Lssn 13 Ch 11 How Genes are Controlled (Finals)

gene regulation

The turning on and off of specific genes within a living organism.

operon

A unit of genetic regulation common in prokaryotes; a cluster of genes with related functions, along with the promoter and operator that control their transcription.

therapeutic cloning

The cloning of human cells by nuclear transplantation for therapeutic purposes, such as the replacement of body cells that have been irreversibly damaged by disease or injury. See also nuclear transplantation; reproductive cloning.

A eukaryotic gene was inserted into the DNA of a bacterium. The bacterium then transcribed this gene into mRNA and translated the mRNA into protein. The protein produced was useless and contained many more amino acids than the protein made by the eukaryotic cell. Why?

The mRNA was not spliced as it is in eukaryotes.

gene expression

The process whereby genetic information flows from genes to proteins; the flow of genetic information from the genotype to the phenotype: DNA → RNA → protein.

regeneration

The regrowth of body parts from pieces of an organism.

complementary DNA (cDNA)

A DNA molecule made in vitro using mRNA as a template and the enzyme reverse transcriptase. A cDNA molecule therefore corresponds to a gene but lacks the introns present in the DNA of the genome.

Carcinogen

A cancer-causing agent, either high-energy radiation (such as X-rays or UV light) or a chemical.

oncogene

A cancer-causing gene; usually contributes to malignancy by abnormally enhancing the amount or activity of a growth factor made by the cell.

Adult stem cell

A cell present in adult tissues that generates replacements for nondividing differentiated cells.

Enhancer

A eukaryotic DNA sequence that helps stimulate the transcription of a gene at some distance from it. An enhancer functions by means of a transcription factor called an activator, which binds to it and then to the rest of the transcription apparatus. See silencer.

Silencer

A eukaryotic DNA sequence that inhibits the start of gene transcription; may act analogously to an enhancer, binding a repressor.

tumor-suppressor gene

A gene whose product inhibits cell division, thereby preventing uncontrolled cell growth.

DNA microarray

A glass slide containing thousands of different kinds of single-stranded DNA fragments arranged in an array (grid). Tiny amounts of DNA fragments, representing different genes, are attached to the glass slide. These fragments are tested for hybridization with various samples of cDNA molecules, thereby measuring the expression of thousands of genes at one time.

homeotic gene

A master control gene that determines the identity of a body structure of a developing organism, presumably by controlling the developmental fate of groups of cells. (In plants, such genes are called organ identity genes.)

proto-oncogene

A normal gene that can be converted to a cancer-causing gene.

growth factor

A protein secreted by certain body cells that stimulates other cells to divide.

repressor

A protein that blocks the transcription of a gene or operon.

activators

A protein that switches on a gene or group of genes by binding to DNA.

promoter

A specific nucleotide sequence in DNA, located at the start of a gene, that is the binding site for RNA polymerase and the place where transcription begins.

nuclear transplantation

A technique in which the nucleus of one cell is placed into another cell that already has a nucleus or in which the nucleus has been previously destroyed. The cell is then stimulated to grow, producing an embryo that is a genetic copy of the nucleus donor.

alternative RNA splicing

A type of regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.

embryonic stem cell (ES cell)

Any of the cells in the early animal embryo that differentiate during development to give rise to all the kinds of specialized cells in the body.

Your body is composed of a dazzling array of different cell types. Each cell type develops its own unique properties. How does this happen?

All cells (with very few exceptions) contain the same set of genes, but the process of gene expression determines which genes are active in each cell.

X chromosome inactivation

In female mammals, the inactivation of one X chromosome in each somatic cell. Once X inactivation occurs in a given cell (during embryonic development), all descendants of that cell will have the same copy of the X chromosome inactivated.

Which of the following is a valid difference between embryonic stem cells and the stem cells found in adult tissues?

In nature, only embryonic stem cells give rise to all the different types of cells in the organism.

operator

In prokaryotic DNA, a sequence of nucleotides near the start of an operon to which an active repressor can attach. The binding of repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon.

transcription factor

In the eukaryotic cell, a protein that functions in initiating or regulating transcription. Transcription factors bind to DNA or to other proteins that bind to DNA.

The lac operon controls expression of three genes that produce lactose-digesting enzymes. What role does lactose play in regulating the lac operon?

It binds to and disables the repressor protein, thereby allowing production of the three enzymes.

What kinds of (somatic) cell gene mutations can frequently lead to the first stages of cancer?

Mutations in genes that regulate cell division

All of your cells contain proto-oncogenes which can change into cancer-causing genes. Why do cells possess such potential time bombs?

Proto-oncogenes are necessary for normal control of cell division.

cellular differentiation

Specialization in the structure and function of cells that occurs during the development of an organism; results from selective activation and deactivation of the cells' genes.

reproductive cloning

Using a somatic cell from a multicellular organism to make one or more genetically identical individuals.

A genetic defect in humans results in the absence of sweat glands. Some men express this defect all over their bodies but in women it is usually expressed differently. A woman with this defect typically has small patches of skin with sweat glands and other patches without. This pattern of sweat gland distribution can best be explained by

X chromosome inactivation

Within an operon, repressors _____.

block gene transcription to RNA by attaching to the operator

Your bone cells, muscle cells, and skin cells look different because

different genes are active in each kind of cell.

All of the cells in your body have the same complete set of DNA, however, they have different functions because

different genes are switched on and off in each type of cell

Which of the following cells is LEAST differentiated?

embryonic stem cells

In a multicellular organism cells in one area of the body may regulate gene expression in a distant cell by secretion of

hormones

The regulation of gene expression must be more complex in multicellular eukaryotes than in prokaryotes because

in a multicellular eukaryote, different cells are specialized for different functions.

The tumor-suppressor gene is important in the prevention of cancer because it

produces gene products that prevent uncontrolled cell growth

Operons are a standard method for gene regulation in _____.

prokaryotes but not eukaryotes

The nucleus of an intestinal cell of a tadpole (baby frog) is transferred to an egg whose nucleus has been removed (nuclear transplantation); some of the eggs will develop into normal tadpoles. This demonstrates

that differentiated cells have retained all of their genetic potential

To begin the process of gene transcription, RNA polymerase attaches to _____.

the promoter associated with the target gene

In humans, most cancers are caused by

tobacco

A DNA microarray is used to

visualize patterns of gene expression