GLYCOLYSIS

-

 

GLYCOLYSIS – Full Process (Embden–Meyerhof–Parnas Pathway)

Glycolysis is a 10-step metabolic pathway occurring in the cytoplasm, where one molecule of glucose (6-C) is converted into two molecules of pyruvate (3-C) with the production of ATP and NADH.

PHASES OF GLYCOLYSIS

Glycolysis has two phases:

  1. Energy Investment Phase (Steps 1–5)
    – 2 ATP are used
    – Glucose is phosphorylated and split into two 3-carbon sugars

  2. Energy Payoff Phase (Steps 6–10)
    – 4 ATP and 2 NADH are produced
    – 2 pyruvate molecules formed

⭐ STEPS OF GLYCOLYSIS (10 Steps)

Phase I – Energy Investment

Step 1: Phosphorylation of Glucose

Enzyme: Hexokinase
Reaction: Glucose → Glucose-6-phosphate (G6P)
ATP Used: 1
Purpose: Traps glucose inside the cell.

Step 2: Isomerization

Enzyme: Phosphoglucose isomerase
Reaction: G6P → Fructose-6-phosphate (F6P)
Forms a keto sugar required for next phosphorylation.

Step 3: Second Phosphorylation (Key Regulatory Step)

Enzyme: Phosphofructokinase-1 (PFK-1)
Reaction: F6P → Fructose-1,6-bisphosphate (F1,6BP)
ATP Used: 1
Rate-limiting step of glycolysis.

Step 4: Cleavage of F1,6BP

Enzyme: Aldolase
Reaction: F1,6BP → DHAP + G3P
(DHAP = Dihydroxyacetone phosphate, G3P = Glyceraldehyde-3-phosphate)

Step 5: Isomerization

Enzyme: Triose phosphate isomerase
Reaction: DHAP → G3P
Now 2 molecules of G3P proceed to phase II.

Phase II – Energy Payoff

Step 6: Oxidation and NADH formation

Enzyme: Glyceraldehyde-3-phosphate dehydrogenase (GAPDH)
Reaction: G3P → 1,3-BPG (1,3-bisphosphoglycerate)
Produces: 2 NADH (one per G3P)

Step 7: ATP Formation (Substrate-Level Phosphorylation)

Enzyme: Phosphoglycerate kinase
Reaction: 1,3-BPG → 3-PG
ATP Produced: 2 ATP (one per G3P)
First ATP-yielding step.

Step 8: Mutase Reaction

Enzyme: Phosphoglycerate mutase
Reaction: 3-PG → 2-PG

Step 9: Dehydration

Enzyme: Enolase
Reaction: 2-PG → PEP (Phosphoenolpyruvate)
Forms a high-energy compound.

Step 10: Second ATP Formation & Pyruvate Formation

Enzyme: Pyruvate kinase
Reaction: PEP → Pyruvate
ATP Produced: 2 ATP
Highly exergonic reaction.

NET GAIN OF GLYCOLYSIS

ItemAmount
ATP used2
ATP produced4
NET ATP2 ATP
NADH produced2 NADH
End Product2 Pyruvate

REGULATION OF GLYCOLYSIS (Important for exams)

Major regulatory enzymes:

  • Hexokinase (Step 1) – inhibited by G6P

  • PFK-1 (Step 3) – main regulatory enzyme; inhibited by ATP and citrate; activated by AMP

  • Pyruvate kinase (Step 10) – inhibited by ATP; activated by fructose-1,6-bisphosphate

FATE OF PYRUVATE

Depending on oxygen availability:

1. Aerobic:

Pyruvate → Acetyl-CoA → enters TCA cycle

2. Anaerobic (animals):

Pyruvate → Lactate

3. Anaerobic (yeast):

Pyruvate → Ethanol + CO₂

Popular posts from this blog

transport of metabolites from source to sink

-
  The transport of metabolites from a source to a sink location, primarily in plants, is a crucial process for nutrient distribution and growth. This process is mainly carried out by the   phloem , a vascular tissue. Here's a breakdown of the process: 1. Defining Source and Sink Source:  Any part of the plant that produces or releases metabolites in excess of its own needs, typically through photosynthesis or storage breakdown. Primary sources include mature leaves (producing sugars) and storage organs during mobilization (e.g., tubers converting starch to sugar). Sink:  Any part of the plant that consumes or stores metabolites. Sinks include growing regions (e.g., roots, young leaves, developing fruits, flowers, shoot tips), and storage organs during accumulation (e.g., tubers, fruits). 2. The Phloem Transport System The phloem consists mainly of: Sieve tube elements:  Living cells that form the transport pathway, specialized for bulk flow by lacking a nucleus ...
Read more

STRESS RELATED PROTEIN IN PLANT STRESS PHYSIOLOGY

-
  In plant stress physiology, stress-related proteins are a diverse group of proteins whose synthesis is upregulated or whose activity is altered in response to various environmental stressors. These proteins play crucial roles in enabling plants to perceive, respond to, and ultimately survive adverse conditions. Here are key types and their functions: ### Key Categories of Stress-Related Proteins 1. **Heat Shock Proteins (HSPs)** * **Function:** Act as molecular chaperones, helping to prevent the denaturation and aggregation of other proteins under heat stress and assisting in the refolding of misfolded proteins. They are also involved in protein transport and degradation. * **Examples:** HSP100, HSP90, HSP70, HSP60, and Small HSPs (sHSPs). Present in all cellular compartments. 2. **Late Embryogenesis Abundant (LEA) Proteins** * **Function:** Synthesized during dehydration stress (e.g., drought, salinity, freezing). They are largely hydrophilic and believed...
Read more

Chelating agents

-
  Chelating agents in plants play a crucial role in nutrient dynamics and heavy metal detoxification. They are organic molecules that can bind to metal ions, forming a stable, water-soluble complex called a chelate. This process significantly influences the availability and movement of essential micronutrients and toxic heavy metals within the plant and its environment. Here are the key functions of chelating agents in plants: Enhancing Micronutrient Availability and Uptake: Solubilization:  Many essential metal micronutrients (e.g., iron (Fe), zinc (Zn), manganese (Mn), copper (Cu)) exist in the soil in forms that are insoluble or poorly available for plant uptake, especially in alkaline soils. Chelating agents bind to these metal ions, converting them into soluble complexes that plants can more easily absorb through their roots. Transport:  Once absorbed, chelating agents can facilitate the transport of these metals from the roots to other parts of the plant (stems, lea...
Read more