bio 3/21

Extra Credit Overview

  • Extra Credit in Blackboard: Columns will be added for each extra credit opportunity; total grade calculated based on 450 points.

  • Max Possible Points: With extra credit included, total points can reach 458.

Basics of Cellular Metabolism

  • Metabolism Control by Cells: Cells manage metabolism by altering product and reactant ratios, which can shift reaction thermodynamics from unfavorable to favorable.

  • Energy Production: Cells evolve mechanisms for ATP production through efficient energy shuttling between ADP and ATP instead of synthesizing each ATP anew.

ATP Structure and Function

  • ATP Structure: ATP contains phosphoanhydride bonds; breaking these bonds releases energy due to strong electronegativity between phosphates.

  • Coupling Mechanism: ADP + Phosphate ➔ ATP; ADP is regenerated from ATP by removing phosphate, conserving energy.

Biochemical Mechanisms of ATP Generation

  • Conservative Mechanisms: Cells use three main processes to convert ADP to ATP:

    1. Substrate Level Phosphorylation

    2. Oxidative Phosphorylation

    3. Photophosphorylation

  • Substrate Level Phosphorylation: High-energy substrates donate phosphates to ADP but produce relatively low ATP amounts. Important in glycolysis and the citric acid cycle.

Oxidative Phosphorylation

  • Electrons and Carriers: Involves transferring electrons from glucose to carriers like NAD+ forming NADH, which carries energy.

  • NADH Structure: Contains ribose sugar and a nitrogenous base; can exist in oxidized (NAD+) or reduced (NADH) forms based on electron transfer during redox reactions.

  • Electron Transport Chain: NADH donates electrons to the chain embedded in mitochondrial membranes, creating a proton gradient and ultimately combining with oxygen to form water.

Stages of Cellular Respiration

  1. Glycolysis: Occurs in the cytosol; glucose ➔ pyruvate with a net of 2 ATP and 2 NADH produced.

  2. Citric Acid Cycle: Pyruvates oxidized to acetyl CoA; further electron capture by NADH and FADH2; results in some ATP via substrate level phosphorylation.

  3. Oxidative Phosphorylation: Most ATP formation occurs here through electron transport and ATP synthase processes, primarily utilizing NADH and FADH2 produced earlier.

Summary of Key Pathway Inputs/Outputs

  • Glycolysis:

    • Input: Glucose, NAD+

    • Output: Pyruvate, NADH, ATP (net 2)

  • Citric Acid Cycle:

    • Input: Acetyl CoA

    • Output: NADH, FADH2, ATP, CO2

  • Oxidative Phosphorylation:

    • Input: NADH, FADH2, O2

    • Output: ATP, H2O

Efficiency of Cellular Respiration

  • Approximately 36-38 ATP produced per glucose molecule; process is 39% efficient in energy conversion.

Conclusion

  • Cellular respiration involves complex pathways and mechanisms; focus on processes rather than memorizing each step for understanding.

  • Know the where (cytosol, mitochondria) and what occurs in glycolysis, Krebs cycle, and oxidative phosphorylation.