cells18-translation-2009

cells18-translation-2009 - BIO 106 Fall 2009 Professor Owen...

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Unformatted text preview: BIO 106 Fall 2009 Professor Owen 10/21/2009 DNA Activities • Replication= making more DNA helices • Transcription= making an RNA copy of DNA (Translation = turning DNA code into linked chain of amino acids) Transcription: DNA to mRNA ECB2 7-1 Transcription Copies One Strand of DNA into an RNA The strand opposite the template strand is sometimes called the coding strand because its sequence is equivalent to the RNA product. ECB2 7-6 RNA RNA Polymerase Copies One Strand of DNA into an RNA RNA polymerase unwinds the DNA, adds RNA nucleotides using the DNA template, then allows DNA to rewind into a helix. ECB3 7-6, 7 RNA polymerase reads the template strand in a 3’ 5’ direction, making RNA in 5’ 3’ direction. movie 7.2 Transcription RNA polymerase II uses start and stop sequences in the DNA to make the correct RNA. Start promoter 5’ 3’ TATAA gene Transcription RNA polymerase uses start and stop sequences in the DNA to make the correct RNA. Stop terminator 3’ 5’ 3’ RNA polymerase II 5’ RNA ECB3 7-9 18: Transcription & Translation 1 BIO 106 Fall 2009 Professor Owen 10/21/2009 Promoter Sequence TATA box A well-conserved nucleotide sequence appears in the promoter (start signal) region of many genes, usually 10 bases from the start of transcription. It is usually called the “TATA box”. modified from ECB2 7-9 In eucaryotes, the coding regions of genes are interrupted = introns. They are removed from the primary RNA transcript through a process called splicing. In contrast, bacterial genes are directly transcribed into RNA. ECB3 7-17 Identification of Introns Cooper 5.3 PrePre-mRNA Processing The pre-mRNA transcript is modified before it is functional for translation: 1. Cap added to 5’ end (m7Gppp; aids translation) 2. Poly-A tail added Polyto 3’ end (for mRNA stability) 3. Splicing (removal of introns) Cooper 7.44 In an experiment where the mRNA was bonded to its gene gene (single stranded DNA), large loops of nonnon-bonded DNA could be seen protruding. Structure of Eukaryotic Genes mRNA significantly differs from the prepre-mRNA transcript in that … A. the primary transcript has a 3’ cap B. mRNA has the exons removed C. mRNA has the introns removed D. ? What’s a pre-mRNA transcript? pre- Cooper 5.2 Most eukaryotic genes contain segments of coding sequences (codons) interrupted by non-coding sequences (introns). codons) non(introns). 18: Transcription & Translation 2 BIO 106 Fall 2009 Professor Owen 10/21/2009 PrePre-mRNA Splicing Splicing of prepremRNA RNA splicing is catalyzed by an assembly of snRNPs (small nuclear RNAs (small nuclear RNAs with with proteins). Cooper 7.45 movie 7.5 Cooper 7.47 snRNPs RNA splicing is catalyzed by an assembly of snRNPs (small nuclear RNAs with protein). Alternative Splicing WHAT?! RNA RNA with enzymatic enzymatic activity! Thomas Cech and Sidney Altman awarded Nobel Prize in Chemistry (1989) for this work. Cooper 5.5 http://nobelprize.org/chemistry/laureates/1989/ Genes can be spliced in different patterns. Genes for new proteins could have evolved quite rapidly by the recombination of parts of existing genes. An estimated 60% of human genes likely undergo alternative splicing. Alternative Splicing Eucaryotic vs. Procaryotic Genes can be spliced in different patterns. Genes for new proteins could have evolved quite rapidly by the recombination of parts of existing genes. An estimated 60% of human genes likely undergo alternative splicing. 2 ECB 7-18 ECB2 7-20 18: Transcription & Translation 3 BIO 106 Fall 2009 Professor Owen 10/21/2009 Eucaryotic Eucaryotic Transcription The DNA stays safely in the nucleus The RNA “messenger” carries the gene information to the protein-making machinery in the cytoplasm. ECB2 7-20 Where in the cell is mRNA synthesized and modified? A. ER B. cytoplasm C. nucleus D. nucleolus E.Golgi E. Golgi The Biology Project Web Site Also check out the “Cell Biology” section In case you are wondering…. http://www.biology.arizona.edu/ END OF MATERIAL FOR EXAM 2 Go to the “Molecular Biology” section The Biology Project Nucleic Acids Problem 12, initiation, and translation translation And other problems! are a good review of the material. Translation From mRNA to Protein 18: Transcription & Translation 4 BIO 106 Fall 2009 Professor Owen 10/21/2009 If only 4 nucleotides make up the genetic code, how do we get proteins made from combinations of 20 amino acids? Nucleotides Amino Acids Ponder: DNA and RNA are each composed of only 4 nucleotides, but proteins are made from combinations of 20 amino acids. • 1 nucleotide : 1 aa not enough variability 2=16) • 2:1 (4 still not enough • 3:1 (43=64) 64 possible amino acids using sequences of 3 nucleotides (Enough) Thus, the genetic code translates into groups of 3 nucleotides for 1 amino acid = codons A. You can’t! B. Use combinations of nucleotides – 2 at once Use combinations of nucleotides at once C. Use combinations of nucleotides – 2 at once D. Use combinations of nucleotides – 2 at once E. The amino acids directly read the nucleotide bases 18: Transcription & Translation 5 ...
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