E3 Flashcards
You have measured the absorbance of a sample of DNA in solution and found that the ration A260nm/A280nm = 1.26. What can you conclude about this sample of DNA?
It is likely contaminated with protein.
Which is more stable, DNA or RNA?
DNA
What is the complementary sequence to CATTACGT?
ACGTAATG
Which piece of DNA will have the higher Tm, one with a cytosine plus guanine content of 30% or one with a cytosine plus guanine content of 50% if both are heated under the same experimental conditions?
50% cytosine plus guanine will have the higher Tm.
Chromatin interacts with the DNA backbone. Therefore, the primary structure of chromatin should have a high percentage of the following amino acids:
Lysine, Arginine
Which bases pair with one another in DNA? Classify each as a purine or a pyrimidine. How many hydrogen bonds form between each of these pairs?
Purine (A) bonds with Pyrimidine (T) w/ double H bond. Purine (G) bonds with Pyrimidine (C) w/ triple H bond.
Nucleobase
- a nitrogen-containing compound. (C)ytosine, (G)uanine, (A)denine (found in both DNA and RNA) (T)hymine (found only in DNA), and (U)racil (found only in RNA) 5 in DNA & RNA,
Nucleoside
are components of nucleotides, have a nitrogenous base and a five-carbon carbohydrate group
Nucleotides
are simply a nucleoside with one or more phosphate groups attached
Nucleic acid
They are composed of nucleotides, monomer components: a 5-carbon sugar, a phosphate group and a nitrogenous base.
Describe and explain how the Griffith Experiment and the Avery-MacLeod-McCarty experiments demonstrated that DNA is the genetic material
showed transforming substance in bacteria could change harmless strains to virulent ones. Avery-MacLeod-McCarty Experiments (1944) identified this substance as DNA by destroying proteins, RNA, or DNA in the transforming mix, revealing the destruction of DNA stopped the transformation.
Chargaff observed that the total amount of A+G was equal to the total amount of C+T regardless of the source of DNA. Explain the structural basis for this observation
the structural stability and specificity of the DNA double helix. Chargaff’s rules of base pairing= transmission of genetic information.
Describe the major feature of the DNA double helix. What force is primarily responsible for the stability of the structure?
DNA made of two strands that wind around each other resemble a twisted ladder, helix-like shape. Each strand has backbone made of sugar (deoxyribose) and phosphate groups. base pairing between complementary strands and stacking between adjacent bases
Bacteria produce restriction endonucleases as a defense mechanism against phages. Explain why the enzymes do not cleave the bacteria’s genomic DNA?
restriction enzymes can’t cleave methylated DNA. bacterial genome is methylated, and resistant to enzymes. phage DNA is not methylated and so is cleaved by enzymes
LacZ
codes for beta-galactosidase
ApR
codes for beta-lactamase (ampicillin resistance)
Ori
origin of replication, so the bacteria can replicate the plasmid
Which restriction enzyme cut sites would you use to clone your blue pigment gene into pUC19 and why?
Any of the restriction cut sites located in the multiple cloning site (MCS), these sites only cut the plasmid once. Also the sites are in the lacZ gene and so facilitate blue/white screening.
You digest the plasmid and your blue pigment gene with the restriction enzymes chosen in step b. Explain how the two fragments will stick together, and explain how you will stitch the phosphate backbone back up
fragments stick by base pairing, bc of complementary sticky ends made by digesting gene and plasmid w/ same restriction enzymes. backbone would repair w/ adding DNA
ligase
Following transformation of the plasmid, how would you ensure that the bacteria you isolate have successfully taken up the plasmid
By using antibiotic selection. Plate the bacteria on agar containing antibiotic (ampicillin), only bacteria that w/ the plasmid (and antibiotic resistance) will survive.
How would you know which bacteria have a plasmid with your gene inserted?
Blue/white screening. Place X-gal in agar, if bacteria produce lacZ colonies will be blue, if not the colonies will be white. Since the gene in the middle of lacZ, that will make the protein inactive, so the white colonies will have the correct gene insert.
You are now interested in inserting your blue pigment gene into a tomatoes plant. You assume that people would love to eat blue tomatoes. Explain how you might go about inserting this gene into the plant
You would use the Ti plasmid from Agrobacterium tumefaciens. remove tumor causing genes from plasmid and replace with blue pigment gene. plasmid would be reintroduced back into the bacteria, that would be used to infect the plants. plasmid would go into the plant’s chromosome changing it with the gene.
What is Taq polymerase? Where was it isolated and from which organism? Why is it crucial for the polymerase chain reaction?
Taq polymerase is a heat stable DNA polymerase. If was isolated from the bacteria Thermus aquaticus in a hotspring in Yellowstone National park. The enzyme is important in PCR because it does not denature at high temperature, so new enzyme does not have to be added at each cycle of the reaction
Describe using a diagram how the polymerase chain reaction works and results in exponential amplification of DNA. What steps are involved, what temperatures are required, and what components are needed for the reaction to occur.
- Denaturation: 94 °C, DNA strands separate
- Annealing: Cool to ~55 °C, synthtetic DNA primers form duplex with the separated DNA strands.
- Extension: 72 °C, stable DNA polymerase copies the DNA chain Repeat steps 1-3 25-30 times
To perform the reaction you will need -heat stable DNA polymerse (Taq or equivalent)
-dNTP (deoxy nucleotide triphosphates)
-template
-primers
-Mg2+