what is glycolysis and kerbs cycle ?

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All organisms produce ATP by releasing energy stored in glucose and other sugars.

Plants make ATP during photosynthesis.
All other organisms, including plants, must produce ATP by breaking down molecules such as glucose

Aerobic respiration - the process by which a cell uses O₂ to "burn" molecules and release energy

The reaction: C₆H₁₂O₆ + 6O₂ >> 6CO₂ + 6H₂O

Note: this reaction is the opposite of photosynthesis

This reaction takes place over the course of four major reaction pathways

Glycolysis
Conversion of Pyruvate to Acetyl CoA (Oxidation of Pyruvate or Pyruvate Processing)
The Krebs Cycle
Electron Transport Phosphorylation (chemiosmosis)

Glycolysis (glyco = sugar; lysis = breaking)

Goal: break glucose down to form two pyruvates
Who: all life on earth performs glyclolysis
Where: the cytoplasm
Glycolysis produces 4 ATP's and 2 NADH, but uses 2 ATP's in the process for a net of 2 ATP and 2 NADH

NOTE: this process does not require O₂ and does not yield much energy

The First Stage of Glycolysis

Glucose (6C) is broken down into 2 PGAL's (Phosphoglyceraldehyde - 3Carbon molecules)
This requires two ATP's

The first stage of glycolysis

The Second Stage of Glycolysis

2 PGAL's (3C) are converted to 2 pyruvates
This creates 4 ATP's and 2 NADH's
The net ATP production of Glycolysis is 2 ATP's

The second stage of glycolysis

ATP is produced through substrate-level phosphorylation
- A phosphate is transfered from a molecule to ADP producing ATP

Oxidation of Pyruvate and the Krebs Cycle (citric acid cycle, TCA cycle)

Goal: take pyruvate and put it into the Krebs cycle, producing NADH and FADH₂
Where: the mitochondria
There are two steps
- The Conversion of Pyruvate to Acetyl CoA
- The Krebs Cycle proper
The Krebs cycle and the conversion of pyruvate to Acetyl CoA produce 2 ATP's, 8 NADH's, and 2FADH₂'s per glucose molecule

The Oxidation of Pyruvate to form Acetyl CoA for Entry Into the Krebs Cycle

2 NADH's are generated (1 per pyruvate)
2 CO₂ are released (1 per pyruvate)

The conversion of Pyruvate to Acetyl CoA

The Krebs Cycle

6 NADH's are generated (3 per Acetyl CoA that enters)
2 FADH₂ is generated (1 per Acetyl CoA that enters)
2 ATP are generated (1 per Acetyl CoA that enters)
4 CO₂'s are released (2 per Acetyl CoA that enters)
Therefore, the total numbers of molecules generated in the Oxidation of Pyruvate and the Krebs Cycle is:
- 8 NADH
- 2 FADH₂
- 2 ATP
- 6 CO₂

Electron Transport Phosphorylation (Chemiosmosis)

Goal: to break down NADH and FADH₂, pumping H⁺ into the outer compartment of the mitochondria
Where: the mitochondria
In this reaction, the ETS creates a gradient which is used to produce ATP, quite like in the chloroplast
Again, electrons move down an energy gradient until the meet the ultimate electron acceptor, oxygen gas (O₂)
Electron Transport Phosphorylation typically produces 32 ATP's
ATP is generated as H+ moves down its concentration gradient through a special enzyme called ATP synthase

Net Engergy Production from Aerobic Respiration

Glycolysis: 2 ATP
Krebs Cycle: 2 ATP
Electron Transport Phosphorylation: 32 ATP
- Each NADH produced in Glycolysis is worth 2 ATP (2 x 2 = 4) - the NADH is worth 3 ATP, but it costs an ATP to transport the NADH into the mitochondria, so there is a net gain of 2 ATP for each NADH produced in gylcolysis
  - Plants are a bit more efficient and they don't have to spend 2 ATP to transport NADH into their mitochondria
- Each NADH produced in the conversion of pyruvate to acetyl CoA and Krebs Cycle is worth 3 ATP (8 x 3 = 24)
- Each FADH₂ is worth 2 ATP (2 x 2 = 4)
- 4 + 24 + 4 = 32
Net Energy Production: 36 ATP (38 ATP for Plants)!
- Obviously, nothing is perfect, and the actual yeild of ATP is less than 36, but this is theoretical max
Respiration animation

Fermentation

Goal: to reduce pyruvate, thus generating NAD⁺ in the absense of O₂
Where: the cytoplasm
Why: in the absence of oxygen, it is the only way to generate NAD⁺

