Overview
This lecture covers the structure and function of ATP, mechanisms of ATP synthesis, metabolic pathways, enzyme activity and regulation, as well as the roles of co-factors and co-enzymes.
ATP Structure and Function
- ATP (adenosine triphosphate) is the main energy carrier in cells and is a modified nucleotide.
- ATP consists of ribose sugar, adenine base, and three phosphate groups attached to the 5' carbon.
- The energy of ATP is stored in the high-energy bonds between phosphate groups.
- Hydrolysis of ATP (removing a phosphate group) releases energy (exergonic process), converting ATP to ADP.
- ATP synthesis from ADP and phosphate is endergonic and requires energy input.
ATP Synthesis Mechanisms
- Substrate-level phosphorylation: an enzyme transfers a phosphate from a donor to ADP to form ATP.
- Oxidative phosphorylation: ATP is produced using an electron transport chain, mainly during cellular respiration.
- Photophosphorylation: similar to oxidative phosphorylation, but occurs in photosynthesis using light energy.
Metabolic Pathways
- Metabolic pathways are series of chemical reactions, not single steps, and can be linear, branched, or cyclical.
- Each step (arrow) in a pathway is catalyzed by a unique enzyme.
- Starting compound is called the substrate/reactant; end product is the final product; intermediates are transient compounds formed between.
Enzyme Function and Specificity
- Enzymes are biological catalysts (usually proteins) that speed up reactions by lowering activation energy.
- The enzyme's active site binds specifically to its substrate, functioning like a lock and key.
- Enzymes are not consumed in reactions and can be reused.
Enzyme Helpers: Co-factors and Co-enzymes
- Co-factors are small inorganic ions (e.g., zinc, iron) required for enzyme activity.
- Co-enzymes are larger organic molecules (e.g., coenzyme A, NAD+, FAD) that assist enzymes, especially in electron transfer (redox) reactions.
Factors Affecting Enzyme Activity
- Enzymes have optimal temperature and pH at which they function best.
- Deviations from optimal temperature or pH can denature enzymes and reduce activity.
- Ion concentration in the environment can also impact enzyme function.
Enzyme Regulation and Inhibition
- Allosteric regulation involves molecules binding to an allosteric site, changing enzyme conformation to regulate activity.
- Feedback inhibition occurs when the end product of a pathway inhibits an early enzyme, shutting down the pathway.
- Competitive inhibitors mimic the substrate and bind to the active site, blocking substrate binding.
- Non-competitive inhibitors bind to the allosteric site, changing enzyme shape and inhibiting function.
Key Terms & Definitions
- ATP (Adenosine Triphosphate) — Main energy carrier molecule in cells.
- Hydrolysis — Breaking a bond using water, releasing energy.
- Exergonic — Process that releases energy.
- Endergonic — Process that requires energy input.
- Substrate-level phosphorylation — Direct transfer of phosphate to ADP by an enzyme.
- Oxidative phosphorylation — ATP formation using electron transport chains.
- Enzyme — Biological catalyst that speeds up chemical reactions.
- Active site — The region on an enzyme where substrate binds.
- Co-factor — Inorganic ion aiding enzyme function.
- Co-enzyme — Organic molecule aiding enzyme function.
- Allosteric site — Alternate enzyme site for regulatory molecule binding.
- Denatured — Loss of protein structure and function due to environmental changes.
Action Items / Next Steps
- Memorize the cellular respiration equation.
- Review enzyme structure and function.
- Understand differences between types of inhibitors.
- Prepare for cellular respiration in the next lecture.