EVPP 110 Lecture
Dr. Largen - Fall 2002

Matter & Energy:
Thermodynamics, Enzymes, Membranes, Diffusion

• Energy
• the capacity to do work
• to move matter in a direction it would no move if left alone
• all organisms require energy to stay alive
• energy exists in two states
• kinetic energy
• potential energy

• Energy exists in two states
• kinetic energy
• the energy of motion
• moving objects perform work by causing matter to move
• potential energy
• stored energy
• objects that are not actively moving but have the capacity to do so possess energy

• Energy exists in two states
• potential energy vs kinetic energy
• a boulder perched on a hilltop has potential energy
• as it begins to roll down the hill some of the energy is converted into kinetic energy
• much of the work that living organisms carry out is involves transforming potential energy to kinetic energy

• energy exists in many forms
• mechanical energy
• heat
• sound
• electric current
• light
• radioactive radiation
• chemical energy
• the potential energy of molecules
• most important type of energy for living organisms

• there are many ways to measure energy
• most convenient way to measure energy is in the form of heat
• =a measure of the random motion of molecules
• because all other forms of energy can be converted into heat

• Life depends on the fact that energy can be converted from one form to another
• thermodynamics
• the study of energy transformations that occur in a collection of matter
• Laws of Thermodynamics
• a set of universal laws that govern all energy changes in the universe
• from nuclear reactions to buzzing of a bee

• First Law of Thermodynamics
• concerns the amount of energy in the universe
• states that energy can be changed from one form to another but can neither be created or destroyed
• total amount of energy in the universe remains constant

• First Law of Thermodynamics
• in any living system, potential energy can be shifted to other molecules, stored in different chemical bonds, convert into other forms
• during each conversion some of the energy dissipates into the environment in the form of heat
• although amount of energy in universe remains constant, energy available to do work decreases as progressively more of it dissipates as heat

• Second Law of Thermodynamics
• concerns the transformation of potential energy into heat, or random molecular motion
• states that the disorder (or entropy) in the universe is continuously increasing; disorder is more likely than order
• entropy is a measure of the disorder of a system
• heat is one form of disorder

• Second Law of Thermodynamics
• entropy increases
• when universe was formed 10-20 billion years ago it had all the potential energy it will ever have
• has become more disordered ever since
• every energy exchange has increased the amount of entropy in the universe
• more likely that a column of bricks will tumble over than spontaneously arrange themselves to form a column

• Chemical reactions, including those within cells, are of two types
• endergonic reactions
• "energy in"
• require a net input of energy
• exergonic reactions
• "energy out"
• release energy

• endergonic reactions
• yield products rich in potential energy
• start with reactants molecules that have little potential energy
• absorb energy from the surroundings as the reaction occurs
• such that the products store more energy that the reactants did
• don’t proceed spontaneously
• requires input of energy
• example is photosynthesis

• exergonic reactions
• reactants store more energy than products
• energy is released to the surroundings as reaction proceeds
• tend to proceed spontaneously
• does not require an input of energy
• example is cellular respiration
• the energy-releasing breakdown of glucose molecules
• storage of energy in a form the cell can use to perform work

• Cellular metabolism
• the sum of the exergonic and endergonic reactions carried out by working cells

• ATP (adenosine triphosphate)
• has 3 parts, connected by covalent bonds
• adenine = a nitrogenous base
• ribose = a 5-carbon sugar
• phosphate groups = a chain of 3 phosphate groups

• The ATP cycle (ATP is renewable resource)
• hydrolysis of ATP to ADP + P
• removes a phosphate
• is an exergonic reaction
• releases energy for endergonic reactions
• dehydration synthesis of ADP + P to ATP
• adds a phosphate
• is an endergonic reaction
• that requires energy from exergonic reactions

• Energy of activation (E_A)
• the amount of energy that reactants must absorb to start a chemical reaction
• can be thought of as an energy barrier
• since most reactions require energy to get started
• ATP and other vital molecules in our cells do not break down spontaneously

