[Music] hi welcome back to three sight lessons cold got UK by the end of this video you should be able to describe the stages of protein synthesis and this is for triple biology higher-tier only now I need to point out a couple of things here this topic and was a lot of detail also since this is specifically a triple biology topic the exam question could be quite tricky so you should watch this video a couple of times in the last video we saw that DNA is a double-stranded polymer of molecules called nucleotides there are four different nucleotides and I'm showing them here each nucleotide has a different base and scientists call these a T G and C and this shows you a short stretch of the DNA molecule remember that the two strands are complementary as a always pairs with T on the opposite strand and C always pairs with G so in this video we're looking at how DNA determines the structure of proteins in a previous video we saw that proteins are polymers of amino acids most proteins contain hundreds of mino haces joined together in humans there are 20 different amino acids I'm showing you here two different proteins as you can see they both have a different order of amino acids now the specific order of the amino acids determines the shape of the protein and the shape of the protein determines its function for example protein a might be an enzyme molecule such as amylase whereas protein B could form a structural protein such as collagen other proteins could become hormones such as insulin so as we've seen the order of amino acids in the protein determines its shape and its function now the key factors are the order amino acids in a protein is determined by the sequence of bases in the gene for that protein imagine that the cells making a protein for example an enzyme I'm showing you a short stretch of the gene here I should point out that this only shows you one of the strands of DNA but remember that the other strand is complimentary to this one the cell reads the DNA sequence as triplets of bases on each triplet and codes for a specific amino acid in the protein I'm showing you the amino acids here okay now protein synthesis consists of two stages the first stage takes place in the nucleus and the second stage takes place in the cytoplasm the first stage is called transcription in this stage that base sequence of the gene is copied into a complementary template molecule scientists call this template messenger RNA or mRNA for short you'll notice that mRNA is a single-stranded molecule the mRNA now passes after the nucleus and into the cytoplasm the second stage of protein synthesis is called translation in this stage the mRNA molecule attaches to a ribosome amino acids are now brought to the ribosome on cavea molecules these carrier molecules are called transfer RNA or tRNA for short the ribosome now reads The Triplets of bases on the mRNA and uses this to join together the correct amino acids in the correct order once the protein chain is complete it now folds into its unique shape and remember that the shape enables a protein to do its job remember you'll find plenty of questions on protein synthesis in my vision workbook and you can get that by clicking on the link above you [Music]