Transcription and translation 10T2K© Transcription and translation
Thing 1: Transcription makes one gene’s worth of RNA In order for the information in one gene (DNA that is the recipe for a protein) to be used to make a protein, it first has to be copied as RNA. Reading DNA to make RNA is called transcription.
Thing 2: The bases in a gene determine the bases in RNA During transcription, the DNA strands separate from each other (like opening a cookbook to the correct page). An enzyme “reads” the bases in the DNA, and makes RNA that is complementary to it. When transcription is done, the RNA leaves the DNA, and the DNA strands pair back together (like closing the cookbook after you copied a recipe).
DNA: GATCTTACG RNA: CUAGAAUGC
Thing 3: mRNA contains codons The kind of RNA that is the recipe for making a protein is called messenger RNA, or mRNA. mRNA contains codons. A codon is three bases, and is the recipe for one amino acid. A protein that is 100 amino acids long needs an mRNA that has 101 codons (including the stop codon).
Thing 4: Stop codons Some codons are called stop codons. They are the signal that a protein is finished being made.
Thing 5: The genetic code The genetic code is the meaning of each codon. Different organisms have the same genetic code. That is, UUU means phe in people and poodles and bacteria and mushrooms. We can use the genetic code table to figure out what amino acids are encoded in an mRNA.
The genetic code table
Thing 6: Translation is protein synthesis The process of reading an mRNA and making a protein is called translation.
Thing 7: tRNA is needed for translation Translation requires many molecules of tRNA (transfer RNA). Each tRNA has one anticodon, three bases that form base pairs with a codon. Each tRNA carries one amino acid. tRNAs with the same anticodon carry the same amino acid.
Two views of tRNA
Thing 8: tRNAs bring amino acids in order to mRNA The order of codons in mRNA determines the order that tRNAs are used during translation. The order of tRNAs determines the order that amino acids are added to a protein.
Thing 9: Translation happens in ribosomes Ribosomes make proteins by binding to mRNA and tRNAs, then catalyzing the assembly of the amino acids into a protein. tRNAs ACC GCU mRNA ||| ||| UGG CGA ||| ||| Trp Arg Ribosome
Thing 10: Where do transcription and translation happen? In eukaryotes, transcription happens in the nucleus because that’s where the DNA is. The mRNA then leaves the nucleus to be translated in the cytoplasm. Because prokaryotes don’t have membrane-bound organelles, both transcription and translation happen in the cytoplasm.