exam #1 is t 9/23 in class (bring cheat sheet)

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Exam #1 is T 9/23 in class (bring cheat sheet)

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Exam #1 is T 9/23 in class (bring cheat sheet). 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. Signal Transduction. External. Stimulus. Internal. Effector…. - PowerPoint PPT Presentation

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•Exam #1 is T 9/23in class(bring cheat sheet)

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Protein

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?

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Stimulus

Signal Transduction

Stimulus

Perception(by receptor)

EffectorResponse

(change in cellular components and/or gene expression)

Effector…Effector

Effector

External

Internal

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How do cells express genes?

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a gene

The relationship between DNA and genes

promoter coding region terminator non-geneDNA

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Combinations of 3 nucleotides code for each 1 amino acid in a protein.

Fig 13.2

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• Overview of transcription Fig 12.2

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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

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Fig 12.8

What is so magic about adding nucleotides to the 3’ end?

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Fig 12.7

How does the RNA polymerase know which strand to transcribe?

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5’5’3’

3’5’

Reverse promoter, reverse direction and strand transcribed.

RNA

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DNARNA RNA

DNA

UU

Why do polymerases only add nucleotides to the 3’ end?

similar to Fig 11.11

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P

Error

P-P

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The 5’ tri-P’s can supply energy for repair

Error

P

P-P-PPU

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3’

5’Error repair on 5’ end not possible.

Incoming nucleotide

similar to Fig 11.11

U

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DNARNA RNA

DNA

UU

Need for error repair limits nucleotide additions to 3’ end.

similar to Fig 11.11

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a gene

When to express a gene is critical

promoter coding region terminator non-geneDNA

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Promoter sequences in E. coli Fig 12.5

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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

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Termination of Transcription Fig 12.11

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Eukaryotic promoters are more diverse and more complex

Fig 12.13

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Fig 12.14

in eukaryotes: transcription factors are needed before RNA polymerase can bind

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Transcription overviewFig 12.3

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Some genes code for RNA (tRNA, rRNA, etc) mRNA is used to code for proteins

Protein

RNA synthesis

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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 guanineFig 12.23

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Addition of the 3’ poly-A tail Fig 12.24

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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4.7% 0.34% 0.22%100%

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The cap and tail have overlapping and distinct functions

Protects from degradation/ recognition for ribosome

Protects from degradation/ transport to cytoplasm

5’ untranslatedregion

3’ untranslatedregion

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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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• 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

Fig 15.16

(-tropomyosin)

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Fruit fly DSCAM, a neuron guide,115 exons over 60,000 bp of DNA20 exons constitutively expressed95 exons alternatively splicedFor over 38,000 possible unique proteins

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Size and Number of Genes for Some Sequenced Eukaryotic Genomes

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RNA editing:Some mRNAs are changed after transcription by guide RNA

http://www.cc.ndsu.nodak.edu/instruct/mcclean/plsc731/genome/genome9.htm

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/RNA_Editing.html

Tbl 12.3

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A processed mRNA ready for translation

5’ untranslatedregion

3’ untranslatedregion

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•Exam #1 is T 9/23in class(bring cheat sheet)