DNA Replication and Protein Synthesis

So DNA replication begins at a specific point in the DNA molecule called the origin of replication. First, the enzyme Helicase separates (or unzips) a portion of the DNA molecule.This causes two single stranded regions of DNA to form. Next, RNA primase comes along on the lagging strand and builds RNA primer. RNA primer is necessary in DNA replication because without it DNA polymrase III cannot not begin a new chain of DNA. And so, the next step is obviously DNA pulymerase III building a new chain of DNA. Then, DNA polymerase I comes in and replaces the RNA primer with DNA nucleotides, leaving fragments know as Okazaki fragments. Lastly, the DNA ligase enzyme swoops in and bonds these fragments together, completing the process of replication. 

It is also important to know that you read the strand from 3' to 5', but it is built from 5' to 3'. 



Protein synthesis is a whole other process. It starts off with Transcription, which is the separation of the double helix. This happens in a eukeryotic cell, a cell with a nucleus. The double helix has to be separated because a full DNA strand is too big to leave the nucleus. Therefore, it must transcribe so that it can fit and change from DNA to mRNA. Before the mRNA can leave the nucleus, the introns on the strand must be cut out (splicesome). The exons are then glued together. A G-cap (Guanine nucleotide) and Poly-A tail (Adenine nucleotides) are put on each end of the strand so that it does not get eaten by enzymes. These two protect the message. Finally, it can leave the nucleus.

Next, Translation occurs. The mRNA will now translate into an amino acid.The mRNA is decode by the ribosome to produce a specific amino acid chain. Met (AUG) is always the first amino acid in the chain. The ribosome reads the codons from 5' to 3'. Translation occurs in the cell's cytoplasm, where the ribosome are located, and they bind to the mRNA. The ribosome makes decoding easier by binding tRNAs with anticodon sequences on the mRNA. tRNA acts as a bus for amino acids and carries them to the mRNA. These amino acids are binded together by peptide bonds into a polypeptide. The amino acids are chained together into polypeptides while the mRNA passes through the ribosome and is read by the ribosome.