within cells Within body

Larry Frolich, Molecules and Diffusion Feedback Mechanisms Negative Feedback Examples—more common –home heating system –Glucose regulation in blood

Larry Frolich, Molecules and Diffusion Feedback Mechanisms Negative Feedback Examples –home heating system –Glucose regulation in blood Positive Feedback Examples –Fire-Starting –Blood clotting