Translation and Protein Synthesis

Some Review… RNA is transcribed from DNA The three types of RNA previously discussed (mRNA, tRNA, and rRNA) are all important for protein synthesis, the production of proteins. Keep in mind that it is the amount and type of protein a cell produces that gives that cell its identity and function.

Review Vocabulary… Polymer: compound built of many monomers bonded together Polypeptide Chain: long chain of amino acids (a protein) Amino Acid: one of 20 monomers that bond to form proteins

Protein Structure A protein (or polypeptide chain) is a polymer. Proteins are made of several amino acids attached by peptide bonds. There are 20 possible amino acids. A protein is made of hundreds or thousands of these. The sequence of amino acids determines a protein’s structure and even function. The amino acid sequence directs how the amino acid chain will twist and fold into the 3D structure of the protein. Protein function depends on the shape of the protein. Shape affects which molecules the protein can interact with and bind with in a cell.

The Amino Acids

The Genetic Code The genetic code is determined by the arrangement of bases in a DNA molecule. During protein synthesis, the sequence of nucleotides in an mRNA transcript is translated into a sequence of amino acids. The protein message coded for in the mRNA nucleotides is the genetic code.

The Genetic Code

The Central Dogma of Biology DNA  RNA  Protein RNA is transcribed from DNA Protein is translated from RNA The Central Dogma Song!

The Codon Each amino acid is associated with a series of three mRNA nucleotides. The 3 nucleotides that code for an amino acid is called a codon. There are 64 possible codons. These 64 codons provide the information used by nearly every organism on the planet. Because the genetic code is practically universal, it supports the idea that all organisms are related through evolution.

The Codon Notice that several codons code for the same amino acid. For example, Proline has 4 codons. AUG is the START codon. This signals the start of a protein. UAA, UAG, & UGA are the 3 STOP codons. These signal the end of a protein.

Translation Translation is the process where the message encoded in the mRNA transcript is used to make protein. Remember, mRNA is produced by transcription of DNA, and mRNA’s job is to travel to the ribosomes for translation and protein synthesis.

tRNA Amino acids float freely in the cytoplasm. tRNA carries amino acids to the ribosomes during protein synthesis.

The Anticodon The bottom region of the tRNA has a RNA nucleotide sequence called the anticodon. The anticodon has an mRNA sequence complementary to the codon. For example, the codon for Leucine is UUA, so its anticodon is AAU. The anticodon binds to a codon to hold an amino acid in place for binding to other amino acids.

Role of the Ribosome Ribosomes are made of rRNA and either float in the cytoplasm or stick to the ER. Free floating ribosomes produce protein for use inside the cell. ER Ribosomes make proteins that will be exported to other cells.

The Role of the Ribosome Ribosomes have 3 binding sites; 1 to bind to mRNA and 2 to bind to tRNAs so their anticodons can pair with mRNA codons.

Translation Video Let’s view how the process works… http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

The Translation Process A ribosome attaches to the AUG (start) codon on an mRNA chain. A tRNA with the anticodon UAC binds to the start codon. The tRNA is carrying the amino acid Methionine. The ribosome moves down the mRNA and tRNA keeps bringing amino acids. When the ribosome reaches a stop codon translation stops. mRNA is released from the ribosome and the new protein is sent out for use.

Let’s Practice Translation AUG: Met (Start) Anticodon: UAC GGC: Gly Anticodon: CCG ACU: Thr Anticodon: UGA UCG: Ser Anticodon: AGC UGA: Stop Anticodon: ACU

Videos & Practice Translation Video: Other Videos/Practice: http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120077/micro06.swf::Protein Other Videos/Practice: http://biology.clc.uc.edu/courses/bio104/dna.htm http://www.biostudio.com/demo_freeman_protein_synthesis.htm