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bio 172 exam 3

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Which of the following best describes the way in which you would use restriction enzymes as you engineered bacterial cells to produce human proteins?
The same restriction enzyme would be used to cut both the donor DNA and the vector DNA.
Restriction enzymes:
recognize certain DNA sequences. Some of them will cut straight through; others will leave an overhang at both ends of the cut.
Which statement about plasmids is true?
Plasmids are circular pieces of DNA that can replicate independently of the main chromosome.
Transposable elements are:
DNA sequences that can insert themselves into new positions within the genome.
There is no correlation between genome size and complexity of an organism.
true
What is the name of the class of enzymes that recognizes a specific sequence of DNA and cuts it?
restriction endonucleases
Forensic technicians unearth a skeleton from a shallow grave. They extract a tiny amount of DNA from the pulp found in the teeth. How could they obtain sufficient DNA for an analysis of the victim's genes?
use the polymerase chain reaction
Restriction enzymes
cut stretches of DNA at specific sites known as recognition sequences.
What is the correct order of steps in a PCR reaction?
Denature the DNA, anneal DNA primers, and extend the chain with DNA polymerase
The larger the organism, the more genes the organism will have in its genome.
false
A LINE is an example of
a transposable element
Transposable elements make up about 75% of the DNA in the human genome.
False
Which of the following does not contribute to the tremendous amount of noncoding DNA in eukaryotic genomes?
Exons that can be alternatively spliced
Sequence assembly is accomplished by:
aligning the fragments by using a complex computer program.
Whole genome sequencing is often approached by a shotgun sequencing approach in which:
large genomes are randomly digested, short fragments are sequenced, and the overlapping sequences are assembled in order.
An operator is:
a regulatory region in DNA; the binding site for the repressor
Which gene encodes the protein β-galactosidase?
lacZ
What percentage of the human genome actually codes for proteins?
2.5%
The number of genes in an organism's genome is not a perfect indication of the organism's complexity because
-alternative splicing can increase the number of proteins made from a single pre-mRNA
-individual polypeptides can interact to form multiple types of protein complexes
-post translational modifications can increase the types of proteins produced by a single gene
Why is an open reading frame more difficult to find in a eukaryote than a prokaryote?
Because of the presence of introns
True or False: Positive regulation of transcription requires an activator protein to help RNA polymerase bind.
True
What is the function of the enzyme β-galactosidase ?
It cleaves lactose into glucose and galactose.
In <em>E. coli</em>, lactose binds with:
the lactose operon repressor, preventing it from binding to the operator. This allows the <em>lacZ</em> and <em>lacY</em> genes to be transcribed.
What characteristic of genes would classify them as belonging to the same operon?
They are under the control of the same promoter and operator sequence.
In an E.coli mutant β-galactosidase is not expressed whether or not lactose is present. Which of the following can explain this phenotype?
A mutation in the LacI protein which prevents binding to lactose
DNA wrapped around a group of histone proteins is called a
nucleosome
Enhancers are
DNA sequences to which regulatory transcription factors bin
Positive and negative transcriptional regulation differ in that:
in positive regulation, the binding of a regulatory protein to the DNA is necessary for transcription to occur; in negative regulation, such binding prevents transcription
In prokaryotes, inducers are small molecules that
bind to repressors and promote transcription
Which of the following genes might not be constitutively expressed?
The gene encoding stress hormone
What happens to the repressor protein when lactose is present?
The repressor protein is unable to bind to DNA
Why isn't the lac operon expressed at high levels in the presence of both glucose and lactose?
Because glucose suppresses cAMP levels.
__________is a positive regulator of the lac operon. _____________is a negative regulator.
CRP-cAMP complex; Repressor protein
For the lactose operon, lactose is a(n):
inducer.
In the presence of glucose
β-galactosidase is not produced.
What is a nucleosome?
DNA wrapped around a group of histone proteins
In DNA methylation, which nitrogenous base is most frequently methylated?
cytosine
In the lactose operon, the repressor binds to:
operator
You wish to identify a bacterial mutant that can't utilize galactose as a sugar source. How would you perform the replica plating?
First plate the bacteria on glucose, then replica plate onto a galactose only plate.
Chromatin remodeling refers to the process by which:
nucleosomes are repositioned to expose different stretches of DNA to the nuclear environment.
Which one of the following statements about gene regulation is incorrect?
