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RNA Chapter 13 Learning Objectives Contrast RNA and DNA. Explain the process of transcription. Text video Complete Study Guide RNA carries DNA’s instructions. • The central dogma states that information flows in one direction from DNA to RNA to proteins. DNA is the genetic material that carry a code (genes) Genes carry instructions for making proteins The first step in making a protein is making a copy of the instructions RNA is the copy of the instructions Comparing RNA and DNA The sugar in RNA is ribose instead of deoxyribose. single-stranded, not double-stranded. RNA contains uracil in place of thymine. The Role of RNA The roles played by DNA and RNA molecules in directing protein production are like the two types of plans builders use: A master plan A blueprint Types of RNA The three main types of RNA are: Transfer RNA Ribosomal RNA Messenger RNA Messenger RNA An mRNA molecule is a copy of the portion of DNA that will be used to make a protein. After being made in the nucleus, mRNA travels to the cytoplasm, the site of protein synthesis (ribosome). Ribosomal RNA (rRNA) • Protein synthesis occurs on ribosomes, which are made up of two subunits. • rRNA makes up part of the ribosome. Transfer RNA During protein synthesis, transfer RNA molecules (tRNA) carry amino acids from the cytoplasm to the mRNA. RNA Synthesis: Transcription In transcription, segments of DNA serve as templates to produce complementary mRNA molecules. Steps in Transcription 1. RNA polymerase binds to DNA and unzips DNA beginning at the gene (one strand acts a template) 2. Free nucleotides pair with their complementary bases on the exposed DNA template 3. RNA polymerase continues until it reached the terminator sequence and stops 4. mRNA is released and goes to the ribosome 5. DNA helix reforms. RNA Synthesis: RNA Editing New RNA molecules sometimes require a bit of editing before they are ready to be read. Exons Cap Introns Tail Transcription video Ribosomes and Protein Synthesis Learning Objectives Identify the genetic code and explain how it is read. Summarize the process of translation. Describe the central dogma of molecular biology. Complete 13-2 Outline/Study Guide The first step in decoding the message (instructions) is to transcribe the base sequence form DNA to RNA DNA carries the instructions for making proteins (polypeptides) Proteins have specific amino acid sequences RNA carries this code to the ribosome for translation (the second step in protein synthesis) The Genetic Code RNA has four bases: adenine, cytosine, guanine, and uracil. These bases form a “language”: A, C, G, and U. The Genetic Code: Codons The genetic code is read in three-letter groupings called codons. (a group of three nucleotide bases in mRNA that specifies a particular amino acid) AUG AAC UCU Genetic Code Table There are 64 possible three-base codons in the genetic code. Reading Codons Start at the middle of the circle with the first letter of the codon and move outward. CAC = Histidine Start and Stop Codons The methionine codon AUG serves as the “start” codon for protein synthesis. There are three “stop” codons. UAA, UAG, and UGA are “stop” codons AUG = methionine = “start” codon Translation Transcribed mRNA directs the translation process. • Translation is the process that produces proteins by decoding the sequence of mRNA codons. Translation Steps of Translation 1. Ribosome attaches to an mRNA molecule. 2. tRNA molecules, carrying amino acids with them, bind to mRNA codons. anticodon Translation: The Polypeptide Assembly 3. The ribosome helps form a peptide bond. It breaks the bond holding the first tRNA molecule to its amino acid. Translation: Completing the Polypeptide 4. The ribosome reaches a stop codon, releasing the newly synthesized polypeptide and the mRNA molecule, completing the process of translation. Roles of RNA in Translation All three major forms of RNA—mRNA, tRNA, and rRNA—are involved in the process of translation. The Molecular Basis of Heredity The central dogma of molecular biology is that information is transferred from DNA to RNA to protein. Gene Expression When a gene (segment) of DNA code is used to build a protein, scientists say that gene has been expressed. Mutations Learning Objectives Define mutations and describe the different types of mutations. Describe the effects mutations can have on genes. Transcription/translation video Game What happened when the genetic message or instructions change? Mistakes can happen in copying (wrong, missing, or extra bases) Mutations Mutations are heritable changes in genetic information. Types of Mutations Mutations fall into two basic categories: Gene mutations Chromosomal mutations Gene Mutations: Point Mutations A point mutation is a change in a single nucleotide. There are three types of point mutations Point Mutations: Substitutions In a substitution, one base is changed to a different base. Point Mutations: Insertions and Deletions Insertion mutation: when a single extra base is added into the code Deletion mutation: when a single base is removed from the code -insertions and deletions are called frameshift mutations because the shift the reading frame of the genetic message • change in amino acid sequence • Can cause change in the protein Chromosomal Mutations Involve changes in the number of chromosomes. Types Deletion Duplication Inversion Translocation Effects of Mutations Mutations can harm, help, or have no effect on an organism. Some mutations arise from mutagens—chemical or physical agents in the environment (mutagens) Effects of Mutations: Harmful Some of the most harmful mutations are those that dramatically change protein structure or gene activity. Example: Sickle cell disease affects the shape of red blood cells. Sickle cell Normal red blood cell Diseases caused by a point mutaton Effects of Mutations: Beneficial Mutations often produce proteins with new or altered functions that can be useful to organisms in different or changing environments. Gene Regulation and Expression Learning Objectives Describe gene regulation in prokaryotes. Explain how most eukaryotic genes are regulated. Relate gene regulation to development in multicellular organisms. Prokaryotic Gene Regulation DNA-binding proteins in prokaryotes regulate genes by controlling transcription. -can help them respond to changing environments by turning genes off and on when needed Eukaryotic Gene Regulation - Gene expression is more complicated. Genetic Control and Development Cell Specialization Complex gene regulation in eukaryotes is what makes differentiation so the can specialize in structure and function. Genetic Control of Development Regulating gene expression is important in shaping how a multicellular organism develops. Each of the specialized cell types found in the adult originates from the same fertilized egg cell. Homeotic, Homeobox, and Hox Genes Homeotic genes regulate organ development. Homeobox genes code for transcription factors. Hox genes determine the identities of each body segment. Environmental Influences Environmental factors can affect gene regulation. Metamorphosis is an example of how organisms can regulate gene expression in response to change in their environment.