DNA Structures and Chromosome Organisation
" Brevis esse laboro
Obscuro fio. "
Introduction: DNA Compaction in chromosomes (again!) A Brief overview of eukaryotic chromosome architecture Fragile X-syndrome and nucleosome positioning Centromeric DNA A few more words about curved DNA yeast Autonomously Replicating Sequences Human centromeric DNA
Telomeric DNA Telomeric DNA Sequences 4-stranded DNA structures Telomerase enzyme Heterochromatin vs. Euchromatin Heterochromatin and repetitive DNA sequences
Euchromatin and the organisation of genes
Introduction to Eukaryotic Chromosomes
A brief REVIEW (stuff you should've learned in Biology 101 or High School biology)
DNA for human chromosome # 1 would be more than 2 cm long, in its B-DNA
A Fragile-X syndrome and nucleosome positioning
There are certain DNA sequences that are associated with the centromeres of chromosomes. Knowledge of this was essential in the construction of Yeast Artificial Chromosomes (or YACs, as they're usually called).
here's an oversimplified view of the attachment of the kinetochore
telomeric DNA can fold back on itself. This is necessary to allow for DNA synthesis (this isn't a problem for circular chromosomes!).
The ends of the chromosomes get shorter every time the cells divide, because part of the bases are used to template off of themselves. Thus, after every round of replication, the chromosome gets a bit shorter. This is kind of like "planned obscelence", where the cells basically have so many divisions and then they fall apart. However (fortunately!) the cells have a mechanism for extending the length of the telomeres - the cells have an enzyme which can make the telomeres longer. The TELOMERASE enzyme is a ribozyme - that is, it contains a necessary piece of RNA which serves as the template for synthesizing the new strand. It has been found that in many cases cancer cells have a mutation such that the telomerase gene is overexpressed, thus allowing the cells to "live forever". Early results from clinical trials show that by specifically inhibiting the activity of the telomerase protein, they can slow or completely stop the growth of many types of cancer. More recently, the idea of using telomerase gene therapy to prevent people from getting old has received much attention in the media.
Figure 6.26 from Hartl & Jones (page 250).
Two types of chromatin:
Euchromatin - this is where the "active" genes are - usually this region is much less condensed.