Respiration is a Amphibolic & exergonic cellular process.
Respiration is an enzymatic process, which is also known as internal respiration / tissue respiration/dark respiration / cellular respiration / mitochondrial Respiration.
An important feature of respiration is liberation of metabolic energy as ATP.
Respiratory substrate :
(Carbohydrates→ Fats→ Protein→ others)
When respiratory substrates are carbohydrates like glycogen, starch, sucrose, hexose or fats, then respiration is known as floating respiration.
When protein is oxidised in respiration, then respiration is Known as protoplasmic respiration protoplasmic components or cellular proteins may oxidised at the time of starvation & disease.
Exceptionally oxidation of proteins in legume seeds is called floating respiration.
Types of respiration :
(A) Aerobic respiration :- The complete oxidation of food with the use of oxygen and when entire carbon released, as CO2 is called as aerobic respiration.
(B) Anaerobic respiration :- This is an incomplete oxidation.
When food is oxidized into alcohol or organic acids without use of oxygen. During it most of the energy is lost in form of heat. It occurs in cytoplasm and only 2ATP are produced.
Anaerobic respiraton was first reported by Kostytchev.
Anaerobic respiration may takes place in bacteria, some lower parasitic animals (Ascaris, Taenia) plants, R.BCs. & muscles of human body. When oxygen is not available, then food is incompletely oxidised in to some organic compounds like ethanol, acetic acid, lactic acid.
In muscle cells & some bacteria, the energy is produced by breaking of glucose into lactic acid inside the cells.
The amount of energy released in anaerobic respiration is much less than aerobic respiration.
Fermentation is performed by only some fungi & some bacteria (only by microbes) and is an extracellular process. No ATP is produced. If occure inside the cell then 2ATP forms.
In energy generating processes either inorganic or organic compounds function as electron acceptors. The terms aerobic respiration, anaerobic respiration and fermentation are often used on energy generating processes.
Both anaerobic respiration and fermentation are incomplete oxidations.
Inhibitory effect on respiration high conc. of oxygen is called Pasteur effect.
STEPS OF RESPIRATION
(1) Glycolysis – Occurs in cytosol/cytoplasm
(2) Formation of Acetyl COA – (Link Reaction) Perimitochondrial space (outer chamber)
(3) TCA cycle or Kreb's cycle – Matrix of mitochondria & cytosol in bacteria
(4) ETS – Occurs in cristae or inner memberane of mitochondria and Oxidative phosphorylation – Occrus in Oxysome head (F1 particle)
(1) Glycolysis – EMP – (Embden, Meyerhof, Parnas) pathway.
The glycolysis is common phase for aerobic & anaerobic respirations both.
Glycolysis involves a series of ten biochemical reactions in cytoplasm.
In glycolysis, neither consumption of oxygen nor liberation of CO2 take place.
In glycolysis, 1 glucose, produces 2mol. of pyruvic acids (3C)
2NADH2 & 2ATP are generated in glycolysis, which are equal to 8 ATP.
Substrate level phosphorylation forms 4 ATP :- [When the substrate releases energy for phosphorylation of ADP OR formation of ATP, without ETS then called as substrate level phosphorylation]
Glycolysis is also known as oxidative anabolism or catabolic resynthesis, because it links with anabolism of fats and amino acids. An intermediatePGALis used for the synthesis of glycerol later formsfatsorlipid.PGA is used for synthesis of Serine, Glycine, Cystine. Alanine forms from pyruvate.
1, 3, 10 are irrev. reactis in EMP pathway.
Glucose + 2ADP + 2 ip + 2NAD 2, Pyuvic Acid + 2ATP + 2NADH2
Phosphofructokinase is an allosteric enzyme. The phosphorylation of fructose 6 phosphate is the most important regulation point of glycolysis.
Phosphofructokinase has multiple allosteric modulator. It's activity is inhibited by ATP (–ve modulator) and stimulated by ADP & AMP (+ve modulator). Most of the biochemical reactions catalysed by allosteric enzymes are irreversible type and these are control point of glycolysis.
(2) Formation of Acetyl-Co-A :- (Link/Gateway reaction)
When respiration is aerobic, then pyruvic acid is oxidised to form 2C compound – Acetyl Co-A. It occurs in presence of O2and CO2is released first time during it.
Acetyl Co-A is a connecting link between glycolysis & Krebs-cycle. Decarboxylation and dehydrogenation (Oxidative decarboxylation) take place during formation of acetyl Co-A.
Acetyl Co-A is formed in perimitochondrial space by enzyme pyruvate dehydrogenase complex. (Mg++, LA (Lipoic Acid), TPP(Thiamine pyrophosphate), NAD, CoA)
Acetyl Co-A is also common intermediate between fat & carbohydrate metabolism.
(3) Kreb cycle / TCA (Tricarboxylic acid) Cycle / Citric acid cycle :-
This cycle was discovered by H.A. Kreb. (Nobel prize)
TCA cycle occurs in mitochondrial matrix or power house of cell.
Kreb cycle begins by formation of citric acid [TCA(Tri carboxylic acid)] & O.A.A. is the acceptor molecule of Acetyl CoA in Kreb's cycle.
A number of Krebs cycle intermediates are used in synthetic (anabolic) pathways, thus TCA cycle is also called amphibolic pathway or anaplerotic pathway.
Succinyl CO–A is important for synthesis of porphyrin ring compounds like Chlorophylls, Phytochromes, Cytochromes, Haemoglobin etc.
a-ketoglutaric acid (5c) involves in Amino Acid formation (Nitrogen-metabolism)
Oxidation occurs at 4 sites in Kreb cycle.
3NADH2, 1FADH2 & 1GTP (ATP) produced by each turn of TCA cycle.(=12 ATP)
All the enzymes of TCA cycle, except marker enzyme Succinic dehydrogenase (on inner mitochondrial membrane) present in matrix.
Bio Chemical reactions in Krebs Cycle ⇒
2 Acetyl Co-A + 6NAD+ + 2 FAD+ + 2 GDP or ADP + 2ip 4CO2 + 6NADH2 + 2FADH2 + 2GTP or ATP + Co-A (2C + 2C)
Ex. Glutamic acid + Pyruvic acid l α–Ketoglutarate + alanine.
(4) ETS & Oxidative phosphorylation : (Terminal oxidation of NADH2 & FADH2)
ETS (Respiratory chain) consists of four components
(i)FP(FMN), (ii)Fe–S Protein, (iii)Co-Q(UQ) & (iv)Cytochromes.
Cytochromes are cyto.-b, cyto. – C1 & cyto. – C, cyto-a & cyto a3.
Now components of ETS are categorise as follows :
Name of complexes
Components of ETS
CoQ/UQ-FADH2 dehydrogenase /Succinate dehydrogenase
Cytochrome b-Cyto c1
Cyto. a and Cyto. a3
Rotenone & amytal
UQ and Cyto. c are mobile e– carriers in mitochondrial ETS. (PQ and PC is mobile in z-scheme)
Cytochrome a3 is last cytochrome in respiratory chain or electron transport chain (ETC).
O2 is last e– acceptor in oxidative phosphorylation & due to this metabolic water is formed.
DNP (Dinitrophenol) and oligomycin both are called uncouplers.
Enzyme Cytochrome oxidase is responsible for oxidation of cyto. a3 & reduction of O2.
Enzyme Cytochrome oxidase has cyto. a & a3 as its components. (Cu present in cyto a and cyto. a3)
Cytosolic or extra mitochondrial or glycolytic 2NADH2 comes at ETS by two type of shuttles (Only in eukaryotes)