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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
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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.