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This article explores the groundbreaking work of Watson and Crick regarding DNA structure and its implications for replication and protein synthesis. It discusses the semi-conservative replication process where each DNA strand serves as a template, facilitated by key enzymes like helicase and DNA polymerase. Furthermore, it delves into protein synthesis involving transcription and translation, highlighting the roles of different types of RNA (mRNA, tRNA, rRNA), the significance of promoter regions, and the intricacies of mRNA splicing. The article provides a comprehensive overview of these fundamental biological processes.
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Watson and Crick…again • After describing the structure of DNA, they released a second paper • Basically stated that the base pairing model indicated a method for replication • Each strand would serve as a template for a new companion chain, called the complement
As a result, each daughter strand has a strand from the original molecule • This is referred to as semi-conservative replication • So, from the parent strand, new bases are added to added according to the base pairing model • A strand of ATTCGACT would match up with TAAGCTGA
Enzymes • A wide variety of enzymes are used during the replication process (recall anything ending in –ase is an enzyme) • The enzyme that opens the parent molecule by breaking the hydrogen bonds is helicase • It “unzips” the molecule • The other principle enzyme is DNA polymerase (actually three variations on it!) • It moves along the unwound strand, adding the appropriate bases
Another version of the polymerase “checks” to ensure that no mistakes were made
Protein Synthesis • Now that we know the structure of DNA, we can analyze how proteins are made • Broken down into two processes: transcription and translation • This is where RNA is used in our body • Structurally, RNA contains a ribose sugar • The 2’ carbon contains a hydroxyl group as opposed to a hydrogen
Additionally, RNA tends to be single stranded, and contains a uracil in the place of thymine
Different Types of RNA • In protein synthesis, three unique types of RNA are used: Messenger RNA (mRNA) • RNA copy of the DNA strand to be “read” during translation Transfer RNA (tRNA) • Carries individual amino acids to site of replication
Ribosomal RNA (rRNA) • Attached to ribsome complex, site of protein synthesis rRNA tRNA
Transcription • A complementary strand of mRNA is made, first by unzipping the DNA molecule • This time, by RNA polymerase • This only happens on specific regions of DNA known as promoter regions • That way, it isn’t just a random region • Similar regions cause the transcription process to stop
RNA Splicing • Certain regions of DNA do not code for any proteins that we use, called introns • We mentioned these before as the “junk” regions • The introns must be spliced out, joining all the coding regions known as exons • Finally, a 5’ cap and poly A tail must be tacked on to the ends to finish the editing process
Translation • The processed mRNA is now reading to be decoded • The “language” is spoken in three base “words”
Translation begins when the mRNA binds to the rRNA on a ribosome • This moves along the sequence until an AUG codon is found • This is the start codon, and the methionine code, hence all protains begin with Met • tRNA then attaches and drops off the appropriate amino acid • It does this by have a matching anticodon • Sequential amino acids are linked by peptide bonds • So, it is called a polypeptide
This process continues until a stop codon is found • Polypeptide and mRNA are release • Polypeptide goes through up to four stages of folding to become a mature protein
