Transcript RNA
RNA = RiboNucleic Acid Structure of RNA Single stranded Ribose Sugar Phosphate group Base: Adenine, Uracil, Cytosine, Guanine Three Types of RNA 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 The Genetic Code “Words” are 3 RNA sequences called codons. aaacgttcgccc DNA sequence Complimentary mRNA codons Amino acids uuugcaagcggg uuu-gca-agc-ggg Lysine – Arginine – Serine - Proline Genetic Codes: Codon Chart Translation During translation, the cell uses information from messenger RNA to produce proteins. 1.Transcription occurs in nucleus. 2.mRNA moves to the cytoplasm then to the ribosomes. tRNA “read” the mRNA and obtain the amino acid coded for. 3.Ribosomes attach amino acids together using a peptide bond, forming a polypeptide chain. 4.Polypeptide chain keeps growing until a stop codon is reached, creating a protein. Translation to Protein Mutations Mutations are changes in the DNA code. Gene mutations result from changes in a single gene. Chromosomal mutations involve changes whole chromosomes. Gene Mutation Gene Mutation Point Mutation – Affect one nucleotide thus occurring at a single point on the gene. Usually one nucleotide is substituted for another nucleotide. Gene Mutation Frameshift Mutation – Inserting an extra nucleotide or deleting a nucleotide causes the entire code to “shift”. Mutations More Mutations Gene Regulation All (with a few exceptions) of an organism’s cells have the same DNA. Why then are there different cells? The gene expression is different. In other words, cells ‘differentiate’ by expression of some genes and suppression of others. Cells respond to their environment by producing different types and amounts of protein. Can you think of a situation where this might happen? Gene Regulation: Producing Proteins Injury repair: cells can adapt to environmental changes such as an injury which requires repair by activating new genes Cancer is a disease of uncontrolled and invasive cell reproduction. Cancers result when the genes responsible for coding the proteins that regulate cell division mutate and divide rapidly. Complete the Chart Questions Which base in RNA is replaced by uracil? How many mRNA codons are illustrated on the previous slide? What is the name of the enzyme that creates the mRNA copy from DNA? What is the name of the sugar in the mRNA nucleotides? What is the mRNA transcript for the DNA sequence, TTACGC Complete the Chart Questions What structure assists tRNA in translating the mRNA in the cytoplasm? The role of tRNA is to carry a(n): 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. 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. 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