Describe the process of DNAreplication in a prokaryotic organism. Start with the

Question

Describe the process of DNAreplication in a prokaryotic organism. Start with the origin ofreplication. Describe what enzymes are involved in the process ofuncoiling, straightening and stabilizing the strands, and anyenzymes and processes involved in initiating replication as well asenzymes and processes used in the actual DNA replication. Explainhow and why the replication process varies on the two DNA templatestrands. Finally, describe how the cell is able to correct anyerrors that have occurred in the replicationprocess.

Explanation / Answer

The hereditary material in a cell is coded in the sequence ofthe heterocyclic amines of DNA. There are normally46 strands of DNA called chromosomes in humancells. Specific regions, called genes, on eachchromosome contain the hereditary information which distinguishesindividuals from each other. The genes also contain the codedinformation required for the synthesis of proteins and enzymesneeded for the normal functions of the cells. Bacterial cells mayhave 1000 genes, while the human cell contains more than a milliongenes. A single E. coli (bacteria) chromosome of double helical DNAconsists of 3.4 million base pairs.

Prior to cell division, the DNA material in the original cellmust be duplicated so that after cell division, each new cellcontains the full amount of DNA material. The process of DNAduplication is usually called replication. Thereplication is termed semiconservative since each new cell containsone strand of original DNA and one newly synthesized strand of DNA.The original polynucleotide strand of DNA serves as a template toguide the synthesis of the new complementary polynucleotide of DNA.A template is a guide that may be used for example, by a carpenterto cut intricate designs in wood.

DNA Replication Process:

Several enzymes and proteins are involved with the replicationof DNA. At a specific point, the double helix of DNA is caused tounwind possibly in response to an initial synthesis of a short RNAstrand using the enzyme helicase. Proteins are available to holdthe unwound DNA strands in position. Each strand of DNA then servesas a template to guide the synthesis of its complementary strand ofDNA. DNA polymerase III is used to join the appropriate nucleotideunits together. The replication process is shown in graphic on theleft.

Template #1 guides the formation of a new complementary #2strand. The DNA template guides the formation of a DNAcomplementary strand - not an exact copy of itself. For examplelooking at template # 2, this process occurs because theheterocyclic amine, adenine (A), codes or guides the incorporationof only thymine (T) to synthesize new DNA #1. The replication ofDNA is guided by the base pairing principle so that no otherheterocyclic amine nucleotide can hydrogen bond and fit correctlywith cytosine. The next heterocyclic amine, cytosine (C), guidesthe incorporation of guanine (G) while similar arguments apply tothe other bases. Exactly the opposite reaction occurs usingtemplate # 2 where cytosine (C) guides the incorporation of guanine(G) to form a new complementary #2 strand.

It is so important that the cells duplicate the DNA geneticmaterial exactly, that the sequence of newly synthesizednucleotides is checked by two different polymerase enzymes. Thesecond enzyme can check for and actually correct any mistake ofmismatched base pairs in the sequence. The mismatched nucleotidesare hydrolyzed and cut out and new correct ones are inserted.

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