Конспект урока по билингвальной биологии "Белки"

Protein

Proteins are complex organic molecules. They contain carbon, hydrogen, oxygen and nitrogen. Some also have sulfur.

1 gram = 4 Cal. of energy . Proteins are very abundant organic compounds in cells.

They are most essential substances for life. Some participate part of cells structure, other regulate and control a cell’s function. They are used in biochemical reactions occurring in a cell or as a structural element. They make up the structure of some hormones, antigens, antibodies, and enzymes as biochemical catalysts in occurring reaction in a cell.

(Functions in movement, transport, fighting infection.)

1. Structural parts of cells and of body tissues, such as hair and nails, and the tough materials of cartilage and connective tissue.

2. Pigments in animal blood, skin, and eyes, and chlorophyll in green plants.

3. Hormones, the chemical messengers that regulate body functions in plants and animals.

4. Contractile material of muscle tissues. Actin and myosin

5. Antibodies, which protect animal bodies against foreign substances and disease organisms.

6. Enzymes, which enable complex chemical reactions to take place with precision and speed.

Aminoacids are the monomers of proteins. There are over 20 amino acids. The order and number of the amino acids dictates the type of protein. In the proteins; amino acids are linked to each other by a chemical bond known as Peptide bond and formed dipeptide. Many aminoacids are linked by peptide bonds and formed polypeptide. A polypeptide has between 6-40 aminoacids.

The smallest proteins have about 50 amino acids. The largest protein molecules have over 100.000 amino acids.

Insulin is a hormone that is composed of protein.

Aminoacids consist of a central carbon atom, which are bonded 1-A carboxyl group (COOH) 2-An amino group (NH2) 3-Radical group 4-A single hydrogen atom (H)

There are many different proteins. Because

1. Each different sequence makes a different protein.

2. Each different number of aminoacid makes a different protein

3. Each different kind of aminoacid makes a different protein.

Proteins are not usually used energy source. Because protein participate cell structure.

Proteins are heat sensitive. High temperature breaks certain bonds within protein molecules. This causes chance in protein structure change shape. Such a change in shape protein molecule is called denaturation.

The catabolization of proteins produce wastes, Urine, Uric acid, Ammonia.

Structure of Proteins

The primary structure refers to amino acid linear sequence of the polypeptide chain. Secondary structure refers to highly regular local sub-structures. Two main types of secondary structure, the alpha helix and the beta strand or beta sheets. Tertiary structure refers to three-dimensional structure of a single protein molecule. The alpha-helices and beta-sheets are folded into a compact globule. Quaternary structure is the three-dimensional structure of a multi-subunit protein and how the subunits fit together.

ENZYMES

Importance of Enzymes: Enzymes are one of the most important types of proteins. An enzyme is a catalyst; it speeds up the reaction but is not used up in the reaction. . Enzymes enter into a chemical reaction only temporarily—just long enough to cause it to happen. Enzymes lower the activation energy of the reaction. Enzymes are not changed by the reaction. They remain to be used again and again for the same chemical step with other molecules. A substance that affects a reaction without being changed itself is called a catalyst. Enzymes are organic catalysts.

The substance that an enzyme acts upon is called its substrate. The enzyme contains a site on its molecule called the active site .The names of enzymes usually end with the suffix -ase, and the name is often derived from the name of the substrate. For example, the enzyme that acts to split maltose into two glucose molecules is called maltase.

The enzyme bends the substrate, reducing the amount of activation energy thus allowing the substrate to split fairly quick.

Enzymes are specific and can only work on certain molecules. This is called the form-fit hypothesis.

How Enzymes Work

The ability of enzymes to act as catalysts depends on their shape. Somewhere on the surface of each enzyme there is a region called the active site. The substrate molecules fit the shape of the active site. When the substrate molecule comes in contact with the active site of the enzyme, it forms a temporary union with the enzyme. This is called an enzyme-substrate complex. During this time, the enzyme may break bonds within the substrate molecule and thus separate it into two smaller molecules.

