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Lecture 15 - Respiration
Respiration
It is an energy yielding process in which the energy substrate is oxidized using the exogenous or externally derived electron acceptor. Respiration may be aerobic or anaerobic. In aerobic respiration oxygen serve as final electron acceptor and in anaerobic respiration inorganic compounds can serve as final electron acceptors. During respiration energy (ATP)is produced via oxidative phosphorylation
Oxidative phosphorylation
If the organism is a respiratory type (that means complete oxidation of glucose), it
needs four essential metabolic components for their respiration and oxidative
phosphorylation.
a. Tricarboxylic acid cycle (also known as citric acid cycle or Kreb’s cycle) The pyruvate formed during glycolysis will be completely oxidized to 3 CO2 by the use of this cycle. During oxidation of one pyruvate through TCA cycle, 4 NADH2, 1 FADH2 and 1 GTP are produced along with 3 CO2.
b. A membrane and associated Electron Transport System (ETC) The electron transport chain is a sequenctial transfer of electrons through electron carriers to a terminal electron acceptor. During this flow of electron in the membrane, a proton motive force across the membrane leads to the formation ATP (is referred as electron transport phosphorylation).
c. An outside electron carrier: for aerobic respiration, O 2 is the terminal electron acceptor and reduced to H 2 O. This is normal for higher organisms. But in anaerobic bacteria, the terminal electron acceptor may be of nitrite, nitrate, sulphate or carbon dioxide.
d. A membrane bound ATPase enzyme: The proton motive force developed during ETC leads to formation of ATP by enzyme ATPase present in the membrane.
a. Tricarboxylic acid cycle/ Kreb cycle/ Citric acid cycle
The tricarboxylic acid (TCA) cycle is a sequence of reactions that generates energy in the form of ATP and reduced coenzyme molecules (NADH 2 and FADH 2 ). It also performs other functions. Many intermediates in the cycle are precursors in the biosynthesis of amino acids, purines, pyrimidines, etc. For example, oxaloacetic acid and α – ketoglutaric acid are amino acid precursors.
Thus the TCA cycle is an amphibolic cycle , which means that it functions not only in catabolic (breakdown) but also in anabolic (synthesis) reactions.
The overall reaction of the TCA cycle can be summarized as follows:
Acetyl - CoA + 3 H 2 O + 3 NAD+^ + FAD + ADP + Pi 2CO 2 +CoA + 3NADH 2 +FADH 2 +ATP
Since the breakdown of glucose by glycolysis yields two acetyl - CoA molecules which can enter this cycle, the overall equation for the cycle, per glucose molecule breakdown, is twice as above.
Energy yield
ATP YIELD per molecule of glucose broken down in aerobic respiration 18 ATP (6 NADH 2 )
- 6 ATP(2 NADH 2 ) 4 ATP (2 FADH 2 )
- 2 ATP 6 ATP(2 NADH 2 ) 2 ATP (2 GTP )
- 8 ATP 6 ATP 24 ATP = 38 ATP
- Glycolysis Gateway Step TCA Cycle
Electron transport chain (ET)
- ETC is the sequences of O/R reactions that occur in cells
- ET involves Initial e- donor, Terminal e- accepter and e- carriers In Eukaryotes, ETC are in mitochondria or chloroplast membrane In Prokaryotes, ETC in cytoplasmic membrane
Components of Respiratory chain/ ETC
- It consists of enzymes or co enzymes
- NAD/NADP ……> NADH / NADPH
- FAD / FMN …….> FADH2 / FMNH
- Coenzyme Q --- Ubiquinone
- Cytochromes -- Cyt a,b,c
Respiratory chain / ETC
OXIDIZEDSUBSTENCE
REDUCEDSUBSTENCE
NADH
NAD
FMN
FMNH
ADP+Pi
ATP
FAD
FADH
COQH
CO Q
Aerobic and anaerobic respirations with specific examples
Terminal electron acceptor
End product Process name Organism
O 2 H 2 O Aerobic respiration Streptomyces
NO 3 NO 2 , N 2 Denitrification Pseudomonas
denitrificans
SO 4 S or H 2 S Sulphate reduction Desulfovibrio
desulfuricans
Fumarate Succinate Anaerobic
respiration
Escherichia
CO 2 Methane (CH 4 ) Methanogenesis Methanococcus
