Biochemistry 1

Amphipathic compounds

Dispersion of lipids in water; each lipid molecule forces surrounding H2O molecules to become highly ordered The number of ordered water molecules and therefore magnitude of entropy decreases, is proportional to the surface area of the hydrophobic solute amphipathic compounds contain regions that are polar (charged) and regions that are non-polar; when an ampipathic compound is mixed with water, the polar (hydrophilic) region interacts with the solvent and dissolves, by the non-polar hydrophobic region tends to avoid contact with the water Figure: long -chain fatty acids have very hydrophobic alkyl chains, each of which is surrounded by a layer of highly ordered water molecules. (b) By clustering together in micelles, the fatty acid molecules expose the smallest possible hydrophobic surface area to water and fewer water molecules are required in the shell of order water. the energy gained by freeing immobilized water molecules stabilizes the micelle;;;; the non-polar region cluster together to present the smallest hydrophobic area possible to the solvent; these stable structures are referred to as micelles; interactions that hold the non-polar regions together are referred to as hydrophobic interactions; results from achieve thermodynamic stability by minimizing the number of ordered water molecules required to surround hydrophobic portions -many proteins are amphipathic, as they have both polar and non-polar regions; stabilized through hydrophobic interactions among the non polar regions; important in determining structure of membranes;

Geometric Isomers

Geometric Isomers: maleic acid and fumaric acid cannot be interconverted without breaking covalent bonds, which requires the input of much more energy than the average kinetic energy of molecules at physiological temperatures **configurational isomers canon be interconverted without temporarily breaking one or more covalent bond geometric isomers: differ in the arrangement of their substituent groups with respect to the non rotating double bond

Weak acids and bases

HA (acid) <--> A- (base) + H+ Keq = [H+][A-] / [HA] pKa = -logKa

Hydrogen bonding in ice

In ice each water molecule forms four hydrogen bonds, the maximum possible for a water molecule, creating a regular crystal lattice. By contrast in liquid water at room temperature and atmospheric pressure, each water molecule hydrogen bonds with an average 3.4 other water molecules. This crystal lattice structure makes ice less dense than water, and thus ice floats on liquid water -breaking H bonds to destabilize a crystal lattice of ice requires much thermal energy, which accounts for the high melting point of water -during evaporation, the entropy (s) increases, as water molecules relax and hydrogen bonded becomes less ordered

Conformations

Many conformations of ethane (for example) are possible because of the freedom of rotation around c-c single bond. In the eclipsed conformation, the potential energy of the molecule rises to a maximum in the fully eclipsed conformation. In the staggered conformation, the potential energy of the molecules falls to a minimum. Because the energy differences are small enough to allow rapid interconversion, the eclipsed and staggered forms cannot be separately isolated.

Amphipathic compounds...

Micelles: all hydrophobic groups are sequestered from water; ordered shell or water molecules is minimized and entropy is further increased

Human Blood

Must be kept around a neutral pH of 7.4 acidosis; drop in pH alkalosis: increase in pH **changes in pH of blood can be fatal

The universal features of living cells

Nucleus: contains DNA and associated proteins Plasma Membrane: tough, flexible lipid bilayer. Selectively permeable to polar substances. Includes membrane proteins that function to transport, signal reception, and as enzymes Cytoplasm: Aqueous cell contents and suspended particles and organelles

L-Amino acids

Only L amino acids are constituents of proteins. For almost all amino acids, the L-isome has 5 (rather than R) absolute configurations

Sources of Energy and Sources of Carbon

Organisms are classified by how they obtain energy

Eukaryotic Cell - Plant

Plant Cell plasma membrane; mitochondrian; RER; nucleolus; nucleus; nuclear envelope; ribsome; SER; cytoskeleton; golgi; cell wall; gloxysome; plasmodesma; vacuole; cell wall; thylakoids; starch granule; chloroplast

Cellular Macromolecules

Polymers 1. Proteins 2. Nucleic Acids 3. Polysaccarides Monomer Units 1. small compounds 2. MW of 500 or less *synthesis is a major energy consuming activity of cells

RS System

R = clockwise S = counterclockwise -OCH3> OH> NH2> COOH> CHO> CH2OH> CH3>H For compounds with more than one chiral center, the most useful system of nomenclature is the RS system. In this system of nomenclature is the RS system. Each group attached to the carbon, is assigned a priority. If priority of the substituents is clockwise order, the configuration is R. If priority of the substituents is counterclockwise order, the configuration is S.

