Biology 205 Regulation of Gene Expression

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I. Explain the importance of Regulation of gene expression

A. Give examples of rapid response to environmental changes

B. Define differentiation and development as used for eukaryotic organisms.

C. Distinguish between the following types of genes

• Regulated (up regulated vs down regulated)
• Constitutive genes = housekeeping genes

II. Chapter 16 Gene expression and regulation in prokaryotes involves operons

A. Explain the concept of an inducible gene

• Define induction, inducer, effector molecules
• Sketch the general organization of an inducible gene. See fig 16.1

B. Explain Jacob and Monad's operon model for the lac genes and associated regulatory elements. See fig 16.5

• Diagram the basic parts of the lac gene system
• Explain how the operon operates in the presence and absence of lactose

C. Distinguish between positive and negative control of operons by a repressor protein. (Confusing!)

• Negative control- repressor protein blocks transcription of the "structural genes"when the inducer is absent
  • Example: In the lac operon in which the repressor protein binds to the operator and prevents transcription when allolactose the inducer is absent.
• Positive control- repressor protein blocks transcription of the "structural genes" when the inducer is present. When the inducer is absent, the repressor protein cannot block transcription and gene structural genes are expressed.
  • Example: In the trp operon, the regulatory protein, is an activator which turns on transcription of the structural genes when tryptophan is absent. When tryptophan is present (as the product of the metabolic pathway catylised by the enzymes coded for by the trp structural genes) or added to the bacteria's environment, the tryptophan+regulatory protein complex inhibits transcription of the trp structural genes.
  • Note: Generally operons involved in anabolic pathways are positively controlled by the regulatory protein, and operons involved in catabolic pathways are negatively controlled by the regulatory protein.

D. Explain positive control of the lac operon p 328

• When only lactose present, CAP(Catabolite activator protein) binds to cyclic AMP to make CAP-cAMP
• the CAP-cAMP complex llows RNA polymerase to bind to lac operon promoter. See figure 16.11
• This is positive control of the lac operon by CAP-cAMP since the binding of the CAP-cAMP promotes binding of RNA polymerase to the lac operons promoter, and hence allows allows a large amount of expression of the lac operon's structural genes.

III. Chapter 17: Gene expression in Eukaryotes.

A. Describe the main levels of control. Fig 17.1

• Modification of DNA bases to serve as chemical signals
• Transcriptional control Fig 17.2 Often involves regulatory proteins but no operons
• Histones and gene regulation
  • Histones compete with proteins that promote transcription for TATA boxes in promoter regions. See p 347. If histones bind on the TATA box transcription does not happen.
• Steroid hormones and gene regulation p 349 - 350 and fig 17.6.
• Contrast the general mechanisms of hormone operation. Steroid Vs peptide hormones.
• RNA processing control - Differential splicing p 3511, See Fig 17.7
• mRNA translation, degradation control p 353 - 354

B. Development and differentiation

• Describe the evidence for constancy of the genome during development
• Define totipotency
• Regeneration of carrot plants - Steward
• Cloning animals- explain the procedure by Wilmut to clone sheep
• Give examples of differential gene activity during development.
  • Hemoglobin
  • Explain what is meant by Polytene chromosomes and the significance of chromosome 'puffs'

C. Chromosomal changes in development

• Explain the basic structure of antibodies
• Explain the basic mechanism leading to antibody diversity
• Explain the concept of clonal selection in the immune system

D. Embryonic development in Drosophila Fig 17.26 and p 360-365

• Types of genes involved. Segmentation genes Vs homeotic genes
• Maternal effect genes -expressed by the mother during oogenesis - sets up chemical gradients in the egg.
• Segmentation genes in the embryo - created segmented body plan
• Homeotic genes specify what structure develops in what segment.

pgd revised 10/27/03