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Transcript
Chapter – 10 Part II Molecular Biology of the Gene Genetic Transcription and Translation The Structure of Proteins • Made up of amino acids • There are 20 amino acids involved in protein synthesis • Amino acids combine together to form the peptide linkage (link between amino group of one amino acid with the carboxyl group of adjacent amino acid) • Many peptide linkages form a polypeptide chain • Polypeptide chains fold to form a protein. The Structure of Proteins Stages of protein synthesis Two major stages involved: • The first stage is called transcription – The 2 strands of the DNA molecule unwind and mRNA copies the genetic code (letters A, C, G and T) from DNA, the master molecule. Stages of protein synthesis • mRNA then comes out from the nucleus to cytoplasm • The second stage is called translation – mRNA and tRNA (carrying amino acids) reach the cytoplasmic ribosome (composed of two protein subunits and rRNA) where the mRNA code is used to assemble amino acids – These amino acid chains elongate and fold to form proteins. Protein Synthesis Summary: The process of copying DNA into RNA is called transcription and the Process of assembling proteins from RNA instructions is called translation Transcription Triplet Code • Three mRNA bases code for a specific amino acid is called code / codon ( three nucleotides). Triplet Code • Three mRNA bases code for a specific amino acid is called code / codon ( three nucleotides). Translation • mRNA (carrying instructions for sequence of amino acid in a protein) comes out of the nucleus and reaches the cytoplasm to the site of ribosome, the location of protein synthesis. • rRNA a structural component of ribosome Translation • tRNA (translator molecule) – Anticodon of tRNA attracts a specific amino acid – tRNA matches the codon in the mRNA – Part of the tRNA binds an amino acid and the other end has three nucleotides, anticodon that forms a base pair with the codon in the mRNA) – Amino acids of neighboring tRNA’s link to form the polypeptide chains. – Lengthened amino acid chains fold to form the protein molecule. Types of RNA Translation Steps in Translation • mRNA binds to the small subunit of the ribosome. Start codon AUG, brings in initiator tRNA with the amino acid methionine, and then large subunit binds. • tRNA that matches the next codon brings in the appropriate amino acid in to the “A” site. Steps in Translation • Then the ribosome joins the mRNA to the next codon, moving the newly formed peptide to the “P” site. This continues until a stop codon is reached. • At the stop codon, no new tRNA comes into the “A” site and the whole complex falls apart, releasing the new protein. Steps in Translation Editing out Genetic Material • Intron is a segment of DNA, (or the mRNA transcript complementary to it), that does not encode information for the sequence of amino acids in protein. • Exon is the segment of DNA or mRNA ,that encodes information for the sequencing of amino acids in protein. • A segment of DNA that makes transcript is called gene • Genome size for human is 3 billion.