Transcript RNA
RNA ch 12 sec 3 Ribonucleic Acid Structure of RNA Single stranded Ribose Sugar 5 carbon sugar Phosphate group Adenine, Uracil, Cytosine, Guanine Types of RNA Three main types Messenger RNA (mRNA) – transfers DNA code to ribosomes for translation. Transfer RNA (tRNA) – brings amino acids to ribosomes for protein synthesis. Ribosomal RNA (rRNA) – Ribosomes are made of rRNA and protein. Transcription RNA molecules are produced by copying part of the nucleotide sequence of DNA into complementary sequence in RNA, a process called transcription. During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of mRNA. mRNA How Does it Work? RNA Polymerase looks for a region on the DNA known as a promoter, where it binds and begins transcription. RNA strands are then edited. Some parts are removed (introns) - which are not expressed – and other that are left are called exons or expressed genes. The Genetic Code This is the language of mRNA. Based on the 4 bases of mRNA. “Words” are 3 RNA sequences called codons. The strand aaacguucgccc would be separated as aaa-cgu-ucg-ccc the amino acids would then be Lysine – Arginine – Serine - Proline Genetic Codes Translation During translation, the cell uses information from messenger RNA to produce proteins. A – Transcription occurs in nucleus. B – mRNA moves to the cytoplasm then to the ribosomes. tRNA “read” the mRNA and obtain the amino acid coded for. C – Ribosomes attach amino acids together forming a polypeptide chain. D – Polypeptide chain keeps growing until a stop codon is reached. Translation to Protein Translation 12-4 Mutations Gene mutations result from changes in a single gene. Chromosomal mutations involve changes whole chromosomes. Gene Mutation Point Mutation – Affect one nucleotide thus occurring at a single point on the gene. Usually one nucleotide is substituted for another nucleotide. Frameshift Mutation – Inserting an extra nucleotide or deleting a nucleotide causes the entire code to “shift”. Gene Mutation Chromosomal Mutations Deletion – Part of a chromosome is deleted Duplication – part of a chromosome is duplicated Inversion – chromosome twists and inverts the code. Translocation – Genetic information is traded between nonhomologous chromosomes. Chromosomal Mutations Mutations More Mutations 12-5 Gene Regulation In simple cells (prokaryotic) lac genes which are controlled by stimuli, turn genes on and off. In complex cells (eukaryotic) this process is not as simple. Promoter sequences regulate gene operation. Gene regulation continued An operon is a group of genes that operate together The lac genes are turned off by repressors and turned on by the presence of lactose. An operator is a region to which a repressor can bind, preventing transcription of genes Eukaryotic Gene Regulation Most eukaryotic genes are controlled individually. They have regulatory sequences that are much more complex than those of the lac operon The TATA box (lol) is a sequence that helps position RNA polymerase Hox genes control where organs and tissues will develop in various parts of an embryo Summary of Gene Regulation in Prokaryotes Lac genes in E. coli bacteria are turned on by the presence of lactose and turned off by repressors If no lactose is presentrepressor binds to operatorno transcription occurs If lactose is presentrepressor is released from operatortranscription begins Summary of Gene Regulation in Eukaryotes TATA box=30 base pairs long; the DNA sequence will be TATATA or TATAAA before the start of transcription Review