Biology 3 Transcription, Translation, and Mutations Dr. Terence Lee Overview 1. DNA and RNA structure 2. DNA replication 3. Transcription – makes RNA 4. Translation – makes protein James Watson, Francis Crick, and Rosalind Franklin discovered the structure of DNA 1 Image of DNA DNA Structure • Deoxyribonucleic acid (DNA) is a type of nucleic acid • Three parts: 1. Sugar group ( deoxyribose ) 2. Phosphate group 3. Nitrogenous base • Adenine • Guanine • Thymine • Cytosine 2 DNA provides the instructions for building virtually every organism on earth! The protein, influenced by the environment and in some cases other genes, then produces the trait. Central Dogma of Biology 3 DNA Replication • Process by which a cell makes another copy of its DNA • Pairing Rules: – A = T – G = C • The structure of DNA is a double helix • Shaped like a twisting ladder 4 RNA Structure • Ribonucleic acid (RNA) is a type of nucleic acid • Three parts 1. Sugar group ( ribose ) 2. Phosphate group 3. Nitrogenous base • Adenine • Guanine • Uracil • Cytosine How is RNA different from DNA? 1. Ribose has –OH group 2. RNA has uracil instead of thymine 3. RNA is a single strand 4. DNA stays in nucleus 5. RNA is made from DNA in nucleus and then moves to cytoplasm. 5 HOW GENES WORK: AN OVERVIEW TRANSCRIPTION TRANSLATION Inside nucleusThe sequence for a gene Cytoplasm The sequence for a is copied from DNA to a gene, now encoded in middleman molecule mRNA, is used to direct called mRNA. the production of a mRNA protein. DNA Genes Protein molecule Nuclear pore Grandmother’s Copying cookie Index card Combining and Chocolate cookbook recipe to index card with recipe baking ingredient chip cookies Transcription • Transcription is the process of using DNA as a template to synthesize RNA. – 1.) The DNA strands separate. – 2.) RNA Polymerase reads the DNA and builds the RNA strand. – 3.) Three types of RNA can be made: 1. mRNA – messenger RNA 2. rRNA – ribosomal RNA 3. tRNA – transfer RNA 6 • Promoter sequence – specific sequences of DNA that the RNA Polymerase recognizes. • Protein code – the DNA sequence that holds the genetic material to create each protein . • Termination sequence – Tells the RNA Polymerase to stop transcription . TRANSCRIPTION DNA 1 RECOGNIZE and BIND 2 TRANSCRIBE 3 TERMINATE Once RNA polymerase As the DNA strand is processed When the RNA polymerase recognizes a promoter site, through the RNA polymerase, encounters a code signaling it binds to one strand of the the RNA polymerase builds a the end of the gene, it stops DNA and begins reading single-strand copy of the gene, transcription and releases the gene’s message. called the mRNA transcript. the mRNA transcript. RNA RNA polymerase RNA polymerase polymerase Promoter site Termination site mRNA transcript mRNA transcript UNWIND and REWIND As the RNA polymerase 4 moves down the strand of CAPPING and EDITING DNA, the helix unwinds so Before the mRNA that the DNA can be read. At transcript can be the same time, the DNA that Tail translated into a protein, has already been transcribed a cap and tail are often rewinds back to its original Cap Non-protein-coding added for protection and to promote recognition, double-helix form. regions of mRNA Helix unwinds and non-coding sections are removed. Helix unwinds mRNA transcript leaves nucleus to be translated into a protein. Translation • Translation is the process of using the information in mRNA to direct protein synthesis. • Relies on sets of 3 nucleotides called codons . • Each codon codes for a specific amino acid. 7 Translation • Ribosome – 2 subunit non-membrane organelle – Holds the mRNA and tRNA during protein formation • tRNA – Transfer RNA – Reads the codons and finds the correct amino acids . Translation 1. Initiation 2. Elongation 3. Termination Translation • Initiation: 1. Ribosome small subunit binds to mRNA 2. Finds the start codon 3. The tRNA binds to the codon and brings the first amino acid 4. The large subunit joins the small subunit and protein formation can begin. 8 Translation • Elongation: 1. A new tRNA arrives and reads the codon . 2. The next amino acid arrives and binds to the previous amino acid . 3. The process continues until a polypeptide (protein) is formed. 9 Translation • Termination: – Occurs when the ribosome reaches a stop codon. – The two subunits come apart. – The mRNA is released. Summary of Protein Synthesis 10 5.4 Not all DNA contains instructions for making proteins. The Proportion of the DNA That Codes for Genes 11 Introns and Exons • Portions of the mRNA are removed before translation. Mutations • Point Mutation – change in a single nucleotide of the DNA sequence. • Insertions and Deletions – changes one or more nucleotides in the DNA sequence. 12 A “fast- flush” response 13.