Exam 2 Flashcards
(31 cards)
What property of the model for DNA structure that Watson and Crick published suggested a mechanism for how one DNA molecule could divide during mitosis to create two exact copies that end up in the two daughter cells?
The complementary pairing of bases between the two strands
because of the rules of base-pairing (C with G, G with C, A with T, T with A), if you have one strand of DNA you can easily make the other strand following these rules. This provides an easy way for one strand to divide into two. none of the other elements listed explain that fact.
What is the role of peptidyl transferase in translation?
it creates a peptide bond between amino acids in the A and P sites
Parvoviruses are animal viruses that cause disease in dogs, cats, other animals and rarely humans. The genome of one parvovirus contains about 6000 bases and encodes 2 proteins (parvo means ‘tiny’ in Latin). Determination of the nucleotide composition of feline panleukopenia virus shows that it contains 18% G, 25% C, 31% T and 26% A. What type of genome is this?
single-stranded DNA
has T so DNA
T not equal to A, G not equal to C, so single-stranded DNA
During translation initiation, when does the 50S ribosomal subunit bind to the 30S ribosomal subunit?
when charged initiator tRNA-fMet is present in the P site
How does the eukaryotic translation initiation complex locate the start codon in an mRNA?
the ribosome uses the first AUG it finds downstream of the 5’ Cap as the start codon
In their genetic screen in Neurospora, Beadle and Tatum identified:
auxotrophic mutants that were unable to grow on minimal medium
In the polypeptide Met-Phe-Leu, which amino acid(s) will have a free amino group?
Met
Which type of RNA never leaves the nucleus in eukaryotes?
all of these types of RNA leave the nucleus
tRNA, rRNA, mRNA
binds the mRNA during initiation
rRNA
has peptidyl transferase activity
rRNA
site where the incoming aminoacyl-tRNA binds during elongation
A site
site where the first tRNA binds during initiation
P site
binds a stop codon
release factor
provides the energy for translocation
GTP
What is the consequence of polyadenylation?
an mRNA transcript is protected from degradation in the cytoplasm
Hydrogen bonds are weak bonds that can be easily broken, for example by raising the temperature of the solution in which a protein is present. Lysozyme is a protease found in the liquid inside a chicken egg (the ‘egg white’) that can degrade the outer capsule of bacteria, leading to their lysis and death (protecting the developing embryo from infection). What would you predict would be the effect on the lysozyme protein if you were to heat up a solution of egg white lysozyme to 95° C (the boiling point of water is 100°C)?
The lysozyme would lose its three dimensional conformation, and would be unable to perform its function
The 3D structure of a protein is necessary to perform its function. The 3D structure is a consequence of 2° and 3° structure, which are dependent on hydrogen bonds, so the 3D structure would be disrupted and the protein could not do its job. The 1° structure of a protein is the covalent bonds between amino acids - this is not affected by heating the protein.
BTW, this is what happens when you fry an egg, the ‘white’ is the unfolded lysozyme protein.
How many of the following enzymes can polymerize nucleotides?
topoisomerase
DNA polymerase III
DNA polymerase I
telomerase
primase
RNA polymerase II
helicase
five do
DNA polymerase III
DNA polymerase I
telomerase
primase
RNA polymerase II
What happens if DNA polymerase uses it 5’->3’ polymerase activity?
A nucleotide is added on the new strand
During the process of transcription in E. coli, when does the sigma subunit fall off the RNA polymerase holoenzyme?
After polymerization of the first 8-10 RNA nucleotides
In prokaryotes, sigma factor falls off holoenzyme after the polymerase has made 8-10 nucleotides of RNA.
In eukaryotes, the general transcription factors stay assembled at the promoter and the RNA polymerase moves away as it starts elongating a transcript
one ring = pyrimidine, two rings = purines
2’OH = ribose = RNA, 2’H (no OH) = deoxyribose = DNA
It is a purine nucleotide that would be found in RNA
Which of the following are all found in a typical prokaryotic mRNA?
UTR regions, uninterrupted open reading frame
Why is the polypeptide released when the ribosome encounters a stop codon?
there is no amino acid in the A site to accept the polypeptide chain from the tRNA in the P site
A blood disorder called beta thalassemia is caused by mutations in the beta globin gene. Beta thalassemia is fairly common, with an incidence of 1 in 100,000 births worldwide. In beta thalassemia, too little or no beta globin is produced, resulting in mild to severe anemia. Β0 is a mutation that causes no beta globin protein to be made. The normal (non-disease causing allele) at the beta globin gene is designated A. How much beta globin protein would be present in a red blood cell from a person who is a carrier for the beta thalassemia causing mutation, compare to the amount in a person homozygous for the A alelle of beta globin?
50%
if they are a carrier, then their genotype is AO. The O allele makes no protein. The A allele make 50% of the protein found in a person with two A alleles (AA).
What is the proper order of events in the expression of a bacterial gene?
1) first phosphodiester bond formation
2) transition from closed to open complex
3) binding of sigma factor to the promoter
4) binding of Rho to the mRNA
5) sigma factor is released
3-2-1-5-4
