Lecture 10 / Chapters 11 and 12 - DNA Replication and Packaging Flashcards
True or False?
The data obtained from the Meselson–Stahl experiment after one generation of replication eliminated the dispersive model of DNA replication.
False.
(The data obtained from the Meselson–Stahl experiment after one generation was consistent with both the semiconservative and the dispersive model of DNA replication. The conservative model of DNA replication was eliminated because it predicted that there would be two bands representing the original DNA at one density and the newly replicated DNA at a different density.)
Which enzyme catalyzes the addition of nucleotides to a growing DNA chain?
- Telomerase
- Helicase
- Primase
- DNA polymerase
DNA polymerase
DNA polymerase catalyzes the addition of nucleotides to a growing DNA chain.
Which of the following statements about DNA replication is true?
- DNA gyrase unwinds the DNA double helix.
- Okazaki fragments are DNA fragments synthesized on the leading strand.
- Single-stranded binding proteins stabilize the open conformation of the unwound DNA.
- DNA polymerase adds dNTP monomers in the 3’—5’ direction.
Single-stranded binding proteins stabilize the open conformation of the unwound DNA.
(Once helicase unwinds the double helix, single‑strand binding proteins bind to the open DNA and prevent it from winding together again.)
Which of the following terms accurately describes the replication of DNA in vivo?
- nonreciprocal
- nonlinear
- dispersive
- semidiscontinuous
- conservative
Semidiscontinuous
What is the function of helicase?
Helicase breaks the hydrogen bonds between the parental DNA strands and unwinds the double helix.
What is the function of the single-stranded binding proteins?
Single-stranded binding proteins bind to the single strands of DNA, preventing them from reannealing and allowing synthesis to occur on both strands.
What is the function of DNA polymerase III?
DNA polymerase III synthesizes the new strands, but it requires an existing 3′ hydroxyl (—OH) group to add nucleotides.
What is the function of primase?
Primase creates short RNA primers, initiating DNA synthesis on both template strands.
What is the function of DNA polymerase I?
DNA polymerase I removes the RNA primers and replaces them with DNA nucleotides.
What is the function of DNA ligase?
On the lagging strand, DNA ligase joins Okazaki fragments by forming phosphodiester bonds between them, thus completing DNA replication.
Which DNA polymerase is mainly responsible for genome replication in E. coli?
- DNA polymerase III
- DNA polymerase alpha
- DNA polymerase I
- DNA polymerase II
DNA polymerase III
DNA polymerase III is responsible for the synthesis of the bulk of the DNA in E. coli.
DNA polymerase III adds nucleotides ________.
- In the place of the primer RNA after it is removed
- to the 5’ end of the RNA primer
- to internal sites in the DNA template
- to the 3’ end of the RNA primer
- to both ends of the RNA primer
To the 3’ end of the RNA primer
Which activity of DNA polymerase I is responsible for proofreading the newly synthesized DNA?
- 5’ to 3’ polymerase
- 3’ to 5’ exonuclease
- 3’ to 5’ endonuclease
- 5’ to 3’ exonuclease
3’ to 5’ exonuclease
(If the wrong nucleotide is inserted, normal base pairing will not be observed and the base in error will be removed from the newly synthesized strand before subsequent nucleotides are added.)
DNA polymerase I is thought to add nucleotides ________.
- to the 3’ end of the primer
- In the place of the primer RNA after it is removed
- on single-stranded templates without need for an RNA primer
- to the 5’ end of the primer
- In a 5’ to 5’ direction
In the place of the primer RNA after it is removed
Which protein is responsible for the initial step in unwinding the DNA helix during replication of the bacterial chromosome?
DnaA
During DNA replication, an open section of DNA, in which a DNA polymerase can replicate DNA, is called a _____.
replication fork
The new DNA strand that grows continuously in the 5’ to 3’ direction is called the ______.
leading strand
The enzyme that can replicate DNA is called _______.
DNA polymerase
_________ are the short sections of DNA that are synthesized on the lagging strand of the replicating DNA.
Okazaki fragments
After replication is complete, the strand of new DNA, called _______, is complementary to the parental strand.
daughter DNA
Describe the helicase protein
- Binds at the replication fork
- Breaks H-bonds between bases
Describe the topoisomerase protein
- Binds ahead of the replication fork
- Breaks covalent bonds in DNA backbone
Describe the single-strand binding protein
- Binds after the replication fork
- Prevents H-bonds between bases
Describe the synthesis of the leading strand
- Made continuously
- Daughter strand elongates toward replication fork
- Only one primer needed
Describe the synthesis of the lagging strand
- Made in segments
- Daughter strand elongates away from replication fork
- Multiple primers needed
In what direction is both the leading strand and the lagging strand synthesized?
