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MCB3208Ch2 - MCB32F08 Chapter#2: Outline...

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MCB 32 F08 Chapter #2: Important Molecules in Physiology Outline Water, H 2 O: polar covalent bonds, hydrogen bonds Ions: cations and anions, extracellular and intracellular concentrations and electroneutrality Acids, bases, pH Gases: O 2 and CO 2 , partial pressures Carbohydrates: monosaccharides and polysaccharides; energy storage Amino acids, peptides and proteins: molecular functions, primary, secondary, tertiary and quaternary structure Lipids and fats; energy storage and cell membranes Nucleic acids: DNA and RNA and genetic code Water Most important molecule in biology. Covalent bonds (shared electrons between atoms) lead to molecule that overall has no charge. Because the electrons are unequally shared between O and H, the H 2 O molecule is polar , leading to association between water molecules, called hydrogen bond . Weak bond, but many of these bonds can add up to be quite strong. Example : water bonds to itself, leading to surface tension. Examples: water drop between two slides; meniscus. This surface tension is one of the most important forces that is overcome during breathing. Surface tension is reduced by the presence of a soap-like molecule called surfactant, so that the effort of breathing is reduced to a manageable level. Surface tension arises because the forces among water molecules are unopposed at the surface, leading to unopposed tension or forces of attraction among the water molecules. Example: water drop between two slides; meniscus Ions and other molecules that dissolve easily in water are hydrophilic . Molecules that are uncharged and nonpolar (equal sharing of the electrons among the atoms of the molecule) are often insoluble in water and are therefore hydrophobic . Such hydrophobic molecules often are soluble in non-aequeous solvents like acetone or benzene or alcohol. Body water Intracellular 2/3 of body water (total body water = 65-75% of total body weight) Extracellular 1/3 of body water) Interstitial : fluid in space between cells in the body; tissue fluid Plasma : cell-free fluid of blood 1
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Ions Charged because they either take on or lose electrons, leading to unequal numbers of protons and electrons and a net charge. Form ionic bonds, through charged interactions. Ions dissolve in water (with equal numbers of positive and negative charges, overall electroneutrality ), with water surrounding the ions. Cations like Na + , K + , Ca 2+ and Mg 2+ are positively charged. Anions like Cl - and HCO 3 - are negatively charged. Concentrations of ions usually given in physiology in moles/l (M) or millimoles/l (mM or 10 -3 M). Normal concentrations of ions in the extracellular and intracellular space in mM: 150 mM NaCl added to water yields 150 mM Na + and 150 mM Cl - Extracellular Intracellular Na + 150 15 K + 5 120 Ca 2+ 1 0.0001 Mg 2+ 1 1 Cl - 125 25 HCO 3 - 25 15 Acids, Bases One of the most important ions is the proton, H +
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