CH. 18 - Gene expression

What is a primary reason that organisms control the expression of their genes?

- Adaptation/Survival changes needed for survival - To produce proteins - Conserve resources and energy

Describe one aspect of transcriptional control or processing seen in eukaryotes.

- Alternate splicing - Cap and tail added - Activated proteins bind to control elements - Inhibition of RNA polymerase

In addition to the resource-use control seen in prokaryotes, what effects of gene expression control are seen in eukaryotes?

- Cell differentiation

What is a reason that some people are more likely to develop cancer than others?

- Mutated genes are passed down. - Being exposed to environmental factors with harmed chemicals. - Bad habits such as smoking. - Age.

What types of regulation exist for gene expression in eukaryotes that DON'T exist for bacteria?

- Protein processing - Histone acetylation - The movement of mRNA from the nuclear pores of the nucleus - Chromatin accessibility - DNA methylation - Eukaryotic gene expression is regulated during transcription and RNA processing

Describe a type of gene whose alteration can result in cancer development.

- Ras gene: Mutations in this gene can lead to production of a hyperactive Ras protein and increased cell division. - Tumor suppressor genes: help prevent uncontrolled cell growth. - p53: prevents a cell from passing on mutations due to DNA damage. - Gene's that code for protein kinases - Genes that causes dedifferentiation

What would be the effect on embryo development if you eliminated one type of cytoplasmic determinant in an egg cell?

- The cell would migrate towards a different section of the body to exhibit a different function. - Change cell function.

How is differential gene expression triggered in developing embryos?

1) Cytoplasm determinants. 2) Induction by nearby cells.

How do enhancers effect transcription if they can be far upstream of the promoter?

An enhancer doesn't need to be located near the transcription initiation site to affect transcription.

How can chromosomal translocations lead to oncogene activation?

Chromosomal translocations leading to cancer are generally via two ways: formation of oncogenic fusion protein or oncogene activation by a new promoter or enhancer.

Bacteria control expression of related gene products by grouping them into operons. How do eukaryotes approach this control issue?

Different control groups allow for different genes to be coded, some can be activated or repressed.

How does the effect of the increase in histone acetylation compare with the effect of the increase of DNA methylation?

Histone acetylation appears to promote transcription by opening up the chromatin structure (Figure 18.7b), while addition of methyl groups can lead to the condensation of chromatin and reduced transcription.

What is the central feature of bacterial operon gene structure?

It can regulates the expression of the genes encoding the enzymes.

What is the mechanism by which Bicoid works in embryo development?

It is a gene that affects the front half of the body. • An embryo whose mother has a mutant Bicoid gene lacks the front half of its body and has duplicate posterior structures at both ends.

How does the regulation of the lac operon differ from the regulation of the trp operon?

Lac operon regulation is using inducer to inactivate the repressor while trp operon regulation is one which repressor is activated.

What's the effect of miRNA?

MicroRNAs (miRNAs) are small single- stranded RNA molecules that can bind to mRNA. • These can degrade mRNA or block its translation.

What is meant by the term embryonic pattern formation?

Pattern formation is the development of a spatial organization of tissues and organs. • In animals, pattern formation begins with the establishment of the major axes.

What is one way that proto-oncogenes can stimulate the development of cancer?

Proto-oncogenes can be converted to oncogenes which lead to abnormal stimulation of the cell cycle. This is made in three ways: - Movement of DNA within the genome: if it ends up near an active promoter, transcription may increase - Amplification of a proto-oncogene: increases the number of copies of the gene - Point mutations in the proto-oncogene or its control elements: causes an increase in gene expression

What is epigenetic inheritance?

The inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence. - Parent's experiences, in the form of epigenetic tags, can be passed down to future generations.

What does the presence of a CAP binding site in the lac promoter do for regulation of that operon?

When glucose is scarce, activated CAP attaches to the promoter of the lac operon and increases the affinity of RNA polymerase, thus accelerating transcription.

In the trp operon, how do TrpR and tryptophan interact to control expression of the trp genes?

When tryptophan is present, it binds to the trp repressor protein, which turns the operon off.

