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Protein Synthesis-Translation Warm-up #6 1. 2. 3. 4. How is RNA different than DNA? Name the 3 steps of transcription. What is the end product of transcription? What is the difference between the sense and antisense DNA strands? 5. What is the role of RNA polymerase? 6. Describe the initiation step in transcription. 7. What are the “extra” things that happens to the mRNA in eukaryotic cells BEFORE it leaves the nucleus? aa From nucleus to cytoplasmaa aa aa aa aa aa transcription DNA mRNA aa aa protein aa translation trait nucleus cytoplasm Things you will need to know in order to understand translation: 1. mRNA codon chart 2. Redundancy of the code 3. Structure of tRNA 4. Ribosome structure Redundant but not Ambiguous • Codons GAA and GAG both specify glutamic acid (redundancy) • Neither of them specifies any other amino acid (no ambiguity) mRNA Codons: · codon = group of 3 mRNA nucleotides **1 codon codes for 1 amino acid · During translation, proteins are synthesized according to the genetic message of sequential codons along the mRNA The mRNA code • For ALL life! – strongest support for a common origin for all life • Code has duplicates – several codons for each amino acid – mutation insurance! Start codon AUG methionine Stop codons UGA, UAA, UAG shows the “dictionary” for the mRNA codons and their corresponding amino acids (know how to use) 1. DNA: AGC-GTG-CCA 2. mRNA: 3. amino acid chain (protein): ______________________ shows the “dictionary” for the mRNA codons and their corresponding amino acids (know how to use) 1. DNA: AGC-GTG-CCA 2. mRNA: UCG-CAC-GGU 3. amino acid chain (protein) = Serine- Histadine- Glycine tRNA Structure · Transfer RNA (tRNA) is the interpreter between the 2 forms of information: base sequence in mRNA and amino acid sequence in polypeptides -an enzyme links a specific amino acid from the cytosol/cytoplasm to each tRNA molecule on the 3’ end (CCA) using ATP for energy Amino acid location (CCA) 3 exposed bases LE 17-14b Amino acid attachment site 5 3 Hydrogen bonds 3 Anticodon Three-dimensional structure 5 Anticodon Symbol that is widely used LE 17-15 Amino acid Aminoacyl-tRNA synthetase (enzyme) Pyrophosphate Phosphates tRNA AMP Aminoacyl tRNA (an “activated amino acid”) Amino acid · Molecules of tRNA are specific for only 1 amino acid -one end of tRNA attaches to a specific amino acid -the other end Hydrogen bonds to mRNA codon by base pairing (anticodon = a sequence of 3 bases on tRNA) Ribosome Structure • large ribosomal subunit (50s) • small ribosomal subunit (30s) – each subunit = ribosome/protein complex • Consists of an mRNA binding site plus 3 tRNA binding sites E P A LE 17-16b P site (Peptidyl-tRNA binding site) A site (AminoacyltRNA binding site) E site (Exit site) E P A mRNA binding site Schematic model showing binding sites Large subunit Small subunit Process of Translation • Translation includes 4 processes: initiation, elongation, translocation, and termination 1. Initiation of Translation • mRNA binds to small ribosomal subunit • Initiator tRNA brings1st amino acid, Methionine (Met) to the initiation site on mRNA (start codon AUG= And U Go) • the Large ribosomal subunit binds – Met is in the “P” site – “A” site is available for the next tRNA LE 17-17 Large ribosomal subunit P site Initiator tRNA GTP GDP E A mRNA 5 3 Start codon (AUG) mRNA binding site Small ribosomal subunit 5 3 Translation initiation complex 2. Elongation • The next tRNA anticodon complementary base pairs with the mRNA codon in the “A” site aligning the appropriate amino acid next to “Met.” • Ribosome forms a peptide bond between “Met” and the 2nd amino acid and it passes the elongating polypetide chain to the tRNA in the “A” site 3. Translocation • Ribosome moves (translocates-change location) the tRNA in the “A” site to the “P” site • The empty tRNA moves to the “E” site where it is released • mRNA moves along/through the ribosome to expose the next mRNA codon to the “A” site • the protein chain is growing longer LE 17-18 Fueled by GTP= Guanosine Triphosphate Amino end of polypeptide E 3 mRNA Ribosome ready for next aminoacyl tRNA P A site site 5 2 GTP 2 GDP E E P A P GDP GTP E P A A 4. Termination • When a “STOP” codon (UGA, UAA, UAG) is reached on the mRNA, there isn’t a complementary tRNA so…. – UGA = U Go Away – UAA= U Are Awesome – UAG= U Are Great 4. Termination • A “release factor” binds to the “A” site – Causes the addition of a water molecule to the polypeptide which hydrolyzes the completed polypeptide from the tRNA • Ribsomal subunits dissociate (break apart from the mRNA) • Newly formed protein goes to rough ER for modification, then to golgi for packaging then released from cell (exocytosis)