Biol 301 Regulation of Gene Expression Notes la

Regulation of Gene Expression

I. Regulating Gene expression
A. Why is gene regulation necessary?
1. Not all genes or their products are needed at all times
2. More efficient if they are made only when needed and turned off when not
needed
B. Levels at which gene expression is regulated in prokaryotes
1. Transcription
a) DNA →
2. RNA processing
a) RNA transcript →
3. RNA stability
a) mRNA →
4. Translation
a) Protein →
5. Post-translation
a) Function performed by protein
C. Housekeeping genes are expressed constitutively (rRNAs, structural proteins,
tRNAs)
1. These genes are always expressed the same way at the same rate/time,
behave the same in various environments
D. Regulated genes usually have specialized functions
1. Growth
2. Defense mechanism
3. Induced genes - characteristics of catabolic pathways
a) Lactose, galactose, arabinose utilization)
4. Repressed genes - characteristics of anabolic pathways
a) Tryptophan biosynthesis
5. Regulator genes control the expression of these induced/repressed
genes
a) Kinda vague
b) Better called
(1) Activators
(2) Repressors
E. Positive control of gene regulation
1. The regulator gene product is called an activator
a) Causes transcription to increase
b) Induced
2. These activators bind to their regulatory protein binding sites and
increase the transcriptional output of genes
3. Activator binding is influenced by effector molecules (inducers and
corepressors) that cause a conformational change:
a) Induced fit