Ch 18-20 Review

The control of gene expression is more complex in eukaryotic cells because...

gene expression differentiates specialized cells.

Yeast has become important in genetic engineering because it...

has RNA splicing machinery, has plasmids that can be genetically engineered,allows the study of eukaryotic gene regulation and expression, and grows readily and rapidly in the laboratory.

In the control of gene expression in bacteria, a regulatory gene...

has its own promoter, is transcribed continuously, is not contained in the operon it controls, and codes for repressor proteins.

Virus particles are formed from capsid proteins and nucleic acid molecules...

by spontaneous self-assembly.

DNA methylation of cytosine residues...

may be a mechanism of epigenic inheritance when mathylation patterns are replaced in daughter cells.

Cytoplasmic determinants are...

unevenly distributed cytoplasmic components of an unfertilized egg, often involved in transcriptional regulation, usually serparated in the first few mitotic divisions following fertilization, and maternal contributions that help to direct the initial stages of development.

Retroviruses have a gene for reverse transcriptase that...

uses viral RNA as a template for DNA synthesis.

Example: Chromatin structure

DNA packing into nucleosomes; histone tail acetylation increases, whereas deacetylation and methylation of tails decreases transcription; methylation of DNA may be involved in long-term inactivation of genes; small RNAs may promote heterochromatin.

What enzyme is used in the polymerase chain reaction?

RNA polymerase.

Example: Post- transcriptional regulation

RNA processing; mRNA degradation by shoertening of poly-A-tail, removal of 5' cap, and miRNA targeting.

Summarize the flow of genetic information during replication of a retrovirus. Indicate the enzymes that catalyze this flow. ----> -----> Enzymes:

RNA--->DNA--->RNA; viral reverse transcriptase, host RNA polymerase.

What might be a proto-oncogene code for?

Receptor proteins for growth factors.

The untranslated regions (UTR) at both the 5' and 3' ends of mRNA may contribute to regulation of gene expression. Describe their different effects.

Regulatory proteins may bind to sequences in the 5' UTR and block attachment of ribosomes, thus decreasing gene expression. Sequences in the 3' UTR may affect the length of time an mRNA remains intact, thus either increasing or decreasing gene expression.

Example: Transcriptional regulation

Repressor may prevent ribosome binding so mRNA can be stockpiled; activation of intiation factors.

What is the first enzyme used in the production of RFLPs?

Restriction Enzyme

What is the first enzyme used in the production of cDNA?

Reverse transcriptase.

The MyoD protein has been shown to be able to transform some, but not all, differentiated cells into muscle cells. Why doesn't work on all kinds if cells?

The action of MyoD must depend on a combination of regulatory proteins, some of which may be lacking in the cells that is not able to transform into muscle cells.

Inducible enzymes usually function in ___________ pathways.

catabolic

A eukaryotic cells typically doesn't have...

an operator.

Repressible enzymes usually function in ____________ pathways.

anabolic

Inducible enzymes...

are produced when a small molecule inactivates the repressor protein.

A mutation that renders nonfunctional the product of a regulatory gene for a repressible operon would result in...

continuous transcription of the genes of the operon.

The pathway's product server as a ________ to activate the repressor and turn off enzyme synthesis and prevent overproduction of the product of the pathways.

corepressor

In E. coli, tryptophan switches off the trp operon by...

binding to the repressor and increasing the later's affinity for the operator.

A tumor-suppressor gene could cause the onset of cancer if...

both alleles have mutations that decrease the activity of the gene product, and a proto-oncogene has also become an oncogene.

What would be the fate of a Drosophila larva that inherits two copies of a mutant bicoid gene?

It develops normally but, if female produces mutant larvae that have two tail regions.

a. Why is PCR often used prior to cloning a gene in cells? b. Why even bother cloning genes in cells, since PCR produces so many copies so fast?

a. By amplifying the gene prior to cloning, the later task of identifying clones carrying the desired gene is simplified. b. There is a limit to the number of accurate copies that be made due to the accumulation of relatively rare copying errors. Large quantities of a gene are better prepared by DNA cloning in cells.

What is the difference between determination and differentiation?

A cell is said to be determined when its development fate is set. Its series of gene activations and inactivations has set it on the path to express the genes for tissue-specific proteins. When it produces these proteins and develops its characteristic structure, the cell has become differentiated.

Describe the process of protein degradation in a cell.

A cell marks a protein for destruction by attaching molecules of ubiquitin to the protein. Giant proteasomes chop up the marked proteins.

What is apoptosis?

A cell suicide program may be initiated by p53 protein in response to DNA damage.

What would you expect to find as part of a receptor protein that binds with a steroid hormone?

A domain that binds to DNA and protein-binding domains.

A virus has a base ratio of (A+G)/(U+C)=1. What type of virus is this?

A double-stranded RNA virus.

Compare genomic and cDNA libraries with regard to their advantage and disadvantage.

A genomic library contains copies of DNA segments from the entire genome. Thus, all genes should be represented, along with regulatory sequences and introns. A cDNA library allows you to sequence only the exons of a gene, and also indicates which genes are expressed either in different cell types or at different stages of development in the same cell type.

What DNA sequence would most likely be a restriction site?

AAGG TTCC

Give an example of highly methylated and inactive DNA common in mammalian cells.

Barr body- compacted X chromosome in cells of female

What type of evidence established that Bicoid protein is a morphogen that determines the anterior end of a fruit fly?