• Energy of activation (E_A)
• illustrated with "jumping bean" (JB) analogy
• JBs in left side of container represent reactants of a chemical reaction that must have enough energy to jump over the "energy barrier" to make it to product side
• beans vary in amount of energy they have
• may take a very long time for a significant number of "reactant" beans to get over barrier to become "product" beans
• and reaction may take too long to be of any use to cell

• solution for speeding up a reaction lies in enzymes
• protein molecules that serve as biological catalysts
• increase the rate of a reaction without being changed into a different molecule
• does not add energy to a cellular reaction
• speeds up reaction be lowering the Energy of activation (E_A), or energy barrier
• without enzymes, many reactions would occur too slowly to sustain life

• In jumping bean analogy, an enzyme would lower the partition between containers, or lower the energy barrier
• making it possible for beans with less energy to clear the barrier
• resulting in more beans being able to clear the barrier in a given amount of time
• leading to the speeding up of the reaction

• enzymes
• can lower E_A by holding reactant molecules in a particular position
• are selective in which reactions they catalyze
• have a unique 3-dimensional shape (since it’s a protein) that determines specificity
• recognize only the substrate(s) of the reaction it catalyzes
• substrate is substance enzyme acts on

• catalyzing a reaction
• enzyme binds to its substrate
• only at small part of enzyme, its active site
• a pocket or groove on surface of enzyme
• enzyme is specific because its active site fits only one substrate molecule
• while joined, substrate changes into product
• enzyme releases the products
• enzyme emerges from the reaction unchanged

• enzyme emerges from the reaction unchanged
• its active site now ready for another substrate molecule and another cycle
• a single enzyme molecule may act upon thousands or millions of substrate molecules per second

• Activity of an enzyme is affected by its environment
• for each enzyme, there are conditions under which it is most effective
• any chemical or physical factor that alters an enzyme’s three-dimensional shape can affect its ability to catalyze a reaction

• Factors affecting enzyme activity
• temperature
• pH
• salinity

• Factors affecting enzyme activity
• temperature
• at optimum temperatures (35-40°C)
• highest rate of contact occurs between enzyme’s reactive site and substrate
• because temperature affects molecule motion
• at high temperatures
• enzyme can be denatured, lose its 3-dimensional shape, and lose its function

• Factors affecting enzyme activity
• pH and salinity
• cause variations in number of salt and hydrogen ions
• that can interfere with some of the chemical bonds that maintain protein structure
• optimum pH = 6-8
• optimum salinity = cell salinity

• Factors affecting enzyme activity
• presence of non-protein helpers called cofactors
• required by some enzymes
• cofactors
• may be inorganic molecules, called cofactors
• such as zinc, iron, copper
• may be organic molecules, called coenzymes
• such as vitamins or vitamin products

• A chemical that interferes with an enzyme’s activity is called an inhibitor
• two types of inhibitors
• competitive inhibitor
• non-competitive inhibitor

• competitive inhibitor
• resembles enzyme’s normal substrate
• competes with substrate for enzyme’s active site
• when bound to active site it prevents enzyme from acting

• non-competitive inhibitor
• does not compete with active site
• binds to enzyme outside of active site
• binding causes shape of enzyme to change
• such that active site no longer fits substrate

• Many metabolic reactions occur simultaneously in a cell
• chaos would result if cell were not highly organized and able to time reactions precisely
• teams of enzymes function like assembly lines
• right enzymes have to be in right place at right time
• Membranes provide the structural basis for metabolic order

• For all types of cells
• the plasma membrane is the edge of life
• forming the boundary between living cell and its surroundings
• For most eukaryotic cells
• membranes form
• most organelles
• compartments within cells that contain enzymes

• All membranes are selectively permeable
• control passage of molecules into and out of cell (or organelle)
• takes up substances needed by cell
• disposes of cell waste
• allows some substances to cross more easily
• blocks passage of some substances entirely

• Plasma membrane (cell membrane)
• very thin
• 20 times too small to be seen by light microscope
• can be seen by electron microscope
• shows up as three zones
• much knowledge of plasma membranes come from study of red blood cells
• obtaining plasma membrane from "ghosts"
• split and emptied red blood cells

