1. Genetics and Information
08 Gene regulation
Gene regulation and expression
Specialization of cells
Cell signals mediate gene expression
Environment and gene expression
Timing and coordination of tissues

2. Gene Regulation Holtzclaw: 132-136
Cell activities are determined by proteins
determined by genes transcribed
determined by regulatory mechanisms

3. Regulatory elements
There are multiple regulatory elements in the genome that play a role in controlling gene expression.
Some regulatory DNA sequences:
Promoter: sequenced in front of a transcribed gene recognized by RNA polymerase and transcription factors.
Enhancers: sequences further “upstream” of a gene that increase transcription.

4. A “gene” is not just a transcript

5. Transcription factors and regulatory sequences serve as molecular switches that control gene expression

6. Prokaryotic Gene Regulation

7. Prokaryotic Control of Gene Expression
Prokaryotes control gene expression almost entirely by controlling transcription.

8. Operons Groups of metabolically related genes with a single promoter.
Common in prokaryotes.

9. Operon Operation
The presence or absence of a metabolite controls the transcription of operon genes by controlling
the access of
RNA polymerase by
controlling
the binding
of a repressor
protein.

10. Operon Logic
The logic of an operator depends upon the nature of the metabolic pathway that it controls.

11. Inducible Operons Default state: Off.
Involved in metabolic pathways that are only occasionally used.
The lac operon is turned on in the presence of lactose

12. Repressible Operons Default state: On.
Involved in metabolic pathways that are frequently used
The trp operon is turned off in the presence of tryptophan
tryptophan is an essential amino acid

13. Upregulation
Refers to increasing the baseline amount of transcription through the binding of an upregulator.
Ex. The CAP/cAMP Complex

14. Constitutive Genes
Genes that are not under operon control and need to be continually expressed for normal cell function.
Ex. Ribosomal RNA

15. Eukaryotic Gene Regulation

16. More Complex Controls
Eukaryotes control gene expression at all levels of the process, from pre-transcription to post-translation.

17. Access to DNA
Most of the DNA in a eukaryotic cell is unavailable for transcription.
The addition/removal of acetyl groups from the histone proteins that DNA is wound around leads to tighter or looser “packing” of the DNA.

18. Pre-transcriptional controls
Eukaryotes control transcription by controlling the transcription factors present in the cell.

19. Post-Transcriptional/Pre-Translational Controls
Eukaryotic mRNA’s are extensively processed after being transcribed.
“alternate splicing”: combining different exons in a transcript to produce multiple functional transcripts.

20. RNA Interference (RNAi): micro RNA’s are produced that bond with specific transcripts and block translation.

21. Post-Translational Controls
Protein targeting: signal sequences on polypeptides will target the production of the polypeptide into the cytoplasm or into the endomembrane system.

22. Protein Activation & Degradation
Proteins for certain cellular pathways are made in inactive forms that are only activated when specific signals are received.
Proteasomes: organelles that target and destroy proteins that have been “tagged” to be degraded in the cell.

23. Gene Regulation → Phenotype

24. Genetics and Information
08 Gene regulation
Gene regulation and expression
Specialization of cells
Cell signals mediate gene expression
Environment and gene expression
Timing and coordination of tissues

25. Gene Expression Controls Phenotypes
Phenotypes are the result of protein interactions.
Control of gene
expression leads
to control of
proteins, which
leads to control
of phenotypes.
Ex. X-inactivation

26. Differential Gene Expression
Multicellular organisms use differential gene expression to accomplish the process of “cellular differentiation”.
Different cellular phenotypes are due to different genes being expressed in different cell types.

27. Gene Expression is Unique
Gene expression is due to both genome content and environmental interactions. This accounts for some phenotype differences among genetically identical individuals
The kitten on the left is a clone of the cat on the right

28. Genetics and Information
08 Gene regulation
Gene regulation and expression
Specialization of cells
Cell signals mediate gene expression
Environment and gene expression
Timing and coordination of tissues

29. Gene Expression is a Cellular Response
One of the major ways that cells respond to changes is by altering gene expression.
Signals that affect gene expression can be internal or external to the cell.
SARA
CYTOPLASM
NUCLEUS
TRANSCRIPTION
Transcription

30. External Signals
External signals are transmitted between cells, or are present in a cell’s environment.
Ex. Mating in yeast- controlled by the presence of mating pheromones.

31. Internal Signals
Internal signals are molecules present inside of cells that control gene expression.
Ex. Hox gene products: control the development of animal body segments

33. Interplay of internal and external signals controls gene expression

34. Genetics and Information
08 Gene regulation
Gene regulation and expression
Specialization of cells
Cell signals mediate gene expression
Environment and gene expression
Timing and coordination of tissues

35. Phenotype = Genotype + Environment
Phenotypes arise from interactions between the genome and the environment of the organism.
The environment directly controls certain phenotypes.
The genome can also respond to environmental changes by altering gene expression.

36. Ex. Soil pH and Hydrangea Color

37. Ex. Gender Determination in Reptiles is controlled by temperature.

38. Ex. Winter and Summer coat coloration in the Arctic Hare

39. Ex. The Tanning Response in Humans

40. Plasticity of the Genome
Different traits will interact with the environment in different ways.

41. Image Credits All images taken from wikimedia commons. Exceptions:
Slide 34: O. L. Miller, Jr., B. A. Hamkalo, and C. A. Thomas, Jr.
Slide 37-39: Allen Gathman
Slide 117: From on.html
Slide 119: From tml
Slide 125: Sigma Aldritch
Slide 126: From