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Alcohol Fermentation - occurs in yeasts in many bacteria
- The product of fermentation, alcohol, is toxic to the organism

Lactic Acid Fermentation - occurs in humans and other mammals
- The product of Lactic Acid fermentation, lactic acid, is toxic to mammals
- This is the "burn" felt when undergoing strenuous activity

The only goal of fermentation reactions is to convert NADH to NAD⁺ (to use in glycolysis).
No energy is gained
Note differences - anaerobic respiration - 2 ATP's produced (from glycolysis), aerobic respiration - 36 ATP's produced (from glycolysis, Krebs cycle, and Oxidative Phosphorylation)
Thus, the evolution of an oxygen-rich atmosphere, which facilitated the evolution of aerobic respiration, was crucial in the diversification of life

Photosynthesis: 6 CO₂ + 6 H₂O >> C₆H₁₂O₆ + 6 O₂

Respiration: C₆H₁₂O₆ + 6 O₂ >> 6 CO₂ + 6 H₂O

Notice that these reactions are opposites - this is important since the earth is a closed system

All life has a set amount of natural materials to work with, so it is important that they all be cycled through effectively and evenly

Energy Yields:

Glucose: 686 kcal/mol
ATP: 7.5 kcal/mol
7.5 x 36 = 270 kcal/mol for all ATP's produced
270 / 686 = 39% energy recovered from aerobic respiration

Glycolysis (from glycose, an older termfor glucose + -lysis degradation) is the metabolic pathway that converts glucose C₆H₁₂O₆, into pyruvate, CH₃COCOO⁻ + H⁺. The free energy released in this process is used to form the high-energy compounds ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide).

GLYCOLSIS:---------

Glycolysis is a purely anaerobic reaction. While it can happen in the presence of oxygen, oxygen is never involved in the reaction, nor does it alter it. Terms like "aerobic glycolysis" are a misnomer, but are sometimes used to describe the environment of the cell and how it affects the metabolic breakdown of the pyruvate product.

Glycolysis is a determined sequence of ten reactions involving ten intermediate compounds (one of the steps involves two intermediates). The intermediates provide entry points to glycolysis. For example, most monosaccharides, such as fructose, glucose, and galactose, can be converted to one of these intermediates. The intermediates may also be directly useful. For example, the intermediate dihydroxyacetone phosphate (DHAP) is a source of the glycerol that combines with fatty acids to form fat.

It occurs, with variations, in nearly all organisms, both aerobic and anaerobic. The wide occurrence of glycolysis indicates that it is one of the most ancient known metabolic pathways. It occurs in the cytosol of the cell.

The most common type of glycolysis is the Embden–Meyerhof–Parnas (EMP pathway), which was first discovered by Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas. Glycolysis also refers to other pathways, such as the Entner–Doudoroff pathway and various heterofermentative and homofermentative pathways. However, the discussion here will be limited to the Embden–Meyerhof–Parnas pathway.

The entire glycolysis pathway can be separated into two phases:

The Preparatory Phase – in which ATP is consumed and is hence also known as the investment phase
The Pay Off Phase – in which ATP is produced.

KREB'S CYLE:----------

The citric acid cycle — also known as the tricarboxylic acid cycle (TCA cycle), or the Krebs cycle.— is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidization of acetate derived from carbohydrates, fats and proteins into carbon dioxide. In addition, the cycle provides precursors including certain amino acids as well as the reducing agentNADH that is used in numerous biochemical reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular metabolism and may have originated abiogenically.

The name of this metabolic pathway is derived from citric acid (a type of tricarboxylic acid) that is first consumed and then regenerated by this sequence of reactions to complete the cycle. In addition, the cycle consumes acetate (in the form of acetyl-CoA) and water, reduces NAD⁺ to NADH, and produces carbon dioxide. The NADH generated by the TCA cycle is fed into the oxidative phosphorylation pathway. The net result of these two closely linked pathways is the oxidation of nutrients to produce usable energy in the form of ATP.

In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion. Bacteria also use the TCA cycle to generate energy, but since they lack mitochondria, the reaction sequence is performed in the cytosol with the proton gradient for ATP production being across the plasma membrane rather than the inner membrane of the mitochondrion.

Several of the components and reactions of the citric acid cycle were established in the 1930s by the research of the Nobel laureate Albert Szent-Györgyi, for which he received the Nobel Prize in 1937 for his discoveries pertaining to fumaric acid, a key component of the cycle.

The citric acid cycle itself was finally identified in 1937 by Hans Adolf Krebs whilst at the University of Sheffield, for which he received the Nobel Prize for Physiology or Medicine in 1953.