Winter_2025_BIS2A_Lecture_17_presingle

Lecture Overview

• Instructor: Prof. Marc Facciotti, UC Davis

• Course: BIS2A

• Focus Topic: Photosynthesis and energy transfer in biological pathways.

Exam Information

• Date: Friday, February 21st

• Format: Regular exam plus two Extra Credit (EC) questions; total of 18 EC points.

• Reference Materials: Key figures on metabolic pathways will be provided.

• Preparation Resources: Practice exam available at BIS2A.com (optional).

Key Questions in Decision Making

• Context: Understanding effective strategies for decision-making in biochemical contexts.

• Key Considerations:

  • When/where to make decisions?

  • What information is most relevant?

  • Mechanisms for making decisions (allosteric binding via pathways).

Metabolic Pathways

• Pyruvate Dehydrogenase: Enzyme crucial for converting phosphoenolpyruvate into pyruvate while producing ATP:

  • Reaction: Phosphoenolpyruvate + ADP + H+ → Pyruvate + ATP

  • Free energy change: -31.7 to -23.0

• NAD+/NADH, ATP: Central molecules in energy transfer and regulatory roles in metabolism.

• Allosteric Regulation: Feedback mechanisms on enzyme activity through acetyl-CoA levels.

TCA Cycle and Regulatory Points

• Similarities in regulation among metabolic cycles.

• Importance of fixed carbon, electron donors, and energy sources derived from carbohydrates, lipids, nucleotides, and amino acids.

Energy Sources and Building Blocks

• Carbon and Energy Sources: Including trace elements and vitamins essential for biosynthesis of new molecules.

• Byproducts: Carbon dioxide and waste products generated during the consumption of various macromolecules.

Energy Harvesting and ATP Production

• ATP Generation: Coupling processes that utilize energy gradients for ATP synthesis, emphasizing electron flow and proton gradients.

• Role of Light: Utilization of absorbed light energy to drive upward electron flow to create reduced cytochrome carriers (e.g., NADPH).

Photosystem Details

• Pigments and Electrons: Photosystem I (P700) and Photosystem II (P680) harness light to excite electrons:

  • Photosystem I: Higher redox potential than many substrates, mediating energy capture.

  • Photosystem II: Generates oxygen as a byproduct of water splitting.

  • Order of standard reduction potentials of different pigments and electron carriers crucial for efficiency.

Photosynthesis Mechanisms

• Photosynthetic Pathway: Integrates ATP/NADPH production and Calvin cycle.

• Calvin Cycle: Consumes NADPH and ATP to produce sugars from CO2.

Pentose Phosphate Pathway (PPP)

• NADPH Production: Essential for biosynthetic reactions even in non-photosynthetic organisms.

• Key Intermediates: Glucose-6-P, Ribulose-5-P; branched pathways generating various building blocks.

Building Blocks for Cellular Synthesis

• Main Substrates: Identified as critical for synthesizing biomolecules:

  • Glucose-6-P

  • Glyceraldehyde 3-phosphate

  • Fructose-6-phosphate

  • Acetyl-CoA, among others.

• Integration with Processes: Linkages between glycolysis, TCA, and PPP to provide comprehensive metabolic framework.