Prokaryotic Cell

Ribosomes: bacterial ribosomes are smaller than eukaryotic ribosomes, but serve the same function protein synthesis from an RNA message Nucleoid: contains a ingle, simple, long circular DNA molecule Pili: provide points of adhesion to surface of other cells Flagella: propel cell through its surroundings Cell envelope: structue varies with type of bacteria

Stereoisomer

Stereoisomers-molecules with the same chemical bonds but with different configuration

Phylogeny of life

The basis for this tree is the similarity in nucleate sequences of the ribosomal RNAs of each group; the more similar the sequence, the closer the location of the branches with the distance between branches representing the degree of difference between the two sequences. Pylogenetic tree can also be constructed from similarities across species of the amino acid sequences of a single protein

..Structure of water molecules

The dipolar nature of water is shown; there is nearly a tetrahedral arrangement of the outer-shell electron pairs around the oxygen atom; the 2 hydrogens have localized partial positive charges and the oxygen atom has a partial negative charge. two water molecules joined by a hydrogen bond between the oxygen atom of the upper molecule and a hydrogen atom of the lower atom (H bonds are longer and weaker than covalent OH bonds) -each H atom of a water molecule shares an e- pair with the central oxygen atom; oxygen is more electronegative (shared electrons are more in the vicinity of oxygen); results in 2 electric dipoles and each H bears a partial positive charge; there is an electrostatic attraction between the oxygen of one water molecule and the hydrogen of another, referred to as hydrogen bond.

Geometric Isomers.

The initial event in light detection is the absorption of visible light by 11-cis-retinal to all-trans-retinal; triggering electrical changes in the retinal ell that leads to a nerve impulse cis-trans isomers: differ in the arrangement of their substituent groups with respect to the non rotating double bond; cis (same) trans (across)

Water as Solvent

Water dissolved many crystalline salts by hydrating their component ions. The NaCL crystal lattice is disrupted as water molecules cluster about the Cl- and Na+ ions. The ionic charges are partially neutralized and the electrostatic attractions necessary for lattice formation are weakened Increase in entropy explains why salts such as NaCl can be easily dissolved in water; entropy (randomness) increases as crystalline substances (NaCl) dissolve

...Importance of Water

Weak interactions are key to molecular recognition; examples include enzyme-substrate, hormone-receptor, antibody-antigen the strength of these interactions are dependent on the medium (water) present

Molecular Asymmetry.

When a tetrahedral carbon has only three dissimilar group (same group occurs twice), only one configuration is possible and the molecule is symmetric or a chiral.

Geometry of Carbon Bonding

a. tetrahedral arrangement b. c-c single bonds have freedom of rotation c. double bonds are shorter and do not allow free rotation

Biologically important hydrogen bonds

alcohols, aldehydes, ketones, and compounds containing N-H bonds all form hydrogen bonds with water molecules and tend to be soluble in water

Ionization

although in the equilibrium we write H2O <--> H+ + OH- more accurately is is represented as H20 + H2O <--> H30+ + OH- **in this reaction, water is acting both as an acid and as a base -the ionization of water can be measured by its electrical conductivity; pure water carries electrical current as H3O+ migrates toward the cathode and OH- toward the anode. Kw = [H+][OH-] Kw = 1.0 x10e-14 (constant) 1.0 x10e-14 = [H+][OH-]

