RNA & Protein Synthesis Continued: Translation

Translation: mRNA Protein Translation is taking mRNA and making proteins Sequence of nucleotide bases in mRNA molecules serves as instructions for the order of amino acids to make proteins Ribosome is assembly site for proteins Decoding of an mRNA message into a protein chain is translation During translation, the cell uses information from mRNA to produce proteins

Steps of Translation A) mRNA transcribed from DNA in nucleus is sent to the cytoplasm

Steps of Translation (continued) B) mRNA attaches to ribosome. As each codon of mRNA molecule moves through the ribosome, the proper amino acid is brought into the ribosome and attached to the growing chain of amino acids. tRNA (transfer RNA) brings correct amino acid into the ribosome. tRNA has an amino acid on one end and a region of three bases at the other, called the anticodon (these three bases are complementary to the mRNA codon).

Steps of Translation (continued) tRNA anticodon –Example: tRNA anticodon – UAC mRNA codon – AUG – methionine (start) Ribosome allows 2nd tRNA molecule to fit, and attach amino acid to protein What is the complementary strand of DNA to this mRNA codon? TAC

Steps of Translation (continued) C) Ribosome puts amino acids together, and moves 1st tRNA molecule out of ribosome, allowing next tRNA to fit into ribosome (only 2 tRNAs at a time in ribosome)

Steps of Translation (continued) Protein chain continues to grow in length until ribosome reaches stop codon on mRNA. When stop codon reached, protein is released and folds into its 3-D shape.

Translation U C A U G C C G A A U C G C U A C U G A U A A C G G  mRNA  anticodon  amino acid START CODON

Translation U C A U G C C G A A U C G C U A C U G A U A A C G G

Translation U C A U G C C G A A U C G C U A C U G A U A A C G G

Translation U C A U G C C G A A U C G C U A C U G A U A A C G G

Translation U C A U G C C G A A U C G C U A C U G A U A A C G G

Translation U C A U G C C G A A U C G C U A C U G A U A A C G G

Translation U C A U G C C G A A U C G C U A C U G A U A A C G G

Translation U C A U G C C G A A U C G C U A C U G A U A A C G G STOP CODON

Translation U C A U G C C G A A U C G C U A C U G A U A A C G G Amino acid chain folds into 3-D protein shape.

Messenger RNA Messenger RNA is transcribed in the nucleus. Transfer RNA The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon. mRNA Start codon Ribosome Methionine Phenylalanine tRNA Lysine Nucleus mRNA Translation

The Polypeptide “Assembly Line” The ribosome joins the two amino acids— methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids. Ribosome Translation direction Lysine tRNA Ribosome Growing polypeptide chain mRNA Completing the Polypeptide The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

Translation

Genes and Proteins Proteins are enzymes that speed up and regulate chemical reactions Genes coding for an enzyme to produce pigment can control color of flower Genes for certain proteins can regulate the rate and pattern of growth throughout an organism, controlling size and shape of that organism