mcb exam iii

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Which one of the following statements about the nucleus is correct?

The aqueous environment inside the nucleus is referred to as the nucleoplasm.

Which of the following 13 base DNA probes would best be able to detect the following segment of a gene of interest during FISH? (Note: Real probes need to be longer to reduce the likelihood of this sequence being present somewhere else in the genome, but these sequences will suffice for this question.)
5'-AGTCCTAGCTGCAATATAGCGATAGCTGCATTGCAGCTAA-3'

5' AATGCAGCTATCG 3'

Mitosis is responsible for what key process in multicellular eukaryotes?

asexual reproduction
wound repair
growth
All of the responses are correct.

During what phase of the cell cycle does the DNA become replicated?

s

What role(s) do gap phases play in the cell cycle?

What role(s) do gap phases play in the cell cycle?

They allow cells to replicate organelles and manufacture additional cytoplasm.

All of the following structures are found within the nucleus of a eukaryotic cell except

speckles.
Cajal bodies.
promyeloctic leukemia (PML) bodies.
nucleolus.

You conduct an experiment by incorporating purple fluorescent dNTPs early in S phase, followed by gold fluorescent dNTPs late in S phase. At the conclusion of S-phase, you examine the nucleus of the cell using a fluorescent microscope and see that the only incorporated fluorescence is purple. Which one of the following represents the most likely interpretation of your results?

DNA synthesis initiates early during S-phase but not late during S-phase.

The higher the gene density in a particular unit of DNA,

the more likely it will exist as euchromatin.

The nucleolus

contains the NOR of rRNA genes.

DNA replication is highly accurate. It results in about one mistake per billion nucleotides. For the human genome, how often would errors occur?

on average, six times each time the entire genome of a cell is replicated

The epsilon (ε) subunit of DNA polymerase III of E. coli has exonuclease activity. How does it function in the proofreading process? The epsilon subunit _____.

removes a mismatched nucleotide

Which of the following statements about rRNA is/are correct?
Choose all that apply.

The tandem arrays of 5S rRNA genes are located in an NOR.
The 45S pre-rRNA transcript is processed by complexes of RNA and protein known as snoRNPs.
RNA Polymerase II transcribes the 5S rRNA genes.
The 45S rRNA genes have very strong promoters for optimal transcription.
No productive association of the small and large ribosomal subunits occurs until the subunits are exported into the cytoplasm.
The 45S and 5S rRNA genes are located on chromosomes 13, 14, 15, 21 and 22.

b, d, e

Which of the following is least likely to be found in the dense fibrillar region of the nucleolus?

Pre-ribosomal particles

Which one of the following is least likely to cause mutations in DNA?

light from an incandescent bulb

Which of the following statements about mutations is incorrect?

Mistakes in transcription lead to alterations in the nucleotide sequence in the DNA.
If a mutation occurs in a bacterial cell, all subsequent progeny cells will carry that mutation.
If a mutation occurs in a germ line cell, the resulting fertilized embryo will carry the mutation in every cell.
Mistakes in translation are not as critical as mistakes in replication.
Proofreading by DNA polymerases helps reduce a cell's observed frequency of mutation.

a

Researchers found E. coli that had mutation rates one hundred times higher than normal. Which of the following is the most likely cause of these results?

The proofreading mechanism of DNA polymerase was not working properly.

A point mutation that results in the substitution of one amino acid for another within a protein is a ______.

missense mutation

A nonsense mutation in a gene _____.

introduces a premature stop codon into the mRNA

Which one of the following players in the E. coli DNA mismatch repair system possesses the ability to hydrolyze a phosphodiester linkage in a molecule of deoxyribonucleic acid? [Note: remember that to be a correct answer to the question, the option must satisfy all of the conditions of the question.]

MutH

Which of the following statements about the correction of errors in DNA replication is/are correct?
Choose all that apply.

DNA polymerases have 3'-5' exonuclease activity.
3'-5' exonuclease activity depends on the methylation state of the DNA strand.
E. coli does not methylate DNA in a particular region once replication has occurred in that region.
The methylation sequence in E. coli recognized by a particular methylase is 5'-GATC-3'.
3'-5' exonuclease activity results in 100-fold reduction in error rates.

a,d,e

A mutation that has no effect on fitness is a ______.

neutral mutation

The mutation resulting in sickle-cell disease changes one base pair of DNA so that a codon now codes for a different amino acid so it is an example of a _____.

missense mutation

What is the function of the nuclear pore complex found in eukaryotes?

It regulates the movement of proteins and RNAs into and out of the nucleus.

The system of rope-like fibers that give shape and stability to the nucleus is made up of proteins called:

lamins.

A nucleotide like ATP, which has a molecular weight of approximately 570 Daltons, would enter the nucleus by way of:

passive diffusion through nuclear pore complexes.

Which molecules do not normally cross the nuclear membrane?

DNA

Which of the following statements about the nuclear envelope is false?

The nuclear envelope is composed of two lipid bilayers.
The nuclear envelope is continuous with the Golgi apparatus.
Nuclear pores are made up of a group of proteins that are collectively called the nuclear pore complex.
Molecules pass into and out of the nucleus through nuclear pores.

b

In experiments to test whether a protein can enter the nucleus, why would proteins be labeled with fluorescent molecules?

To make the proteins easy to see

ucleoplasmin is a nuclear protein. This protein was divided into two segments and linked to the same large cytoplasmic protein, generating two fusion proteins. After injecting these fusion proteins into a cell, one of the proteins was found in the nucleus and the other in the cytoplasm. Which of the following conclusions can be drawn from these results?