Cytoplasm

aqueous cell contents and suspended particles and organelles supernatant: cytosol concentrated solution of enzymes, RNA, monomeric subunits, metabolites, inorganic ions pellet: particles and organelles, ribosomes, storage granules, mitochondria, chloroplasts, lysosomes, endoplasmic reticulum

colligative properties

colligative properties: effects of solutes on all four properties (vapor pressure, boiling point, melting point, osmotic pressure) has the same basis: the concentration of water is lower in solutions than in pure water -solutes alter colligative properties of aqueous solution by lowering the effective concentration of water; solute concentration depends on the NUMBER of soute particles -water moves from a region of higher water concentration to now of lower water concentration

Three dimensional structure via configuration and conformation

configuration: fixed spatial arrangement of atoms conferred by the present of double bonds (1) or chiral centers (2) **configurational isomers canon be interconverted without temporarily breaking one or more covalent bond *stereoisomers are molecules with the same chemical bonds but different configurations (fixed spatial arrangement of atoms) *interactions between biomolecules are invariably stereospecific, requiring specific configuration in the interacting molecules Conformation: variable spatial arrangement due to freedom of rotation about single bonds (spatial arrangement of substituent groups that without breaking any bonds are free to assume different positions in space because of the freedom of rotation about single bonds)

Electrostatic Interactions

depends on the electrical charge on atoms Energy=kq1q2/Dr q1/q2=atom charges r=distance between atoms D=constant of the medium k=constant 332

Structural Hierarchy

level 4: the cell and its organelles level 3: supramolecular complexes level 2: macromolecules level 1: monomeric units

Amphipathic compounds.

long chain fatty acids have very hydrophobic alkyl chains, each of which is surrounded by a layer of highly ordered water molecules hydorphobic interactions: strength of such interactions is due to achieving thermodynamic stability by minimizing the number of ordered water molecules required to surround hydrophobic portions of solute molecules

Ionization of water

pH = -log[H+]

pOH

pOH = -loh[OH-] pH + pOH = 14

pH optima of some enzymes

pepsin is a digestive enzyme secreted into gastric juice, which has a pH of -1.5, allowing pepsin to act optimally. trypsin a digestive enzyme that acts in the small intestine has a pH optimum that matches the neutral pH in the lumen of the small intestine. Alkaline phosphatase of bone tissue is a hydrolytic enzyme thought to aid in bone mineralization pH optimum: enzymes show maximal catalytic activity at a characteristic pH EX: trypsin red pH optimum of 6

...Polar/ Nonpolar/ Amphipathic

polar - glucose, glycine, aspartate, lactate, glycerol nonpolar - typical wax amphipathic (compounds that contain regions that are polar/charged and regions that are non polar)- phenylalanine, phosphatidylcholaine

Polyfunctionality

several common functional groups within a single biomolecule

Henderson-Hasselbalch Equation

shape of the titration curve of any weak acid is described by the HH equation, which is important for understanding buffer action and acid-base balance in the blood and tissue of vertebrates

conjugate acid and base pairs

some compounds give up only one proton. others are diuretic or triprotic. The dissociation reactions for each pair are shown where they occur along a pH gradient. The equilibrium or dissociation constant Ka and its neg log, the pKa are shown for each reaction. -acids may be defined as proton donors and bases as proton acceptors. a proton donor and its corresponding proton acceptor make up a conjugate acid-base pair. CH3COOH (proton donor) and CH3COO- (proton acceptor) constitute a conjugate acid-base pair CH3COOH <--> CH3COO- + H+ -each acid has a tendency to lose its proton in an aqueous solution; the stronger the acid, the greater its tendency to lose its proton HA (acid) <--> A- (base) + H+ Keq = [H+][A-] / [HA] **acid dissociation constants; equilibrium constants for ionization reactions pKa = -logKa *the stronger the tendency to dissociate a proton, the strong the acid and the LOWER its pKA; low pKa correlates with a strong acid pKa is pH?

