Unit 3: Cellular Energetics Flashcards
enzymes
biological catalysts made of proteins with 3D tertiary structure specific to their function
ribozymes
biological catalysts made of RNA
active site
interacts with substrate; shape and charge of active site must match substrate to interact
substrate
reactant of enzyme; specific to shape and charge of active site
enzymes catalyze reactions most efficiently at…
optimum temperatures and pHs that are specific to the enzyme
if the temperature in the environment is too low…
the rate of collisions between the enzyme and its substrate will be reduced, slowing the reaction
if the temperature in the environment is too high…
bonds that hold the enzyme together may be disrupted, and the enzyme’s shape can be altered
a pH too far from optimum can…
disrupt bonds in the enzyme and result in a change in its tertiary structure
denaturation
change to an enzyme’s structure, which can limit the enzyme’s ability to catalyze chemical reactions; this can sometimes be reversed when optimum conditions are reached
competitive inhibitors
- similar in shape to substrates and compete with them for the active site of an enzyme
- competition lowers the rate of enzyme-catalyzed reactions
- the effect of competitive inhibitors can be diluted by adding higher concentrations of substrate so that the substrates can outcompete the inhibitors
noncompetitive (allosteric) inhibitors
- bind to the allosteric site of an enzyme
- binding changes the shape of the enzyme, affecting its function
- adding higher concentrations of substrate does not affect the actions of a noncompetitive inhibitor
- function in feedback mechanisms, adjusting the rate of chemical reactions in the cell to suit changing environmental conditions
cofactors
inorganic molecules that increase the efficiency of enzyme-catalyzed reactions by binding to active site or substrate to enhance the binding of the substrate to the active site
coenzymes
organic molecules that increase the efficiency of enzyme-catalyzed reactions by binding to active site or substrate to enhance the binding of the substrate to the active site
endergonic reactions
products with higher free energy level than its reactants; considered energetically unfavorable
exergonic reactions
products with lower free energy level than its reactants; considered energetically favorable
activation energy
energy used to start a reaction; difference between energy level of the reactants and the transition state of the reaction
higher activation energies result in….
slower chemical reactions
lower activation energies allow chemical reactions to…
proceed at a faster rate
enzymes speed up chemical reactions by…
lowering the activation energy of the reaction
how do enzymes lower the activation energy of a reaction?
1) bringing substrates together in the proper orientation for a reaction to occur
2) destabilizing chemical bonds in the substrate by bending the substrate
3) forming temporary ionic or covalent bonds with the substreate
enzymes cannot…
change an endergonic (energetically unfavorable) reaction into an exergonic (energetically favorable) reaction
energy input into the cell must be _________ than the energy requirements of the cell to maintain life
greater
energy coupling
combination of endergonic and exergonic reactions that occur in multiple steps to allow for controlled transfer of energy between molecules to increase efficiency; coupling allows energy released in exergonic reaction to “drive” the endergonic reaction; ex. exergonic breakdown of ATP into ADP releases more than enough energy to power formation of sucrose from glucose and fructose
photosynthesis
carbon atoms from carbon dioxide gain hydrogen atoms and the oxygen atoms in water lose hydrogen atoms; consists of light-dependent and light-independent reactions
light-dependent reactions
use energy from sunlight to split water, producing oxygen gas, protons, and high-energy electrons; the oxygen gas is released into the atmosphere and the protons and high-energy elections are used to power the production of ATP and NADPH, which are then sent to the light-independent reactions
light-independent reactions
use ATP and NADPH from light-dependent reactions, along with carbon dioxide, to produce sugars; then, they send ADP, P, and NADP+ back to the light-dependent reactions so photosynthesis can continue
in plants, light-independent reactions take place in the…
stroma
in plants, light-dependent reactions take place in the…
thylakoid membrane
in prokaryotes, light-dependent reactions take place in the…
plasma membrane
in prokaryotes, light-independent reactions take place in the…
cytosol
phosphorylation
- in light-dependent reactions, light energy is used to drive ATP production
- light energy excites electrons in the chloroplast to higher energy levels, releasing energy
- at the end of the light-dependent reactions, NADP+ accepts these electrons, forming NADPH, which reduces power for the light-independent rections
chlorophyll
light-absorbing pigment that captures the energy of photons from the sun; primary light-absorbing pigment in photosynthesis; found in PSI and PSII
photosystems
composed of proteins, chlorophyll, and other light-absorbing pigments called accessory pigments; PSI and PSII contain different types of chlorophyll that absorb the most light energy at different wavelengths; located in the thylakoid membrane of the chloroplast and are connected by an electron transport chain
photolysis