Gene regulation occurs only in prokaryotes.
In an E.coli mutant β-galactosidase is expressed at high levels whether or not lactose levels are high. Which of the following can explain this phenotype?
A mutation in the operator which prevents LacI binding to it.
Epigenetic mechanisms of gene regulation involve:
the way in which DNA is packaged within chromosomes.
Proteins which bind to a gene's promoter to recruit factors necessary to start transcription are called
general transcription factors
Which one of the following can lead to changes in chromatin structure and is often associated with activation of transcription?
addition of acetyl groups to lysines located in the histone tail
DNA methylation patterns can be inherited from cell generation to the next because...
An enzyme called DNA methyltransferase recognizes hemimethylated DNA and methylates the other strand`
A transcription factor bound to an enhancer may recruit a(n) ___________________, while a transcription factor bound to a silencer may recruit a(n) _____________________.
histone acetyltransferase, histone deacetylase
Which of the following is true of DNA methylation?
DNA methylation is a chemical modification to the DNA which can influence gene expression
Which of the following is not an example of post-translational modification of a protein?
Changing the mRNA codon sequence
The human body contains approximately 200 major cell types. They look and function differently from one another because:
each expresses a different set of genes.
Histone modification:
can change over time in response to environmental cues, allowing genes to be turned on or off as needed.
Muscle cells and nerve cells in a single organism owe their differences to
Expressing different genes
Posttranslational modifications include
Addition of phosphate groups to amino acid side chains in the protein
When does post-translational control take place?
After a protein is synthesized.
Regulation of STAT activity was described in lecture 24. Based on the model, what would be the outcome if the STAT genes contained a mutation that makes the STAT protein unable to bind DNA?
phosphorylated STAT protein dimers would accumulate in the nucleus, but transcription would not be activated
Runner is a protein that can be used for cellular movement. The runner protein in white blood cells is 140 amino acids long while the runner protein in skin cells is 110 amino acids long. What can account for this difference?
There is alternate splicing of the runner mRNA.
If a cell is exposed to high temperatures and a large amount of protein misfolding will kill the cell, why is modifying ribosomal activity a good strategy for cell preservation?
It would prevent a large number of misfolded proteins from accumulating within the cell.
A protein on a cell surface that binds to a signaling molecule is an example of which of the following elements of cellular communication?
a receptor molecule
Which type of cell signaling does not rely on the diffusion of a chemical signal molecule?
juxtacrine
What region of an mRNA plays a role in mRNA stability?
The 3' UTR.
How do miRNAs regulate a specific mRNA?
Through complementary base pairing with the mRNA.
Proteasomes
help to regulate protein levels
A chemical that binds to a cell to cause its activity to change is an example of which of the following elements of cellular communication?
a signaling molecule
The correct sequence of steps in the M phase of the cell cycle is ____________ .
prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis
Phosphatases are a family of enzymes that specifically remove phosphate groups from proteins that were added by protein kinases. Vanadate is an inhibitor of phosphatases in eukaryotic cells. What effect would vanadate have on the response of cells to signals received by receptor kinases?
The response of the cell would last longer than it normally would.
When a __________ reaches its __________ , there is a specific means of receiving it and acting on the message. This task is the responsibility of specialized proteins called __________ .
signaling molecule; target cell; receptors
The centromere is...
a constriction on the chromosome, the point where sister chromatids are held together.
What happens in telophase?
nuclear envelopes re-form around newly segregated chromosomes.
According to Fig. 9.6, what is a key difference between cell signaling mediated by a surface receptor, compared to that mediated by an intracellular receptor?
Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules.
Which of the following is true about a hydrophilic signaling molecule?
Its effect is transduced across the cell but the signal never enters the cell itself
Which of the following is NOT true of G-protein coupled receptor signaling?
The signal indirectly responsible for G-protein activation is hydrophobic
What is interphase?
The period of time between two successive M phases.
How are steroid hormone receptors and cell-surface receptors similar?
Both types undergo a conformational change when they bind to their ligand.
What occurs during S phase?
Replication of DNA
During the G0 phase of the cell cycle,
cells are performing activities specific for their cell functions.
Second messengers:
-amplify the effects of the signal.
-are small intracellular molecules that participate in signal transduction.
-are removed in order to terminate a cellular signaling response.
-play a role in activation of intracellular signal transduction.