AB + E ABE A + B + E

Substrate + enzyme Enzyme-substrate complex End product + End product + enzyme

An enzyme may also cause two molecules to join. In this case, there are two substrates. Each fits into the active site in such a way that they are brought into close contact. This enables bonds to form, joining the two substrate molecules.

A + B + E ABE AB + E

End product + End product + enzyme Enzyme-substrate complex Substrate + enzyme

The theory of enzyme action in which the enzyme and substrate fit together at an active site is called the

lock-and-key model. The notched surface of a key can open only one lock. In a similar way, the shape of the active site of an enzyme fits the shape of only certain substrates. Thus, each enzyme can catalyze a reaction only of those substrates.

Characteristics of Enzyme Action

The following statements are generally true of enzyme action.

1- Small amounts of an enzyme can cause the reaction of large quantities of substrate. The time required for an enzyme-substrate complex to form and a reaction to occur is very short. A single enzyme molecule can catalyze thousands of substrate reactions each second. Thus, only small amounts of any enzyme need be present in a cell at any given time.

2-Enzymes enable cell reactions to proceed at normal temperatures. Many chemical reactions that occur very slowly at ordinary temperatures can be speeded up by raising the temperature. However, high temperatures would destroy living cells. Enzymes speed up reactions in the cell without requiring high temperatures.

3-Enzymes work best at certain temperatures. Enzyme action depends on the random motion of molecules, which brings the substrates into contact with the enzymes. This random motion increases as the temperature rises. If the temperature is low, the rate at which enzyme-substrate complexes form will be low (see Figure). The effect of the enzyme will therefore be reduced. At somewhat higher temperatures, the enzyme becomes more effective, because complexes are forming at a faster rate. At still higher temperatures, however, the enzyme protein starts to break down, a process called denaturation. The shape of the enzyme molecule changes. its active site no longer fits the substrate molecule, and it loses its effectiveness. There is therefore a particular temperature—the optimum temperature—at which enzyme effectiveness is greatest. Optimum temperatures for enzymes in living cells are usually close to the normal cell temperature.

4-Each enzyme works best at a certain pH. The effectiveness of an enzyme depends on the pH of the surrounding medium (see Figure). The pH of the contents of the human stomach, for example, is slightly acid. The enzyme pepsin, which starts the digestion of proteins in the stomach, is most effective at this pH level (pH: 2-3-4). The pH in the intestine is slightly basic. Here the enzyme trypsin, which continues the digestion of proteins, works best at pH: 10-11-12.

5-The rate of an enzyme-controlled reaction depends on the concentrations of enzyme and substrate. If relatively little enzyme is present, the number of substrate molecules it can act on in a given time is limited. Increasing the amount of enzyme will increase the rate at which the reaction products are formed (see Figure). When, however, all the substrate molecules are being acted on, a further increase in enzyme concentration will have little or no effect on output. Likewise, when all the enzyme molecules and substrate molecules are in the process of reaction, adding more substrate will have no effect on rate of output.

6-Some enzymes need substances called coenzymes in order to function. Many enzymes do not work by themselves. They require some sort of a helper. This helper is a molecule that aids in the reaction by removing one of the end products or by bringing in part of the substrate. Such helpers are called Coenzymes. They are organic substances but are not proteins, enable enzymes to perform their catalytic function. Some vitamins are needed in the body because they are coenzymes. They are necessary for good health.

7-Some enzymes function inside the cell, others act outside the cell. Most of these enzymes are used within the cell. However, some enzymes are passed out of the cell to catalyze reactions outside the cell. All digestive enzymes produced in the human digestive tract are of this type. For example, pepsin is made inside the cells of glands in the stomach wall. It then leaves the cells and mixes with food in the stomach. Here, proteins in the food are broken down to simpler molecules, which can later be absorbed through cell membranes and enter the bloodstream. Another example of extracellular enzyme action is digestion in fungi.