Describe the different processes of release of energy from glucose in living organisms.
Answers
Answer:Plants utilize photosynthesis for the production of sugar and oxygen from carbon dioxide and water. ... Cellular respiration is the synthesis of ATP using energy released by the breakdown of sugar to carbon dioxide and water. As energy is released by the reaction, the breakdown of sugar is exergonic.
Answer:
•Glycolysis
During glycolysis, glucose molecules (six-carbon molecules) are split into two pyruvates (three-carbon molecules) during a sequence of enzyme-controlled reactions. This occurs in both aerobic and anaerobic respiration.
•Phosphorylation
During phosphorylation glucose is converted into glucose 6-phosphate using energy and phosphate groups from ATP. This is converted to fructose 1,6-diphosphate, again using ATP as a source of energy and phosphate groups. ATP is hydrolysed to ADP + phosphoric acid (Pi).
Tose 1, 6-diphosphate breaks down into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.
These three-carbon molecules are phosphorylated further, forming diphosphates. This reaction requires phosphoric acid and energy gained from the reduction of NAD+ (oxidised form of nicotinamide adenine dinucleotide) to NADH (reduced form 1,3-diphosphate molecules are dephosphorylated to form glycerate 3-phosphate molecules (a hydrolysis reaction). The energy released and the phosphate group that splits out are used to make more ATP from ADP.
To a pyruvate molecule. Again, the energy released and the phosphate group that splits out are used to make more ATP from ADP.
•The link reaction
This links glycolysis to the Krebs Cycle (sometimes called the citric acid cycle). Pyruvate molecules are decarboxylated (they lose a molecule of carbon dioxide) in the mitochondria. Pyruvate molecules are oxidized and converted to acetylcoenzyme A, usually abbreviated to acetyl CoA.
2CH3COCOO + 2NAD+ + 2H2O --> 2CH3COO- + 2NADH + 2H+ + 2CO2
The oxidised form of nicotinamide adenine dinucleotide, NAD+, is reduced to its reduced from NADH.
•The Krebs cycle
This is a complicated cycle. It may be summarised:
Citrate (a six-carbon molecule) forms when an acetyl CoA molecule combines with oxaloacetate (a four-carbon atom molecule) in a condensation reaction. The citrate then undergoes a sequence of redox reactions:
two decarboxylations (oxidation - removal of carbon dioxide); in each case NAD+ is reduced to NADH
two dehydrogenations (removal of hydrogen);
The overall reaction is:
2 acetyl CoA + 6NAD+ + 2FAD + 2ADP + 2H3PO4 --> 4CO2 + 6 NADH + 6H+ + 2FADH2 + 2ATP
•Oxidative phosphorylation
NADH 'carries' hydrogen ions and high-energy electrons. In oxidative phosphorylation the hydrogen ions combine with oxygen to form water and the electrons pass along an electron transfer chain (also called the respiratory chain) using their energy to form ATP molecules. One molecule of NADH forms three ATP molecules.
ATP production is greatly increased by oxygen. By combining with hydrogen ions (and accepting electrons) to form water it allows more hydrogen ions to be released from the electron carrier system.
During aerobic respiration, oxidation of one molecule of glucose produces 38 ATP molecules (net).
Anaerobic respiration in humans may be summarised by the word equation:
glucose --> lactic acid + energy
In yeast anaerobic respiration may be summarised by:
glucose --> ethanol + carbon dioxide + energy
During glycolysis, glucose molecules (six-carbon molecules) are split into two pyruvates (three-carbon molecules) during a sequence of enzyme-controlled reactions. This is the same reaction as occurs in aerobic respiration. Without oxygen, pyruvate is converted to lactic acid in animals or ethanol in plants and yeast. It produces only about 10% of the energy released in the complete oxidation of glucose.
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