Chapter 6 - an introduction to energy, enzymes, and metabolism

Question 1

First law of thermodynamics

Answer 1

• “law of conservation of energy”
• energy cannot be created or destroyed, but it can be transformed form one type to another

Question 2

second law of thermodynamics

Answer 2

• transfer of energy from one form to another increases the entropy of a system
• as entropy increases, less energy is available for organisms to use to promote change

Question 3

Enthalpy (H)

Answer 3

• total energy of a system
• H=G+TS

Question 4

Entropy (S)

Answer 4

• degree of disorder in a system
• cannot be harnessed to do work
• unusable energy

Question 5

Gibbs free energy (G)

Answer 5

• the amount of usable energy
• energy available to do work

Question 6

exergonic reactions

Answer 6

• occur without input of additional energy
• ∆G is negative -> process is exergonic and spontaneous
• energy released by reaction
• not necessarily fast
  ∆G = ∆H - T∆S

Question 7

endergonic reactions

Answer 7

• not spontaneous
• ∆G is positive
• requires addition of energy to drive reaction
  ∆G = ∆H - T∆S

Question 8

is hydrolysis of ATP ender or exergonic

Answer 8

• exergonic
  ∆G = -7.3kcal/mol
• favors formation of products
• energy released used to drive a variety of cellular processes

Question 9

how do biological systems perform endergonic reactions?

Answer 9

• they are coupled to an exergonic reaction
• as long as the net ∆G is negative for both processes together, the reactions will be spontaneous
• endergonic doesn’t necessarily have to happen second

Question 10

catalyst

Answer 10

• an agent that speeds up the rate of a chemical reaction without being consumed during the reaction
• can bring reactants together make the reaction happen faster

Question 11

enzymes

Answer 11

• protein catalysts in living cells
• when substrates bond, the enzyme changes its conformation to force the reactants to interact
• new products have new shape and no longer fit in the enzyme, so they release

Question 12

ribozymes

Answer 12

• RNA molecules with catalytic properties

Question 13

How do enzymes lower activation energy?

Answer 13

• straining the bonds in reactants to make it easier to achieve transition state
• positioning reactions together
• changing local environment
  
  • direct participation through very temporary bonding

Question 14

active site

Answer 14

• location where reaction takes place

Question 15

substrates

Answer 15

• reactants that bind to active site

Question 16

enzyme-substrate complex

Answer 16

• formed when enzyme and substrate bind

Question 17

induced fit

Answer 17

• when a substrate binds to an enzyme and the enzyme undergoes. a conformational change that causes the substrate to bind more tightly

Question 18

do enzymes have high or low specificity?

Answer 18

high

Question 19

lock and key metaphor

Answer 19

• only the right key (substrate) will fit in the lock (enzyme)

Question 20

saturation

Answer 20

• plateau where nearly all active sites are occupied by substrate
• Vmax = velocity of reaction near maximal rate

Question 21

Michaelis constant, Km

Answer 21

• substrate concentration where velocity is half maximal value
• high Km enzyme needs higher substrate concentration
• inversely related to affinity between enzyme and substrate

Question 22

competitive inhibition

Answer 22

• molecule binds to active site
• inhibits ability of substrate to bind
• apparent Km increases - more substrate needed

Question 23

noncompetitive inhibition

Answer 23

• lowers Vmax without affecting Km
• inhibitor binds to allosteric site