• Plasma membrane (cell membrane) is composed mainly of phospholipids
• phospholipid molecule has two parts, which interact oppositely with water
• "head"
• glycerol and phosphate group
• polar = hydrophilic
• " tail"
• two fatty acid tails
• non-polar = hydrophobic

• Structure of phospholipids is suited to their role in membranes
• in water, they spontaneously form a stable two-layer sheet, a phospholipid bilayer
• hydrophilic (polar) heads face outwards towards the water
• hydrophobic tails point inward, shielded from the water
• this is the arrangement of membrane phospholipids in aqueous environment living organisms

• membranes are selectively permeable
• partly due to hydrophobic interior of the bilayer
• nonpolar, hydrophobic molecules are soluble in lipids
• can easily pass through membranes
• polar, hydrophilic molecules are not soluble in lipids
• passage of polar molecules is dependent on protein molecules within the phospholipid bilayer

• Structure of plasma membrane is described as a fluid mosaic
• mosaic = surface made of small fragments
• membrane has diverse protein molecules embedded w/in framework of phospholipids
• fluid = moveable
• most of the protein and phospholipid molecules can drift laterally w/in membrane
• "kinked" tails of fatty acids keeps phospholipids from packing tightly together, helps maintain fluidity

• The two surfaces of the plasma membrane are different
• outer surface (exterior of cell)
• has carbohydrates covalently bonded to proteins and lipids in the membrane
• glycoproteins, glycolipids
• inner surface (interior of cell)
• has microfilaments of cytoskeleton, proteins

• Diffusion
• the tendency for particles of any kind to spread out spontaneously to regions where they are less concentrated
• it requires no work, results from
• random motion (kinetic energy)
• universal tendency of order to deteriorate into disorder (entropy)
• diffusion of molecules across a biological membrane is called passive transport
• since it requires no work

• passive transport
• concentration affects the direction in which a substance diffuses across a membrane
• substance moves from area of higher concentration to area of lower concentration until equilibrium is reached
• a substances diffuses down its concentration gradient
• at equilibrium, there is no net change in concentration on either side of membrane

• Passive transport
• different substances diffuse independently of one another
• each down its own concentration gradient
• is extremely important to all cells
• oxygen passes from lungs into red blood cells
• carbon dioxide passes from red blood cells into lungs

• Osmosis
• is a special case of passive transport involving diffusion of water molecules across a selectively permeable membrane
• water molecules move down their concentration gradient
• plays role because cells contain and are surrounded by aqueous solution
• solution contains solutes
• solutes also diffuse down their concentration gradient

• Osmosis
• the aqueous solution on either side of the membrane can be described on the basis of the concentrations of their solutes
• solution with higher concentration of solutes is said to be hypertonic
• solution with lower concentration of solutes is said to be hypotonic
• when solutions on both sides of membrane have same concentration of solutes, they’re said to be isotonic

• Osmosis
• as solutes diffuse
• from the hypertonic solution (area of higher concentration) across the membrane into the hypotonic solution (area of lower concentration)
• water molecules will move via osmosis
• from hypotonic solution (area of higher concentration of water molecules) across the membrane into the hypertonic solution (area of lower concentration of water molecules)

• If an animal cell is immersed in
• an isotonic solution
• cell’s volume remains constant
• gains water at same rate it loses it
• a hypotonic solution (lower solute conc than cell)
• cell gains water (loses solutes), swells, may lyse (pop)
• a hypertonic solution (higher solute conc than cell)
• cell loses water (gains solutes), shrivels, may die

• If a plant cell is immersed in
• an isotonic solution
• cell is flaccid, plant wilts
• needs a net inflow of water (to balance transpiration), has no net change in water conc in this scenario

• If a plant cell is immersed in
• a hypotonic solution (lower solute conc than cell)
• cell is turgid, plant is healthiest
• has net inflow of water (balances transpiration) (loses solutes), cell wall helps prevent cell from bursting
• a hypertonic solution (higher solute conc than cell)
• cell loses water (gains solutes), shrivels, may die

• Substances can be moved across a membrane against its concentration
• in a process called active transport which
• requires a cell to expend energy
• usually in the form of ATP
• a transport protein actively pumps a substance across the membrane against the substance’s concentration gradient