Genes and Proteins Lecture 15 Objectives At the end of this series of lectures, you should be able to: Define terms. Explain the central dogma of molecular biology. Describe the locations, reactants, and products of transcription and translation. Explain how mrna is produced using DNA. Explain how RNA is processed before leaving the nucleus. 1
Objectives Diagram the overall process of transcription and translation. Describe the major types of mutations, causes of mutations, and potential consequences. Types of RNA mrna Messenger RNA Carries the instructions from the nucleus to the ribosome rrna Ribosomal RNA Made in the nucleolus and makes up part of the ribosome trna Transfer RNA Carries the amino acids to the ribosome 2
Central Dogma The central dogma of molecular biology consists of three parts. DNA undergoes replication to create a copy of itself. DNA undergoes transcription to create RNA. RNA undergoes translation to create proteins. Daniel Horspool, CC BY SA 3.0, http://en.wikipedia.org/wiki/central_dogma_of_molecular_biology 3
Transcription Occurs in the nucleus during G 1 and G 2. The information contained in the DNA is converted to RNA. Sequence of nucleotides specifies the sequence of amino acids in a protein. mrna Transcription 1. Initiation RNA polymerase binds to the promoter region. DNA unwinds. 4
Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0 Transcription 2. Elongation RNA nucleotides pair with their DNA complements. Sugar phosphate bonds are forged. (RNA polymerase) 5
Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0 Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0 6
Transcription 3. Termination RNA polymerase reaches the terminator DNA and becomes detached from the DNA. mrna is released. Transcription 1. Initiation RNA polymerase binds to the promoter region. DNA unwinds. 2. Elongation RNA nucleotides pair with their DNA complements. Sugar phosphate bonds are forged. (RNA polymerase) 3. Termination RNA polymerase reaches the terminator DNA and becomes detached from the DNA. mrna is released. 7
The Genetic Code Triplet code (three nucleotides specify one amino acid) Codon 64 possible codons for 20 amino acids The code is redundant several different codons specify the same amino acid. The code is degenerate if the first two nucleotides of the codon are the same the third can vary and still specify the same amino acid. mrna Processing Cap and tail are added to mrna Helps in moving the mrna out of the nucleus Introns are removed Exons are spliced together 8
Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0 Daniel Horspool, CC BY SA 3.0, http://en.wikipedia.org/wiki/central_dogma_of_molecular_biology 9
Ribosomes One type of organelle that occurs in the cytoplasm. Made from two pieces (a large and a small) Each subunit is a mix of proteins and rrna Site of protein synthesis LadyofHats, Public Domain, http://commons.wikimedia.org/wiki/file:ribosome_mrna_translation_pl.svg#mediaviewer/file:ribosome_mrna_translation_en.svg 10
Vossman, CC BY SA 3.0, http://en.wikipedia.org/wiki/ribosome#mediaviewer/file:ribosome_shape.png Central Dogma The central dogma of molecular biology consists of three parts. DNA undergoes replication to create a copy of itself. DNA undergoes transcription to create RNA. RNA undergoes translation to create proteins. 11
Daniel Horspool, CC BY SA 3.0, http://en.wikipedia.org/wiki/central_dogma_of_molecular_biology Translation Occurs in the cytoplasm at the ribosomes. mrna moves from the nucleus to the ribosome. 12
Translation 1. Initiation mrna binds to the smaller part of the ribosome trna bringing the first amino acid (methionine) to the ribosome. The large part of the ribosome joins with the smaller part. Kelvinsong, CC BY SA 3.0, http://en.wikipedia.org/wiki/translation_(biology)#mediaviewer/file:protein_synthesis.svg 13
Translation 2. Elongation Codon recognition The trna with the appropriate anticodon and amino acid pairs with the codon on the mrna. Peptide bond formation Catalyzed by the ribosome Translocation Repeats until stop codon is reached. Kelvinsong, CC BY SA 3.0, http://en.wikipedia.org/wiki/translation_(biology)#mediaviewer/file:protein_synthesis.svg 14
Translation 3. Termination Stop codon is reached. Ribosome pieces separate. mrna is released. Protein is released. Kelvinsong, CC BY SA 3.0, http://en.wikipedia.org/wiki/translation_(biology)#mediaviewer/file:protein_synthesis.svg 15
Translation 1. Initiation mrna binds to the smaller part of the ribosome trna bringing the first amino acid (methionine) to the ribosome. The large part of the ribosome joins with the smaller part. 2. Elongation Codon recognition The trna with the appropriate anticodon and amino acid pairs with the codon on the mrna. Peptide bond formation Catalyzed by the ribosome Translocation 3. Termination Stop codon is reached. Ribosome pieces separate. mrna is released. Protein is released. Mutations A change in the sequence of nucleotides in DNA. Point mutations Substitution Silent mutations does not change the amino acid specified. Missense mutations does change the amino acid specified. Nonsense mutation a missense mutation that is harmful. New stop codons might be introduced. 16
DNA: 5' ATG ACT CAC CAC GCG CGA AGC TGA 3' 3' TAC TGA GTG GTG CGC GCT TCG ACT 5' mrna: 5' AUG ACU CAC CAC GCG CGA AGC UGA 3' Protein: Met Thr His His Ala Arg Ser Stop DNA: 5' ATG ACT CAC CCC GCG CGA AGC TGA 3' 3' TAC TGA GTG GGG CGC GCT TCG ACT 5' mrna: 5' AUG ACU CAC CCC GCG CGA AGC UGA 3' Protein: Met Thr His Pro Ala Arg Ser Stop Wikipedia, CC BY SA 3.0, http://en.wikipedia.org/wiki/missense_mutation Jonsta247, CC BY SA 3.0, http://commons.wikimedia.org/wiki/file:point_mutations en.png 17
Mutations Frame shift mutations Reading frame Changes how codons are interpreted downstream of the mutation. DNA: 5' ATG ACT CAC CAC GCG CGA AGC TGA 3' 3' TAC TGA GTG GTG CGC GCT TCG ACT 5' mrna: 5' AUG ACU CAC CAC GCG CGA AGC UGA 3' Protein: Met Thr His His Ala Arg Ser Stop DNA: 5' ATA CTC ACC CCG CGC GAA GCT GA 3' 3' TAT GAG TGG TGC GCG CTT CGA CT 5' mrna: 5' AUA CUC ACC ACG CGC GAA GCU GA 3' Protein: Ile Leu Thr Thr Arg Glu Ala? Adapted from: Wikipedia, CC BY SA 3.0, http://en.wikipedia.org/wiki/missense_mutation 18