**Mutations in which of the following types of genes can contribute to the transformation of cells into cancer cells? -tumor suppression genes -growth factor receptor genes -G proteins in signal transduction pathways -both b and c are correct -a, b and c are all correct

a, b and c are all correct

**Which of the following regulatory mechanisms is found in eukaryotes but not in bacteria? -alternative splicing of mRNA -histone acetylation -enhancer elements -both a and b are correct -a, b and c are all correct

a, b and c are all correct

*Muscle cells differ from nerve cells mainly because they a. express different genes. b. contain different genes. c. use different genetic codes. d. have unique ribosomes.

a. express different genes.

*Absence of bicoid mRNA from a Drosophila egg leads to the absence of anterior larval body parts and mirror-image duplication of posterior parts. This is evidence that the product of the bicoid gene a. normally leads to formation of head structures. b. normally leads to formation of tail structures. c. is transcribed in the early embryo. d. is a protein present in all head structures.

a. normally leads to formation of head structures.

*The functioning of enhancers is an example of a. a eukaryotic equivalent of prokaryotic promoter functioning. b. transcriptional control of gene expression. c. the stimulation of translation by initiation factors. d. post-translational control that activates certain proteins.

b. transcriptional control of gene expression.

**Which of the following statements accurately apply to bacterial operons? -multiple genes are controlled by a single promoter -multiple genes are translated off of a single mRNA -alternative splicing produces different mature mRNA from a single gene -both a and b are correct -a, b and c are all correct

both a and b are correct

**How is the regulation of the lac operon different from the regulation of the trp operon? -the default state of the lac operon is off while the default state of the trp operon is on -the default state of the lac operon is on while the default state of the trp operon is off -both allolactose and tryptophan bind to their respective repressor molecules (LacR and TrpR) -both a and c are correct -both b and c are correct

both a and c are correct

*Which of the following statements about the DNA in one of your brain cells is true? a. Most of the DNA codes for protein. b. The majority of genes are likely to be transcribed. c. It is the same as the DNA in one of your liver cells. d. Each gene lies immediately adjacent to an enhancer.

c. It is the same as the DNA in one of your liver cells.

*If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then a. the amino acid inactivates the repressor. b. the repressor is active in the absence of the amino acid. c. the amino acid acts as a corepressor. d. the amino acid turns on transcription of the operon.

c. the amino acid acts as a corepressor.

*Within a cell, the amount of protein made using a given mRNA molecule depends partly on a. the degree of DNA methylation. b. the rate at which the mRNA is degraded. c. the number of introns present in the mRNA. d. the types of ribosomes present in the cytoplasm.

c. the number of introns present in the mRNA.

*Cell differentiation always involves a. transcription of the myoD gene. b. the movement of cells. c. the production of tissue-specific proteins. d. the selective loss of certain genes from the genome.

c. the production of tissue-specific proteins.

*Which of the following is an example of post-transcriptional control of gene expression? a. the addition of methyl groups to cytosine bases of DNA b. the binding of transcription factors to a promoter c. the removal of introns and alternative splicing of exons d. gene amplification contributing to cancer

c. the removal of introns and alternative splicing of exons

**Cytoplasmic determinants in egg cells... -are evenly distributed throughout the egg -can influence the formation of axes in the embryo -only control the expression of genes in the egg and not in the embryo -are always miRNA

can influence the formation of axes in the embryo

*Proto-oncogenes can change into oncogenes that cause cancer. Which of the following best explains the presence of these potential time bombs in eukaryotic cells? a. Proto-oncogenes first arose from viral infections. b. Proto-oncogenes are mutant versions of normal genes. c. Proto-oncogenes are genetic "junk." d. Proto-oncogenes normally help regulate cell division.

d. Proto-oncogenes normally help regulate cell division.

*What would occur if the repressor of an inducible operon were mutated so it could not bind the operator? a. irreversible binding of the repressor to the promoter b. reduced transcription of the operon's genes c. buildup of a substrate for the pathway controlled by the operon d. continuous transcription of the operon's genes

d. continuous transcription of the operon's genes

MyoD controls the expression of multiple muscle-related genes, but what controls the expression of myoD?

myoD controls myoD - Signals from other cells activate myoD to make MyoD protein - Transcription factors