BIO 101 Lecture Notes for Respiration, Fermentation, and Photosynthesis Respiration During aerobic respiration, glucose is completely oxidized (all H’s removed) leaving CO2 as an endproduct. The H’s are taken by coenzymes (NAD and FAD) to the electron transport chain. There the energy is drained from the hydrogen electrons and the energy is used to make ATP. The H’s are ultimately accepted by O2 to make H2O as an endproduct. Respiration occurs in three major stages: 1) Glycolysis – occurs in the cytoplasm for both prokaryotic and eukaryotic cells One glucose (6C) is broken into two 3C molecules – 2 pyruvic acids (pyruvate) • One oxidation step produces two molecules of reduced coenzyme – 2NADH • One step produces energy in the form of ATP – 2ATP • The pyruvic acids continue to the next stage – the Krebs Cycle • The 2 NADH proceed to the third stage – ETC • The 2 ATP are available to do cellular work 2) Krebs Cycle – occurs in the cytoplasm for prokaryotic cells and in the matrix of the mitochondria for eukaryotic cells Each pyruvic acid is completely oxidized in the Krebs Cycle to yield 3 CO2 • Five oxidation steps produce 4 molecules of reduced NADH and 1 molecule of reduced FADH2 • One step produces energy directly in the form of ATP(1 ATP • Since glycolysis produces 2 pyruvic acids, the total endproducts of the Krebs cycle produced from the complete oxidation of both pyruvic acids is: 6CO2, 8NADH, 2FADH2, and 2ATP • The 6 CO2 are released as waste The 8 NADH and 2 FADH2 proceed to the third stage – ETC • The 2 ATP are available for cell work 3) Electron Transport Chain (ETC) – in cell membrane for prokaryotic cells; in cristae of mitochondria for eukaryotic cells • The high energy electrons taken from glucose by the coenzymes NAD and FAD are passed down a chain of protein carriers. The energy is drained from the electrons and used to produce ATP. Three ATP are produced for every NADH and 2 ATP for every FADH2, yielding a total of 34 ATP from the ETC.
The H’s are accepted by O2 to form 6 H2O to end respiration. Respiration – exergonic reaction (releases energy) glucose completely oxidized to form CO2 Review of Respiration Fermentation Fermentation is the incomplete oxidation of fuel molecules like glucose. Fermentation begins with glycolysis, but, since it is an anaerobic process, no Krebs Cycle or ETC operate. Endproducts are gases (i. e. CO2), and alcohols (i. e. ethanol) or organic acids (i. e. lactic acid). Only 2ATP are generated for every glucose fermented.
Photosynthesis During photosynthesis, energy from the sun is used to reduce CO2 to form glucose. The H’s used to reduce CO2 are taken from H2O and carried to CO2 by the coenzyme NADP. The removal of the H’s from H2O leaves O2 as an endproduct. Photosynthesis occurs in two stages: 1) Light reactions – occur in thylakoids in chloroplasts for eukaryotic cells and in the cell membrane for prokaryotic cells • Light energy from the sun is converted into chemical energy – ATP.
This process requires photosynthetic pigments (i. e. chlorophyll) that can absorb light energy creating high energy electrons. The high energy electrons are passed down an ETC to produce ATP just as in respiration. • A fresh supply of electrons is supplied to the pigment molecules by H’s taken from H2O. Removal of H’s from water leaves O2 as an endproduct. • The H’s from H2O are eventually picked up by NADP to form NADPH • The O2 is released by the plant • The ATP and NADPH are used in the second stage ) Dark reactions (or Calvin Cycle) – occur in the cytoplasm for prokaryotic cells and in the stroma of the chloroplast for eukaryotic cells. • The ATP produced in the first stage provides the energy necessary for NADPH to reduce CO2 to form glucose. Review of Photosynthesis Photosynthesis – endergonic reaction (requires energy) CO2 reduced to form glucose ———————– [pic] [pic] [pic] Krebs Cycle or [pic] [pic] and 2 FADH2 34 [pic] [pic] [pic] 10 6 O2 6 H2O [pic] Energy from sun + [pic] [pic] glucose [pic] x 6 = 6 H2O 6 CO2 6 6 6