1. Eukaryotic Genomes:
The Organization
and Control

2. Chromatin Actually a complex of DNA and proteins
DNA Packing •histone protein
+ charged amino acids (lots of argenine & lysine)
~ phosphates of DNA have a (-) charge
Nucleosome-(basic unit of DNA packing)
DNA wound around a cluster of 8 histones “beads on a string”
Heterochromatin •highly condensed interphase DNA (can not be transcribed)
Euchromatin •less compacted interphase DNA (can be transcribed)
Which is which depends on the type of cell….

3. DNA Packing
D:\bc_campbell_biology_7\0,7052, ,00.html

4. Lots of DNA…but…… Lots of genes???? Not really:
Most Eukaryotic DNA does NOT code for mRNA
30-50% is introns!!
Another 10-15% is “Tandemly Repetitive Sequences”-
-short sequences that repeat up to 1000s of times
-unique nucleotide ratio gives it a lower density during centrifugation
so sometimes is called “satellite DNA”
-mostly located at telomeres & centromeres
Still more (up to 25-40%) is “Interspersed non-coding”-
-thought to be mostly transposons
- some are considered “pseudogenes”
-still others are thought to be inactive parts of multigene families

5. (again) For 10th edition, see:
section (pp )
Multigene Families:
A collection of genes which are similar or identical.
Presumably of common ancestral origin…
Can be clustered or dispersed.
Identical-
Probably arose from repeated duplication
-many code for rRNA (make lots quickly!)
Non- Identical-
Mutations in the duplicated gene(s)
Most are just PSEUDOGENES:
Non-functional genes which are similar but lack
expression mechanisms.
Some ARE functional. Example: Hemoglobin

6. Transcription factors
REMEMBER!!!
Unlike prokaryotic operons, eukaryotic genes
coding for enzymatic pathways may be scattered
over different chromosomes!!
Yet- they can be coordinately expressed by common….
Transcription factors
D:\bc_campbell_biology_7\0,7052, ,00.html

7. Epigenetics literally means "above" or "on top of" genetics.
It refers to external modifications to DNA that turn genes "on" or "off."
MicoRNA & siRNA
Blocking of RNA by siRNA is RNA interference. (Remember? RNAi!)
These modifications do not change the DNA sequence, but instead, they affect how cells "read" genes.

8. Molecular Biology of Cancer
Oncogene •cancer-causing genes
Proto-oncogene •normal cellular genes
How? movement of DNA; chromosome fragments that have rejoined incorrectly amplification; increases the number of copies of proto-oncogenes proto-oncogene point mutation; protein product more active or more resistant to degradation
Tumor-suppressor genes •changes in genes that prevent uncontrolled cell growth (cancer growth stimulated by the absence of suppression)