Complementary fit between a macromolecule and a small molecule

the amino acid fits into a pocket on the RNA surface and is held in this orientation by several non covalent interactions with the RNA.

Directionality of the hydrogen bond

the attraction between the partial electrical charges is greatest when the three atoms involved in the bond (OHO) lie is a straight line (maximizes electrostatic interactions; positive charge is directly between the negative charges). When the hydrogen bonded moieties are constrained (bent), the result is a weaker hydrogen bond

water binding in hemoglobin

the crystal structure of hemoglobin shown (a) with bound water molecules (red) and without water molecules (b). The water molecules are so firmly bound to the protein that they affect the x-ray diffraction pattern as though they were fixed parts of the crystal. the two alpha subunits of hemoglobin are shown in grey. The two beta subunits are in blue. -water so tightly bound that they are a part of the structure; tightly bound water is essential to the function of hemoglobin;

...Propertites of water

the heat energy required to convert 1.0 g of a liquid at its boiling point and at atmospheric pressure into its gaseous state at the same temperature; it is a direct measure of the nervy required to overcome the attractive forces between molecules in the liquid phase

...Common hydrogen bonds in biological systems

the hydrogen acceptor is usually oxygen or nitrogen; the hydrogen donor is another electronegative atom -readily form with electronegative atoms -hydrogen atoms bonded to carbon atoms do not participate in hydrogen bonding because carbon is only slightly more electronegative

comparison of titration curves of three weak acids

the predominant ionic forms at the disginated points in the titration are given in boxes. the grions of buffering capacity are indicated at the right. conjugate acid-base pairs are effective buffers between approximately 10%-90% neutralization of proton-donor species *blue is the strongest acid

Representation of molecules

three ways to represent the structure of amino acids

water chain in cytochrome

water is bound in a protein channel of the membrane protein cytochrome f. Five water molecules are hydrogen-bonded to each other and to functional groups of the protein. Electron flow is coupled to the movement of protons across the membrane, which involved proton hopping through this chain of bound water molecules. -EX of role water plays in pathways

Ionization of pure, distilled water

water molecules have a slight tendency to undergo reversible ionization to yield a hydrogen ion (proton) and hydroxide ion H2O <--> H+ + OH- Equilibrium Constant, Keq, is the position of equilibrium of any given chemical reaction Keq = [H+][OH-] / [H2O]

release of ordered water favors formation of an enzyme substrate complex

while separate, both enzymes and substrate force neighboring water molecules into an ordered shell. Binding of substrate to enzyme releases some of the ordered water, and the resulting increase in entropy provides a thermodynamic push toward formation of the enzyme substrate complex --disordered water displaced by substrate-enyme interaction; interactions stabilized by hydrogen bonding and hydrophobic interactions

Osmosis and the measurement of osmotic pressure

(a) initial state. the tube contains an aqueous solution, the beaker contains pure water, and the semipermeable membrane allows the passage of water but not solute. Water flows from the beaker into the tube and equalize its concentration across the membrane (water molecules diffuse from the region of higher water concentration to the region of lower water concentration); osmosis is the water movement across a semipermeable membrane driven by differences in osmotic pressure (b) final state. water has moved into the solution of the non permeant compound, diluting it and raising the column of water within the tube. at euiblirum, the force of gravity operating on the solution in the tube exactly balances the tendency of water to move into the tube, where its concentration is lower (c) osmotic pressure is measured as the force that must be applied to rerun the solution in the tube to the level of that in the beaker. This force is proportional to the height.

