protein synthesis

• what is protein synthesis

  it is how the body makes proteins
• each aminoacid is coded for by a specific sequence of 3 bases ( a codon ) the order of the bases on the dna tell us the order for combining amino acids to create particular proteins.

  we can change the proteins made by a gene by altering the sequence of bases in that gene
• the process of making proteins involves transcription and translation.
• transcription

  double stranded dna is "un-zipped" and one strand is used to make a template of the dna code in the form of mRNA (messenger RNA) which is like DNA however the base A now pairs with U (uracil) instead of pairing with T (thymine) the mRNA template then leaves the nucleus.
• why does a template of dna leave the nucleus

  as the whole of DNA is to large to leave the cell so the DNA is in the code form mRNA
• transcription

  the template (mRNA) is then used to guide protein synthesis on ribosomes located in the cytoplasm, specific amino acids are delivered by carrier molecules to add to the forming protein chain
• after the 2 stages

  the long protein chains folds up giving it a unique strucutre, the unique structure is essential to the proteins functions in the forms of enzymes, hormones or structural proteins like collagen
• DNA helix unwinding

  1. Breaking of weak Hydrogen bonds between base pairs

  2. Caused by helicase enzyme
• Helicase enzyme

  Enzyme that unwinds the DNA helix
• Transcription

  1. RNA polymerase attaches to DNA in non-coding region

  2. RNA polymerase moves along DNA strand

  3. Free RNA nucleotides form hydrogen bonds with exposed DNA nucleotides by complementary base pairing

  4. Strand of mRNA formed
• RNA nucleotides

  Contain the same bases as DNA, except that T is replaced by U
• U base

  Pairs with A
• The strand of mRNA is an opposite copy of the DNA strand (except that U replaces T)
• The newly formed strand of mRNA is now ready to leave the nucleus and travel to the ribosome
• mRNA translation

  1. mRNA strand travels through cytoplasm

  2. mRNA strand attaches to ribosome

  3. mRNA strand passes through ribosome
• Codon

  Every three mRNA bases
• Protein synthesis

  1. Ribosome lines up one complementary tRNA molecule for every three mRNA bases

  2. tRNA molecules transport specific amino acids to ribosome

  3. tRNA molecules leave amino acids behind at ribosome

  4. Used tRNA molecules exit ribosome and collect another amino acid

  5. Chain of several hundred amino acids in correct order forms polypeptide
• Triplet code

  Three mRNA bases for each tRNA molecule
• A chain of several hundred amino acids in the correct order according to the original DNA is then made. This is called a polypeptide.
• protein synthesis happens in two stages; transcription and translation