Exam 4 - Chapter 18 Flashcards
gene expression
- nearly all somatic cells contain an individuals entire genome
- differences in gene expression result in different types of cells with different structions and fucntion
gene regulation in prokaryotes
-control mostly at the transcription level
operon = promoter + operator = genes
repressor
produced in the cell, binds to operator and prevents transcription by blocking RNA polymerase
activator
produced in the cell, binds to promoter and increases transcription
inducer
may be produced by the cell or available in the environment, can activate or repress transcription
Negative gene regulation
operons switched off by active form of repressor
Repressible operon
usually on, binding of repressor to operator shuts off transcription
trp operon
controls the synthesis of the amino acid tryptophan
trp reporessor
only active in the presense of its corepressor tryptophan
inductible operon
usually off, an inducer inactivates the repressor and turns on transcription, example is the lac operon
positive gene regulation
regulatory protein binds to control region and turns on transcription
eukaryotic gene regulation - access to genes
- dna loosely wraps around histone proteins to form chromatin
- histone package and order dna into units within chromatin called nucleosomes
- regions of chromatin can be condensed into heterchromatin
- epigenetic modifications are when gene expression is altered by the dna itself is not
Histone modifications
- acetyl groups loosen chromatin
- phosphate groups (-) loosen chromatin
- methyl groups condense chromatin
DNA methylation
- addition of methyl groups (condenses DNA) reduces transcription
- can cause long-term gene inactivation/silencing
eukaryotic gene regulation - transcriptional controls
- transcription factors bind to the promoter to bring in RNA ploymerase
- control elements regulate transcription
- transcription factors and activators bind increasing transcription through enhancers
- repressors can bind to promoter or enhancer for a gene to block transcription