Announcements. Tuesday afternoon lab section: lab start time next week is 3pm. 2-3 pm might be a good time to do problem set 6! 2. No advance reading for next week’s lab; focus on your lab report. 3. Problem set 5 due at start of class today. 4. Reading - Ch. 16: skip btm. 442- top 444.
Tuesday afternoon lab section: lab start time
next week is 3pm. 2-3 pm might be a good time to do problem set 6!
2. No advance reading for next week’s lab; focus on your lab report.
3. Problem set 5 due at start of class today.
4. Reading - Ch. 16: skip btm. 442- top 444.
Review of Last Lecture
1.The lac operon - in detail; know roles of all components
2. The trp operon - very briefly
Outline of Lecture 27
I. Eukaryotic Gene Expression: it’s more complicated being multicellular
II. The Promoter
V. Alternative splicing
I. Problems of Multicellularity
+ insulin- insulin
Levels of Regulation of Eukaryotic Gene Expression
The interphase nucleus
Chromosome structure is continuously rearranged, so that transcriptionally active genes are cycled to edge of territories.
Organization/ packaging of DNA
Nucleus= 5-10 m
Diploid genome= 6.4x109 bp
II. Promoters: Eukaryotic vs. Prokaryotic
RNA pol II
Promoters: sequences adjacent to genes, where RNA pol binds to initiate transcription
Euk. - Chromatin and TFs
Prok. - Naked DNA and no TFs needed
“Promoter-Bashing” Mutations Determine the Critical Regions of DNA for Gene Expression
TBP-TATA binding protein
TAFs- TATA assoc. factors
III. Eukaryotic Enhancers and Promoters
Promoters- needed for basal level transcription
Enhancers- needed for full level transcription; location and orientation variable
Two types of transcription factors bind enhancers and affect levels of txn: true activators and anti-repressors
Combinatorial Model of Gene Expression
No reg.TFs in this cell for albumin enhancer
Binding of True Activator TFs to Enhancers Greatly Stimulates Transcription
Looping of DNA allows Activator TF bound to Enhancer to interact with Promoter, facilitating binding of Basal TF complex.
Types of Regulatory Transcription Factors
Helix-Turn-Helix (HTH) TFs
(binds operator DNA)
Zinc Finger TFs
Leucine Zipper TFs
Helix-Loop-Helix (HLH) TFs
Antirepressor Transcription Factors
TFs can recruit HATs or HDs
IV. Control of gene expression by DNA Methylation
V. Post transcriptional gene regulation
If humans have approximately the same number of genes as a fruit fly, and we require more complex cellular functions (presumably with a larger number of proteins) - how do we accomplish this?
1. Chromosomal ratio activates txn of Sxl in females only
2. SXL controls splicing of tra-2 mRNA
3. Females: exon 2 (which has a stop codon) is removed via SXL
Males: exon 2 is not removed.
Males: no active TRA
Females: TRA is made.
5. TRA directs splicing of dsx mRNA in specific manner; in males default splicing occurs.