Bicoid mRNA was shown to be localized at one end of the unfertilized egg; later in development, Bicoid protein was concentrated in the anterior cells of the embryo. Also, injection of bicoid mRNA into various regions of early embryos caused anterior structures to form at those sites.

Petroleum-lysing bacteria are being engineered for the treatment of oil spills. What is the most realistic danger of these bacteria to the environment?

Destruction of natural oil deposits.

What is not true about enhancers?

Each gene may have several enhancers, and each enhancer may be associated with and regulate several genes.

Genes for unducible enzymes are usually switched _______ and the repressor in synthesized in an ________ form.

Off; active

What are proteasomes?

Enormous protein complexes that degrade proteins marked with ubiquitin.

Do small RNAs regulate gene expression through affecting translation or transcription?

Evidence indicated that they do both. MicroRNAs affect translation by degrading mRNA or blocking translation. Several experiments have shown that small RNAs may silence transcription by changing chromatin structure.

Would histone tail deacetylation increase or decrease the transcription of a gene located in that nucleosome.

Histone tail deacetylation would decrease transcription because it would make genes in the nucleosome less accessible.

Nutrient molecules serve as _________ to stimulate production of the enzymes necessary for their breakdown.

Inducers

What would most likely account for a family history of colorectal cancer?

Inheritance of one mutated APC allele that regulates cell adhesion and migration.

A larger portion of the DNA in a eukaryotic cell is transcribed that would be predicted by the proteins made by the cell. What is being transcribed and what is its function?

Many RNA coding genes are transcribed. Precursor RNAs fold into hairpin structures, which are cut and processed into miRNAs that regulate translation for mRNAs.

What is the difference between microRNAs and small interfering RNAs?

MicroRNAs are coded for by RNA coding genes in a cell and processed. Small interfering RNAs are longer, double-stranded RNA molecules that are introduced ino a cell, which are then processed by the cell and function like miRNAs.

How mught the mechanism of transcriptional regulation differ for the cell-cell signaling involved in induction?

Most cytoplasmic determinants are mRNA for transcription factors that are divided by the first few mitotic divisions. They are present in the cells and their translated product can enter the nucleus and regulate transcription. Inducers must communicate between cells. They are often proteins that bind to cell surface receptors and initiate a signal transduction pathway involving a cascade of enzyme activations, usually leading to the activation of transcription factors within the target cell.

Example: Post-transcriptional regulation

Protein processing by cleavage of modification; transport to target locatoin; selective degradation by proteasomes of proteins marked with ubiquitin.

How is the coordinated transcription of genes involved in same pathway regulated?

The genes have the same combination of control elements in the enhancer.

Describe the sequence from the formation of a primary miRNA transcript to the blocking of transcription of an mRNA.

The primary miRNA transcript fold on itself by hydrogen bonding between complementary bases, forming loops called hairpins. Each hairpin is cut, trimmed by Dicer, and one strand is degraded. The single-stranded miRNA forms a complex with proteins. The complex binds to mRNA with complementary base sequences, and the mRNA is degraded or translation is blocked.

What is difficult in getting prokaryotic cells to express eukaryotic genes?

The signals that control gene expression are different and prokaryotic promoter regions must be added to the vector.

Which of these DNA sequences would most likely function as a restriction site for a restriction enzymes? Why? 1.**CAGCAG** 2.**GTGCTG** 3.**GAATTC** 4.**GTCGTC** 5.**CACGAC** 6.**CTTAAG**

The third sequence, because it has the same sequence running in opposite directions. The enzyme would probably cut between G and A, producing AATT and TTAA sticky ends.

What is not true of adult stem cells?

They are differentiated cells that can be induced to dedifferentiate and become totipotent.

What is true of prions?

They are infectious proteins that may convert brain proteins into misfolded forms.

What is not true about restriction sites?

They signal the attachment of RNA polymerase.

You are attempting to introduce a gene that imparts larval moth resistance to bean plants. What vector would you most likely use?

Ti plasmid.

Example: Trancriptional regulation

Transcription factors bind with enhancers, then interact with mediator proteins and promoter region to form transcription initiation complex; repressor can inhibit transcription; steroid hormones or other chemical messages may bind with receptor proteins, producing transcription factors.

Complementary DNA does not create as complete a library of genes as the shotgun approach because...

a cell produces mRNA for only a small portion of its genes.

The study of viruses hasn't done...

illuminate the sexual reproductive cycles of viruses.

Drugs that are effective in treating viral infections...

interfere with the synthesis of viral nucleic acid.

A gene can develop into an oncogene when...

it is present in more copies that normal, it undergoes a translocation that removes it from its normal control region, a mutation results in more active or resistant protein, and a mutation in a control element increases expression.

Viral genomes may not be...

misfolded infectious proteins.

Genes for repressible enzymes are usually switched _________ and the repressor is synthesized in an __________ form.

on; inactive

Pattern formation in animals is based on...

positional information a cell receives from gradients for morphogens.

The role of restriction enzymes in DNA technology is to...

product a cut at specific restriction sites in DNA.

What is not an example of the control of gene expression that occurs after transcription?

rRNA genes amplified in multiple copies in the genome.

Bacteria defend against viral infection through the action of...

restriction enzymes that chop up foreign DNA.

Beijerinck concluded that the cause of tobacco mosaic disease was not a filterable toxin because...

the infectious agent reproduced and could be passed on from a plant infected with filtered sap.

Vertical transmission of a plant viral disease may involve...

the inheritance of an infection from a parent plant.