Respiration In Living Organisms
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Respiration In Living Organisms
The plants can convert the light energy into chemical energy in the photosynthesis process & store it in the form of high energy compounds as glucose which can transferred from one cell to another & from living organism to another.
Q. Differentiate between gaseous exchange (breathing) & cellular respiration.
Ans.
Gas exchange
It is the exchange of O2 and CO2 between the living organism &the outer medium in unicellulars or through the respiratory system in multicellulars.
Cellular respiration:
It is the process by which energy is extracted from the chemical bonds in the food molecules, this energy is utilized in generating ATP molecules, which is used in performing its vital activities of the cells, and the best food material used in this process is glucose.
Structure of ATP High E. bones
Adenine Ribose Three phosphate groups
Adenosine
1- A nitrogenous base called Adenine (A)
2- A molecule of pentose sugar (R)
3- Three phosphate groups
The weak bonds between phosphate groups are easy to be broken to release energy.
ATP ADP + 7 : 12 K.Cal.
The amount of the released energy is enough to cover the need of simple cellular activities as keeping the body temperature constant.
The following equation summonses the process of cellular respiration & shows the amount of the released energy.
C6 H12 O6 + 6O2 respiration 6CO2 + 6H2O + 38 ATP.
Oxidation of glucose molecules during cellular respiration process takes place in three steps which are:
1- Glucolysis, {It takes place in cytosole (the clearest part of cytoplasm)}.
2- Krebs cycle (It takes place in mitochondria).
3- Electron transport (It takes place in the mitochondria).
Stages of glucose Oxidation
Hydrogen atoms are removed from the carbonic skeleton of the glucose molecule, then pass to the hydrogen carriers (co-enzymes.)
2 NAD+ + 2H 2 NADH + H+{ receives one proton & 2e-}
2ADP+2PO4 2ATP
FAD + 2H Energy FADH2
Structure of the Mitochondria
It surrounded by double membrane.
The outer membrane is smooth but the inner membrane folded forming Cristae.
The Cristae contains enzymes,
electron carriers called cytochromes
& hydrogen carriers
The matrix is a dense fluid
contains enzymes, Co- enzymes,
H2O phosphate & other materials.
1- Glucolysis (Splitting of the glucose molecule)
In the Cytoplasm each glucose molecule is oxidized & split into two molecules of Pyruvic acid (3C) through series of biochemical reactions.
fermentation
C6H12O6 respiratory enzymes 2 C3H4O3 + 2 ATP
Glucose (6C) Pyruvic acid (3C)
Glucose change into Glucose 6 phosphate,then fructose 1-6 diphosphate
Fructose 1-6 diphosphate divided into two molecules of phosphoglyceraldehyde (PGAL)
PGAL is oxidized into two molecules of pyruvic acid but two molecules of co-enzyme NAD+ are reduced into NADH & two molecules of ATP are formed in the cell cytosole .
Glucolysis does not require O2 therefore it known as anaerobic respiration or fermentation step.
2- The Krebs cycle ( Oxidation steps (in the matrix) (by Sir Hans Krebs)
Each of The 2 Pyruvic acid molecules pass across the two membranes of the mitochondria& changes into 2 molecules of acetyle CO.(A) at the presence of CO.enzyme (A) & 2 molecules of CO2 release and two molecules of 2NADH are formed.
Co.enzyme (A) act as carrier for the acetyle group from the Matrix to the Cristae.
fats molecules and amino acids are broken to form acetyle group it also combine with CO.enzyme (A) to form acetyle CO. (A).
The acetyle group & the Co-(A) are separated, Co.(A) combine with another group while the acetyle group (2C) combine with Oxalo acetic acid (4C) to form Citric acid (6C).
Citric acid (6C) passes through three intermediate compounds the first is Ketoglutaric acid (5C)the second is Succinic acid (4C)while the third is Malic acid (4C)which converted into Oxalo acetic acid (4C).
Oxalo acetic acid (4C) which combine with the second acetyle group to form Citric acid (6C) that repeat the cycle therefore kerbs cycle is called Citric acid cycle.
During oxidation of the carbon atoms of the organic molecules energy is released & used in the formation of ATP from ADP.
Part of the energy is used to convert NAD+ into NADH (3 molecules in each cycle) & some energy is used to convert FAD into FADH2 (1 molecule in each cycle).
Each glucose molecule initiates two Krebs cycles.
NAD = Nicotinamide Adenine Dinucleotide.
FAD = Flavin Adenine Dinucleotide
Q. GR.. Krebs cycle does not need Oxygen?
Ans. Because oxidation of organic molecules takes place by the release of electrons, The released electrons & protons are received directly by the Co-enzymes NAD+ & FAD.
Q. GR.. Krebs cycle does not need Oxygen but it can not start at the absence of oxygen !!!?
B- Electron transport:
½ O2 + 2H+ + 2 e- H2O
law energy water
electron vapour
When FAD & NAD+ receive hydrogen from the oxidized glucose molecule FADH2 & NADH release the gained electrons down a chair of electron acceptors called Cytochromes.
When the electrons descend step by step down the energy levels of the Cytochromes the energy is released.
This energy is used to form ATP molecules from ADP & E.
ADP + P energy ATP (Oxidative Phosphorilation)
When the electrons reach the lowest energy level of the Cytochromes, they combine with protons (2H+) to form hydrogen molecules (H2 ).
Oxygen is considered as the last receptor of the electrons in the chain of electron transport because (H2) combine with half O2 to form H2O.
That means 2 electrons combine with 2 protons and an O2 atom to form one H2O molecule. ½ O2 + 2H+ + 2e- H2O
Oxidative Phosphorilation
It is the formation of ATP molecules from ADP molecules by using the energy that released when the electrons descend step by step down the energy levels of the Cytochromes during the electron transport .
Respiration occurs in the absence of O2 or the absence mitochondria it starts & finishes in the cytoplasm.
Glucose Oxidized into Pyruvic acid & 2ATP are produced.
Pyruvic acid reduced into either ethyle alcohol or lactic acid according to the type of the respiratory cell.
Pyruvic acid is not converted into acetyle group
❶ In yeast and plant seeds (Alcoholic fermentation)
C6H12O6 C2H5OH + CO2 + 2ATP
Glucose Ethyle alcohol carbon dioxide
❷ In animal cells and Bacteria ( Acidic fermentation )
C6H12O6 C3H6O3 + 2ATP
Glucose Lactic acid
C6H1 2O6
Glucose molecule (6C)
2NAD ADP
2NADH2 ATP
2 CH3CO-COOH 2 Pyruvic acids (3C)
2 NADH2 2 NADH2
2NAD 2 NAD
CO2
C2H5OH C3H6O3
Ethyle alcohol Lactic acid
(Alcoholic fermentation) ( Acidic fermentation )
Although Krebs cycle does not need O2
but it can not start at the absence of O2.
Comparison between aerobic and anaerobic respiratio
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