Izabella Zamiatala
Period: 5th
November 27th, 2012
AP Biology : Chapter 15
Review Questions 1. Cells are equipped with controls that govern gene expression; that is, which gene products appear, when, and what amounts. When control mechanisms come into play depends on cell type, on prevailing chemical conditions, and on signals from other cell types that can change a target cell’s activities. Cells of complex organisms inherit the same genes, yet most become specialized in composition, structure, and function. This process of cell differentiation arises when different populations of cells activate and suppress their genes in highly selective, unique ways.

2. By negative control, regulatory proteins slow down or curtail gene activity. By positive control, regulatory proteins promote or enhance gene activities. Control is exerted through chemical modifications that inactivate or activate specific gene regions or the histone proteins that organize the DNA. For instance, regions of newly replicated DNA can be shut down by methylation, the attachment of methyl group to nucleotide bases.

3. A. Repressor protein: protein that binds with an operator on bacterial DNA to block transcription. A special regulating protein formed in bacterial cells that halt transcription, which is the synthesis of messenger ribonucleic acid (m-RNA) from a specific operon (a group of genes that carry out the synthesis of functionally related enzymes). The number of different repressors corresponds to the number of operons.
Activator protein: regulatory protein that enhances a cell activity (e.g., a radiolarian or heliozoan). For instance: CAP – this activator exerts positive control over the lactose operon by making a promoter more inviting the RNA polymerase.

B. Promotor: base sequences that signal the start of a gene. Operator: a binding site for a repressor protein that can prevent gene transcription.
C. Methylation: attachment of a methyl group to an organic compound; a common gene control. Acetylation: attachment of an acetyl group to a compound, such as DNA.

4. When lactose is present, the lack genes are expressed because allolactose binds to the Lac repressor protein and keeps it from binding to the lac operator.
Allolactose is an isomer of lactose. Small amounts of allolactose are formed when lactose enters E. coli. Allolactose binds to an allosteric site on the repressor protein causing a conformational change. As a result of this change, the repressor can no longer bind to the operator region and falls off. RNA polymerase can then binds to the promoter and transcribe the lac genes. When the genes in an operon are transcribed, a single mRNA is produced for all the genes in that operon. This mRNA is said to be polycistronic because it carries the information for more than one type of protein.

5. Gene amplification is when immature amphibian eggs and glandular cells of some insect larvae copy the same genes again and again when they require enormous numbers of the products. Sometimes, multiple rounds of DNA replication produce hundreds or thousands of copies prior to transcription. DNA rearrangements are when some genes have many base sequences in the DNA, and they are put together in different ways to make different product molecules. Chemical modification is when histones and other proteins interact with eukaryotic DNA in organized ways. The DNA- protein packaging, plus chemical modifications to particular sequences, influences gene expression. Pre – mRNA transcripts undergo modifications before they leave the nucleus. Transcripts stability affects how many protein molecules can be produced from it. Enzymes digest transcripts from the poly – A tail on up. The tail’s length and its attached proteins affect how fast it is digested. Also after leaving the nucleus, some transcripts are temporarily or permanently inactivated. Compared to prokaryotic cells, eukaryotic cells use more complex gene controls. Gene expression changes in response to external conditions and is subject to long – term controls over growth and development. Prokaryotic cells do not have great structural complexity and do not undergo complex development.

6. A Barr body is a randomly condensed one of two X chromosomes in cells of female mammals. Female human and female calico cats have two X chromosomes in their diploid cells, one is in its threadlike form; the other one is scrunched up even during interphase. The scrunched up cells is programmed to shutdown of all but about three dozen genes on one of two homologous X chromosomes. This X inactivation occurs in diploid cells. The condensed one looks like a dense spot inside the interphase nucleus. She is a mosaic female. The X chromosome is not condensed this way in human male cells.

