Bio Chemistry

There are defined temperature ranges under which enzymes operate. There is a specific temperature-level where the enzymes have maximum efficiency. Therefore, temperature variations affect enzymatic activity and the speed of the reactions they catalyze.

In addition, as proteins, enzymes can be denaturated under extreme temperatures.

Initially as substrate concentration increases the speed of the reaction increases, this happens because free activation centers of the enzyme bind to free substrates. Once all activation centers of the available enzymes become bound to their substrates new increments of the substrate concentration will have no effect in the speed of the reaction.

Pepsin acts within the stomach so its optimum pH is around 2, an acid pH. When the enzyme passes to the duodenum, it meets a higher pH and its enzyme activity ends.

Most enzymes act in pH between 6 and 8, a range that corresponds to the general acidic level of cells and blood. There are enzymes however, that act only under very acid or very basic pH. Therefore, enzyme activity depends on a pH interval.

In the stomach, for example, the gastric juice has a very low pH, around 2, and there the enzyme pepsin acts intensively digesting proteins. In the duodenum, pancreatic secretions increase the pH of the enteric juice for the action of other digestive enzymes, for example, trypsin.

In the addition of the hydrogen, halide to unsaturated alkenes in the presence of peroxides the halide adds to the carbon atom linked to more number of hydrogen atoms and hydrogen adds to the carbon atom linked to lesser number of hydrogen atoms. This is called Peroxide effect (or) Kharasch effect.

CH3-CH2-CH2BRàCH3-CH=CH2+HBr-

N Prophyl bromide

The curve of variation of speed of the enzymatic reaction as function of growing substrate concentration is a growing curves until the point where it stabilizes due to the saturation of the activation centers of the enzymes.

The curve of variation of speed of the enzymatic reaction as function of growing temperature has a crescent portion, reaches a peak (the optimum temperature) then it decreases, and reaches zero in the point of inactivity of the enzymes by denaturation.

Some enzymes need other associated molecules to work. These molecules are called enzyme cofactors and they can be, for example, organic ions, like mineral salts, or organic molecules.

Inactive enzymes for not being bound to their cofactors are called apoenzymes. Active enzymes bound to their cofactors are called holoenzymes.

The concentration of hydrogen ions in solution affects the enzyme activity. Each enzyme has maximal efficiency under an optimum pH.

Since pH is one of the factors for the denaturation of proteins, if an enzyme is submitted to a pH level under which, it is denaturated there will be no enzymatic activity.

Benz amide on treatment with bromide and Caustic potash produce aniline

C6H5NH2+2KBr+2H2O+K2CO3àC6H5CoNH2+Br2+4KOH

Allosteric enzymes are those that have more activation center and to which other substances called allosteric regulators bind.

Allosteric regulators can be allosteric inhibitors or allosteric activators. The interaction between an allosteric enzyme and the allosteric inhibitor disallows the binding of the substrate to the enzyme. The interaction between the allosteric enzyme and the allosteric activator allows the binding of the substrate to the enzyme and sometimes increases the affinity of the enzyme for the substrate. This regulatory phenomenon of the enzyme activity is called allosterism.

Enzyme Activity: allosteric enzymes

Zymogens, or proenzymes, are enzymes secreted in inactive form. Under certain conditions, a zymogen shifts to the active form of the enzyme. Zymogen secretions in general happen because the enzyme activity can harm the secretory tissue.

For example, the pepsinogen secreted by the stomach becomes active under acid pH turning into the enzyme pepsin. Other well-known zymogens are trypsinogen and chymotrypsinogen. Enzymes are secreted by the exocrine pancreas and respectively trypsin and chymotrypsin.

Penicillin, discovered by the Scottish doctor Alexander Fleming, in 1928, is a drug that inhibits enzymes necessary for the synthesis of peptidoglycans, a constituent of the bacterial cell wall. With the inhibition, the bacterial population stops to grow because there is no new cell wall formation.

Fleming won the Nobel Prize in Medicine for the discovery of penicillin.

DNA and RNA, the nucleic acids, are the molecules responsible for the hereditary information that commands the protein synthesis in the living beings. The name “nucleic” derives from the fact that they were discovered (by the Swiss biochemist Friedrich Miescher, in 1869) within the cell nucleus. In that time, it was not known that those substances contained the hereditary information.

Protease inhibitors are some of the antiretroviral drugs used to treat HIV infection. Protease is an enzyme necessary for the assembling of the HIV after the synthesis of its proteins within the host cell. The protease inhibitor binds to the activation center of the enzyme blocking the formation of the enzyme-substrate complex and the enzyme activity thus impairing the viral replication.

Nucleic acids are formed by sequences of nucleotides.

Nucleotides are constituted by one molecule of sugar (ribose in DNA and deoxyribose in RNA) bound to one molecule of phosphate and to one nitrogen-containing base (adenine, uracil, cytosine, or guanine, in RNA, and adenine, thymine, cytosine, and guanine, in DNA).

Nucleic Acid Review - Image Diversity: nucleotide structure nitrogen-containing bases

In eukaryotic cells, DNA is found within the cell nucleus. In prokaryotic cells, DNA is found dispersed in the cytosol, the fluid space inside the cell.

Other DNA molecules can also be found within mitochondria and chloroplasts, specialized organelles of eukaryotic cells.

Pentoses are carbohydrates made of five carbons. Deoxyribose is the pentose that constitutes DNA nucleotides and ribose is the pentose that is part of RNA nucleotides.

The nitrogen-containing bases that form DNA and RNA are classified as pyrimidine and purine bases.

By the analysis of the structural formulas of those nitrogen-containing bases, it is possible to realize that three of them, cytosine, thymine and uracil, have only one nitrogenized carbon ring. The others, adenine and guanine, have two nitrogenized associated carbon rings.

Nucleic Acid Review - Image Diversity: pyrimidine bases purine bases

Watson (North American), Crick (British) and Wilkins (New Zealander) were the discoverers of the molecular structure of DNA, the double helix made of two polynucleotide chains paired by their nitrogen-containing bases. They won the Nobel Prize of Medicine in 1962 for the discovery.

Nucleic Acid Review - Image Diversity: Watson and Crick

The phosphate group of one nucleotide binds to the pentose of the other nucleotide and so on to make the polynucleotide chain.

Each extremity of a DNA or RNA chain can be distinguished from the other extremity according to their terminal chemical entity. The phosphate-ended extremity is called 5’-extremity and the pentose-ended extremity is called 3’-extremity. So DNA or RNA chains can be run along the 5’-3’ way or along the 3’-5’ way. These ways are important in several biological functions of DNA and RNA since some reactions specifically occur following one way or the other way.