Energy in the cell. Use and storage of
I wanted to dedicate this article to the cell nucleus and DNA. But before that you need to touch on how the cell stores and uses energy (thanks to Spidgorny ). We will deal with issues related to energy almost everywhere. Let's figure it out in advance.
What can I get energy from? Yes from all! Plants use light energy. Some bacteria, too. That is, organic substances are synthesized from inorganic due to light energy.
+ There are hemotropics. They synthesize organic substances from inorganic due to the energy of oxidation of ammonia, hydrogen sulphide and other substances.
And there are we with you. We are heterotrophs. Who are they? These are those who do not know how to synthesize organic substances from inorganic substances. That is chemosynthesis and photosynthesis, this is not for us. We take the finished organic (eat). We disassemble it into pieces and either use it as a building material or destroy it to obtain energy.
What exactly can we disassemble for energy? Proteins (first sorting them into amino acids), fats, carbohydrates and ethyl alcohol (but this is optional). That is, all these substances can be used as energy sources. But for its storage we use fats and carbohydrates . I love carbohydrates! In our body, the main storage carbohydrate is glycogen.
It consists of glucose residues. That is, it is a long, branched chain consisting of identical links (glucose). If necessary, in energy, we split off one piece from the end of the chain and oxidize it yields energy. This method of obtaining energy is characteristic of all cells of the body, but especially a lot of glycogen in the cells of the liver and muscle tissue.
Now let's talk about fat. It is stored in special cells of connective tissue. The name is adipocytes. In fact, they are cells with a huge fat droplet inside.
If necessary, the body extracts fat from these cells, partially splits and transports. At the place of delivery, the final splitting takes place with the release and transformation of energy.
Quite popular question: "Why can not you store all energy in the form of fat, or glycogen?"
These sources of energy have different purposes. Of glycogen, energy can be obtained fairly quickly. Its cleavage begins almost immediately after the beginning of muscular work, reaching a peak to 1-2 minutes. The splitting of fats proceeds several orders of magnitude more slowly. That is, if you sleep, or slowly go somewhere - you have a constant energy expenditure, and it can be provided by splitting fats. But as soon as you decide to accelerate (dropped the server, ran to raise), sharply need much energy and quickly get it splitting fats will not work. Here we need glycogen.
There is one more important difference. Glycogen binds a lot of water. Approximately 3 g of water per 1 g of glycogen. That is, for 1 kg of glycogen it is already 3 kg of water. Not optimal With fat is easier. Molecules of lipids (fats = lipids) in which energy is stored are not charged, unlike water molecules and glycogen. Such molecules are called hydrophobic (literally, afraid of water). The water molecules are polarized. It looks like this.
In fact, positively charged hydrogen atoms interact with negatively charged oxygen atoms. It turns out a stable and energetically favorable condition.
Now imagine the molecules of lipids. They are not charged and can not normally interact with polarized water molecules. Therefore, the mixture of lipids with water is energetically unfavorable. Lipid molecules are not able to adsorb water, as glycogen does. They are "milled" into so-called lipid droplets, surrounded by a membrane of phospholipids (one side is charged and facing the water from the outside, the other is not charged and looks at the lipid droplets). As a result, we have a stable system that effectively stores lipids and nothing superfluous.
Okay, we figured out the forms in which the energy is stored. And what happens to her next? Here we have split the glucose molecule from glycogen. Turned it into energy. What does it mean?
Let's make a small digression.
In the cell there are about ?00?00?000 reactions every second. When the reaction proceeds, one substance is transformed into another. What happens with his inner energy? It can decrease, increase or not change. If it decreases -> energy is released. If it increases -> you need to take the energy from outside. The body usually combines such reactions. That is, the energy released during the course of one reaction goes to the second.
So in the body there are special compounds, macroergies, which are able to accumulate and transmit energy during the reaction. In their composition, there is one or several chemical bonds in which this energy accumulates. Now you can go back to glucose. The energy released during its decay is stored in the links of these macroergs.
We will analyze on an example.
The most common macroerghe (energy currency) of the cell is ATP (adenosine triphosphate).
It looks something like this.
It contains a nitrogenous base of adenine (one of the 4 used to encode information in DNA), sugar of ribose and three residues of phosphoric acid (and therefore adenosine triphosphate). It is in the bonds between the residues of phosphoric acid that energy is accumulated. When one residue of phosphoric acid is cleaved, ADP is formed (adenosine diphosphate). ADP can release energy, tearing off another residue and turning into AMP (adenosine monophosphate). But the efficiency of the second residue cleaved is much lower. Therefore, usually, the body tends to get ATP from ADP again. There is it approximately so. In the decay of glucose, the energy released is spent on the formation of a bond between two residues of phosphoric acid and the formation of ATP. The process is multi-stage and so far we will omit it.
The resulting ATP is a universal source of energy. It is used everywhere, starting from protein synthesis (for the connection of amino acids energy is needed), finishing with muscular work. Motor proteins that perform muscle contraction use the energy stored in ATP to change their conformation. Changing the conformation is the reorientation of one part of a large molecule relative to another. It looks something like this.
That is, the chemical energy of the bond goes into mechanical energy.
Here are real examples of proteins using ATP for work.
Meet, this is myosin . Motor protein. It carries out the movement of large intracellular formations and participates in muscle contraction. Pay attention, he has two "legs". Using the energy stored in 1 ATP molecule, it performs one conformational change, essentially one step. The most obvious example of the transition of the chemical energy of ATP into a mechanical one.
The second example is the Na /K pump. At the first stage, it binds three molecules of Na and one ATP. Using the energy of ATP, it changes the conformation, throwing Na out of the cell. Then he connects two molecules of potassium and, returning to the initial conformation, transfers potassium to the cell. Stuck is extremely important, it allows maintaining the level of intracellular Na in the norm.
But seriously, then:
Pause. Why do we need ATP? Why can not we use the stored energy in glucose directly? It's trite, if you oxidize glucose to CO2 at a time, very much energy is instantaneously released. And most of it will dissipate in the form of heat. Therefore, the reaction is broken down into stages. At each little energy is released, it is stored, and the reaction continues until the substance is completely oxidized.
I'll post it. Energy is stored in fats and carbohydrates. Of carbohydrates it can be extracted more quickly, but in fats you can store more. To carry out reactions, the cell uses high-energy compounds, in which the energy of decay of fats, carbohydrates and so on is stored ATP is the main such compound in the cell. In fact, take and use. However, not the only one. But more on that later.
P.S. I tried to simplify the material as much as possible, so there were some inaccuracies. I ask the zealous biologists to forgive me.
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