What is Glycolsis ? Definition, Important Points

Gly­col­y­sis is a sequence of reac­tion which con­verts glu­cose and relat­ed hex­ose into two mol­e­cule of pyru­vate with net pro­duc­tion of 2 ATP molecules.It is the most impor­tant path­way in ener­gy metab­o­lism present in both aer­o­bic and anaer­o­bic organisms.The cycle is com­plet­ed in 10 steps with the help of enzymes present in the cytoplasm.None of the reac­tions are oxy­gen depen­dent. in evo­lu­tion­ary terms it is regard­ed as a prim­i­tive pathway.

Glycolsis
  • Save
Mol­e­cule

High­lights of glycolysis

  • Gly­col­y­sis is also called EMP path­way as elu­ci­dat­ed by the sci­en­tist name­ly Emb­den, Mey­er­hof and Parnas.
  • It is a major path­way for the pro­duc­tion of ATP in tis­sues lack­ing mito­chon­dria: exam­ple RBC cells and cornea of the eye
  • Gly­col­y­sis can occur in the absence of Oxy­gen anaer­o­bic in such con­di­tion lac­tate instead of pyru­vate ‚is a major end product.
  • Many of the inter­me­di­ates of this part we pro­vide branch point to oth­er Pathways,Example dihy­drox­y­ace­tone phos­phate is a source of glyc­erol that com­bines with fat­ty acid to form triglycerides.
  • All the inter­me­di­ates of the path­way are phos­pho­ry­lat­ed and what water soluble.
  • Only 3 reac­tion out of 10 are Irre­versible in this pathway.

This path­way can be divid­ed into three dis­tinct phases

A. Ener­gy invest­ment phase

B. Split­ting phase

C. Ener­gy gen­er­a­tion phase

A. Ener­gy invest­ment phase : 

This phase involves reac­tion which require input of ener­gy in the form of ATP. this ener­gy is ini­tial­ly con­sumed by the cell to acti­vate the glu­cose and form high ener­gy inter­me­di­ate in the form of phos­pho­ry­lat­ed products.The sit­u­a­tion is sim­i­lar to our day to day life expe­ri­ences as we invest small amount of mon­ey to get bet­ter returns lat­er. this phase involve fol­low­ing reactions:

  1. Glu­cose is irre­versibly phos­pho­ry­lat­ed to glu­cose 6 phos­phate by hex­ok­i­nase or glu­cok­i­nase in the pres­ence of mag­ne­sium ions .One mol­e­cule of ATP is utilised in the step.Glucokinase hav­ing (low affin­i­ty for glu­cose) present in liv­er catal­y­ses phos­pho­ry­la­tion of only glucose.Similarly hex­ok­i­nase (hav­ing high affin­i­ty for glu­cose )present in almost all the tis­sues cat­alyzes phos­pho­ry­la­tion of var­i­ous hex­ose (fruc­tose, glu­cose, man­nose etc)
  2. Glu­cose 6 phos­phate under­goes iso­mer­iza­tion to pro­duce Fruc­tose 6 phos­phate in the pres­ence of phos­pho­hex­ose and mag­ne­sium ion.
  3. Fruc­tose-6-phos­phate is irre­versibly phos­pho­ry­lat­ed by phos­pho­fruc­tok­i­nase in to Fruc­tose 1, 6 bis phos­phate. in this reac­tion one mol­e­cule of ATP is con­sumed. this reac­tion is reg­u­la­to­ry step in glycolysis.

B. Split­ting Phase:

This phase lead to split­ting of high ener­gy 6 car­bon inter­me­di­ate into two car­bon prod­ucts involv­ing the fol­low­ing reactions:

  1. Enzyme aldolase cat­alyzes the split­ting of fruc­tose 1 ‚6 bi phos­phate ( 6 C) into glyc­er­alde­hyde 3 phos­phate( 3C) and dihy­drox­y­ace­tone phos­phate( 3C).
  2. The enzyme Phos­pho­triose iso­merase cat­a­lyst inter­con­ver­sion of glyc­er­alde­hyde 3 phos­phate and dihy­drox­y­ace­tone phos­phate. Thus, two mol­e­cules of glyc­er­alde­hyde 3 phos­phate are pro­duced from one mol­e­cules of glucose.

C. Ener­gy gen­er­a­tion phase:

This Phase includes reac­tion which final­ly return the prin­ci­pal ener­gy ini­tial­ly con­sumed by cell with inter­est and involves the fol­low­ing reactions:

  • Save
Enzyme
  1. Enzyme glyc­er­alde­hyde 3 phos­phate dehy­dro­ge­nase con­verts glyc­er­alde­hyde 3‑phosphate into 1, 3 by phos­pho­glyc­er­ate. In this reac­tion ‚NADH + H + are pro­duced and it in turns is oxi­dised via elec­tron trans­port chain to syn­the­size ATP molecules.
  2. Phos­pho­glyc­er­ate kinase cat­alyzed Irre­versible con­ver­sion of 1,3 bi phos­pho­glyc­er­ate into three phos­pho­glyc­er­ate. In this process sub­strate lev­el phos­pho­ry­la­tion occurs at ATP is syn­the­sized direct­ly from the sub­strate with­out involv­ing ETC.
  3. 3‑phosphoglycerate is iso­mer­ized into 2- phos­pho­glyc­er­ate by phos­pho­glyc­er­ate mutase.
  4. Enzyme eno­lase catal­yse the con­ver­sion of 2 — phos­pho­glyc­er­ate into phos­pho­enol pyruvate.This reac­tion requires Mg2+ or Mn2+ and is inhib­it­ed by fluoride.
  5. The enzyme pyru­vate kinase cat­alyzes Irre­versible pro­duc­tion of pyru­vate from phos­pho­enol pyruvate.This reac­tion is also an exam­ple of sub­strate lev­el phos­pho­ry­la­tion where ATP is pro­duced with­out involve­ment of ETC. 

Ener­gy invest­ment phase involve reac­tion for con­ver­sion of glu­cose to fruc­tose 1,6 bis­pho­s­phate with invest­ment of two ATP mol­e­cules. Split­ting phase results in split­ting of 6 C mol­e­cule to two 3 C mol­e­cule which can inter­con­vert . Ener­gy gen­er­a­tion phase. Pro­ceeds with two 3 C mol­e­cules , there­fore, all reac­tion will be dou­bled . it results in gen­er­a­tion of ener­gy rich mol­e­cules ; 4 ATP by sub­strate lev­el phos­pho­ry­la­tion and 2 NADH.

Over­all Reaction

Glu­cose + 2ADP + 2 pi + 2NAD+ ——-> 2pyruvate + 2ATP + 2 NADH + 2 H +

Sug­ars oth­er than glu­cose such as fruc­tose, galac­tose are con­vert­ed into one of the inter­me­di­ate of glycolysis.

Leave a Comment

Share via
Copy link
Verified by MonsterInsights