Unit 3: Cellular Energetics

Question 1

enzymes

Answer 1

biological catalysts made of proteins with 3D tertiary structure specific to their function

Question 2

ribozymes

Answer 2

biological catalysts made of RNA

Question 3

active site

Answer 3

interacts with substrate; shape and charge of active site must match substrate to interact

Question 4

substrate

Answer 4

reactant of enzyme; specific to shape and charge of active site

Question 5

enzymes catalyze reactions most efficiently at…

Answer 5

optimum temperatures and pHs that are specific to the enzyme

Question 6

if the temperature in the environment is too low…

Answer 6

the rate of collisions between the enzyme and its substrate will be reduced, slowing the reaction

Question 7

if the temperature in the environment is too high…

Answer 7

bonds that hold the enzyme together may be disrupted, and the enzyme’s shape can be altered

Question 8

a pH too far from optimum can…

Answer 8

disrupt bonds in the enzyme and result in a change in its tertiary structure

Question 9

denaturation

Answer 9

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

Question 10

competitive inhibitors

Answer 10

• 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

Question 11

noncompetitive (allosteric) inhibitors

Answer 11

• 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

Question 12

cofactors

Answer 12

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

Question 13

coenzymes

Answer 13

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

Question 14

endergonic reactions

Answer 14

products with higher free energy level than its reactants; considered energetically unfavorable

Question 15

exergonic reactions

Answer 15

products with lower free energy level than its reactants; considered energetically favorable

Question 16

activation energy

Answer 16

energy used to start a reaction; difference between energy level of the reactants and the transition state of the reaction

Question 17

higher activation energies result in….

Answer 17

slower chemical reactions

Question 18

lower activation energies allow chemical reactions to…

Answer 18

proceed at a faster rate

Question 19

enzymes speed up chemical reactions by…

Answer 19

lowering the activation energy of the reaction

Question 20

how do enzymes lower the activation energy of a reaction?

Answer 20

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

Question 21

enzymes cannot…

Answer 21

change an endergonic (energetically unfavorable) reaction into an exergonic (energetically favorable) reaction

Question 22

energy input into the cell must be _________ than the energy requirements of the cell to maintain life

Answer 22

greater

Question 23

energy coupling

Answer 23

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

Question 24

photosynthesis

Answer 24

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

Question 25

light-dependent reactions

Answer 25

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

Question 26

light-independent reactions

Answer 26

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

Question 27

in plants, light-independent reactions take place in the…

Answer 27

stroma

Question 28

in plants, light-dependent reactions take place in the…

Answer 28

thylakoid membrane

Question 29

in prokaryotes, light-dependent reactions take place in the…

Answer 29

plasma membrane

Question 30

in prokaryotes, light-independent reactions take place in the…

Answer 30

cytosol

Question 31

phosphorylation

Answer 31

• 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

Question 32

chlorophyll

Answer 32

light-absorbing pigment that captures the energy of photons from the sun; primary light-absorbing pigment in photosynthesis; found in PSI and PSII

Question 33

photosystems

Answer 33

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

Question 34

photolysis