Lecture 2 – Cells, Water, and ChemicalsThe Cell Theory1. All living organisms are made of cells (and the products of cells)2. All cells are produced by other cellsCells need to:- Transform matter - build and break molecules, structures- Acquire, store and produce energy - chemical and kinetic (movement)- Stay organized, and often coordinate with other cells- Acquire and save information, from environment, from self, from parent cell/ pass someinformation to offspringWhat are cells made of?Most of your water in intracellular (inside cells)- 67% intracellular fluidCell: chemical reactions in a bag of water?- Plasma membrane (cell membrane)- Intracellular (inside) = cytoplasm (cytosol)- Extracellular (outside) cell wall or extracellular matrixCells are mostly water with other stuff, surrounded by a membrane.- Why water?- It is a great solvent: many (but not all) molecules dissolve in waterThis is important because dissolved molecules (solutes) can:- … diffuse between parts of a cell- Diffusions moves things over short distances from region of high concentration toregion of low concentration- … bump into each other- … undergo chemical reactionsTo understand how water dissolves things, we need to review chemical bonds:- Covalent bonds )non-polar and polar) - atoms sharing electrons- Bonds via electrical attraction - ionic bonds, hydrogen bonds, van der Waals bonds,etc.Covalent bonds are formed by sharing electrons between two atoms- Representation:- HF- H-F- H:FAtoms want to share enough electrons to have a full outer valence shell- Innermost shell: full = 2 electrons- Outer shells: full = 8 electronsElectronegativity - how much an atom attracts electronsIons and Ionic Bond- When strongly electronegative atom completely gains electron from weaklyelectronegative atom, they form ions- Electrons not “shared”, but ions attracted if they are opposite electric charges (+ and -) =ionic bond- Example: sodium chloride (NaCl) is Na+and Cl-binding in salt crystalPolar Covalent Bonds- Polar covalent bonds - unequal electron sharing between atoms with differentelectronegativity- Gives parts of a molecule partial (less than an electron’s) charges (𝛿+ or 𝛿-)- Ex: H2O - O has a partial negative charge and H has a partial positive chargeCan use electronegativity to predict polar or ionic bonds. Know this:1. Biological molecules commonly contains: carbon, hydrogen, nitrogen, oxygen,phosphorus2. H, C, P have about equal electronegativity, O and N more electronegative than H, C, or PElectronegativity increase up and to the rightPolar molecules can be attracted by hydrogen bonds- Electrical attraction between the positively and negatively charged ends- Approximately 1/20th the strength of a covalent bond- Even weaker van der Waals bonds due to temporary polarizationCovalent bonds (non-polar and polar) - atoms sharing electrons- Often stronger, .ore “permanent”Bonds via electrical attraction - Hydrogen bonds, van der Waals bonds, etc.- Often weaker, more “temporary”Adhesion - polar water molecules are electrically attracted to ions, polar, and charged moleculesWater is a solvent: binds and suspends “hydrophilic” molecules (water-liking = polar orcharged)Life-enhancing properties of water:1. Adhesion to other molecules2. Polar water bind to polar wat - “cohesion”3. Water requires higher heat ot input to increase temperature (vibrate) than many othersubstances - high specific heat4. Greater spacing between water molecules when it is solid crystal (ice)a. So ice is less dense (weight per volume) than liquid waterb. So ice floats5. Water can ionizea. H2O can break into H+and OH-[x] = molar concentration of xpH = -log10[H+]pH 7 = neutral, equal [H+] and [OH-]pH > 7 = acidic, higher [H+]pH < 7 = basic, higher [OH+]Chemical bonds- Covalent bonds, both non-polar and polaar- Share electrons, equally or unequally- Ionic bonds- Electrical attraction between ions- Hydrogen bonds (and other similar bonds)- Electrical attraction of polar to polar or ionic molecules- van der Waals bonds- Electrical attraction between temporary polarization (dipoles)- Hydrophobic “bonds” – not really a bondHydrophobic interactions- Water would rather bind to water than sit next to hydrophobic (Water-fearing, unchargedor nonpolar) molecules- Maximize water / water interfaces, minimize water/hydrophobic interfaces- Pushes hydrophobic molecules together = hydrophobic “interaction”, acts like a kind ofbondCell membranes: partially hydrophobic- Membranes reduce diffusion of water, hydrophilic molecules- Allows concentration of some molecules and their chemical