Purpose of translation DNA contains information necessary to make proteins Proteins make up most tissue in your body Proteins are made of amino acids Ribosomes link amino acids together (condensation) to create polypeptides Ex: leucine – cysteine – serine – tryptophan – leucine
DNA’s role DNA determines the AA sequence DNA is a code – trapped inside the nucleus: how can message reach ribosome? mRNA is made from DNA (transcription) in the nucleus mRNA goes to cytoplasm Ribosome “reads” mRNA Every 3 bases = codon = 1 amino acid
CodonAmino Acid Use a codon chart to determine which AA’s are being made Example: mRNA = AUG – CCA – AGC – GGU – GCA – UGA Polypeptide = ?
mRNA x Polypeptide Some cases: One gene one mRNA one polypeptide Other cases: One gene one mRNA mRNA modified different polypeptides
Protein synthesis = Translation Ribosomes made of rRNA and proteins contains 2 subunits: large and small has 2 binding sites for tRNA (P and A) and 1 for mRNA synthesize protein (polypeptide chains) in a process called Translation.
Steps of Translation ribosome attach to mRNA 2 mRNA codons get “read” by the ribosome. tRNA brings carrying an AA will come in tRNA anticodon will have a complementary binding with the mRNA codon amino acids associated with tRNA’s get connected ribosome recognizes STOP codon polypeptide is released
The Code is Degenerate and Universal Genetic Code = based on a set of 3 nucleotides (CODONS). If we had 2 nucleotides = 16 aa (not enough to code for 20 aa) we must have 3 nucleotides = 64 (more than necessary – code is degenerate – more than 1 codon will code for the same aa) Ex: CUU, CUC, CUA and CUG make leucine code is universal= for every organism, same codon codes for same aa
Steps in Translation - HL Initiation mRNA , the first tRNA, and the ribosomal subunits come together Elongation A succession of tRNA’s add their amino acids to the polypeptide chain as mRNA is moved through the ribosome, one codon at a time Termination Ribosome recognizes the stop codon and polypeptide is terminated and release Translocation: Moving from one spot to the other.
Structure of tRNA Clover-shaped Anticodon on one end CCA on the other end, where amino acid will bind. AA attached to tRNA 3’ terminal by tRNA activating enzyme 20 types of enzymes = 20 AAs ATP is needed for this (later used to link AA to polypeptide chain)
Binding Sites A site: hold a tRNA carrying the next amino acid to be added to chain P site: hold the tRNA carrying the growing polypeptide chain E site: exit site
Direction of Translation Occurs in 5’3’ direction with regard to the mRNA. Because start codon is found on the 5’ end
Other Translation terms to know Polysomes Ribosomes that are clustered together on the mRNA, creating several copies of the same polypeptide at the same time Start codons Found at the 5’ end of mRNA AUG Stop codons Translation stops- A site is not copied UAG, UAA, UGA
Free vs. Bound Ribosomes Free ribosomes: synthesize proteins for use within the cell Bound ribosomes : (rough ER) synthesize proteins for secretion or for lysosomes.