Where does the signal bind to the receptor?
The ligand binding site
Prokaryotic cells and eukaryotic cells reproduce by cell division. Regardless of the type of cell, all cells must ____________ before they divide.
make an exact copy of their genetic information
Which of the following statements is NOT true about sister chromatids?
They are formed when the prokaryotic circular chromosome attaches at the plasma membrane.
Predict what would happen to the daughter cells if the G1 phase of the parent cell is shortened?
The cells would be smaller than normal.
In what state are the chromosomes at the end of telophase?
Decondensed and unattached to the centrosome
What is a cyclin-dependent kinase?
a kinase present throughout the cell cycle, but is only active when bound to a cyclin
What is the role of cyclins in the cell cycle?
They activate CDKs
The p53 gene product is involved in
inducing apoptosis in damaged cells
Which of the following is NOT a function of MPF?
Phosphorylation of S phase proteins
What is the type of protein found on the surface of metastatic cancer cells that interacts with the basal lamina?
Integrins
What is a tumor suppressor?
Genes that encode proteins that function to inhibit cell division.
When nutrients are suboptimal for cell growth and division, the cell cycle arrests. At which stage of the cell cycle/checkpoint would you predict this arrest to occur?
G1 checkpoint
Which best describes E2F?
E2F is a transcription factor which regulates transcription of S phase proteins
Progression through the cell cycle is regulated by fluctuations in the concentration of
cyclins
Tumor suppressor genes are..
genes whose normal activities inhibit cell division.
Tumor development involves...
the accumulation of multiple mutations.
Which of the following would most likely contribute to uncontrolled cell proliferation (i.e., cancer)?
A mutant CDK that was active in the absence of its cyclin binding partner.
Which of the following is true of p53?
It acts as a transcription factor to turn on genes that inhibit the cell cycle in response to DNA damage
Many normal genes that have important functions in cell growth and division sometimes acquire mutations that cause the products of these genes to have negative effects including the development of cancer. These genes (when not mutated) are called:
proto-oncogenes.
Proto-oncogenes
are normal genes that, when mutated, have the potential to cause cancer.
Which major checkpoint delays the cell cycle when DNA replication is incomplete?
G2 checkpoint
Which of the following is not true regarding the protein Rb?
Phosphorylation of Rb promotes its binding to E2F.
What type of mutation in Rb is the least likely to promote tumor development?
a mutation that prevents phosphorylation of Rb
Inhibition of VEGF is a potential way to treat cancer because...
VEGF promotes angiogenesis
Which of the following statements is true about p53?
is a transcription factor that activates transcription of proteins that will inhibit the cell cycle
What properties are associated with a malignant cancer?
-fast growing
-metastatic
-invades surrounding tissue
Which of the following statements is true about retinoblastoma (Rb)?
Both copies of the Rb gene must be mutated for sporadic Rb to occur.
Which of the following would be most likely to lead to the development of cancer?
the activation of an oncogene and an inactivating mutation in a tumor suppressor gene
Cancer can be characterized by:
-cells with an enhanced ability to adhere to proteins in the basal lamina.
-All of these choices are correct.
-a mass of rapidly dividing cells called a tumor.
-metastasized tumor cells that leave the tumor and invade distant parts of the body
How can cancer cells ensure that oxygen levels remain high at the tumor site?
A transcription factor activates synthesis of a secreted factor necessary for angiogenesis.
Ras is a G protein involved in many growth signaling pathways. Which of the following mutations in Ras signaling could lead to a cancer phenotype.
Ras is unable to convert bound GTP to GDP.
Why cannot chromosomes line up in the middle of the cell before prometaphase ?
because the nuclear envelope prevents the microtubules from being able to bind to chromosomes.
Forensic technicians unearth a skeleton from a shallow grave. They extract a tiny amount of DNA from the pulp found in the teeth. How could they obtain sufficient DNA for an analysis of the victim's genes?
use the polymerase chain reaction
What modification takes place when lactose is present in a bacterial cell?
Lactose induces a conformational change in the repressor protein.
The checkpoint that requires a cell to be of adequate size in order to move forward is
G1/S checkpoint
Which of the following does not occur during mitosis?
DNA replication
True or false: using current DNA-sequencing technology, it is possible to sequence an entire chromosome (e.g., human chromosome 1, which contains approximately 250 million nucleotides) at once as one long fragment.
false
A posttranslational modification plays a very prominent role in controlling passage through the cell cycle. What is this modification?
phosphorylation.
