Protein Synthesis

• Protein synthesis is the process of making proteins, which involves two steps: transcription and translation.
• Transcription is the process of taking a single gene of DNA and copying it into a structure called mRNA.
• Translation is the process of taking this mRNA strand and using it to produce a protein.
• Before a protein can be made, the specific sequence of bases has to be read by one of these structures called ribosomes, which are outside of the nucleus.
• The DNA is so big it can't leave the nucleus itself, so if a gene is needed to make a protein, a copy of that gene must be made first.
• The copy of the gene, mRNA, is a small structure that is mostly similar to DNA but has a few important differences: it is shorter, single-stranded, and contains uracil instead of thymine.
• Transcription is the process of forming mRNA from DNA, and involves an enzyme called RNA polymerase binding to the DNA just before where the gene starts, the two strands of DNA separating apart, and the RNA polymerase reading the bases one by one and using them to make an mRNA strand.
• The mRNA bases will always be complementary to the DNA bases, so A on DNA will always pair with G or M on mRNA, T with C, and A with U.
• If there is an A on the DNA strand, it will pair with a U on the mRNA strand because mRNA doesn't have T.
• RNA polymerase builds up the mRNA base by base as it moves along the entire gene.
• The DNA strand keeps on separating just ahead of the RNA polymerase and closing just behind it, so only a small section of the DNA is ever exposed.
• Once the RNA polymerase has finished making the mRNA, it detaches from the DNA and the DNA strands can close back up.
• The mRNA is then free to leave the nucleus and head off to the ribosome.
• The strand of DNA which the RNA polymerase moved along is called the template strand, which is used to make the mRNA.
• Inside the nucleus, there is an mRNA copy of the gene which is free to leave the nucleus and make its way to the ribosome, where it can undergo translation to produce a protein.
• For both DNA and mRNA, each group of three bases which is called a triplet or codon codes for a specific amino acid to make proteins.
• Our cells use 20 different amino acids and each one has a different three base codon.
• The amino acids themselves are brought to the ribosome by molecules called transfer RNA (trna), which stands for transfer rna.
• Transfer RNA molecules have the amino acid at the top and an anticodon at the bottom, which is a sequence of three bases that are complementary to these three bases on the mRNA and it's these three bases on the mRNA that code for the amino acid that the trna is carrying.
• Because each type of transfer RNA molecule is specific to a particular triplet on the mRNA, it can ensure that it always brings down the correct amino acid.
• The process of translation involves the mRNA strand and the ribosome binding together and the ribosome starting to build the protein by adding one amino acid at a time.
• The amino acid chain will detach from the ribosome and then finally the chain can fold up on itself to form a protein.