Cell Differentiation Flashcards
Why are cells different?
They synthesize and accumulate different sets of RNA and protein.
Identical genome that they use in different ways.
Gene expression pattern
Each cell has a characteristic gene expression pattern.
Can be used to identify cancer cells.
Where can regulation of gene expression occur?
Regulation of gene expression can occur on individual genes and genomic regions.
Regulation of gene expression in individual genes
Every step can be controlled.
Transcriptional control is the most important.
Transcriptional control
Genes are turned on | off individually.
Controlled by a regulatory region of DNA near to where transcription begins. Gene regulatory proteins bind to the DNA.
Activators | Repressors
Activators
Gene activation proteins bind to protein sites called enhancers (sequence of DNA recognizable for activator or repressors). They increase the rate of transcription .
Their function is to attract, position and modify the initiation complex.
Promote transcription initiation by changing the chromatin structure of promoter genes, in order to make DNA more accessible.
Repressors
Reduce expression of specific genes by competing with activators or disrupt the initiation complex.
What determines the final rate of transcription.
Which regulatory proteins are available and their quantity.
Chromatin (Exam)
Complex of DNA and protein in the nucleus.
Chromatin structure
- Nucleosome: dynamic structure that allows access to DNA.
- 8 histone proteins: positively charged. Form bobbins that negatively charged DNA can wrap around. Tails can be modified to change the structure.
How does the chromatin structure change?
N-terminal amino acid tail is subject to several covalent modifications that control chromatin structure and function.
Heterochromatin
Highly condensed.
Resistant to gene expression (DNA cannot be read).
Two types:
1. Constitutive: Does not contain genes. Centromeres, telomeres. Always condensed.
2. Facultative: Can choose to be condensed or not. Controls gene expression!
Euchromatin
Loose chromatin. Gene expression is possible (DNA can be read).
Histone code
A specific meaning behind a modification of chromatin structure.
Chromatin modification
N-terminal histone tail modification include Acetylation, Methylation, Phosphorylation. Reversible.
Have a specific meaning (histone code).
Change gene expression of many genes. Large portion of chromosomes.