Which of the following processes produces different proteins in different cells from the same primary transcript? Select all correct choices.
alternative splicing
RNA editing
Within the human genome, 45% of the DNA is composed of what?
transposable elements
What is the role of the protein FtsZ?
It forms a ring at the site of constriction.
You wish to identify a bacterial mutant that can't utilize galactose as a sugar source. How would you perform the replica plating?
First plate the bacteria on glucose, then replica plate onto a galactose only plate.
To promote cancer, proto-oncogenes must be turned ________ and tumor suppressors must be turned ______.
on; off
The prokaryotic protein FtsZ is evolutionarily related to eukaryotic tubulin. What does this mean?
-The overall protein structure of FtsZ is similar to -tubulin.
-The amino acid sequence for FtsZ is similar to tubulin.
-The gene sequence for FtsZ is similar to tubulin.
All of the following are true of kinases EXCEPT
A phosphate group is transferred from a kinase to a protein
All of the following promote cell division EXCEPT
Rb
In response to DNA damage, a kinase activates a protein called ______ by phoshorylating it.
p53
Telomerase is ....
a proto-oncogene; it is more active in cancer cells than in normal cells
True or false: Receptors for signaling molecules are always integral membrane proteins on the surface of responding cells.
false
How does protein phosphorylation regulate protein function?
It causes a conformational change in the protein.
Which of the following is a difference between siRNA and miRNA?
Only siRNA can work at the level of transcriptional control.
Which one of the following is not a result of RNA editing?
the recruitment of RNA polymerase following the binding of general transcription factors
What is responsible for pulling apart the double stranded DNA when running a PCR reaction?
Heat
Which of the following would not lead to a cell becoming cancerous?
An antibody that binds to a receptor and prevents the receptor from binding to a growth signaling molecule.
A chaperone responsible for proper folding of an enzyme is missing from a cell. What might happen to that enzyme?
It could be tagged with ubiquitin.
Cells spend most of their time in what phase?
Interphase
Chaperones
help proteins fold properly.
There is about 1,000 times as much DNA in a human cell as in a bacterial cell, but only 5 times as many genes. What accounts for this discrepancy?
A human cell has much more non coding DNA
Which of the following would NOT be different between your brain cells and your skin cells?
Promoter proximal elements
If there were a mutation in CRP that prevented it from binding to cAMP, what effect would this have on lacZ gene expression?
LacZ would never be expressed at high levels.
Translation can be controlled by which of the following mechanisms?
-the ribosome is phosphorylated in response to viral invasion
-a miRNA binds to the an mRNA to inhibit translation
-a protein binds to the 3' UTR of an mRNA to control the efficiency of translation
How does a ligand gated ion channel work?
When a ligand binds to an ion channel, the channel changes conformation and the ion channel opens, allowing ions to cross the membrane
A photobleaching experiment was presented in class showing that the distance between the bleached area and the chromatids shortened. What explanation could be given if the distance between the bleached area and the centrosome shortened?
Microtubules shorten at the centrosome.
What is the result of DNA ligase's action?
DNA fragments are joined together.
Which of the following is not an example of epigenetics?
Mutation
Both miRNA and siRNA work in conjunction with:
a protein complex called RISC to bind RNA transcripts in the cytoplasm.
Packaging of DNA into chromatin...
inhibits transcription by blocking RNA Polymerase from accessing DNA
The basal transcription complex binds to the _______________, while regulatory transcription factors bind to the __________________.
promoter, enhancer
If the lac operon were constitutively expressed,
the cell would be wasting energy.
Which of the following statements about G proteins is false?
They become activated when bound to GDP
Which of the following will lead to the fastest growing tumors?
less apoptosis and more cell division
In paracrine signaling, the signal affects only
target cells close to the cell from which it was secreted
RNA splicing provides an opportunity for regulating gene expression because:
a spliceosome in one cell can "see" as an intron what another spliceosome in another cell "sees" as an exon, allowing different proteins to be produced from the same primary transcript.
For the lactose operon, the CRP-cAMP is a(n):
activator
cAMP binds to the CRP protein and activates the protein. In other words, cAMP regulates CRP
posttranslationally
What is the major function of the mRNA 5' cap?
Initiation of translation.