Synthesized in the 5’ to 3’ direction.
Indicate the sequence of events in the production of fragment B.
- DNA polymerase III binds to 3’ end of primer B.
- DNA polymerase III moves 5’ to 3’, adding DNA nucleotides to primer B.
- DNA polymerase I binds 5’ end of primer A.
- DNA polymerase I replaces primer A with DNA.
- DNA ligase links fragments A and B.
The discontinuous aspect of replication of DNA in vivo is caused by ________.
- the 5’ to 3’ polarity restriction
- polymerase slippage
- trinucleotide repeats
- topoisomerases cutting the DNA in a random fashion
- sister chromatid exchanges
The 5’ to 3’ polarity restriction.
All EXCEPT which of the following are related to telomeres?
- found in eukaryotes and prokaryotes
- links to the aging process
- telomerase enzyme
- short tandem repeats located at the ends of telomeres
Found in eukaryotes and prokaryotes.
Telomeres are found in eukaryotes but not prokaryotes.
Structures located at the ends of eukaryotic chromosomes are called ________.
- recessive mutations
- telomerases
- permissive mutations
- centromeres
- telomeres
Telomeres
Which structures can be involved in recombination?
- Any two chromosomes
- Chromatids of homologous chromosomes
- Chromosomes in different cells
- Chromatids of nonhomologous chromosomes
Chromatids of homologous chromosomes.
Chromatids of homologous chromosomes can recombine during meiosis.
True or False?
The process that determines the length of heteroduplex DNA on the chromatids is called branch migration.
True.
(The crossbridge DNA structure formed after the initial nick is sealed can migrate along the chromatid. This process is called branch migration, and it increases the length of heteroduplex DNA.)
Which process does not occur during recombination?
- ligation
- nicking of the sugar-phosphate backbone
- DNA polymerization
- strand displacement
DNA polymerization
Recombination does not include the synthesis of new DNA.
In E. coli, the genetic material is composed of ________.
- circular, double-stranded DNA
- polypeptide chains
- circular, double-stranded RNA
- RNA and protein
- linear, double-stranded DNA
Circular, double-stranded DNA
True or False?
The E. coli chromosome is circular and double-stranded DNA.
True
What makes up the protein component of a nucleosome core?
- Eight different histone proteins
- Histone H1 protein
- One tetramer of histone proteins
- Two tetramers of histone proteins
Two tetramers of histone proteins.
(The protein component of a nucleosome is composed of two tetramers of histone proteins. One tetramer is composed of two units each of histones H2A and H2B, and the other is composed of two units each of histones H3 and H4.)
What is the first order of chromatin packing?
- Formation of a 300 nm fiber
- Coiling around nucleosomes
- Looping of 300 nm fibers
- Formation of a solenoid
Coiling around nucleosomes.
(The first order of chromatin packing occurs when DNA coils around nucleosomes, whereby DNA is reduced to about one‑third its original length)
True or False?
The second order of chromatin packing occurs when nucleosomes coil together to form a fiber that is 300 nm in diameter.
False.
(The second order of chromatin packing occurs when nucleosomes coil together to form a solenoid fiber that is 30 nm in diameter.)
Eukaryotic chromosomes contain two general domains that relate to the degree of condensation. These two regions are ________.
- separated by large stretches of repetitive DNA
- each void of typical protein-coding sequences of DNA
- called heterochromatic and euchromatin
- uniform in the genetic information they contain
- void of introns
Called heterochromatin and euchromatin.
Describe the transitions that occur as nucleosomes are coiled and folded, ultimately forming a chromatid.
As chromosome condensation occurs, a 300 A ______ is formed. It appears to be composed of 5 or 6 ________ coiled together. Such a structure is called a _______. These fibers form a _______ that further condense into the chromatin fiber and are then coiled into chromosome arms making up each ______.
Choices:
- series of loops
- solenoid
- fiber
- nucleosomes
- chromatid
- fiber
- nucleosomes
- solenoid
- series of loops
- chromatid
How many histone proteins make up the nucleosome core (the “bead” that the DNA is wrapped around)?
8
How many base pairs of DNA wrap around a single nucleosome “bead”?
146
What are the characteristics of heterochromatin?
- Deeply stained
- More condensed
- Replicated late in S phase
- Few genes present (or repressed genes)
- Associated with telomeres and centromeres
What are the characteristics of euchromatin?
- Weakly stained
- Less condensed
- Replicated early in S phase
- Many genes present (or expressed genes)
