Exam 3 Flashcards
The difference between bright-field and fluorescence microscopy is…
That one views the light passing through the sample and the other actually looks at light emitted from the sample.
One drawback of electron microscopy is that it…
Cannot be used to view living cells
Your lab TA just gave you a culture dish in which he claims there are cells called fibroblasts attached to the bottom. You cannot see anything on the bottom and think the TA is putting one over on you. Which method of microscopy would you use to best and most easily visualize the unstained cells without killing them?
Phase contrast microscopy
Which type of microscopy requires coating the sample with a thin layer of a heavy metal and can produce three-dimensional images of small surface projections from cells?
Scanning electron microscopy (SEM)
Proteasomes act primarily on proteins that have been marked for destruction by the covalent attachment of which small protein?
Ubiquitin
Which of the following statements is NOT true about the differences between liver cells and kidney cells in the same organism?
They contain different genes
After an RNA molecule is transcribed from a eukaryotic gene, portions called ____________ are removed and the remaining ___________ are spliced together to produce an mRNA molecule with a continuous coding sequence.
Introns, exons
Which of the following modifications can be made to an RNA molecule in eucaryotic cells before the RNA molecule becomes a mature mRNA?
Splicing, addition of methylguanosine cap to 5’end, and polyadenylation
Use of this common reporter gene fused to your gene of interest (such as lamins) would allow you to see where the lamins are localized in a living cell and see how the lamin distribution changes during the cell cycle. What is this reporter gene called?
Green fluorescence protein (GFP)
You would like to eliminate or reduce the expression of the intermediate filament vimentin in certain mouse cells you are studying. Which of the following experimental approaches could you potentially use to reduce the gene expression?
Use RNA interference (RNAi) or make a knockout mouse
What is the benefit of phase contrast microscopy?
Ability to see living (or dead) cells without stains
What is the benefit of fluorescence microscopy?
Ability to label specific structures individually and compare fluorescence/distributions
What is the benefit of SEM?
Can see fine details of surfaces (3D)
What is the benefit of DIC?
Ability to see living (or dead) cells without stains and has slightly more 3D than phase contrast
What is the benefit of bright-field?
Can use stains to differentiate and see different cell structures
What is the benefit of TEM?
Better resolution, can see smaller structural details compared to light microscopy
When we say that the gene for a specific type of serotonin receptor is expressed in smooth muscle, what is meant by expressed?
The gene has been transcribed into mRNA
What does it mean to say that a gene is “turned off?”
No mRNA is being transcribed from that gene (it’s present but not expressed)
What would happen to the mRNA if the mRNA wasn’t polyadenylated?
It would likely be degraded more rapidly than if polyadenylated and may not be exported from the nucleus
What does phosphorylation do for RNA processing?
Phosphorylation of the tail of RNA polymerase II allows RNA-processing proteins to assemble there
What does capping do?
Modifies 5’ end of transcript (synthesized first) by addition of an atypical guanine bearing a methyl group after RNA polymerase II has produced some nucleotides
What is polyadenylation?
Provides a newly transcribed mRNA that’s trimmed and another enzyme adds a series of repeated A nucleotides
What is splicing?
Introns removed by spliceosome and exons stitched together with ligase
A major regulator of the cell cycle is a protein called cyclin. Cyclin levels gradually increase before mitosis, and then their levels suddenly drop when mitosis nears completion. Interestingly, mRNA levels for cyclin are constant throughout the cell cycle. What would you expect to be responsible for the rapid drop in cycling levels at the end of mitosis?
Increase in ubiquitin addition to cyclins