Chapter 6A: Cell energetics
Cells use LOTS of energy
ex. ATP hydrolysis as a measurement of energy turnover
use more ATP when you're exercising
half-life of ATP in cells: seconds (brain cells) to minutes (less metabolically active cells)
Brain is particularly sensitive to ATP availability/energy turnover
Na/K pump: neurons use ATP to maintain electrochemical gradients that maintains action potential and enables neurotransmission
Stroke: oxygen deprivation --> neuronal cell death in a few minutes
rapid damage reflects high need for oxygen to generate ATP and low energy reservoir in neurons
ATP hydrolysis: constant flux in energy and in chemical bonds
ATP --> ADP + Pi
changes energy states (lowers potential energy) and molecules -- METABOLISM
Catabolism vs. Anabolism
catabolism: BREAK DOWN organic molecules
Anabolism: BUILD organic molecules
i.e. hydrolysis (SPLITTING BY WATER): large molecule is split by cleavage of bonds, adding H to one section and an OH to the other section (adding a water)
i.e. condensation: 2 molecules are joined together with the loss of water
Organisms can be classified by the source of energy and carbon bonds that they utilize
Phototrophs: energy from sunlight
autotrophs: MAKE THEIR OWN FOOD - carbon from inorganic sources (i.e. CO2)
heterotrophs EAT OTHER ORGANISMS/MOLECULES DERIVED FROM OTHER ORGANISMS: carbon from organic compounds
Chemotrophs: energy from chemical compounds
autotrophs: carbon from inorganic sources
carbon from organic compounds
Energy vs. Work
Energy: sunlight, wind, fossil fuels, food, sugar
Work: synthesis of macromolecules, info storage and transmission, building an electrochemical gradient
First law of thermodynamics: energy is neither lost nor gained — it just changes form (ex. sunlight --> heat)
Forms of energy — conversion of potential --> kinetic is associated with change in objects structure or position
Potential (stored energy): chemical bond, ion differential across a membrane
Kinetic (expressed energy): shape change, location change
ATP stores potential energy in the phosphate bonds
ATP can transport and transmit energy effectively in cells
Negatively charged phosphate groups have the tendency to repel each other but the CHEMICAL BONDS connecting them contain a lot of potential energy to keep the phosphate groups connected
Chemical bonds store energy, tighter bonds store less
C-C bonds and C-H bonds store MORE ENERGY than C-O or C-H bonds
less tight: requires MORE energy to hold together (C-C, C-H bonds)
if they come apart, that energy is released
very tight: takes LESS energy to hold together (CO2, H2O)
invest energy to convert to C-C or C-H bonds
Chemical reaction: changes covalent bonds BETWEEN atoms
Reversible: products can react to form the reactants
ex. FORWARD REACTION carbon dioxide + water --> carbonic acid (CAPILLARIES)
REVERSE REACTION carbonic acid can dissociate to produce carbon dioxide + water (LUNGS)
Reaction direction influenced by concentration of reactants and products (wherever there's a higher concentration, that's where reaction will start)
Second law of thermodynamics: disorder (ENTROPY) in universe is continuously increasing
energy transfers are not fully efficient; "lost" part INCREASES entropy
it takes work to maintain order
inside body, structures are maintaining order because part of the reactions occurring are coming off continuously as heat (increase disorder in the AIR - THE ENVIRONMENT around him
conversion of amino acids --> peptide would yield products with LESS entropy than the starting material because the number of products is less than the reactants
Does a chemical reaction generate energy to do work: is it energetically spontaneous?
Total energy before transformed to
energy (heat) used to increase entropy (change in entropy)
energy available to do work (change in energy available for work)
Energy in system (Enthalpy) = Gibbs free energy + (Entropy x Temperature)
H = G + SxT
Change in free energy = change in enthalpy (available energy/chemical bond energy) - (temperature x change in entropy)
deltaG determines whether a process will occur spontaneously (predict whether something is going to happen in a cell under biological conditions)
NEGATIVE deltaG: exergonic (spontaneous), FORWARD reaction
POSITIVE deltaG: endergonic (not spontaneous), REVERSE reaction
ex. peptide --> collection of aa
collection of aa --> peptide
How are so many endergonic reactions possible? biological systems link chemical reactions
SUM of the 2 reactions controls whether the reaction is spontaneous or not
Endergonic reactions can be driven by:
directly couple exergonic reactions (often involve ATP or other NTPs)
sequential exergonic reactions