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.
◊ 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 increase interactions between molecules.
Substrate: Molecule that is undergoing reaction catalyzed by enzyme
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
- coenzymes – organic cofactor; non-protein (ex. NAD, FAD); less specific than enzymes
- Cofactor – Inorganic, non-protein “helper” molecule
- 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:
- Concentration – of enzymes or substrate
- 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.