Gene Action Protein Synthesis

Overview of Protein Synthesis … the short version DNA contained in genes provides instructions for making protein Information from a specific section of DNA is first transcribed to produce a specific molecule of RNA RNA attaches to a ribosome where the information is translated into a corresponding sequence of amino acids

Protein Synthesis Vocab Nucleotide – building block of nucleic acid: sugar, phosphate, base

Protein Synthesis Vocab Base Triplet – a sequence of three successive DNA nucleotides Codon – a sequence of three successive mRNA nucleotides that correspond with a base triplet

TRANSCRIPTION DNA base triplets  mRNA codons Just copying a message in the same language! Nucleotide  nucleotide Occurs in the Nucleus Catalyzed by the enzyme RNA polymerase Promoter – a special sequence of DNA nucleotides near the beginning of a gene that tell the RNA polymerase where to begin reading

TRANSCRIPTION Nucleotides pair complementarily: DNA RNA C - G G - C A - U T - A

TRANSCRIPTION Terminator – a specific sequence of DNA nucleotides that signals the end of the gene. RNA polymerase detaches from the RNA molecule and the DNA strand. The RNA leaves the nucleus through a nuclear pore

Translation The process in which mRNA associates with ribosomes and directs the synthesis of proteins by converting the sequence on nucleotides in RNA to a sequence of amino acids…HUH? Changing Languages Now… Nucleotide  Amino Acids

Translation http://staff.jccc.net/PDECELL/proteinsynthesis/translation/steps.html

Translation 1. An mRNA molecule binds to the small ribosomal subunit and a special tRNA molecules (the initiator) binds to the start codon (AUG), where translation begins

Translation 2. The large ribosomal subunit attaches to the small subunit, creating a functional ribosome The initiator tRNA binds to the start codon One end of the tRNA carries a specific amino acid, the other consists of a triplet of bases called an anticodon. The anticodon pairs with the complementatry codon on mRNA

Translation 3. The anticodon of another tRNA with its amino acid attaches to the next section of mRNA 4. A peptide bond is formed between the amino acids carried by the 2 tRNA’s

Translation 5. After the peptide bond forms, the tRNA detaches from the ribosome and the ribosome shifts the mRNA strand by 1 codon. A new tRNA with amino acid binds to the exposed codon. Steps 3-5 repeat as the polypeptide lengthens

Protein synthesis ends when the ribosome reaches a stop codon. The new protein detaches, the tRNA detaches and the ribosome splits into its sub units

How fast can this possibly happen? In the body translation occurs at a rate of about 15 amino acids per second! Before 1 ribosome finishes moving down the mRNA another can attach to that same strand allowing large amounts of protein to be built.

tRNA