Energy metabolism is the set of chemical reactions that produce the energy needed to carry out the vital functions of living beings.
Metabolism can be divided into:
- Anabolism: Chemical reactions that allow the formation of more complex molecules. They are synthesis reactions.
- catabolism: Chemical reactions for the degradation of molecules. They are degradation reactions.
Glucose (C6H12O6) is the energy fuel of cells. When it is broken it releases energy from its chemical bonds and waste. It is this energy that allows the cell to carry out its metabolic functions.
ATP: Adenosine Triphosphate
Before understanding the processes of obtaining energy, you must know how energy is stored in cells until it is used.
This is thanks to ATP (Adenosine Triphosphate), the molecule responsible for capturing and storing energy. It stores the energy released in the breakdown of glucose in its phosphate bonds.
ATP is a nucleotide that has adenine as its base and ribose with sugar, forming adenosine. When adenosine binds to three phosphate radicals, adenosine triphosphate is formed.
The bond between phosphates is highly energetic. Thus, when the cell needs energy for some chemical reaction, the bonds between the phosphates are broken and the energy is released.
ATP is the most important energy compound in cells.
However, other compounds should also be highlighted. This is because during the reactions, hydrogen is released, which is transported mainly by two substances: NAD+ and FAD.
Mechanisms for obtaining energy
Cell energy metabolism occurs through photosynthesis and cell respiration.
Photosynthesis
THE photosynthesis is a process of synthesizing glucose from carbon dioxide (CO2) and water (H2O) in the presence of light.
It corresponds to an autotrophic process carried out by beings who have chlorophyll, for example: plants, bacteria and cyanobacteria. In eukaryotic organisms, photosynthesis occurs in the chloroplasts.
Cellular respiration
THE cellular respiration is the process of breaking down the molecule of glucose to release the energy that is stored in it. It occurs in most living things.
It can be done in two ways:
- aerobic breathing: in the presence of ambient oxygen gas;
- anaerobic breathing: in the absence of oxygen gas.
Aerobic respiration occurs through three phases:
Glycolysis
The first step of cellular respiration is the glycolysis, which occurs in the cytoplasm of cells.
It consists of a biochemical process in which the glucose molecule (C6H12O6) is broken down into two smaller molecules of pyruvic acid or pyruvate (C3H4O3), releasing energy.
Krebs Cycle
Krebs Cycle Scheme
O Krebs Cycle corresponds to a sequence of eight reactions. It has the function of promoting the degradation of end-products of the metabolism of carbohydrates, lipids and various amino acids.
These substances are converted to acetyl-CoA, with the release of CO2 and H2O and ATP synthesis.
In summary, in the process the acetyl-CoA (2C) will be transformed into citrate (6C), ketoglutarate (5C), succinate (4C), fumarate (4C), malate (4C) and oxaacetic acid (4C).
The Krebs cycle takes place in the mitochondrial matrix.
Oxidative Phosphorylation or Respiratory Chain
Oxidative Phosphorylation Scheme
THE oxidative phosphorylation it is the final stage of energy metabolism in aerobic organisms. It is also responsible for most of the energy production.
During glycolysis and Krebs cycle, part of the energy produced in the degradation of compounds was stored in intermediate molecules, such as NAD+ and the FAD.
These intermediate molecules release energized electrons and H ions+ that will pass through a set of transporting proteins, which constitute the respiratory chain.
Thus, the electrons lose their energy, which is then stored in the ATP molecules.
The energy balance of this step, that is, what is produced along the entire electron transport chain is 38 ATPs.
Aerobic Breathing Energy Balance
Glycolysis:
4 ATP + 2 NADH – 2 ATP → 2 ATP + 2 NADH
Krebs Cycle: Since there are two pyruvate molecules, the equation must be multiplied by 2.
2 x (4 NADH + 1 FADH2 + 1 ATP) → 8 NADH + 2 FADH2 + 2 ATP
Oxidative Phosphorylation:
2 NADH from glycolysis → 6 ATP
8 NADH of the Krebs cycle → 24 ATP
2 FADH2 of the Krebs cycle → 4 ATP
Total of 38 ATP's produced during aerobic respiration.
The most important example of anaerobic respiration is fermentation:
Fermentation
THE fermentation it consists only of the first stage of cellular respiration, that is, glycolysis.
Fermentation takes place in the hyaloplasm, when oxygen is not available.
It can be of the following types, depending on the product formed by the degradation of glucose:
Alcoholic fermentation: The two pyruvate molecules produced are converted into ethyl alcohol, with the release of two CO molecules2 and the formation of two ATP molecules. It is used for the production of alcoholic beverages.
Lactic fermentation: Each pyruvate molecule is converted to lactic acid, with the formation of two ATP molecules. Lactic acid production. It occurs in muscle cells when there is excessive effort.
Learn more, read also:
- Metabolism
- Anabolism and Catabolism
- Cell Metabolism
- Chemical reactions
- Biochemistry
Entrance Exam Exercises
1. (PUC - RJ) These are biological processes directly related to cellular energy transformations:
a) respiration and photosynthesis.
b) digestion and excretion.
c) breathing and excretion.
d) photosynthesis and osmosis.
e) digestion and osmosis.
a) respiration and photosynthesis.
2. (Fatec) Whether muscle cells can obtain energy through aerobic respiration or fermentation, when an athlete faints after a 1000 m run, for lack of Adequate oxygenation of your brain, the oxygen gas that reaches the muscles is also not enough to meet the respiratory needs of the muscle fibers, which start to accumulate:
a) glucose.
b) acetic acid.
c) lactic acid.
d) carbon dioxide.
e) ethyl alcohol.
c) lactic acid.
3. (UFPA) The cell respiration process is responsible for (a)
a) carbon dioxide consumption and oxygen release to the cells.
b) synthesis of energy-rich organic molecules.
c) reduction of carbon dioxide molecules into glucose.
d) incorporation of glucose molecules and carbon dioxide oxidation.
e) release of energy for vital cellular functions.
e) release of energy for vital cellular functions.