Chapter 11: DNA Replication and Recombination Flashcards
This is the chemical affinity between nitrogenous bases as a result of hydrogen bonding.
Complementarity
Cytosine is a ______.
pyrimidine
Guanine is a ______.
purine
Thymine is a ______.
pyrimidine
Adenine is a ______.
purine
Why isn’t A-G bonding possible?
The double helix must be three rings across. A-G bonding would require four, because both are purines and have two rings each. That would make the DNA too big.
Why isn’t C-T bonding possible?
The double helix must be three rings across. C-T bonding would require two, because both are pyrimidines and have only one ring. That would make the DNA too small.
Why isn’t C-A or G-T bonding possible?
Though it’s purine-pyrimidine, the charges on the molecules would repel each other, and no hydrogen bonding could happen.
What’s the total diameter of a DNA strand?
20 Å
How does the cell know when the wrong base pair has been put in?
The DNA is too wide or too narrow.
This type of DNA makes up the majority of DNA in the body and is the original structure determined by Watson and Crick. It is a right-handed corkscrew.
B-DNA
This type of DNA is a right-handed corkscrew but is twisted a bit tighter and is found only in solution, not in living cells.
A-DNA
This type of DNA is a left handed corkscrew and is twisted a bit looser (12 base pairs per turn). It is found in the body.
Z-DNA
What type of sugar does DNA have?
deoxyribose
What type of sugar does RNA have?
ribose
Which base pairs differ between RNA and DNA?
RNA has uracil instead of DNA’s thymine.
Is RNA single stranded or double stranded?
It’s single stranded except for in some viruses, but it can hydrogen bond with itself to form shapes that are critical to its function.
This type of RNA is never translated into protein, but is an important structural component of ribosomes.
rRNA (ribosomal RNA)
This type of RNA carries information from DNA to the ribosomes, where translation occurs.
mRNA (messenger RNA)
This type of RNA carries amino acids to the ribosome during translation.
tRNA (transfer RNA)
This type of RNA helps process mRNA by getting rid of introns and splice exons.
snRNA (small nuclear RNA)
This type of RNA is involved in DNA replication and is an enzyme RNA that places the telomere on the end of the chromosome.
telomerase RNA
This type of RNA is a short strand that can base pair with an mRNA sequence to prevent expression of that particular gene.
antisense RNA
What does “semiconservative replication” mean?
It means each time DNA is replicated, each of the two original strands gets a new pair strand, so the new DNA molecule has one old strand and one new.
Because of the strength and stability of the DNA molecule, a lot of _____ needs to be used up to pull the two strands apart during replication.
ATP
Energy is used in DNA replication to:
Pull the two strands apart and create new covalent bonds.
Is base pairing during replication an active or passive process?
Passive.
Explain how base pairing is a passive process.
All four different nucleotides bombard the space where the next base pair belongs. They are present in high concentration. Polymerase locks them into place.
In this type of replication, two new strands of DNA are made from the parent strands. The new strands then associate with each other and the old strands reassociate.
Conservative
In this type of replication, new DNA strands are comprised of both old and new DNA.
Dispersive
What did the Meselson-Stahl experiment prove?
That DNA replication is semi-conservative.
In this technique, samples are forced by centrifugation through a density gradient through a heavy metal salt. Molecules of DNA reach equilibrium when their density equals the density of the gradient medium.
Sedimentation equilibrium centrifugation
In the centrifuge, which will reach equilibrium closer to the bottom of the tube –14N DNA or 15N DNA?
14N DNA
How did the Meselson-Stahl experiment prove that DNA replication was semiconservative?
E. coli cells were grown in 15N-labeled medium, labeling the E. coli DNA as 15N. The culture was then centrifuged. That E. coli culture was added to a 14N medium and the cells were allowed to replicate once and centrifuged, then centrifuged again after a second replication and then a third.
What was the ratio of 14N/14N to 14N/15N DNA in the Meselson-Stahl experiment at generation I?
All 15/14N DNA.
What was the ratio of 14N/14N to 14N/15N DNA in the Meselson-Stahl experiment at generation II?
1:1
What was the ratio of 14N/14N to 14N/15N DNA in the Meselson-Stahl experiment at generation III?
1:3
What would be the outcome of the Meselson-Stahl experiment if DNA replication were conservative?
You would just have one band of 14N DNA and one of 15N DNA.
How is semiconservative replication in eukaryotes tested?
We label a chromosome with tridiated thymidine and allow replication to occur. After replication, if you have one labeled and one unlabeled chromosome, there was no sister chromatid exchange; if there was, there will be reciprocal regions on both that are labeled.
Is the prokaryotic chromosome linear or circular?
Circular
How many origins of replication are there in prokaryotic DNA?
Only one.
Is bacterial DNA replication unidirectional or bidirectional?
Bidirectional (two replication forks)
How is torsional stress relieved when replicating the circular prokaryotic chromosome?
The chromosome is broken open into a linear strand, and then DNA gyrase spins the strand to relieve additional stress and to prevent tangling.
Where is DNA gyrase found?
Always ahead of the replication fork.
How many polymerases are involved in bacterial DNA replication?
Five.
In which direction does DNA replication occur?
5’ to 3’
What’s the role of polymerase III in bacteria?
5’ to 3’ polymerization and exonuclease proofreading
What’s the role of polymerases II, IV, and V in bacteria?
DNA repair
Is an RNA primer necessary for prokaryotic DNA replication?
Yes.
This bacterial polymerase is a holoenzyme comprised of multiple subunits.
Polymerase III
How does helical unwinding occur in prokaryotic DNA?
DnaA bonds to 9mers at the origin site, bending the DNA. The replication bubble forms, and DnaB and DnaC come to open the helix further. Single stranded binding proteins hold it apart. DNA gyrase comes in to prevent supercoiling.
Why is a primer needed for bacterial DNA replication?
Polymerase III needs a 3’ end to start adding nucleotides. The RNA primer does not, so it can start, and then it provides that 3’ end.
Is bacterial DNA parallel or antiparallel?
Antiparallel
Why is there a lagging strand?
Because DNA is antiparallel, one strand’s template runs 3’ to 5’, which won’t work. Therefore, many points of initiation are necessary along that template so that synthesis can occur in the proper direction.
What are the fragments of the lagging strand called?
Okazaki fragments
How are Okazaki fragments joined together?
DNA ligase
How can concurrent synthesis occur in bacterial DNA?
A dimer loops the template strand around, inverting it (but synthesis still occurs 5’ to 3’. The other part of the dimer is the beta subunit of the holoenzyme and prevents the core subunit from falling off the template.
How many origins of replication are there in eukaryotic DNA?
Multiple.
Why are there so many origins of replication in eukaryotic chromosomes?
The DNA is extremely long, so this speeds the process up.
Does replication always occur at a constant speed?
No. Embryonic cells, for example, replicate much faster.
How does the cell control speed of replication?
If replication is slower, it will use fewer replication bubbles/origins.
What is the function of DNA polymerase?
It links the nucleotides.
What are the four properties of DNA polymerase?
- Needs all of the four DEOXYnucleosides.
- Needs a template strand.
- Needs a primer.
- Has to go in the 5’ to 3’ direction.
What does the prereplication complex do?
It regulates the timing and sites of replication origin.
What does the origin recognition complex do?
It tags the origin as the site of initiation.
As each nucleotide is added, the last two phosphate groups are hydrolyzed to form _____.
pyrophosphate