Transcript Document
RNA Structure Like DNA, RNA is a nucleic acid. RNA is a nucleic acid made up of repeating nucleotides RNA differs from DNA in three different ways. The sugar in RNA is ribose RNA is single- stranded RNA contains the base uracil instead of thymine. Like thymine, uracil can form bonds with adenine A molecule called RNA – ribonucleic acid is used to decode the instructions in DNA, Transcription The instructions for making a protein are transferred from a gene (DNA) to RNA Transcription = DNA → RNA Segment of DNA unwinds and unzips RNA is produced one nucleotide at a time by matching base pairs with the nucleotides in DNA. After the synthesis is complete, the RNA separates from the DNA and the DNA recoils into its helix. The RNA (mRNA) strand leaves the nucleus and goes into cytoplasm Forms of RNA Messenger RNA - mRNA mRNA carries the information to the cytoplasm where the ribosomes can make it into protein. – "Blueprint" for protein synthesis that is transcribed from one strand of the DNA (gene) and which is translated at the ribosome into a polypeptide sequence . Ribosomal rRNA • a structural component of the ribosome. tRNA molecule that converts nucleic acid sequence to protein sequence tRNA - transfer RNA • carries the amino acid elements of a protein to the appropriate place as coded for by the mRNA. Small, single-stranded RNA molecules that bind to amino acids and deliver them to the proper codon on messenger RNA. Ribosomes take RNA coded information and "translate" that information into chains of amino acids called pollypeptides A protein is made up of one or more polypeptide chains. Messenger RNA (mRNA) is the blueprint for construction of a protein. Ribosomal RNA (rRNA) is the construction site where the protein is made. Transfer RNA (tRNA) is the truck delivering the proper amino acid to the site at the right time. Translation The ribosome reads the mRNA sequence and translates it (or decodes it) into an amino acid sequence in a polypeptide. Polypeptides are chains of amino acids. Proteins are made up of one or more polypeptide molecules. So….the building block of proteins are ___________________. There are 20 essential amino acids that make up proteins. The instructions in DNA specify the order in which the amino acids are put together. RNA – contains 4 different nucleotides. (Language – 4 letters) How can a code with only 4 letters carry instructions for 20 amino acids? # of letters # of words 1 4 2 16 3 64 The genetic code could signify 64 different words The group of 3 nucleotides in mRNA that specifies an amino acid is known as a codon. Think of codons as the words of the genetic message. Example: The following sequence of nucleotides in mRNA • AAACACGGU Would be read as 3 codons AAA- CAC-GGU And each codon represents a different _____. First Second Third U C A G UUU Phenylalanine UCU Serine UAU Tyrosine UGU Cysteine U UUC Phenylalanine UCC Serine UAC Tyrosine UGC Cysteine C UUA Leucine UCA Serine UAA STOP UGA STOP A UUG Leucine UCG Serine UAG STOP UGG Tryptophan G CUU Leucine CCU Proline CAU Histidine CGU Arginine U CUC Leucine CCC Proline CAC Histidine CGC Arginine C CUA Leucine CCA Proline CAA Glutamine CGA Arginine A CUG Leucine CCG Proline CAG Glutamine CGG Arginine G AUU Isoleucine ACU Threonine AAU Asparagine AGU Serine U AUC Isoleucine ACC Threonine AAC Asparagine AGC Serine C AUA Isoleucine> ACA Threonine AAA Lysine AGA Arginine A AUG Methionine ACG Threonine AAG Lysine AGG Arginine G GUU Valine GCU Alanine GAU Aspartic acid GGU Glycine U GUC Valine Valine Alanine GAC Aspartic acid GGC Glycine C GUA Valine GCA Alanine GAA Glutamic acid GGA Glycine A GUG Valine GCG Alanine GAG Glutamic acid GGG Glycine G U C A G Page figure Shows all 64 possible codons of the genetic code. Notice: More than one codon can specify the same amino acid. How do tRNAs recognize to which codon to bring an amino acid? The tRNA has an anticodon that is complementary to the codon on the mRNA. Each tRNA only binds the appropriate amino acid for its anticodon amino acids are carried by the molecules of tRNA. The ribosomes “read” the codons in mRNA allowing tRNA molecules to bring the proper amino acid. (the anti-codon on tRNA bonds to the proper codon on mRNA)