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Download 12-3 RNA and Protein Synthesis
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DNA To RNA To Proteins Transcription, Translation → Proteins Which is The Central Dogma of Biology Foothill High School Science Department The Structure of RNA • Long Chains of Nucleotides – 5 Carbon Sugar ( Ribose ) – Phosphate Group – Nitrogenous Base • A, G, C, U ( no T ) – Single Stranded Foothill High School Science Department Types of RNA RNA Mostly For Protein Synthesis Three Types of RNA Messenger RNA, mRNA Ribosomal RNA, rRNA Transfer RNA, tRNA Foothill High School Science Department Types of RNA mRNA A Copy of the Recipe in the DNA. Transports the Recipe to the Ribosome. rRNA Part of ribosome. It Reads the Recipe in the mRNA Puts the ingredients together tRNA Transports Amino Acids (the ingredients) from cytoplasm to the Ribosomes in the Order Needed to make the Protein (the Cookies) Foothill High School Science Department Transcription (mRNA) The process of copying the DNA nucleotide sequence into a complementary sequence of RNA ( copying the recipe) Requires a special enzyme: RNA Polymerase (Transcription Rate= ~60 nucleotides/second) Foothill High School Science Department RNA Polymerase DNA DNA RNA Polymerase Foothill High School Science Department Transcription Key Concept: During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA Foothill High School Science Department Transcription Promoters – Regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA – Specific base sequences act as signals – Other base sequences indicate stopping points Foothill High School Science Department Transcription The Devil is in the Details RNA Splicing After the DNA is transcribed into mRNA: Editing must be done to the mRNA chain to make the mRNA functional Foothill High School Science Department Transcription The Devil is in the Details Introns need to be removed • These are non-functional segments of the mRNA strand copied from the DNA • Snipped out of the chain in the nucleus Exons need to be glued back together • These segments contain the real recipe and need to be reconnected to make the real, functional mRNA This Process is called: mRNA Splicing Foothill High School Science Department mRNA Splicing Foothill High School Science Department The Genetic Code Proteins are: –long chains of amino acids. • There are 20 different amino acids – The order of amino acids in the protein determine its shape and function Foothill High School Science Department The Genetic Code There are 20 amino acids but only 4 bases in RNA. So, How Can You Design A Code? Adenine Cytosine Guanine Uracil A C G U Foothill High School Science Department RNA Bases The Genetic Code The genetic code consists of “words” three bases long Each “word” is called a Codon: A codon is three consecutive nucleotides that code for a single amino acid Foothill High School Science Department The Genetic Code For Example: UCGCACGGU = RNA Sequence UCG - CAC - GGU = Codons UCG CAC GGU codes for Serine codes for Histidine codes for Glycine Foothill High School Science Department The Genetic Code If you have 4 Bases and…. Codons are defined with 3 Bases….. How many combinations of 3 can you make? There Are 64 Possible 3-base codons Since there are only 20 amino acids, some amino acids are represented by multiple codons Foothill High School Science Department Code Wheel Table On Page 303 Foothill High School Science Department Code Table Foothill High School Science Department 8 Essential Amino Acids Essential AA = An Amino Acid That Can NOT Be Made, It Must Be Eaten Essential AA Meats Grains Legumes Methionine Tryptophan Phenylalanine Leucine Threonine Valine Isoleucine Lysine Foothill High School Science Department Translation Translation is the process of decoding the mRNA and chaining Amino Acids together into the polypeptide chain (making the protein) (See pages 245-247) • Ribosomes – Read mRNA and construct the proteins Foothill High School Science Department Translation Step A Foothill High School Science Department Translation Step B Foothill High School Science Department Translation Step C Step C – Ribosome connects the amino acids together as they come into the ribosome – Ribosome disconnects the the 3rd amino acid from the ribosome to float into the cytoplasm Foothill High School Science Department Translation Step D • Step D – Polypeptide chain grows until the mRNA STOP Codon is reached – The ribosome then releases the polypeptide chain into the cytoplasm Foothill High School Science Department The Roles of DNA & RNA DNA = The Cookbook mRNA = A copy of the recipe from “The Cookbook” Foothill High School Science Department Genes & Proteins • Genes are instructions for assembling proteins (recipes in a cookbook) • Proteins (the cookies from the recipe) are enzymes that catalyze and regulate chemical reactions – Pigments, antigens, regulators – Proteins are the keys to biological function Foothill High School Science Department