Thursday, June 14, 2012

Biological Sciences 3 (Molecular Biology: Eukaryotes)

Molecular Biology: Eukaryotes

Day 6:

Molecular Biology: Eukaryotes

It lacks details, but I find it really funny that the Vacuole is named Señor Vacuole.

A. Eukaryotic Chromosome Organization

1. Chromosomal proteins
Histones are responsible for condensing and protecting chromosomal DNA wound around histone octamers. There are also non-histone chromosomal proteins that regulate and catalyze.

2. Telomeres, centromeres
Telomeres are the ends of a chromosome that become degraded causing aging. Centromeres are either at the center between the short and long arm. Sister chromatids are attached at the centromere following replication. During mitosis, spindle fibers are attached at the centromere and pulls the sister chromatids apart (during telophase).

1) Chromatid 2) Centromere 3) Short Arm 4) Long Arm

Mitosis Video (Centromeres are Shown)

B. Control of Gene Expression in Eukaryotes

1. Transcription Regulation

Transcription factors (proteins) bind to enhancers (increase) or silencers (decrease) on DNA to affect the amount of transcription. 

The transcription factors can be far away from the promoter gene that it effects and can lay in either direction (upstream/downstream). Intermediate proteins cause DNA to loop back on itself so the transcription factor can make contact with the promoter. Operons are rare and attenuation is not present in eukaryotes.

 Regulated Transcription Video from the National Science Foundation

2. DNA Binding Proteins, Transcription Factors
DNA-binding proteins and transcription factors bind to DNA.

DNA-binding domains include helix-turn-helix (HTH, green in top image below), zinc finger (blue in middle image) and basic-region leucine zipper (bZIP, blue in bottom image).

Helix-Turn-Helix DNA-Binding Domain
Zinc Finger DNA-Binding Domain
Basic-Region Leucine Zipper DNA-Binding Domain

3. Cancer as a Failure of Normal Cellular Controls, Oncogenes, Tumor Suppressor Genes

  • Cancer cells don't age because they protect their genetic information by preventing telomeres from degrading, they grow uncontrolled, dividing due to failure to respond to cellular controls. Cancer cells avoid apoptosis that normally occurs during extensive DNA damage. Cancer cells stimulate angiogenesis causing new blood vessels to grow nourishing the cancer cell. Cancer cells metastasize (begin growing in new locations) like Starbucks. 
  • Oncogenes cause cancer when activated, mostly by speeding up cell division. Oncogenes start as proto-oncognes and are harmless until triggered. Ex. SRC (1989 Nobel Prize in Physiology due to link with Colon Cancer). 
  • Viruses can cause cancer, proved in 1911 by Fancis Peyton Rous, who recieved a Nobel Prize in 1966.
  • Tumor suppressor genes slow down or control cell division. If the suppressor fails to function, cancer occurs. 

4. Post-Transcriptional Control, Basic Concept of Splicing (Introns, Exons)
Exons are the important information in RNA, introns are not needed (so they are removed by a spliceosome in RNA splicing). 5' caps and 3' poly-A tails are added after transcription to protect the RNA from breaking down. 

Proteins binding near the GU sequence, causes a loop, a spliceosome cleaves the intron at the 5' GU sequence (forming a lariat at the AG branch site), the 3' end of the intron is cleaved at the AG sequence and the two exons are ligated together. The intron will degrade. 

mRNA Splicing Video from the National Science Foundation

No comments:

Post a Comment