ch 6: cellular respiration + photosynthesis
cellular respiration overview
cellular respiration is the process by which cells produce energy, primarily in the form of atp, which is essential for all cell work.
atp: the cell’s resource
atp (adenosine triphosphate) is the main molecule powering cellular activities. it consists of adenine, ribose, and three phosphate groups. when the bond between the second and third phosphate is broken, energy is released for cell work.
the energy released from breaking the third phosphate bond powers mechanical, chemical, and transport work within the cell.
the "dead battery" form of atp is adp (adenosine diphosphate), which can be recycled back into atp via cellular respiration in mitochondria.
stages of cellular respiration
glycolysis (in cytoplasm)
breaks down glucose (C₆H₁₂O₆) into two pyruvate molecules, each with three carbons .
produces a net gain of 2 atp and 2 nadh molecules.
releases 2 carbon dioxide molecules during the transition to the next stage.
pyruvates are still not ready for the mitochondria until further processing.
transition stage (1.5)
converts pyruvate into acetyl-coa, preparing it for the krebs cycle inside the mitochondria.
this involves modifications, including removal of a carbon as CO₂ and attachment to coenzyme a.
krebs cycle (citric acid cycle)
occurs in the mitochondrial matrix.
acetyl-coa is fully broken down, releasing 4 CO₂ molecules, and generating high-energy electron carriers nadh and fadh₂.
for each glucose, the cycle produces 6 nadh, 2 fadh₂, and 2 atp.
the cycle continuously runs as long as the cell is alive, ripping apart carbons and releasing energy
electron transport chain (etc)
located in the inner mitochondrial membrane.
nadh and fadh₂ donate electrons to the etc, powering a series of protein reactions that produce a large amount of atp (\sim34 molecules).
oxygen acts as the final electron acceptor, forming water .
the total atp yield per glucose molecule is approximately 38, depending on the efficiency and cell conditions
energy carriers
nadh and fadh₂ are crucial for transporting electrons to the etc.
nadh yields 3 atp equivalents, fadh₂ yields about 2 atp.
these molecules are produced at multiple stages: glycolysis, transition, and krebs cycle.
carbon dioxide and waste
the carbons from glucose are ultimately released as CO₂ during the krebs cycle, completing the breakdown of the original six-carbon glucose molecule.
waste products include CO₂ and water, which are expelled from the body.
oxygen’s role and anaerobic respiration
aerobic respiration: this process requires oxygen to efficiently produce a large amount of atp. it involves glycolysis, the krebs cycle, and the electron transport chain, yielding approximately 38 atp molecules per glucose.
anaerobic respiration (Fermentation): occurs in the absence of oxygen. cells switch to fermentation as an alternative, producing only 2 atp per glucose, primarily through glycolysis. this process does not utilize the krebs cycle or electron transport chain due to the lack of oxygen.
fermentation results in byproducts like lactic acid in animals (e.g., during intense exercise) or ethanol and CO₂ in yeast and some bacteria (e.g., in brewing).
organisms are classified as obligate aerobes (require oxygen), facultative anaerobes (can switch between aerobic and anaerobic), or obligate anaerobes (cannot survive in the presence of oxygen) based on their oxygen requirements.
significance of cellular respiration
produces atp necessary for all cellular functions.
the process is tightly linked to oxygen intake and carbon dioxide release.
it is the fundamental energy-generating process for most life forms, enabling survival, growth, and maintenance.
additional notes
the process is highly efficient but depends on oxygen availability.
water and CO₂ are byproducts, with water forming in the etc and CO₂ released during the krebs cycle.
cellular respiration is vital for sustaining life, and its failure leads to cell death due to atp depletion