46 terms

Karp Cell Biology - Chapter 3 - Bioenergetics, Enzymes, and Metabolism

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Bioenergetics
the study of the various types of energy transformations that occur in living organisms
thermodynamics
the study of changes in energy that accompany events in the universe
internal energy (E)
the energy of the system
entropy (S)
is zero at 0 degrees Kelvin
enthalpy (H)
the total energy content of the system; deltaH = deltaG +TAS
free energy (G)
ΔG - the change during a process in the energy available to do work
equilibrium constant, Keq
k1/k2; ratio of product concentration to reactant concentration when a reaction is at equilibrium
standard free energy chage (ΔG^o')
the free energy released when reactants are converted to products under standard conditions (25 degrees C --> 298 degrees K, I ATM, at 1.0 M conc. for all reactants and products except water (55.6M) and 7.0 pH.
ΔGo' = -RTlnKeq'
-2.303RTlogK'eq, where R = 1.987cal/molK (gas constant); and T = 298 degrees K
Free energy changes in metabolic reactions
ATP + H2O --> ADP + Pi
ΔGo' = -7.3kcal/mol
enzymes
1) small amounts 2) are not altered, 3) no effect on thermodynamics 4) can be activated or deactivated by addition of phosphate
cofactors
may be inorganic (metal) or organic (coenzymes)
substrates
the reactants bound by an enzyme
transition state
An unstable grouping of atoms that exists momentarily in the course of a reaction, when a system is highest in energy.
antibodies
normally do not behave like enzymes; simply bind to molecules with high affinity.
- resemble transition state for a reaction, are often able to act like enzymes and catalyze the breakdown of that compound.
active site
Region of an enzyme into which a particular substrate fits.
three mechanisms by which enzymes accelerate reactions
1) substrate orientation; 2) changing substrate reactivity by altering electrostatic configuration; 3) exerting physical stress on bonding in the substrate to be broken
induced fit
the conformational change in an enzyme after the substrate has been bound that allows the chemical reaction to proceed
kinetics
study of the FORCES that act on a system.
maximal velocity (Vmax)
initial velocity at theoretical saturation point
turnover number (catalytic constant, kcat)
the max. number of molecules of substrate that can be converted to product by one enzyme per unit time
michaelis constant (Km)
- Km = substrate conc. when = 1/2 Vmax
- Km = k2 + k3/k1
- Km - independent of enzyme concentration; is constant for a given enzyme
Michaelis-Menten Equation
V = Vmax [S] / ([S] + Km)
[S] substrate concentration; when [S] = Km, (V) = Vmax/2
Enzyme Concentration
doubling concentration of enzyme will double Vmax but not alter Km
Lineweaver-Burke
inverse of Michaelis-Menton; can be used to derive formula for line
enzyme inhibitors
molecules that are able to bind to an enzyme and decrease its activity; 2 types: reversible and irreversible
irreversible inhibitors
bind very tightly to an enzyme often forming a COVALENT bond
reversible inhibitors
2 subtypes (discussed): competitive, noncompetitive
*competitive reversible inhibitor
INHIBITOR COMPETES WITH SUBSTRATE for access to the active site of an enzyme
*noncompetitive reversible inhibitor
inhibitor acts on site other than enzyme's active site; INHIBITOR DOES NOT COMPETE WITH SUBSTRATE for same binding site
oxidation reduction (redox) reactions
oxidized = atom looses e-; reduced = atom gains e'
the two stages of catabolism of glucose
1) glycolysis (anaerobic pathway), 2) TCA (tricarboxylic acid) cycle
dehydrogenase
An enzyme that catalyzes a chemical reaction during which one or more hydrogen atoms are removed from a molecule.
electron transport chain
A series of proteins in which the high-energy electrons from the Krebs cycle are used to convert ADP into ATP
oxidative phosphorylation
Process of extracting ATP from NADH and FADH2; electrons from NADH and FADH2 pass along an electron transport chain
substrate-level phosphorylation
transfer of phosphate group from substrate to ADP
NADH
formed at the expense of NAD+; cells are able to regenerate NAD+ by fermentation - the transfer of e- from NADH to pyruvate.
NADPH
cell's reservoir of NADPH represents its reducing power; production of NADPH favored when energy is abundant
Fermentation
pyruvate --> ethanol (cytosol)
enzymatic regulation of catalytic activity
centered on the modification of the structure of the active site: 1) covalent modification and 2) allosteric modification
protein kinases
enzymes that transfer phosphate groups to other proteins; 2 TYPES: 1) adds phosphate groups to specific tyrosine residues in a substrate protein (2) adds phosphates to specific serine or threonine residues in the substrate
allosteric modulation
inhibition or stimulation of an enzyme by a compound that binds to an ALLOSTERIC SITE that is SPATIALLY distinct from the enzyme's active site
feedback inhibition
enzyme catalyzing first committed step in a metabolic pathway is temporarily inactivated when the concentration of the end product of that pathway reaches a certain level
energy is always lost to
heat
if Km goes up
affinity goes down
viruses
have no plasma membrane