DNA Replication is the process of making 2 identical copies of DNA from one original DNA copy. This process is semi-conservative, meaning that each new copy ends up with one of the original strands of DNA. Essentially the DNA “unzips” and each of the original strands acts as a template for the new strands. DNA is synthesized in a 5’–>3’ direction during the S phase of the cell cycle

• DNA Polymerase is the enzyme responsible for DNA replication. It synthesizes new DNA strands in a 5’–>3’ direction, but also has 3’–>5’ exonuclease proof reading capabilities that removes improper base pairs. In Prokaryotes DNA Pol I mainly handles proofreading & replacement of RNA primer, while DNA Pol III synthesizes most of the DNA.
• Topoisomerase is the enzyme that creates single strand breaks in the DNA’s (Break phosphodiester bond) and allows free rotation to relieve supercoils created by replication/transcription process. Bacterial topoisomerase is the target of the antibiotic Fluoroquinolone (Cipro). An auto-antibody targeted at topoisomerase is common in Scleroderma.

Transcription is whentemplate DNA strand is converted to complementary coding RNA to begin gene expression. The RNA is very similar to DNA, except that it has Uracil (U) in place of Thymine (T) and it is single stranded. RNA is synthesized in a 5′ –> 3′ direction as the RNA Polymerase moves along the DNA in a 3′–> 5′ Direction.

• RNA Polymerase is the enzyme responsible for the conversion of DNA to RNA (transcription). In Eukaryotes RNA Pol I makes Ribosomal RNA (rRNA), II makes Messenger RNA (mRNA) & III makes tRNA.

Post-Transcriptional Modification (RNA Processing) is the process of converting immature RNA to mature RNA that is ready to be translated. A 5’ Cap of a modified guanine is added to the end of the RNA to help the ribosome recognize the RNA. A Poly A Tail is added to the 3’ end. It is a AAUAAA sequence that is added without following a complementary DNA sequence and helps prevent degradation of the RNA. The splicesome also removes introns and joins exons. This splicing can be carried out multiple different ways creating different proteins from a single gene.

Translation is the process by which a RNA sequence is converted into a set of amino acids (AKA a protein). Each amino acid is coded for by a 3 nucleotide sequence called a codon.  The tRNA, which carries the amino acid, has a complimentary anti-codon which recognizes the codon. The mRNA is read in a 5’–>3’ direction. Translation begins at the start codon (AUG) and ends at a stop codon.

Now that you are done with this video you should check out the next video in the Genetics section which covers Epigenetics, Histone Modification, Prader-Willi & Angelman Syndrome. 

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