Summary 2.3 Buffering against pH changes in biological systems

-a mixture of weak acid (or base) and its salt resists changes in pH caused by the addition of H+ or Oh-. the mixture functions as a buffer -the pH of a solution of a weak acid of base and its salt is given by HH equation pH = pKa + log [a]/[ha] -in cells and tizzies, phosphate and bicarbonate buffer systems maintain intracellular and extracellular fluids at their optimum pH, which is close to pH 7. enzymes generally work optimally at this pH. -medical conditions that lower the pH of blood, causing acidosis, or raise it, causing alkalosis, can be life threatening -water is both the solvent in which metabolic reactions occur and a reactant in many biochemical processes, including hydrolysis, condensation, and oxidation-reduction reactions

1.1 Cellular Foundations

-all cells are bounded by a plasma membrane; have a cytosol containing metabolites, coenzymes, inorganic ions, enzymes, and have a set of genes contained within a nucleoid (bacteria and narchaea) or nucleus (eukaryotes) -phototrophs use sunlight to do work; chemotrophs oxidize fuels, passing electrons to good electron acceptors, inorganic compounds, organic compounds or molecular oxygen -bacterial and arc heal cells contain cytosol, a nucleoid, and plasmids. Eukaryotic cells have a nucleus and are multicompartmented with certain processes serrated in specific organelles; organelles can be separated and studied in isolation -cytoskeletal proteins assemble into long filaments that give cells shape and rigidity and serve as rails along which cellular organelles move throughout the cell

2.3 Buffers

-almost all biological processes are pH dependent; small changes in pH can produce big changes *buffers are aqueous systems that tend to resist changes in pH when small amounts of acid (H+) or base (OH-) are added. A buffer system consists of a weak acid (the pronton donor) and its conjugate base (proton acceptor) -buffering region: pH changes least with the addition of H or OH HENDERSON HASSELBALCH EQUATION pH = pKa + log [A-]/[HA]

...Soulubilities of some gases in water

-arrows represent electrical dipoles; there is a partial negative charge at the head of the arrow and a partial positive at the tail *polar molecules dissolve far better evan at low temperatures than do non polar molecules at relatively high temperatures

Formation of enzyme substrate complex

-driving force for binding of a polar substrate to polar enzyme is the entropy increases, as the enzyme displaces ordered water from the substrate -ordered water interacting with substrate and enzyme

..Hydrogen Bonds

-hydrogen bonds are relatively weak interactions with a bond dissociation energy of 23 kj/mol in liquid water -the hydrogen bond is predominately electrostatic interaction -the lifetime of each hydrogen bond is just 1-20 picoseconds. Hence bonds rapidly flicker in and out of existent -in liquid water, each molecule forms hydrogen bonds with an average of 3.4 other molecules -hydrogen bonds between molecules provides cohesive forces that make water a liquid at room temperature and favor strict order typical of crystals.

Prokaryotic Cells

-invariably unicellular -have relatively simple anatomies -approximate size range 1-2 um -are the most numerous and widespread organisms -constitute about half of the earth's biomass

Equilibrium constant

-like all reversible reactions, the ionization of water can be described by an equilibrium constant; when weak acid are dissolved in water, the contribute H+ by ionizing; weak bases consume H+ by becoming protonated; the total hydrogen ion concentration is measurable as the pH of the solution the position of equilibrium of any chemical reaction is given by its equilibrium constant Keq A + B <--> C + D Keq = [C][D]/[A][B} *equilibrium constant can also be defined in terms of the concentrations of the reactants (AB) and products (CD) -Keq is fixed for any given chemical reaction at a specific temperature

weak interactions are crucial to macromolecule structure and function

-noncovalent interactions, such as hydrogen bonds, ionic, hydrophobic, and van der waals are all much weaker than covalent bonds. -can calculate the stability of non-covalent interactions -stability is measured by the equilibrium constant (varies exponentially with binding energy?) -macromolecules and proteins contain numerous sites for hydrogen binding, ionic, van der waals, and hydrophobic interactions; cumulative effect go many small binding forces can be enormous. -EX: for macromolecules, the most stable structure is that in which weak interactions are maximized; chain folds upon itself into a three dimensional shape utilizing weak interactions

