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CHAPTER: 11(B)
Glycolysis


Glycolysis:(Embden – Meyerhof – parnas, or EMP pathway)

•      Glycolysis is derived from the Greek word (glucose-sweet or sugar; lysis- dissolution).
•      It is a universal pathway in the living cells.
•      The complete pathway of glycolysis was elucidated in 1940.
•      The pathway is often referred to as Embden-Meyerhof pathway (EMP).
•      Glycolysis is defined as the sequence of reaction converting glucose to pyruvate or lactate , with the production of ATP.
•      Glycolysis takes place in all cells of the body.
•      The enzymes of this pathway are present in the cytosomal fraction of the cell.
•      Glycolysis occurs in the absence of oxygen (anaerobic) or in the presence of oxygen (aerobic).
•      Lactate is the end product under anaerobic condition.
•      In the aerobic condition, pyruvate is formed, which is then oxidized to carbondioxide and water.

Steps involved in Glycolysis:
•      The sequence of reaction of glycolysis can be divided into three distinct phases:
                        1. Energy investment phase
                        2. Splitting phase
                        3. Energy generation phase



A. Energy investment phase:

  1. Glucose is phosphorylated to Glucose-6-P by hexokinase or  glucokinase  (both are isoenzymes). This is an irreversible rxn. dependent on ATP & Mg2+ .
  2. Glucose-6-P undergoes isomerization to give Fructose-6-P in the presence of the enzyme phosphohexose isomerase & Mg2+ .
  3. Fructose-6-P phosphorylated to Fructose-1,6-bis (P) by phosphofructokinase . This is an irreversible and a regulatory step in glycolysis.
  1. Splitting phase:
  1. The 6-C Fructose-1,6-bis (P) is split (hence the name glycolysis) to two 3-C compounds, Glyceraldehyde-3-(P)  &  Dihydroxyacetone phosphate  by the enzyme  aldolase (Fructose-1,6-bis (P)aldolase).
  2. The enzyme phosphotriose isomerase catalyses the reversible interconversion of G-3-P & DHAP. Thus two molecules of G-3-P are obtained from one molecule of glucose.
  1. Energy generation phase:

  1. G-3-P dehydrogenase converts G-3-P to  1,3 –bisphosphoglycerate. This step is important as it is involved in the formation of  NADH + H+ & a high energy compound 1,3 –bisphosphoglycerate.
  2. The enzyme phosphoglycerate kinase acts on 1,3-bisphosphoglycerate resulting in the synthesis of ATP & formation of 3- Phosphoglycerate.
  3. 3- Phosphoglycerate  is converted to 2- Phosphoglycerate by phosphoglycero mutase.  This is an isomerization rxn.
  4. The high energy compound phosphoenol pyruvate is generated from 2- Phosphoglycerate by the enzyme Enolase.This enzyme requires Mg2+  or Mn2+ .
  5. The enzyme Pyruvate Kinase  catalyses the transfer of high energy phosphate from phosphoenol pyruvate to ADP , leading to the formation of ATP   &  Pyruvate.





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CHAPTER: 10 (A)
Photosynthesis



Introduction to Photosynthesis:
•      The synthesis of complex organic material using carbon dioxide, water, inorganic salts, and light energy (from sunlight) captured by light-absorbing pigments, such aschlorophyll and other accessory pigments.
•      The use of light energy to produce carbohydrates from carbondioxide and a reducing agent such as water is known as photosynthesis.
•      Photosynthesis consists of light reactions and dark reactions.

•      This process can be simplified in this equation:




•      It means photosynthesis is a process in which carbon dioxide (CO2), water (H2O) and light energy are utilized to synthesize an energy-rich carbohydrate like glucose (C6H12O6) and to produce oxygen (O2) as a by-product.
•      Photosynthesis is a vital process among photoautotrophs, like plants, algae and some bacteria that are able to create their own food directly from inorganic compounds using light energy so that they do not have to eat or rely on nutrients derived from other living organisms. 
•      Photosynthesis occurs in plastids (e.g.chloroplasts), which are membrane-bounded organelles containing photosynthetic pigments (e.g. chlorophyll), within the cells of plants and algae.
•       In photosynthetic bacteria (cyanobacteria) that do not have membrane-bounded organelles, photosynthesis occurs in the thylakoid membranes in the cytoplasm.

Significance of Photosynthesis:
(1)   It is the primary source of organic food and food energy (ATP) for all forms of life, either directly or indirectly.
(2)   Excess sugars produced in photosynthesis are either stored in the form of carbohydrates or used in the biosynthesis of other organic compounds.
(3)   In any ecosystem, green plants represent the most essential biotic components as they are the primary producers.
(4)   Photosynthesis helps to purify air and also maintain balance of oxygen and carbon dioxide in the ecosystem.
(5)   Oxygenic photosynthesis was responsible for converting the totally anaerobic condition on earth into aerobic atmosphere present now.
(6)   The fossil fuels (e.g. natural gas, coal, petroleum (oil), etc.) are all energy-rich materials of an organic origin. The energy stored in all these fuels is basically solar energy which was trapped and stored during photosynthesis in the geological past. 


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