RESPIRATION IN PLANTS
ENZYME
Enzymes are proteinaceous, biocatalysts.
Term enzyme was given by Kuhne.
First of all isolated & discovered by Buchner
Zymase (from yeast) was the first discovered enzyme. (Buchner)
The first purified and crystalized enzyme was urease (by J.B.Sumner) from Canavalia/Jack Bean (Lobia plant).
Proteinaceous nature of enzyme was suggested by Northrop and Sumner.
Term enzyme was given by Kuhne.
First of all isolated & discovered by Buchner
Zymase (from yeast) was the first discovered enzyme. (Buchner)
The first purified and crystalized enzyme was urease (by J.B.Sumner) from Canavalia/Jack Bean (Lobia plant).
Proteinaceous nature of enzyme was suggested by Northrop and Sumner.
DEFINITION
Enzymes are biocatalysts made up of proteins (except ribozyme), which increases the rate of bio-chemical reactions
by lowering down the activation energy.
First discovered ribozyme was L19 RNAase by T.Cech from rRNA of a protozoan Tetrahymena thermophila and RNAase P or Ribonuclease P by Altman in prokaryotic cell (Nobel prize).
CHARACTERISTICS OF ENZYMES
1. All enzymes are proteins, but all proteins are not enzymes.
2. Enzymes accelerate the rate of reaction, without undergoing any change in themselves.
3. Molecular weight of enzymes ranges from 6000 (bacterial fd) to 46 lakh (Pyruvate dehydrogenase comp.)
4. Enzymes are colloidal substances, which are very sensitive to pH & temperature. Optimum temperature for enzymes is 20-35°C.
5. Most of enzymes are active at neutral pH, hydrolytic enzymes of lysosomes are active on acidic pH (5).
6. All enzymes are tertiary & globular proteins (Isoenzymes quarternary protein)
7. Enzymes lower down the activation energy of substrate or reactions.
8. Enzymes are required in very minute amount for bio-chemical reactions. Their catalytic power is represented by Michaelis Menten constant or Km constant and turn over number.
"The number of substrate molecules converted into products per unit time by one molecule of the enzyme in favourable conditions is called turn over number." The maximum turn over number is of Carbonic anhydrase, is 360 lakh, for Catalase is 50 lakh, for flavoprotein is 50 & for lysozyme is 30 per minute.
9. Enzymes are very specific to their substrate or reactions.
10. Enzymes are macromolecules of amino acids, which are synthesized on ribosomes under the control of genes.
In cellular respiration, carbohydrates are primary respiratory substrates. Others are Fats, organic acids and proteins. Organic acids are used in CAM plants.
Cellular respiration is an multistep process so that energy released in some steps can be used for ATP synthesis. If it occurs in single step, all the energy may released as heat.
ATP - energy currency of the cell .
Reasons behind absence of specialised respiratory organs in plants -
Very little transport of gases required as each plant part takes care of its own gas exchange needs.
Plants have slow respiration rate.
In plants, most of the living cells located quite close to the surface of the plants.
1. Glycolysis - Greek words Glycos = Sugar, Lysis = Splitting.
Also called EMP pathway (E = Embden, M = Meyerhof, P = Parnas)
Common in both aerobic and anaerobic respiration.
Occurs in cytoplasm and it is the partial oxidation of hexose (glucose or fructose) into two molecules of pyruvic acid.
No use of O2 and no release of CO2.
Net or total ATP gain - 6 ATP or 8 ATP (2 NADH2 = 4 or 6 ATP + 2 ATP by SLP = Substrate level
Direct gain of ATP = 2 ATP (by SLP) [Not count the ATP from NADH2]
In glycolysis during anaerobic respiration, net or total or direct gain of ATP= 2 ATP [as NADH2 not enter into the ETS] Conversion of pyruvic acid to Acetyl CoA (Link reaction) is an oxidative decarboxylation catalysed by pyruvic dehydrogenase. (Occurs in the matrix of the mitochondria)
2. Krebs Cycle -
Also called TCA (Tri Carboxylic Acid) Cycle or CA (Citric Acid) Cycle.
Occurs in the matrix of the mitochondria.
Involve 4 dehydrogenations (3 NADH2 and 1 FADH2) and 2 decarboxylations (2 CO2).
