Biology 6.4 Protein Synthesis

• There are four types of bases found on the mRNA strand - adenine, guanine, cytosine, and uracil.
• Protein synthesis is the process of making proteins.
• Protein synthesis takes place in the ribosomes.
• 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 the mRNA strand and using it to produce a protein.
• Because DNA is too large, it cannot leave the nucleus
• The specific sequence of bases must be read in order to make a protein -this is done by structures called ribosomes.
• Ribosomes are found outside of the nucleus.
• To use a gene for a protein, a copy of the gene must be made first so that it can leave the nucleus.
• The copy of the gene is called mRNA (messenger RNA)
• mRNA is shorter than DNA, is complimentary to DNA, is only a single strand and contains Uracil instead of Thymine.
• An enzyme called RNA polymerase binds to the DNA just before the gene starts, and moves along the template strand, causing the strands of DNA to separate just in front of it, exposing all the bases.
• The enzyme reads the bases as it moves along and creates an mRNA strand, a complimentary strand with complimentary bases.
• As the enzyme moves along, the DNA strands behind it close back up, exposing only a small section each time.
• When the enzyme finishes reading the template strand, it detaches from it and the DNA strands close back up, leaving mRNA that is free to leave the nucleus and go to the ribosomes to carry out translation.
• The mRNA is also split into triplets/codons which code for specific amino acids.
• The mRNA strand leaves the nucleus and binds to the ribosome.
• Ribosomes start to build proteins by adding one amino acid to another.
• Amino acids are brought to ribosomes by molecules called tRNA (transfer RNA).
• tRNA have the amino acid at the top and anti-codons/triplets at the bottom (this is complimentary to the triplet on the mRNA strand)
• The three bases on the mRNA code for the amino acid that the tRNA is carrying.
• tRNA brings the correct amino acid down to the ribosomes in the correct order.
• Translation: The process of converting the information in a gene into a sequence of amino acids.
• The triplet on the mRNA strand will attract the tRNA with the complimentary anti-codon.
• The tRNA molecules will bring the correct amino acids down to the ribosome in the correct order.
• The ribosome can join the amino acids together and start building up a chain.
• The ribosome moves along the mRNA strand.
• As the ribosome moves along the mRNA strand, it brings the next amino acid down, and the first tRNA molecule detaches but leaves behind its amino acid.
• The ribosome carries on moving along the mRNA strand until it reaches the end, where it has joined together a complete chain of amino acids.
• The complete chain of amino acids will detach from the ribosome and fold upon itself, forming a protein.
• A chain of amino acids is called a polypeptide.
• Ribosomes assemble proteins from amino acids