3.18B describe the stages of protein synthesis including transcription and translation, including the role of mRNA, ribosomes, tRNA, codons and anticodons

Proteins are made in 2 steps:
translation and transcription

Transcription:
DNA template is copied to synthesize an mRNA template. This is done by RNA polymerase via transcription.

- Transcription occurs in the nucleus, where there are 4 nucleotides (ATGC)
- RNA polymerase (the enzyme responsible in joining of the bases) binds to unzip the 2 DNA strands to copy complementary base pairs onto mRNA.
- RNA polymerase presents the free nucleotides to form complementary base pairs via hydrogen bonds to form an mRNA transcript.
   - if RNA polymerase presents an incorrect base, the nucleotide will break away.
   - if correct, they bind together to form complementary base pairs via hydrogen bonds.
- This process continues until RNA polymerase reaches the end of the DNA strand, causing mRNA transcript to peel away and exit the nucleus from the nuclear pore.
- RNA polymerase detaches from the DNA strand, and the DNA strand rewinds to its original state.

To summarise: Transcription is taken place in the nucleus, and the base sequence of the gene is copied to a complementary template molecule. This template molecule is called mRNA. mRNA is a single-stranded molecule. the mRNA now passes out of the nucleus and into the cytoplasm.


Translation:
- the second stage of protein synthesis is called translation
- In this stage, the mRNA attaches to a ribosome.
- Amino acids are now brought on the ribosome via carrier molecules called tRNA. 
- The ribosome now reads the triplet of bases (codons) on mRNA and uses this to join together the correct amino acids in the correct order.
- Once the protein chain is complete, it folds into its unique shape.