1. Eukaryotic Gene Expression
Why is gene regulation more complex in eukaryotes than prokaryotes?
Eukaryotes have larger more complex genome
Eukaryotic DNA must be more highly organized than prokaryotic DNA

2. Prokaryotic vs. Eukaryotic DNA
Prokaryotic DNA
circular
smaller than eukaryotic DNA
associated with very few proteins
less structured and folded
Eukaryotic DNA
associated with lots of histone proteins to form chromatin fiber
very extended and tangled during interphase
condensed into discrete chromosomes during mitosis

7. Eukaryotic Development
Cellular differentiation is the specialization of cells during development
Since all cells have the same DNA, how can differentiation occur?
Gene regulation.

8. Selective Gene Expression
How do cells become specialized?
Different genes are activated at different times during development.
Each cell utilizes only about 3% of genome

9. DNA Packing Helps regulate gene expression
DNA in one human cell’s 46 chromosomes would be 3 meters long.
How, then, does it all fit into the nucleus?
DNA packing
Why do densely packed regions of chromosomes inactivate gene expression?
RNA pol can’t get to the gene for transcription.

10. What is the difference between heterochromatin and euchromatin?
Heterochromatin remains highly condensed even during interphase
Barr bodies are X chromosomes condensed into heterochromatin
Telomeres, centromeres also heterochromatin
euchromatin is chromatin that is not condensed and can be transcribed

11. Control of Gene Expression
What are the steps from chromosome to functional protein?
Unpacking Transcription mRNA processing  export from the nucleus  translation  protein modification
ANY of these steps can be regulated in eukaryotes

12. Control of Gene Expression

13. Chromatin modification
DNA methylation; the addition of methyl groups to DNA
essential for inactivation of the DNA
Inactive genes in a cell are methylated
Epigenetic memory due to methylating enzymes that methylate the new daughter strand the same as the parent strand.
Can be passed on in repro
Histone acetylation is the attachment of an acetyl group to histone proteins
acetylation increases likelihood for transcription of the DNA

15. Where is the greatest amount of gene regulation seen?

16. Transcription of the DNA!

17. Transcriptional Control
Transcription factors allow RNA pol to find the promoter region
association between transcriptional factors and enhancer or promoter region regulates gene expression

20. Posttranscriptional control
Regulation of RNA processing
Regulation of mRNA degradation
Can last from hours to weeks
Regulation of translation
initiation sequence can be blocked

22. Protein Degradation; posttranslational control

23. Genome Organization

24. Repetitive DNA In prokaryotes most of the DNA is transcribed
In eukaryotes ~ 97% of the DNA is not transcribed and/or translated!
This DNA includes:
introns
repetitive sequences - repeated nucleotides found between genes

25. Transposons and Retrotransposons

26. Transposons and Retrotransposons
“jumping genes”- make copies of segments and insert in new locations
Retrotransposons: transcribed to RNA, code for reverse transcriptase encoded in transcript, reinsert in new location
Transposons: move by DNA intermediate, may be “cut and paste” or “copy and paste”

27. Alu transposable elements
Comprises 10% human genome
300 bp long
Transcribed to RNA, with no known function

28. Tandem Repeats 0r Satellite DNA
Repeated units are up to 10 base pairs long
Satellite DNA is categorized depending on its length into:
satellite DNA - 100, million bp’s
minisatellite DNA ,000 bp’s
microsatellite DNA bp’s
Huntingtons and fragile X are disorders that occur due to abnormally long tandem repeats.
both of these disease effect nervous system functioning

30. Gene Families What are multigene families?
Identical or similar genes that can be found in the genome
In what way are these multigene families advantageous?
Identical multigenes code for RNA such as rRNA which helps organism get enough ribosomes in the cytosol.
Non-identical multigenes such as hemoglobin parts help hemoglobin change throughout life

32. Evolution of Multigene families
Thought to have occurred from duplication followed by modification
Duplication due to error in Xover
Subsequent modification via other errors in replication or Xover
Theory supported by presence of pseudogenes in gene families.
Pseudogenes: do not produce functional protein
Resembles functional members of family

33. Alteration of Genome via transposons
Transposable elements can:
Promote recombination between homologous chromosomes
Disrupt functional genes /control elements
Carry genes or exons to new locations
In most cases these changes will have no effect or be problematic, VERY occasionally could be beneficial

34. Genetic Control of Embryonic Development
Chapter 21?

35. Genetic Control of Embryonic Development
Embryonic development has 3 stages:
Cell division
Differentiation
Morphogenesis
During which of these stages does differential gene expression play a key role?
All

36. Determination What is determination?
Before a cell has differentiated it is determined.
Determination causes regulation of the genes that will lead to the differentiation into a tissue specific cell.
Differentiated cells will produce only specific proteins

38. Cytoplasmic Determinants
What generates early differences among embryonic cells?
Cytoplasmic determinants found in the egg.
Cytoplasm of the egg is heterogeneous
Cytoplasmic determinants regulate gene expression

40. Induction
The other factor that influences early gene expression is induction
Embryonic cells influence other embryonic cells that induce differentiation
Caused by contact between cells
Or by chemical signals between cells

41. Pattern Formation anterior - posterior (head-tail) axis
dorsal - ventral (front-back) axis
Cytoplasmic determinants in Drosophila egg sets up axis determinants prior to fertilization.

44. Homeotic genes What are homeotic (Hox) genes?
Genes that control the overall body plan of animals by controlling the developmental fate of groups of cells
In Drosophila the homeotic genes specify appendages that attach to different segments
homeotic genes code for transcriptional factors that lead to proteins for anatomical structures

45. Hierarchy of Gene Activity in Drosophila development:
Maternal effect genes (egg polarity genes)
Segmentation genes
Homeotic genes
Other genes

46. Homeobox Genes

47. Homeobox is found within the homeotic gene.
Consists of 180 nucleotides that codes for 60 amino acids of a given homeotic protein.
This 60 aa part of the protein binds to the DNA to regulate transcription
The rest of the protein will determine which specific part of the DNA is being regulated.
Many similar homeobox containing genes have been identified in different animals

48. If the DNA sequences called homeoboxes, which help homeotic genes direct development, are common to flies and mice, then why aren’t flies and mice more alike?
There is more DNA in homeotic genes besides the homeoboxes
Genes regulated by protein products of homeotic genes can be different.

49. Induction Sequential induction drives the formation of organs
Concentration of inducer effects its function
Signal transductions pathways operate in induction
Response of induced cell is activation of transcriptional factors
Differential genetic expresssion leads to development

50. Apoptosis
Proteins for apoptosis are always present in cells in an inactive form
Regulation involves activation of these proteins
Similar apoptosis genes seen in nematodes and mammals incidates evolutionary relatedness.
In vertebrates apoptosis is necessary for development of fingers, toes, nervous system, and immune system.