Summary 2.2 Ionization of water, weal acids, and weak bases

-pure water ionizes slightly, forming equal numbers of hydrogen ions and hydroxide ions. The extent of ionization is described by an equilibrium constant Keq = [H+][OH-] / [H2O] Kw = [H+][OH-] = 10e-14 -the pH of an aqueous solution follows pH = -log[H+] -the greater the acidity of a solution, the lower its pH. Weak acids partially ionize to release a hydrogen ion, thus lowering the pH of the aqueous solution. Weak bases accept a hydrogen ion, increasing the pH. The extent of these processes is characteristic of each weak acid or base as Keq = [H+][A-]/[HA] = Ka pKa = -logKa -the stronger the acid, the lower its pKA. the stronger the basem the higher its pKa. The pKa can be determine experimentally. pKa is the pH at the midpoint of the titration curve for the acid or base.

3. Hydrogen bonds

-relatively weak interactions that are responsible for many of the properties of water -H atom is partially shared between two electronegative atoms, O and N -H bond donor: the atom the hydrogen is most tightly associated with HH bond acceptor: atom that is less tightly linked to the hydrogen -The electronegative atom to which the H bond is covalently bonded pulls e- away from the H atom, giving H a partial positive charge. the H atom can then interact with an atom with a partial negative charge

4. Van der Waals

-the distribution of electronic charge around an atom changes with time -charge distribution is transiently asymmetric and acts via electrostatic interactions to induce asymmetry of neighboring atoms -the attraction between two atoms increases as they come closer to each other until they are separated by the van der waals contact distance -when two uncharged atoms are brought together, their surrounding electron clouds influence each other; may create a dipole; the two dipoles weakly attract each other bringing the two nuclei closer, known as van der waals interactions; as the two nuclei draw closer together, their electron clouds begin to repel each other

pH

-the ion product of water, Kw, is the basis for the pH scale. pH is the concentration of H+ pH = -log [H+] [H] = 10e-9 pH = 9 *7 is neutral pH; human blood

Biochemistry

-the study of the chemical processes/reactions that occur within living organisms -the chemistry of life

Summary 2.1 Weak Interactions in Aqueous Systems

-the very different electronegativities of H and O make water a highly polar molecule capable of forming hydrogen bonds with itself and with solutes; H bonds weaker than covalent bonds; water is a good solvent for polar (hydrophilic) solutes, as it interacts electrosterically -Nonpolar (hydrophobic) compounds dissolve poorly in water, as they cannot H-bond with the solvent; to minimize surface that is exposed to water, non polar compounds such as lipids form micelles, in which hydrophobic regions are in the interior (associated with hydrophobic interactions) and polar regions interact with water -weak, noncovalent interactions, influence folding of macromolecules such as proteins. the most stable macromolecular conformation are those in which hydrogen bonding is maximized within the molecule and between the molecule and the solvent; **folding upon themselves -the physical properties of aqueous solutions are strongly influenced by the concentrations of solutes. when two aqueous compartments are separated by a semipermeable membrane, water moves across that membrane to equalize the osmolarity in the two compartments. this tendency for water to move across a semipermeable membrane is he osmotic pressure.

Eukaryotic Cells

-unicellular or multicellular -vastly more complex than prokaryotes -approximate size range 10-100 um -profusion of membrane enclosed organelles

Water..

-water (which is a polar solvent) is an excellent solvent for polar molecules; likes dissolve like; such as hydrophilic compounds (water-loving); conversely, non polar or hydrophobic solvents are poor solvents. -water weakens electrostatic forces and hydrogen bonds between polar molecules by competing for their interactions; EX: water dissolves NaCL by hydrating and stabilizing Na+ and Cl-, weakening the electrostatic interactions between them. -H atoms of water replaces the amide H atom as the bond donor -O atom of water can replace the carbonyl oxygen at the H bond acceptor A strong H bond between C group and the NH group forms only if water is excluded water weakens electrostatic interactions by forming oriented solvent shells

