unit 3 - enzymes and energy

metabolism overview

form bonds between molecules (stores energy)

• synthesis reactions

• anabolic reactions

break bonds between molecules (releases energy)

• hydrolysis

• digestion

• catabolic reactions

chemical reactions release energy

exergonic

• digesting polymers

• hydrolysis = catabolism

chemical reactions input energy

endergonic

• building polymers

• dehydration synthesis = anabolism

energy comes from…

coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy)

reactions don’t happen spontaneously

because covalent bonds are stable

activation energy

breaking down large molecules requires an initial input of energy

• large molecules are stable

• must absorb energy to break bonds

reducing activation energy

catalysts → reducing the amount of energy to start a reaction 

enzymes

biological catalysts

• proteins and RNA

• increase rate of reaction without being consumed

• reduce activation energy

substrate

reactant that binds to enzyme

product

the end result of a reaction

active site

enzyme’s catalytic site; substrate fits into ____________

properties of enzymes

reaction specific

• each enzyme works with a specific substrate

not consumed in reaction

• a single enzyme can catalyze thousands or more reactions per second

affected by cellular conditions (temp, pH, salinity)

factors that affect enzyme function

enzyme concentration

• as enzymes go up, reaction rate goes up 

• reaction rate levels off 

  • substrate becomes limiting factor

  • not all enzymes can find a substrate 

substrate concentration

• as substrate goes up, reaction rate goes up

• reaction rate levels off 

  • all enzymes have active site engaged 

  • enzyme is saturated 

  • maximum rate of reaction

temperature affects enzymes 

optimum temp = greatest number of molecular collisions

• heat - increased beyond optimum

  • increased energy level of molecules disrupts bonds in enzyme and between the enzyme and substrate

  • denatures enzyme

• cold - decreased beyond optimum

  • molecules move slower

  • decrease collisions between enzyme and substrate

pH affects enzymes

changes in pH

• add or remove H⁺

• disrupts bonds and 3D shape

  • disrupts attractions between charged amino acids

  • denatures protein

salinity affects enzymes

salinity

• adds or removes cations (+) or anions (-)

• disrupts bonds and 3D shape

• denatures protein

• enzymes are intolerant of extreme salinity

compounds that help enzymes 

activators 

• cofactors → inorganic (non-carbon)

• coenzymes → organic (bind temporarily or permanently)

inhibitors

compounds that reduce/regulate enzyme activity

competitive inhibition

inhibitor and substrate compete for active site

• overcome by increasing substrate concentration

noncompetitive inhibition

inhibitor binds to site other than active site

• allosteric inhibitor binds to allosteric site

• causes enzyme to change shape

  • conformational change

  • active site is no longer functional binding site (keeps enzyme inactive)

allosteric regulation

conformational changes by regulatory molecules

inhibitors 

keep enzyme in inactive form

activators

keeps enzyme in active form

irreversible inhibition

inhibitor permanently binds to enzyme

feedback inhibition

regulation and coordination of production

• product is used by next step in pathway

• final product is inhibitor of earlier step

• no unnecessary accumulation of product