EXAM 2 QUESTIONS Flashcards
Name at least 4 structural predictions made by Watson/Crick DNA model.
Base pairs were complementary
The structure formed a Double Helix
The helix was Right-handed
A pairs with T; G pairs with C
The diameter of DNA is 20 Angstroms.
Base pairs are perpendicular to the strands and lie flat.
The strands are antiparallel, where one runs from 3’-5’ and the other 5’-3’.
What are the 3 classes of “functional” (non-mRNA) RNAs?
Briefly describe the role of each class of functional RNA.
tRNA: brings the correct amino acid to the mRNA during translation
rRNA: major component of ribosomes
snRNA: helps process RNA transcripts (especially, helps remove introns).
Discuss the experimental evidence for the semi-conservative replication of DNA determined by in vitro experiments in the bacteria E.Coli.
The scientist started with heavy N-15 DNA, and allowed it to mix with the light N-14 DNA.
The first round of replication yielded identical DNA strands that had one full parent N-15 strand and one new N-14 strand.
These results ruled out the possibility of conservative replication because they were hybrids.
One more trial was needed to rule out the dispersive model of replication.
The second round yielded light-heavy DNA hybrids and light DNA (14/15-N and 14-N).
These results ruled out the dispersive model because the dispersive model would have only yielded hybrids.
Briefly state and describe the 4 primary ingredients that, along with DNA polymerase I, are needed for the in vitro system.
Buffering, temperature, and nonspecific ion concentrations are conditions, not ingredients.
!!!!???
Taken, in part, from Module 2.2 lecture.
- DNA primers/template with partial complement:
strand of nucleic acid that serves as a starting point for DNA synthesis
-dNTPs:
The building blocks for new strands are deoxyribose nucleoside triphosphates (A,T,C, or G)
-MgCl2: (or Mg++)
part of the active site. It helps bind the nucleotides which the DNA polymerase uses to copy the template strand and join to make new DNA
-Phosphate source:
The phosphate bonds to the nucleotide triphosphates and provides the energy
Kornberg used the phage PhiX174 to demonstrate DNA pol 1 was able to produce biologically active DNA in vitro.
Describe in sufficient detail the experimental methods that he used to draw the conclusions in DNA pol 1 could produce biologically active DNA.
The last part comes directly from slides.
The phage would insert the (+) form of its genetic information inside the host. The host would make (-) copies. (+) form phages would leave the cell to do it again. Pol I, and no other polymerase was present, but translation occurred accurately.
Single stranded circular DNA (+) strand infects E. coli.
The (+) strand directs replication of the (-) strand in E. coli, resulting in double-stranded duplex or replicative form (RF).
(+) strands are produced and packaged into viral coats to form mature virus particles.
Final (+) strand of øX174 infected E. coli and produced infectious mature phage particles.
DNA replication was accurate; any alteration the bases of øX174 would have probably rendered it non-viable.
What are 3 ways that miRNA can influence gene expression?
miRNA….
- Represses translation,
- Triggers mRNA degradation,
- Represses transcription of specific genes and larger regions of the genome using
RITS. - Works with RITS for chromatin remodeling and transcriptional silencing.
- miRNA has a role in splicing, and it can get mRNA destroyed. It works with snRNA to regulate mRNA.
correct answer, got from TA:
- degrades mRNA
- condenses chromatin
- prevents processing of ribosome
What experimental methods led Avery, McCarthy, & Macleod to determine that DNA was the “transforming material” in their classic experiments?
They introduced enzymes to the mixtures to degrade one component at a time and see if the genetic material was still passed on or not.
If the genetic material passed to the next generation, then the substance that the enzyme degraded was not the transforming material.
RNAse, for example, was introduced to remove all RNA; the genetic material still passed on, so RNA could not be the genetic material.
DNAse removed all DNA, and no genetic information passed on, so the scientists knew that DNA held the genetic information.
They performed an experiment where they took a large sample of IIIS, centrifuged, and heat killed it.
After that they excised and removed the proteins, carbohydrates, and lipids.
When joined to the active substrate IIR, transformation occurred.
They then treated with protease to get rid of all the remaining protein.
Transformation still occurred proving that protein was not the transforming material.
They then treated with ribonuclease.
Transformation still occurred proving that RNA was not the transforming material.
Lastly. they treated with deoxyribonuclease (DNAse) to get rid of the DNA and no transformation occurred.
This proved that DNA was the transforming molecule.
An organism has a A + T content of 50%.
What is the percentage for C?
25%
Which of the following DNA double helices would be more difficult to separate into single-stranded molecules by treatment with heat (which breaks hydrogen bonds)?
Indicate the reason for your choice.
A:
GCATTAGGGCATCCC
CGTAATCCCGTAGGG
B:
TTAGCGTTATAGCAT
AATCGCAATATCGTA
DNA molecule A would be most difficult to separate, because it has a higher G-C content.
Molecules B has a higher A-T content.
DNA molecule A has a higher A-T content. However, G-C pairs are held together by three hydrogen bonds while A-T bonds are held together by 2 hydrogen bonds. Hence, a higher number of G-C pairs gives a double-stranded DNA a higher heat resistance.
Match with best letter choice:
DNA Ligase
i, phosphodiester bonds at DNA nicks
The 5’ cap on an mRNA is important fro all the purposes listed below, EXCEPT for the ___ of an mRNA molecule.
Transcription
Intron Removal
Stability
Initiation of Translation
Transcription
While actually a form of RNA polymerase, this enzyme lays down the initial nucleotides to set up a condition where DNA polymerase can the take over for replication.
Primase
This new strand of DNA has its 3’ end orientated in the Opposite direction as that in which the replication fork travels.
The lagging strand
Assume the following pathway:
Precursor —> K —> C —> B —> Product
Mutations for 3 genes (genes I, II, and III) have been isolated that interrupt this pathway.
Addition of:
B rescues mutations in gene III
K, C, and B rescues mutations in gene II
C and B rescue mutations in gene I
In what order do genes I, II, and III function in this pathway?
II, I, III
Matching terms:
Primase
synthesis of RNA primer
Matching terms:
SSBP
stabilizing single-stranded DNA
Matching terms:
Helicase
Unwinding DNA
Matching terms:
Gyrase/Topoisomerase
Relieve tension in DNA due to supercoiling
Matching terms:
DNA Polymerase III
initiate DNA synthesis
Matching terms:
DNA ligase
connecting Okazaki frgments
Matching terms:
DNA Polymerase I
Filling the gap left after primers are removed
The ribosome is the primary site of
protein synthesis
The anticodon on the tRNA molecule…
binds to the mRNA in a complementary fashion
What is a gene?
A sequence of DNA that encodes a PROTEIN.