The cytoplasmic protein contains a nuclear localization signal.
One of the fusion proteins entered the nucleus by passive transport.
Nucleoplasmin does not have a nuclear localization signal.
Only one of the two fusion proteins possesses a nuclear localization signal.

d

The sequence of amino acids that serves as a targeting signal for a protein to be transported from the nucleus to the cytoplasm is most accurately referred to as a:

nuclear export signal.

How many protein coding genes are found on the human mitochondrial genome?

13

The energy for mitochondrial protein import comes from __________; the energy for nuclear protein import comes from __________.

ATP; GTP

Which of the following statements about the import of protein to the nucleus is correct?
Choose all that apply.

Ribosomal proteins must display an NLS to be localized to the nucleus, and an NES to be localized to the nucleolus.
GTP is required for an importin to bind to an NLS of a protein destined to be localized to the nucleus.
An NLS can be a monopartite or bipartite signal which includes a significant number of basic amino acids.
The recycling of importins back to their original conformation requires GTP hydrolysis in the cytoplasm.

c,d

Which one of the following statements about mitochondrial proteins is correct?

Only 13 types of proteins are transcribed and translated in a mitochondrion.
Cleavage of a mitochondrial protein's transit sequence is done by transit peptidase using ATP as an energy source.
The proteins in a Tom complex did not, at any point, have a mitochondrial transit sequence.
All proteins that become part of a mitochondrion possess a mitochondrial transit sequence at some point.
The only energy that is used to get an entire protein into the matrix is in the form of the electrochemical gradient.

a

During the localization of a mitochondrial RNA polymerase following its translation, which of the following is least likely to be required?

GTP

Pancreatic cells, which secrete a large amount of digestive enzymes, are labeled with radioactive leucine and then chased for several hours with nonradioactive leucine. Photographic emulsions are prepared at different times during the chase. Where would the black spots appear on an emulsion prepared 3 hours after the pulse?

Exterior of the cell

What path does a protein in the secretory pathway take, starting from its site of synthesis?

Rough ER, Golgi apparatus, secretory vesicles, plasma membrane

During a pulse-chase experiment, photographic emulsions were prepared at different times during the chase, and radioactive spots were detected at the following times and locations: 5 minutes: rough ER; 10 minutes: Golgi apparatus; 40 minutes: endosomes; 70 minutes: lysosomes; 140 minutes: lysosomes. Which of the following conclusions can be drawn from these results?

The final destination of the proteins was the lysosome.

What scientific hypotheses can be tested by a pulse-chase experiment?

Movement of molecules through a cell over time

True or false? Proteins produced during the "chase" phase of a pulse-chase experiment are labeled with radioactive material.

False

What is the first step in a pulse-chase experiment?

Incubating cells with a labeled molecule

How are proteins transported to their correct location in the cell?

Proteins contain molecular "zip codes" that allow them to be shipped to the correct cellular compartment.

Which statement most accurately describes what happens to proteins that lack an ER signal sequence?

They are released into the cytosol.

Scientists have found that polypeptides that are normally synthesized in the endoplasmic reticulum are about 20 amino acids longer when they are synthesized by ribosomes not attached to the endoplasmic reticulum. What is a possible explanation for the greater length of these polypeptides?

The 20 amino acids serve as a signal (peptide) sequence that directs the forming polypeptides to the endoplasmic reticulum, where they are cleaved off during processing.

Which of the following statements about transmembrane proteins is correct?

They usually have one or more helical regions spanning the membrane bilayer.

GPI-anchored proteins are synthesized:

as transmembrane proteins, cleaved, and attached to the GPI group on the lumenal surface of the ER.

The major site at which membrane lipids are synthesized is:

the cytosolic side of the SER membrane.

A radioactively labeled protein is made by cells and followed through the various organelles in the secretory pathway. After six hours, all of the radioactivity is still primarily in the Golgi apparatus. This suggests that the

protein possesses a signal for localization within the Golgi apparatus.

All of the following are part of the core oligosaccharide side chain in the ER, except

erythrose.

A transmembrane protein has its N-terminus in the lumen of the ER, its C-terminus in the cytoplasm, and it spans the membrane five times. What are all the signals that this protein displayed, including any that may have been cleaved? (In the following options "STS" stands for "stop transfer sequence")

N-terminal signal sequence --> STS --> internal signal sequence --> STS --> internal signal sequence --> STS

Which of the following statements about protein modifications is incorrect?

N-terminal signal sequences are removed in the ER lumen.
Chaperone proteins exist in the ER lumen to help with protein folding.
Before a GPI-anchored protein is complete, the originally translated protein will lose amino acids from both the N and C termini.
All glycosylation occurs on the N-terminus of a protein.
Proteins which contain disulfide bonds are translated at the RER.

d

How are these signals read?

They bind to receptor proteins.

Vesicles initially enter the Golgi apparatus by fusing with:

the cis face, then exit from the trans face.

Compared with the trans-Golgi proteins, the cis-Golgi proteins would

be glycosylated only.

The cis-Golgi:

is the portion of the Golgi apparatus closest to the RER and nucleus.

Which one of the following cellular processes is most likely to happen in the Golgi?
Synthesis of sphingomyelin
Synthesis of ceramide
Synthesis of membrane phospholipids
Translation on membrane bound ribosomes
N-linked glycosylation

a

A mannose-6-phosphate group is a chemical signal which directs a protein displaying it to which one of the following locations?

A lysosome

Which of the following statements about the Golgi is/are correct?
The trans face of the Golgi is closest to the ERGIC.
A mannose-6-phosphate targets proteins to the peroxisome.
Vesicles can move from one layer of the Golgi stack to another by budding and fusion.
The majority of metabolism of Golgi in plants is due to cell wall polysaccharide biosynthesis.
A lot of animal cell wall biosynthesis occurs in the Golgi

cd

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