MicroBiology

Have you ever wondered that how life continues in human beings? How do we all human beings share the same characteristic features? Yes, DNA is the answer to all your questions. The most significant mechanism for all the life cells that plays an important role in producing off springs is the DNA replication. DNA replication is the process that duplicates the DNA of a cell.

Each cell in our body consists of one or more than one DNA polymer molecules. These molecules need to be duplicated, so that the process of cell duplication takes place. This is what we call as DNA replication. In living organisms, the formation of DNA takes place in two strands. Each strand contains units of nucleotides. These two strands of DNA appear like two chains forming the DNA Double Helix. The process of DNA replication opens up the Double Helix and separates them into two strands. These two strands are then copied, and the result is that two new molecules of DNA are formed.

Steps involved in the replication of DNA

The first step in the DNA replication process is the breaking of the hydrogen bonds. This is the starting point where the two strands are unwounded. The enzyme that brings about the splitting between the two strands is Helicase and the structure thus created is referred as “Replication Fork”. The next step in the process is binding the RNA primase. The RNA nucleotides are attracted by the RNA Primase that gets bound to the DNA nucleotides because of the presence of hydrogen bonds between the bases. The RNA Primers are very vital for the DNA polymerase for binding the nucleotides, and the result is that the daughter strand is elongated because of this.

The DNA polymerase in the outer strand reads the fragments and thus, the RNA Primers are detached from there. The action of DNA polymerase closes the gaps formed by adding complimentary nucleotides, whereas the DNA Ligase closes the gaps by adding phosphates. Finally, the last step of the process is the termination. This process takes place only after the DNA polymerase reaches towards the end of the strands. DNA replication process is completed only after a repair mechanism fixes all the errors taken place during the replication process. There are enzymes such as DNA polymerase that fills up the gaps and nucleases that eliminates the improper nucleotides.

The speed of DNA replication in human beings is approximately 50 nucleotides/ second/ replication fork. It is relatively low when compared with the speed of DNA replication in bacteria’s. Nevertheless, human genome can be copied in just a few hours as a number of replication forks occur at the same time. This is also known as multiple initiation sites.

DNA replication is also performed artificially with the use of same enzymes that are used within the cell. Artificial DNA Primers and DNA Polymerases are used for initiating the synthesis of DNA at known sequences in a molecule of a template. Common laboratory method and polymerase chain reactions makes use of artificial synthesis rapidly in a cyclic form and particularly intensify the targeted fragment of DNA from the DNA pool.

RNA is one of the nucleic acid. RNA stands for Ribose nucleic acid. RNA consists of long chains of nucleotide units. The nucleotides consist of the nitrogenous base, phosphate and ribose sugar. DNA and RNA are almost the same only there are some structural differences between the both. The structure of the DNA is usually double stranded while on the other hand the structure of the RNA is single stranded.

The nucleotides of DNA contain deoxyribose while that of the RNA contains the ribose only. Both the DNA has thymine as a base while RNA has uracil as the base. The enzyme called the RNA polymerases transcribes from the DNA. Later it gets processed over by some other enzymes as well. RNA is also known as the “main center for the protein synthesis”.

Structure of RNA

Each nucleotide present in the RNA comprises of a ribose sugar with carbons (the carbons are number between 1’ to 5’). Adenine, Cytosine, Guanine, Uracil are attached to the base to the 1’ position. Cytosine and Uracil fall under pyrimidines while the adenine and guanine fall under the purines. At the 3’ position of the ribose and 5’ position a phosphate group is attached. Due to the negative charge carried by the phosphate group, the RNA also becomes charged molecule.

There is a possibility of hydrogen bond formation between the guanine and cytosine or between guanine and uracil by the bases. Many other interactions also take place, interactions which involve group of adenine base binding with each other.

RNA has a hydroxyl group present at the 2’ position of ribose sugar which is one of the most vital features for distinguishing RNA from DNA. A-form geometry is adopted by the helix rather than B form due to the presence of the functional group. Due to this the major deep and narrow groove and wide shallow groove is formed.

Though originally RNA is transcribed of only 4 bases some other sugars and bases also mature in the RNA. A C-N bond to a C-C bond is changed by the Pseudouridine. Also, at number of places ribothymidine is found. Other such type of the modified base is the hypoxanthine whose nucleoside is referred as inosine. Inosine is very important as it plays the main role in wooble hypothesis of genetic code.