By A.K. Matai
If you can’t remember Biology 107 to save your life, take comfort in the fact that you are not alone. This post will be a quick recap of what happened in Biology 107. I would recommend that you have these concepts straight in your head because they will haunt you in the future.
The Central Dogma, Directionality and the Antiparallel Nature of DNA/RNA Synthesis
Figure 1. The Central Dogma. Flow of genetic information from DNA to RNA to Protein.
Figure 2. Antiparallel Nature of DNA. The strands of DNA are parallel but they run in opposing directions.
Figure 3. Antiparallel Nature of RNA Synthesis. Regardless of the DNA strand that serves as the template, the 5′ and 3′ ends of the RNA exhibit an antiparallel nature with is partner DNA strand.
DNA replication starts at the ORI where HELICASE unwinds the DNA double helix. PRIMASE synthesizes a RNA PRIMER which serves as the starting point for new DNA synthesis. After the primer has been laid down, DNA POLYMERASE begins replicating the DNA by matching nucleotides to the original strand. The LEADING STRAND is synthesized continuously in a 5′ to 3′ direction whereas the LAGGING STRAND is synthesized discontinuously in the 5′ to 3′ direction forming short fragments called OKAZAKI FRAGMENTS. Once synthesis is complete, another DNA POLYMERASE comes in and replaces the RNA PRIMER with DNA. The gaps between DNA segments are sealed by DNA LIGASE.
DNA POLYMERASE is an enzyme that works in the 5′ to 3′ direction and can only add DNA nucleotides to an existing sequence (i.e. the RNA PRIMER).
Transcription (RNA Synthesis)
RNA POLYMERASE requires a PROMOTER SEQUENCE to initiate the transcription of a gene. Once transcription is initiated, RNA POLYMERASE begins mRNA synthesis by matching complementary bases to the TEMPLATE STRAND whereas the other strand that remains untouched is simply referred to as the NON-TEMPLATE STRAND. When the RNA POLYMERASE encounters the TRANSCRIPTION TERMINATION SEQUENCE, transcription is terminated. mRNA copies of the gene then go on to serve as the template for protein synthesis.
RNA POLYMERASE synthesizes RNA in a 5′ to 3′ direction.
Translation (Protein Synthesis)
Translation of mRNA occurs in the RIBOSOME. The RIBOSOME binds the mRNA and starts translation when it reaches the start codon, AUG. CODONS are the three letter combinations of nucleotides that correspond with a specific AMINO ACID. A tRNA (TRANSFER RNA) carrying methionine corresponding to AUG is brought to the RIBOSOME. The RIBOSOME continues to translate each codon and the corresponding amino acid is added to the growing chain through a peptide bond. Translation is terminated when the RIBOSOME reaches a stop codon (UAA, UGA, UAG).
Be comfortable using a codon table to translate CODONS on the mRNA into AMINO ACIDS.
Weekly Tip to Succeed
While memorization is a small component of Biology 207, it is a necessary to remember certain basics. My advice to improve your memory is to either apply the information to the extent that it becomes second nature or use a memorization technique that I call “linkage” where key words act as cues or “links” to bigger ideas or concepts.
Questions, Comments or Concerns?
Post a comment down below! I am happy to explain or expand on anything I have written in this post.
Caulton, Simon. Condensing chromosomes. 2012. https://commons.wikimedia.org/wiki/File:CONDENSING_CHROMOSOMES_2.jpg. Web. 12 Feb. 2017.