Ch 18 Control of Gene Expression
What does the term “control gene expression” mean?
Proteins interacting with DNA turn prokaryotic genes off or on in response to environmental changes.
Draw and explain how the Lac Operon is constructed and works.
What is a differentiated cell? How is it different from a stem cell?
A differentiated cell has specialized, turning on or off specific genes. Differentiation results from selective gene expression. Stem cell all genes are still accessible; cell can become any type of cell.
How does DNA packing control gene expression?
DNA is made available for transcription or made unavailable by the state of packing or unpacking. Eg.
Barr bodies in female cells calico male/female.
What are transcription factors? How do they work? [include enhancers, silencers]
Proteins that assist RNA polymerase in transcribing DNA. 1 st bind activator proteins to DNA sequence areas call ENHANCERS. Enhancers are often far from the gene they regulate, unlike operons. 2 nd Binding of activators to enhancers bends the DNA which brings the activators near to the promoter initiating
Transcription. Silencers are proteins that bind to DNA and inhibit the start of transcription.
Explain “RNA may be spliced more than one way”
An RNA molecule may be spliced more than one way. Different parts of the RNA are removed [similar to removing introns] and multiple forms of mRNA produced. Eg. Different splicing is involved in creating the differences in male and female fruit flies. Human genome project suggests alternative splicing is common in humans. Eg. One gene has 7 versions. Seven proteins are produced, the different RNA version depends on the type of cell.
Explain how insulin is “activated”
The initial protein/polypeptide is inactive. A protein cleaves the protein into 2 smaller segments that form the functional shape of insulin. If not cleaved the molecule cannot perform the intended function.
Describe nuclear transplantation/cloning.
Remove the nucleus from an ova. Add a somatic cell from an adult donor. Grow the resulting cell to the blastocyst stage. Implant into surrogate mother. Donor is born.
Therapeutic cloning is different. Explain.
Divide the blastocyst into individual cells, select the stem cells. Induce the stem cells to specialize into various cell types. Aim is to produce cells for repair of damaged or diseased organs. Insulin production from nonfunctioning pancreas cells.
How are drosophila developed. Include egg preparations and post fertilization development.
Drosophila melanogaster
First data linking gene expression and embryonic development. E.g. legs instead of antenna mutant.
Early event determines which end of the egg will become the head and which end the tail.
This occurs in the unfertilized egg, in the ovary-communication between egg and cells around it. Proteins are made and located in different parts of the egg. These proteins are different in the head , tail.
After fertilization mitosis separates the proteins into different cells. These proteins cause the cells to specialize. As cells are made they send signals to other cells help cells organize into segments. Now genes in each segment activate other genes so that fly parts can be made. The process of one gene activating other genes is termed a cascade of gene expression.
Homeotic Gene a master gene that regulates groups of genes that actually determine the anatomy of parts.
E.g one set of homeotic genes in the segments of the head and thorax form legs and antennae-whether head or legs is determined by other genes in the segment.

Draw and explain a signal transduction pathway.
Normal
—growth factor received by receptor on cell surface; relay proteins carry message activating transcription factor protein which connects to DNA resulting in production of proteins that stimulate cell division.
Change a relay protein is changed so it sends a signal/growth factor has been made unnecessary. Cell division is always stimulated.
Normal B –Growth inhibiting factor enters receptor on cell surface; relay proteins carry message activating a transcription factor which connects to the DNA resulting in production of proteins that inhibit cell division
Change a relay protein is changed so it sends a signal/growth factor has been made unnecessary. Cell division is not inhibited.
Describe the three processes that cause a cell to become a cancer cell.
1. An oncogene is activated. A protooncogene is a necessary gene that controls cell growth and differentation. Environmental forces may alter a protooncogene into an oncogene. 2. Additional DNA mutations [eg inactivation of a tumor-suppressor gene] cause growth of small benign tumor, polyp. 3.
Additional mutations lead to formation of a malignant tumor [a carcinoma]. Usually 4 or more mutations required explains why cancers can take a long time to develop.
How are multiple mutations associated with the development of cancer.
A mutation within the gene creates an oncogene, hyperactive form of growth stimulating protein.
Mutation resulting in multiple copies a gene, excess growth stimulating protein.
Gene is moved to a new DNA locus under new controls, excess growth stimulating protein.
Cell signaling systems appeared early in the evolution of life.
YeastSaccharomyces cerevisiae ; bread, wine, beer. Identify mates by chemical signaling. Types a and alpha secrete factors that bind onto receptors of the other type. Causes the cells to grow towards each other. The two cell types fuse soothe genes of both types are in a single cell. A new combination of genetic resources that provide advantages to the cells descendents. Science believes signaling mechanisms originated in bacteria and single celled eukaryotes and then became adapted for new uses in multicellular organisms.
Plant cloning demonstrated differentiated cells retain all of their genetic potential. Grew a carrot from a single cell. All the genes are present in the single cell but some were turned off in the source plant but were reactivated in the single cell. Cloning used extensively in agriculture. Cuttings. Some plants have become sterile so cloning is the only way to reproduce. E.g. orchids