Metabolism and Enzymes: Understanding the Flow of Energy in Living Organisms, Slides of Biology

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Metabolism & Enzymes

From food webs to the life of a cell

energy

energy

energy

Metabolism

• Chemical reactions of life

• forming bonds between molecules
  • dehydration synthesis
  • synthesis
  • anabolic reactions
• breaking bonds between molecules
  • hydrolysis
  • digestion
  • catabolic reactions That’s why they’re called anabolic steroids!

Examples

 dehydration synthesis (synthesis)

 hydrolysis (digestion)

H 2 O

H 2 O

enzyme

enzyme

Chemical reactions & energy

• Some chemical reactions release energy

• exergonic
• digesting polymers
• hydrolysis = catabolism

• Some chemical reactions require

input of energy

• endergonic
• building polymers
• dehydration synthesis = anabolism

digesting molecules= LESS organization= lower energy state

building molecules= MORE organization= higher energy state

Endergonic vs. exergonic reactions

exergonic endergonic

**- energy released

• digestion**
  • energy invested
  • synthesis

- ∆ G

∆ G = change in free energy = ability to do work

+ ∆ G

What drives reactions?

• If reactions are “downhill”, why don’t they just

happen spontaneously?

• because covalent bonds are stable bonds Why don’t stable polymers spontaneously digest into their monomers?

starch

Activation energy

• Breaking down large molecules requires

an initial input of energy

– activation energy

– large biomolecules are stable

– must absorb energy to break bonds

cellulose (^) energy CO2 + H 2 O + heat

Reducing Activation energy

• Catalysts

• reducing the amount of energy to start a reaction Pheeew… that takes a lot less energy!

reactant

product

uncatalyzed reaction

catalyzed reaction

NEW activation energy

Catalysts

• So what’s a cell got to do to reduce

activation energy?

– get help! … chemical help… ENZYMES

∆ G

Call in the ENZYMES!

Enzymes vocabulary

substrate

• reactant which binds to enzyme
• enzyme-substrate complex: temporary association

product

• end result of reaction

active site

• enzyme’s catalytic site; substrate fits into active site

substrate

enzyme

products

active site

Properties of enzymes

• Reaction specific

• each enzyme works with a specific substrate
  • chemical fit between active site & substrate
    • H bonds & ionic bonds

• Not consumed in reaction

• single enzyme molecule can catalyze thousands or more reactions per second - enzymes unaffected by the reaction

• Affected by cellular conditions

• any condition that affects protein structure
  • temperature, pH, salinity

Lock and Key model

• Simplistic model of enzyme

action

• substrate fits into 3-D structure of enzyme’ active site - H bonds between substrate & enzyme
• like “key fits into lock”

In biology… Size doesn’t matter… Shape matters!

Induced fit model

• More accurate model of enzyme action

• 3-D structure of enzyme fits substrate
• substrate binding cause enzyme to change shape leading to a tighter fit - “conformational change” - bring chemical groups in position to catalyze reaction