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Exam #1 is T 9/23 in class (bring cheat sheet)
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How do cells control which genes are expressed?
DNA is used to produce RNA and/or proteins, but not all genes are expressed at the same time or in the same cells. How do cells control which genes are expressed? Protein
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Response (change in cellular components and/or gene expression)
Signal Transduction External Stimulus Internal Effector… Effector Effector Effector Response (change in cellular components and/or gene expression) Perception (by receptor) Stimulus
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How do cells express genes?
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The relationship between DNA and genes
a gene promoter coding region terminator non-gene DNA
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Combinations of 3 nucleotides code for each 1 amino acid in a protein.
Fig 13.2 Combinations of 3 nucleotides code for each 1 amino acid in a protein.
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Overview of transcription
Fig 12.2 Overview of transcription
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Each nucleotide carbon is numbered
Fig 9.8 Each nucleotide carbon is numbered
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Fig 9.22 Each nucleotide is connected from the 5’ carbon through the phosphate to the next 3’ carbon.
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Fig 9.22 Each nucleotide is connected from the 5’ carbon through the phosphate to the next 3’ carbon.
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The relationship between DNA and RNA
Fig 12.8 The relationship between DNA and RNA
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What is so magic about adding nucleotides to the 3’ end?
Fig 12.8 What is so magic about adding nucleotides to the 3’ end?
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How does the RNA polymerase know which strand to transcribe?
Fig 12.7
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Reverse promoter, reverse direction and strand transcribed.
RNA 5’ 3’ 5’ 3’ 5’
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Why do polymerases only add nucleotides to the 3’ end?
RNA RNA DNA DNA U U similar to Fig 11.11
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Error P P-P
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The 5’ tri-P’s can supply energy for repair
Error P The 5’ tri-P’s can supply energy for repair U P-P-P P
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Error repair on 5’ end not possible.
similar to Fig 11.11 Incoming nucleotide Error repair on 5’ end not possible. 5’ U 3’
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Need for error repair limits nucleotide additions to 3’ end.
RNA RNA DNA DNA U U similar to Fig 11.11
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When to express a gene is critical
promoter coding region terminator non-gene DNA
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Promoter sequences in E. coli
Fig 12.5 Promoter sequences in E. coli
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Transcription initiation in prokaryotes: sigma factor binds to the -35 and -10 regions and then the RNA polymerase subunits bind and begin transcription Fig 12.7
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Transcription Elongation
Fig 12.8 Transcription Elongation
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Termination of Transcription
Fig 12.11 Termination of Transcription
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Eukaryotic promoters are more diverse and more complex
Fig 12.13 Eukaryotic promoters are more diverse and more complex
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in eukaryotes: transcription factors are needed before RNA polymerase can bind
Fig 12.14
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Transcription overview
Fig 12.3 Transcription overview
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Some genes code for RNA (tRNA, rRNA, etc) mRNA is used to code for proteins
RNA synthesis Protein
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rRNA is transcribed by RNA polymerase I
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tRNA is transcribed by RNA polymerase III
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mRNA is transcribed by RNA polymerase II
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mRNA is processed during transcription and before it leaves the nucleus.
(transcribed from DNA)
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Addition of the 5’ cap, a modified guanine
Fig 12.23 Addition of the 5’ cap, a modified guanine
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Addition of the 3’ poly-A tail
Fig 12.24 Addition of the 3’ poly-A tail After the RNA sequence AAUAAA enzymes cut the mRNA and add 150 to 200 A’s
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What do the cap and tail do?
(transcribed from DNA)
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Luciferase Gene (from fireflies) Expressed in a Plant
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100% 4.7% 0.34% 0.22%
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The cap and tail have overlapping and distinct functions
5’ untranslated region 3’ untranslated region Protects from degradation/ recognition for ribosome Protects from degradation/ transport to cytoplasm
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DNA Composition: In humans:
Each cell contains ~6 billion base pairs of DNA. This DNA is ~2 meters long and 2 nm wide. ~3% directly codes for amino acids ~10% is genes In a single human cell only about 5-10% of genes are expressed at a time.
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Introns are spliced out of most mRNAs before they leave the nucleus.
(transcribed from DNA)
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Sequences shown in bold are highly conserved
Conserved sequences related to intron splicing Sequences shown in bold are highly conserved Serve as recognition sites for the binding of the spliceosome
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Splicing an intron: intron removal.
Fig 12.22
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Splicing an intron: reattach exons.
Fig 12.22
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Alternate splicing of introns/exons can lead to different proteins produced from the same gene.
Fig 15.16
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Complex patterns of eukaryotic mRNA splicing
(-tropomyosin) Fig 15.16
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Fruit fly DSCAM, a neuron guide,
115 exons over 60,000 bp of DNA 20 exons constitutively expressed 95 exons alternatively spliced For over 38,000 possible unique proteins
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Size and Number of Genes for Some Sequenced Eukaryotic Genomes
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Some mRNAs are changed after transcription by guide RNA
RNA editing: Some mRNAs are changed after transcription by guide RNA Tbl 12.3
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A processed mRNA ready for translation
5’ untranslated region 3’ untranslated region
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Exam #1 is T 9/23 in class (bring cheat sheet)
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