Water

-weak interactions in aqueous systems -ionization of water, weak acids, and weak bases -buffering against pH changes in biological systems -water as a reactant -the fitness of the aqueous environment for living organisms

[H+][OH-]

-when there are exactly equal concentrations of H+ and OH- in pure water, the solution is at NEUTRAL PH [H+] = [OH-] = 10e-7

Elements

1. Bulk elements (H, NA, K, Ca, C, N, O, P, S, Cl) 2. Trace Elements (Mg, V, CR, Mn, Fe, Co, Zn, Mo, Se, I) 3. Most abundant (H, O, M, and C)*99% of the cellular mass

Chemical Bonds in Biochemistry

1. Covalent bonds 2. Electrostatic Interactions 3. van der waals interactions 4. hydrogen bonds 5. hydrophobic interactions 1. Covalent bonds

What are the characteristics of life?

1. a high degree of chemical complexity and microscopic organization 2. systems for extracting, transforming, and using energy from the environment 3. capacity for precise self-replication and self-assembly 4. mechanisms for adapting to the environment

...Water.

1. water is polar; bent, asymmetric charge distribution 2. water is highly cohesive; water molecules react with each other via hydrogen bonds 3. the entropy of water sometimes contributes to what you might think are unexpected properties of biological systems entropy S = correlates to exert of disorder; an increase in disorder correlates with an increase in entropy -water has a higher melting point, boiling point, and heat of vaporization than most other common solvents

Biological Diversity

All organisms are based on same morphological units and share common chemical features

Eukaryotic Cell

Animal Cell ribosomes; peroxisome; cytoskeleton; lysosom; transport vesicles; golgi complex; SER; RER; nucleus; nucleolus; RER; mitochondria; plasma membrane; nuclear envelope

Buffering Systems

CO2 in the air space of the lungs is in equilibrium with the bicarbonate buffer in the blood plasma passing through the lung capillaries. because the concentration of dissolved CO2 can be adjusted rapidly through changes in the rate of breathing, the bicarbonate buffer system of the blood is in near equilibrium with a large potential reservoir of CO2 -bicarbonate buffer system is an effective physiological buffer near 7.4, because the H2CO3 of blood plasma is in equilibrium with a large reserve capacity of CO2 in the air space of the lungs.

Osmolarity

Cell in hypertonic solution, water moves out and cell shrinks; hypertonic solution has higher osmolarity (water concentration) than the cytosol, therefore the cell shrinks and water moves out of the cell Cell in hypotonic solution; water moves in creating outward pressure, cell swells, and may eventually burst; in a hypotonic solution, which has a lower osmolarity than the cytosol, the cell swells as water enters. Possible osmotic lysis EX: prevented in plants via rigid cell walls; EX: in humans, blood plamsa osmolairty is close to that of cytosol to prevent osmotic lysis (buffers can also prevent) solutions of osmolarity equal to that of the cytosol are said to be isotonic; in equilibrium. when a cell in osmotic balance with its surrounding medium = isotonic medium is transferred (b) into a hypertonic solution or (c) a hypotonic solution, water moves across the plasma membrane in the direction that tends to equalize osmolarity outside and inside the cell --effect of solutes on osmolarity depends on the number of dissolved particles

Macromolecules

Charged and Hydrophobic

Molecular Asymmetry

Chiral molecules: a carbon atom with four different substituents is said to be asymmetric and asymmetric carbons are called chiral centers *a molecule with only one chiral carbon can have two stereoisomers when 2 or more chiral carbons are present *when a carbon atom has 4 different substituent groups (A, B, X, Y) they can be arranged in two ways that represent nonsuperosable mirror images of each other (enantiomers); the asymmetric carbon atom is called a chiral atom or chiral center

Amphipathic compounds..

Clusters of lipid molecules: only lipid portions at the edge of the cluster force the ordering of water. Fewer water molecules are ordered and entropy is increased