BCHM Exam I- The lower limit for a cell’s dimensions is the minimum number of biomolecules necessary for survival- The upper limit for a cells’ dimensions is set by the rate of diffusion of solute molecules in aqueous solutionso The rate of diffusion would limit how far away from the surface a reaction that requires oxygen can occur and would define the maximum size- Phototrophs gain energy from sunlighto Autotrophs use carbon from carbon dioxideo Heterotrophs use carbon from inorganic compounds- Chemotrophs gain energy from oxidation of chemical fuelso Organotrophs use organic fuelso Lithotrophs use inorganic fuels- The bond angle between carbon and 4 other atoms is 109.5 degreeso The lightest atoms form the strongest bonds- Living organisms live in a dynamic steady state- System- anything within a defined region of spaceo Universe=system+surroundingso Isolated system- does not exchange matter or energy with its surroundingso Closed system- only exchanges energy with its surroundingso Open system- exchanges energy and matter with its surroundings Ex: is living organisms- 1st Law of Thermodynamics states that for every physical/chemical reaction, the total amount of energy in the universe remains constant- 2nd Law of Thermodynamics states that the total entropy of the universe is always increasing- Entropy (S)- randomness or disorder in a chemical system- Enthalpy (H)- reflects the number and kinds of bonds being broken and formed in a chemical systemo Making bonds, Delta H<0o Breaking bonds, Delta H>0- Free energy is the amount of energy available to do work- Delta G<0: reaction is spontaneous and releases energy- Delta G>0: reaction is non-spontaneous and requires the input of energyo A non-spontaneous reaction will proceed in the reverse direction spontaneously- Endergonic- requires energy to be carried out- Exergonic- reaction releases free energyo exergonic refers to negative free energy change, while exothermic refers to a release of heat- Chemical reactions proceed spontaneously until equilibrium is reached- Exergonic reactions drive Endergonic reactions when coupled together- Hydrogen Bonds: are electronegative interactions between hydrogen and an atom of a much higher electronegativityo 10% covalent (overlapping); 90% electrostatico Lifetime of hydrogen bond is 1-20 picosecondso A single water molecule can form up to 4 hydrogen bonds due to its near tetrahedral shape (104.5 bond angle)o Hydrogen bonds are strongest when atoms are in a straight line- Hydrogen bonds between water molecules make water liquid at room temperature; they give water great internal cohesion- Polar molecules dissolve in water because they replace the water-water bonds with more favorable water-solute bonds- Non-polar molecules interfere with water-water bondso In aqueous solutions, non-polar molecules cluster together and form micelleso the ordering of water molecules around the hydrophobic portions of amphipathic molecules result in a driving force, called the hydrophobic effect, that causes the clustering of these groups together, resulting in structures such as micelles- Water dissolves salts and charged molecules by weakening their electrostatic interactions,thus, counteracting their tendency to form together- Non-polar gases are poorly soluble in water; they create a decrease in total entropyo All molecules in solution interfere with hydrogen bonding, but polar-charged molecules compensate by forming new water-solute bonds- Van der Waals Interactions- occur when 2 uncharged atoms are brought together because their 2 dipoles are weakly attracted to one anothero As their 2 nuclei draw closer, the electron clouds repel each other- Hydrogen bonds, ionic bonds and hydrophobic interactions are much weaker than covalent bonds because they are constantly breaking and re-forming; this contributes to a net decrease in entropyo For macromolecules, most stable structure is that in which weak interactions are maximizedo Hydrophobic interactions between non-polar amino acids stabilize 3-D protein structureo Hydrophobic interactions energetically contribute to: Bind hormones to receptor proteins Enzyme-substrate interactions Membrane structure 3D folding of proteins- Colligative Properties- are properties of solutions that depend on the number of molecules in a given volume of solvent and not on the properties/identity of the given moleculeso **dissolved solutes alter the properties of the solvent by changing the concentration of watero Vapor pressureo Boiling & melting pointo Osmotic pressure- Osmosis- water movement across a semi-permeable membraneo Isotonic solution- osmolarity of solution is equal to osmolarity of cell’s cytosol Cell neither gains nor loses watero Hypertonic solution- osmolarity of solution is greater than osmolarity of cell’s cytosol Cell shrinks as water moves out of cello Hypotonic solution- osmolarity of solution is less than osmolarity of cell’s cytosol Cell swells as water enters cello Storing fuel as polysaccharides rather than monosaccharides avoids an enormous increase in osmotic pressure- Proton-Hopping- the continuous release of a proton and it being picked up by a water molecule to form hydronium- Weak acids do not completely ionize in watero Acids are proton donors; bases are proton acceptorso The stronger the acid, the greater its tendency to release its proton and the lower its pka value- ADP + P  ATP + H2O is a condensation reaction- ATP  ADP + P is a hydrolysis reaction catalyzed by hydroxylaseso An Exergonic reaction; increases entropy by producing 2 molecules from 1- Amino acids are covalently joined through a peptide bond to form a di-peptideo Linkage is formed by the removal of elements of water from alpha carboxyl group and alpha amino groupo It should be noted that the joining of amino acids to form peptide bonds eliminates the acid and basic character of the molecules. The only ionized groups in the finished protein will be the terminal amino and carboxyl groups and also any R groups that happen to contain acidic or basic groups.o Di-sulfide bonds play a special role in protein structure by forming covalent linkages between polypeptide chains- 20 basic amino acids that each have a carboxyl group, amino group, R-group and a hydrogen all bonded to a central alpha carbono Non-polar: alanine, valine, glycine, proline, methionine, leucine, isoleucine o Aromatic: phenylalanine, tyrosine, tryptophano Polar: serine,