Monday WK 5 Notes

Enzymes, ATP & Bioenergetics

Living organisms require an outside energy source (Photo/chemo) & a means for transferring energy. (Metabolism)

Bioenergetics – energy transfer mechanisms associated with living organisms.

Bioenergetics is tied to metabolism. Metabolism is the sum of all chemical RXNs occuring within living organisms.

Oxidation: Looses electrons

Reduction: Gains electrons (ADP + P → ATP )

2 Types of Metabolism:

  • Catabolism: Breakdown RXNs (breakdown into smaller molecules)→ exergonic (release energy)
  • Anabolism: Building or synthesis (build larger molecules) → endergonic (require energy)


Chemical RXNs in living organisms are catalyzed (sped up) by: Enzymes & Ribozymes (specific in action)

  • Enzymes – Organic catalyst; proteins, usually globular sometimes quaternary (complex). These catalyze or speed up chemical RXNs by millions of times.
  • Ribozymes – (Ribo enzymes) RNA molecules with catalytic ability.

ATP – Adenosine Triphosphate; high energy compound (energy currency) 

Cells can make ATP, but not store it in any quantity (requires energy from light or chemicals)

◊ Oxidative, Substrate Level & Photophosphorylation RXNs

ATP is not the only high energy compound there is also GTP, CTP, UTP etc.

Enzymes can be used over & over again, they are not degraded by the RXNs they catalyze. Enzymes can lower the amount of activation energy required to initiate reactions.

Enzymes can increase interactions between molecules.

Substrate: Molecule that is undergoing reaction catalyzed by enzyme

Enzyme Catergories:

1. Endoenzymes vs. Exoenzymes

Active inside the cell vs. Active outside the cell

2. Simple vs. Conjugated

Protein active alone vs. Protein requires some type of helper to be active

Terms for Conjugated enzymes:

Apoenzyme: protein alone = inactive

Holoenzyme: protein + helper = active


  1. coenzymes – organic cofactor; non-protein (ex. NAD, FAD); less specific than enzymes 
  2. Cofactor – Inorganic, non-protein “helper” molecule 
  3. Prosthetic groups – inorganic, and permanently bound (iron, copper and some other metals) 

Note: NAD & FAD – important electron carrier molecules, which are derived from vitamins. Cells use each of theses molecules in specific metabolic pathways to carry pairs of electrons.

Enzymes with Iron Prosthetic groups: Cytochromes

Cytochromes (cell colors): pigmented and involved in electron transport chains; these move H+ across membranes (cell membranes, cristae [mitochandria], or thylakoids [ribosomes])

3. Constitutive vs. Repressible vs. Inducible

Constitutive – always present because they are essential to cell function. Always being made (not inducible or repressible)


Factors Influencing Enzyme Activity:

  1. Temperature
  2. pH
  3. Concentration – of enzymes or substrate
  4. Light
  5. Inhibitors & Enhancers

Inhibitors: Enzyme inhibition can be categorized as competitive or allosteric

Competitive Inhibitor : binds to active site of enzyme, blocking substrate

Allosteric Inhibitor: bind to alternate (allosteric) location on enzyme, causing a change in shape in enzyme so substrate cannot bind to active site.

Active site – site on enzyme that binds to substrate

NOTE : Enzyme names often end in -ase. 

Ex. Luciferase – enzyme used for bioluminescence.

ATP Synthase – Catalyzes formation of ATP.

AMP – Stimulates energy creation

Phosphofructokinase – used to breakdown glucose & makes ATP.






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