Protein Synthesis-Translation

Warm-up #6 1.How is RNA different than DNA? 2.Name the 3 steps of transcription. 3.What is the end product of transcription? 4.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?

mRNA From nucleus to cytoplasm DNA transcription nucleus cytoplasm translation trait protein

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

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 The mRNA code

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

· Transfer RNA (tRNA) is the interpreter between the 2 forms of information: base sequence in mRNA and amino acid sequence in polypeptides tRNA Structure

Amino acid location (CCA) 3 exposed bases -an enzyme links a specific amino acid from the cytosol/cytoplasm to each tRNA molecule on the 3’ end (CCA) using ATP for energy

LE 17-14b Hydrogen bonds Amino acid attachment site Anticodon Symbol that is widely used Anticodon Three-dimensional structure

LE Amino acid Aminoacyl-tRNA synthetase (enzyme) Pyrophosphate Phosphates tRNA AMP Aminoacyl tRNA (an “activated 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) Amino acid

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) E site (Exit site) mRNA binding site A site (Aminoacyl- tRNA binding site) Large subunit Small subunit Schematic model showing binding sites EPA

Process of Translation Translation includes 4 processes: initiation, elongation, translocation, and termination

1. Initiation of Translation mRNA binds to small ribosomal subunit Initiator tRNA brings1 st 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 Met GTP Initiator tRNA mRNA 5 3 mRNA binding site Small ribosomal subunit Start codon (AUG) P site 5 3 Translation initiation complex E A Large ribosomal subunit GDP Met

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 2 nd 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 Ribosome ready for next aminoacyl tRNA mRNA 5 Amino end of polypeptide E P site A site GDP E PA GTP GDP E PA E PA Fueled by GTP= Guanosine Triphosphate

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)