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 PresentationTRANSCRIPT
•Exam #1 is T 9/23in class(bring cheat sheet)
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?
Stimulus
Signal Transduction
Stimulus
Perception(by receptor)
EffectorResponse
(change in cellular components and/or gene expression)
Effector…Effector
Effector
External
Internal
How do cells express genes?
a gene
The relationship between DNA and genes
promoter coding region terminator non-geneDNA
Combinations of 3 nucleotides code for each 1 amino acid in a protein.
Fig 13.2
• Overview of transcription Fig 12.2
Fig 9.8
Each nucleotide carbon is numbered
Fig 9.22
Each nucleotide is connected from the 5’ carbon through the phosphate to the next 3’ carbon.
Fig 9.22
Each nucleotide is connected from the 5’ carbon through the phosphate to the next 3’ carbon.
The relationship between DNA and RNA
Fig 12.8
Fig 12.8
What is so magic about adding nucleotides to the 3’ end?
Fig 12.7
How does the RNA polymerase know which strand to transcribe?
5’5’3’
3’5’
Reverse promoter, reverse direction and strand transcribed.
RNA
DNARNA RNA
DNA
UU
Why do polymerases only add nucleotides to the 3’ end?
similar to Fig 11.11
P
Error
P-P
The 5’ tri-P’s can supply energy for repair
Error
P
P-P-PPU
3’
5’Error repair on 5’ end not possible.
Incoming nucleotide
similar to Fig 11.11
U
DNARNA RNA
DNA
UU
Need for error repair limits nucleotide additions to 3’ end.
similar to Fig 11.11
a gene
When to express a gene is critical
promoter coding region terminator non-geneDNA
Promoter sequences in E. coli Fig 12.5
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
Transcription Elongation Fig 12.8
Termination of Transcription Fig 12.11
Eukaryotic promoters are more diverse and more complex
Fig 12.13
Fig 12.14
in eukaryotes: transcription factors are needed before RNA polymerase can bind
Transcription overviewFig 12.3
Some genes code for RNA (tRNA, rRNA, etc) mRNA is used to code for proteins
Protein
RNA synthesis
rRNA is transcribed by RNA polymerase I
tRNA is transcribed by RNA polymerase III
mRNA is transcribed by RNA polymerase II
mRNA is processed during transcription and before it leaves the nucleus.
(transcribed from DNA)
Addition of the 5’ cap, a modified guanineFig 12.23
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
What do the cap and tail do?
(transcribed from DNA)
Luciferase Gene (from fireflies) Expressed in a Plant
4.7% 0.34% 0.22%100%
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
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.
Introns are spliced out of most mRNAs before they leave the nucleus.
(transcribed from DNA)
• Conserved sequences related to intron splicing
Sequences shown in bold are highly conserved
Serve as recognition sites for the binding of the spliceosome
Splicing an intron: intron removal.
Fig 12.22
Splicing an intron: reattach exons.
Fig 12.22
Alternate splicing of introns/exons can lead to different proteins produced from the same gene.
Fig 15.16
Complex patterns of eukaryotic mRNA splicing
Fig 15.16
(-tropomyosin)
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
Size and Number of Genes for Some Sequenced Eukaryotic Genomes
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
A processed mRNA ready for translation
5’ untranslatedregion
3’ untranslatedregion
•Exam #1 is T 9/23in class(bring cheat sheet)