CHAPTER 8 Flashcards
chemical reaction
-occurs when atoms have enough energy to combine or change bonding partners
-reactants –> products
-chemical reactions in cells are organized in metabolic pathways that er interconnected
metabolism
-sum total of all chemical reactions occurring in a biological system at a given time
metabolic reactions
involve energy changes
energy
-is the capacity to do work, or the capacity for change
-potential or kinetic energy
-energy can be converted from one form to another
potential energy
energy stored as chemical bonds, concentration gradient, or change imbalance
kinetic energy
the energy of movement
anabolic reactions
complex molecules are made from simple molecules; energy is required
catholic reactions
complex molecules are broken down to simpler ones; energy is released
how are catabolic and anabolic reactions linked?
the energy released in catabolic reactions is used to drive anabolic reactions to do biological work; its an on going cycle
laws of thermodynamics
-apply to all matter and all energy transformations in the universe
-energy is neither created nor destroyed
-when energy is converted from one form to another, some of that energy becomes unavailable to do work
entropy
(S): a measure of the disorder in a system
in biological systems:
-total energy is called enthalpy (H)
-free energy (G) is the usable energy that can do work
-unusable energy is represented by entropy (S) multiplied by the absolute temperature (T)
- H = G + TS
change in energy can be measured in?
-calories or joules
change in free energy (ΔG) of a chemical reaction
ΔG = ΔH -TΔS
if ΔG is -
free energy is released
if ΔG is +
free energy is required
if free energy is not available
the reaction does not occur
what does the second law of thermodynamics also state
-that disorder tends to increase because of energy transformations
exergonic reactions
-release free energy (-ΔG)
-cell respiration
-catabolism
catabolism
-breaks down an ordered reactant into smaller, more randomly distributed products –> complexity decreases (generates disorder)
endergonic reactions
-consume free energy (+ΔG)
-active transport
-cell movements
-anabolism
anabolism
-makes a single product (a highly ordered substance) out of many smaller reactants (less ordered) –>complexity (order) increases.
chemical equilibrium
balance between forward and reverse reactions, a state of no net change
ΔG = 0
ΔG is related to the equilibrium point
-the further towards completion the point of equilibrium is, the more free energy is released
-ΔG values near zero are characteristic of readily reversible reactions
-final equilibrium does not change, and ΔG does not change
ATP
(adenosine triphosphate)
-captures and transfers free energy
-can be hydrolyzed to ADP and P, releasing a lot of energy for endergonic reactions
-can also phosphorylate (donate a phosphate group to) other molecules, which gain some energy
formation of ATP
-it is endergonic
-ADP + P + free energy —> ATP +H2O
catalyst
increases rates of chemical reactions; they are no altered by the reactions
most biological catalysts are?
-enzymes (proteins) that act as a framework in which reactions can take place
-enzyme lower the energy barrier for reactions
-enzymes can increase reaction rates by 1 million to 10^17 times
activation energy (Ea)
-the amount of energy required to start a reactions
-some reactions are slow because of an energy barrier
-can come from heating the system
-enzymes lower the energy barrier by bringing the reactants together
transition state
activation energy puts the reactants in a reactive mode
transition state intermediates
activation energy changes the reactants into unstable forms with higher free energy
substrates
-another name for reactants
-substrate molecules bind to the active site of the enzyme
what determines an enzymes specificity
-the 3D shape determines it
-changes in the shape changes the function
-depends on precise interlocking of molecular shapes and interactions of chemical groups at the active site
six categories of enzymes
-oxidoreductases
-transferases
-hydrolases
-lyases
-isomerases
-ligases
enzyme-substrate complex (ES)
-is held together by hydrogen bonds, electrical attraction, or covalent bonds
- E + S –> ES –> E + P
-enzyme may change while bound to the substrate but returns to its original form
an enzyme may use on or more mechanisms to catalyze a reaction:
-orient substrates so they can react
-induce strain by stretching the substrate– makes bonds unstable and more reactive to other substrates
-temporarily add chemical groups
adding chemical groups:
-acid-base catalysis: side chains in the active site transfer H+ to or from the substrate, destabilizing covalent bonds (shift change)
-covalent catalysis: a functional group in a side chain forms a temporary covalent bond with the substrate (break down over time)
-metal ion catalysis: metal ions such as copper, iron, and manganese lose or gain electrons without detaching from the enzymes (important for oxidation-reduction reactions)
induced fit
some enzymes change shape when it binds the substrate, which alters the shape of the active site
ribozymes
-RNA molecules acting as biological catalysts
-EX: RNA molecule catalyzes formation of peptide bonds between amino acids
some enzymes require “partners”
-prosthetic groups: non-amino acid groups bound to enzymes
-inorganic cofactors: ions permanently bound to enzymes
-coenzymes: small carbon-containing molecules; not permanently bound
what does the rate of catalyzed reactions depend on?
-depends on substrate concentration
-concentration of an enzyme is usually much lower than the substrate
-at saturation, all enzyme is bound to substrate; it is working at maximum rate
maximum rate is used to calculate enzyme efficiency:
-molecules of substrate converted to product per unit time (turnover number)
-range 1 to 40 milion molecules/second
enzyme activity can be controlled in two ways:
-regulation of gene expression: how many enzyme molecules are made
-regulation of enzyme activity: enzyme may change shape, or be blocked by regulators
systems biology
-the complex pathways are modeled using computer algorithms
-enzymes help organize and regulate metabolic pathways
enzyme inhibitors
-molecules that bind to the enzyme and slow reactions rate
-naturally occurring inhibitors regulate metabolism
-artificial ones can be used to read disease, kill pests, or study how enzymes work
irreversible inhibition
-inhibitor covalently bonds to side chains in the active site and permanently inactivates the enzyme
reversible inhibition
-inhibitor bonds non-covalently to the active site and prevents substrate from binding
competitive inhibitors
-compete with the natural substrate for binding sites
-degree of inhibition depends on concentration of substrate and inhibitor
-EX: cancer drug methotrexate
uncompetitive inhibitors
-bind to the enzyme – substrate compex, preventing release of products
noncompetitive inhibitors
-bind to enzyme at a different site (not the active site)
-the enzyme changes shape and alters the active sire (allostery)
allosteric regulation
-a non-substrate molecule binds enzyme at a site different from the active site, which changes enzyme shape
-active form: proper shape to bind substrate
-inactive form: cannot bind substrate
-non-substrate molecules may be an inhibitor or an activator
allosteric enzymes
-reaction rate is very sensitive to substrate concentration
-they are very sensitive to low concentrations of inhibitors
-making them important in regulating metabolic pathways
metabolic pathways
-first reaction is the commitment step – other reactions then happen in sequence
-feedback inhibition: the final product acts as a noncompetitive inhibitor of the first enzyme, which shuts down the pathway
how are enzymes regulated? and activated or deactivated?
-many enzymes are regulated through reversible phosphorylation
-can be activated when protein kinase adds a phosphate group, and activated by a protein phosphatase
when are enzymes most active?
-most active at a particular pH, which influences ionization of functional group
enzymes in relation to temperature
-every enzyme has an optimal temperature; high temps, non covalent bonds begin to break; warming up –> speeds up, but too much warming denatures it
-some are adapted to warm temps and do not denature
-ex: most human enzymes are more stable at high temps