Net or total ATP gain - 12 ATP (3 NADH2 = 9 ATP+ 1 FADH2 = 2 ATP+ 1 GTP = 1 ATP).
[If Question is asked for 1 glucose or fructose - in above point no. - (iii) and (iv) calculation will be double as Krebs cycle occurs two times during complete oxidation of 1 molecule of glucose or fructose.]
Cycle has single 5 carbon compound - oc-ketoglutaric acid.
3. Electron transport system (ETS) and oxidative phosphorylation -
ETS is present in the inner mitochondrial membrane.
Five complexes - NADH dehydrogenase (I), FADH2 (II), Cytochrome bc1 (III), Cytochrome a, a3 & 2 C centres (IV) and ATP synthase (V).
In respiration the energy of oxidation - reduction utilised in production of proton gradient t synthesis ATP (Oxidative phosp!iorylation).
Molecular Oxygen (O2) act as the final/ ultimate hydrogen (electron) acceptor and it get reduce, to water.
Mobile electron carrier - Cytochrome C and ubiquinone (UQ) / CoQ.
In aerobic respiration, net or total gain of ATP from one glucose or fructose - 36 ATP or 38 ATP.
In aerobic respiration in prokaryotes - 38 ATP.
Respolaration is an amphibolic pathway (involved in both anabolism and catabolism).
Cellular respiration is an multistep process so that energy released in some steps can be used for ATP synthesis. If it occurs in single step, all the energy may released as heat.
ATP - energy currency of the cell .
Reasons behind absence of specialised respiratory organs in plants -
Very little transport of gases required as each plant part takes care of its own gas exchange needs.
Plants have slow respiration rate.
In plants, most of the living cells located quite close to the surface of the plants.
1. Glycolysis - Greek words Glycos = Sugar, Lysis = Splitting.
Also called EMP pathway (E = Embden, M = Meyerhof, P = Parnas)
Common in both aerobic and anaerobic respiration.
Occurs in cytoplasm and it is the partial oxidation of hexose (glucose or fructose) into two molecules of pyruvic acid.
No use of O2 and no release of CO2.
Net or total ATP gain - 6 ATP or 8 ATP (2 NADH2 = 4 or 6 ATP + 2 ATP by SLP = Substrate level
Direct gain of ATP = 2 ATP (by SLP) [Not count the ATP from NADH2]
In glycolysis during anaerobic respiration, net or total or direct gain of ATP= 2 ATP [as NADH2 not enter into the ETS] Conversion of pyruvic acid to Acetyl CoA (Link reaction) is an oxidative decarboxylation catalysed by pyruvic dehydrogenase. (Occurs in the matrix of the mitochondria)
2. Krebs Cycle -
Also called TCA (Tri Carboxylic Acid) Cycle or CA (Citric Acid) Cycle.
Occurs in the matrix of the mitochondria.
Involve 4 dehydrogenations (3 NADH2 and 1 FADH2) and 2 decarboxylations (2 CO2).
Net or total ATP gain - 12 ATP (3 NADH2 = 9 ATP+ 1 FADH2 = 2 ATP+ 1 GTP = 1 ATP).
[If Question is asked for 1 glucose or fructose - in above point no. - (iii) and (iv) calculation will be double as Krebs cycle occurs two times during complete oxidation of 1 molecule of glucose or fructose.]
Cycle has single 5 carbon compound - oc-ketoglutaric acid.
3. Electron transport system (ETS) and oxidative phosphorylation -
ETS is present in the inner mitochondrial membrane.
Five complexes - NADH dehydrogenase (I), FADH2 (II), Cytochrome bc1 (III), Cytochrome a, a3 & 2 C centres (IV) and ATP synthase (V).
In respiration the energy of oxidation - reduction utilised in production of proton gradient t synthesis ATP (Oxidative phosp!iorylation).
Molecular Oxygen (O2) act as the final/ ultimate hydrogen (electron) acceptor and it get reduce, to water.
Mobile electron carrier - Cytochrome C and ubiquinone (UQ) / CoQ.
In aerobic respiration, net or total gain of ATP from one glucose or fructose - 36 ATP or 38 ATP.
In aerobic respiration in prokaryotes - 38 ATP.
Respolaration is an amphibolic pathway (involved in both anabolism and catabolism).
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