7. Cells, both of an animal or a plant, have many interior structures called organelles. The mitochondria are the organelle that supplies energy to a cell while the nucleus houses genetic information in the form of chromosomes. The tubular network that makes up the endoplasmic reticulum is a cell's transport system and the similarly structured Golgi apparatus acts as a packaging system for a cell. Lysosomes contain digestive enzymes, and Ribosomes are the site of protein synthesis. All organelles are surrounded by a clear, jelly-like substance known as cytoplasm. The cell cycle has built-in checkpoints where proteins monitor chromosome structure and other aspects of the preceding phrase of the cycle (checkpoint genes). In a normal cell the plasma nor the cytoplasm doesn’t change, have a strong adhesion, are non-lethal and lastly the cells don’t abnormally divide. Cells of common skin moles and other noncancerous benign neoplasms grow abnormally but slowly, and they retain the surface recognition proteins that hold then in their home tissue. Abnormally growing and dividing cells of a malignant neoplasm have destructive physical and metabolic effects on the surrounding tissues. They are grossly disfigured, metastasizing cancer cells. They break loose from home tissues, enter lymph or blood vessels, then slip out and invade other tissues where they do not belong. There, they may start growing as new masses.
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Critical Thinking 1. a) Transcription will not be affected. With or without the mutation, transcription will be very low. When lactose is present E.coli cells convert some of it to allolactose. This sugar binds to the repressor and alters its shape. In altered form, the repressor can't bind to the operators. The looped DNA unwinds RNA polymerase can start transcription and so the lactose-degrading enzymes are produced when required.

b) Transcription will not be activated. Normally it would be activated in these conditions. E coli cells activate a set of three adjoining genes coding for lactose-metabolizing enzymes. A promoter precedes the genes in the bacterial DNA, and operators are positioned on both sides of it.

c) Transcription will not be affected. (With or without the mutation, transcription will be very low).

2. Duchenne Muscular Dystophy happens mostly in boys because girls mature at an earlier age than boys, their growth plates change into hard bone at an earlier age. Girls can carry the gene that causes the disease, but they usually have no symptoms. Whether or not someone has a form of muscular dystrophy has already been determined through hereditary factors by the time they are born (even though its effects are not apparent at birth). It also means that the disease is not in any way contagious, and that it is not brought on by anything that might happen in one's everyday life. The defective gene that causes Duchenne muscular dystrophy is located on the X chromosome. The disorder is therefore said to be sex-linked. It also is recessive, which means that females who inherit the defective gene will not usually develop the disease (because they need to have the defective gene on both X chromosomes) but are carriers of it. They can pass it on to the next generation. Affected males always inherit the gene for Duchenne muscular dystrophy from their mothers, and each male born to a mother who is a carrier for the disease has a 50-50 chance of inheriting the gene.

5. There has been much controversy about using animals in experiments for decades. People converse over different alternatives for animal testing and the inhumane way scientists treat these animals in experiments. I am for animal testing for many beneficial reasons that come out of animal testing. Although in some cases animals maybe abused, there have been so many discoveries with medicine with testing these drugs on animals. I believe that scientists should continue experimenting on animals; scientists should treat animals ethically. In human terms, research with animals has led to vaccinations against smallpox, measles, and tetanus; development of anesthesia, antibiotics, and insulin; use of cardiac pacemakers and heart bypass surgery; surgical advancements for organ transplants, hip replacements, and cataract surgery; and treatments for a host of diseases, including diabetes, multiple sclerosis, AIDS, and children's leukemia.
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Self Quiz 1. D. Cell differentiation occurs in all complex multicelled organisms and involves selective gene expression.

2. D. The expression of a given gene depends on the type of cell and its functions, chemical conditions, and environment signals.

3. D. Regulatory proteins interact with DNA, RNA, and gene products.

4. A. A base sequence signaling the start of a gene is a(n) promoter.

5. C. In prokaryotic cells but not eukaryotic cells a(n) operator is a type of base sequence that precedes genes of an operon.

6. A. An operon most typically governs bacterial genes.

7. D. Eukaryotic genes guide fast short – term activities, overall growth, and development.

8. B. X chromosome inactivation is an example of dosage compensation.

9. D. Hormones may promote and inhibit gene transcription in target cells.

10. B. Apoptosis is programmed cell death by suicide.

11. B. ICE – like proteases are lethal weapons.

12. D. Phytochrome – helps plants adapt to daily and seasonal changes in light.
E. Barr body – inactivated X chromosome.
B. Oncogene – mutated form of any gene that can induce cancer.
A. Homeotic gene – helps animal body plan develop.
C. Ecdysone – hormone with key role in insect life cycles.