Lecture 3 (1b) Segmentation in Drosophila melanogaster Flashcards
(54 cards)
Aristotle - 6th century
Preformationism
• adult is pre-formed in egg or sperm
• all organisms were generated at the same time
(Homunculus - curled up in the head of each sperm)
Epigenesis
organisms are progressively built anew in each generation
in contrast to preformationism
DNA gives the instructions
The nucleus of the zygote and every cell that is produced during ontogenesis contains the complete genome
In principle, every cell…
somatic and germ line cells…
can be used to make a new animal
Differentiation - making cells different
The genotype contains a developmental program that unfolds and results in the expression of different sets of genes in different cell types
BY REGULATION OF GENE EXPRESSION
Factors that control gene expression regulate:
- chromatin structure
- initiation of transcription
- RNA processing
- initiation of transcription
In the context of axes formation and segmentation in Drosophila, we are discussing the regulation of
transcription by transcription factors
Chromatin-modifying enzymes provide initial control of gene expression by…
making a region of DNA either more or less able to bind the transcription machinery
• transcription factors then control levels of transcription
(Organization of eukaryotic genes)
Associated with most eukaryotic genes are control elements
segments of noncoding DNA that help regulate transcription by binding certain transcription factors
(Organization of eukaryotic genes)
Control elements and the transcription factors they bind are critical to the
precise regulation of gene expression in different cell types
Eukaryotic gene
a gene is a section of DNA required for the production of a biologically active RNA molecule
(Organization of eukaryotic genes)
Proximal control elements are located close to the
promoter
(Organization of eukaryotic genes)
Distal control elements, groups which are called … may be far away from a gene or even located in an intron
enhancers
Binding of … to … control elements regulates gene expression
Binding of TRANSCRIPTION FACTORS to ENHANCER control elements regulates gene expression
(The roles of transcription factors)
To initiate transcription, eukaryotic RNA polymerase requires the assistance of proteins called
transcription factors
(The roles of transcription factors)
General transcription factors are essential for the transcription of
all protein-coding genes
(The roles of transcription factors)
In eukaryotes, high levels of transcription of particular genes depend on control elements interacting with
specific transcription factors
(The roles of transcription factors)
A given gene may have different control elements (enhancers). Expression depends on the complement of
activator or inhibitor transcription factors present in the cell that can bind to theses control elements
General transcription factors are essential for the transcription of all
protein-coding genes
• TATA box binds TATA BINDING PROTEIN necessary for efficient RNA synthesis
• promoter elements bind transcription factors to help stabilize the RNA TRANSCRIPTION PROCESS
Enhancer elements are brought into contact with the
basal promoter
Basal transcription factors are required for
RNA polymerase II
to bind to promoter regions and initiate transcription
• cell specific transcription factors increase or decrease complex stability, thus increasing or decreasing gene expression
Liver cell nucleus
available activators for albumin =
albumin gene expressed
& crystalline gene not expressed
Lens cell nucleus
available activators for crystalline =
crystalline gene expressed
& albumin gene not expressed
Dorsal protein activates and represses different zygotic genes depending on
twist (?) nuclear concentration
