DNA Replication and Protein Synthesis

DNA Replication and Protein Synthesis

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

DNA Replication and Protein Synthesis