Week 5- DNA Replication Flashcards
What direction do DNA polymerases synthesize DNA?
5’ to 3’
DNA polymerases can only add nucleotides to the free 3’ end of a growing strand.
What are the two types of activity that DNA polymerase possesses?
3’ to 5’ exonuclease activity
This activity allows for proofreading during DNA replication.
What is the size of DNA molecules typically measured in?
Base pairs (bp)
1 bp corresponds to approximately 0.34 nm of length along the strand.
What is the range of DNA sizes mentioned?
5 kb to over 250,000 kb
kb = kilo base pairs, Mb = mega base pairs, Gb = giga base pairs.
What temperature can E. coli undertake DNA replication down to?
70°C
Some extremophiles, like P. halocryophilus, can replicate DNA at -150°C.
Who won the Nobel Prize in 1959 for the discovery of the mechanisms of DNA synthesis?
Arthur Kornberg
He shared the prize with Ochoa.
What is the primary role of DNA polymerase I?
DNA repair
It is involved in removing RNA primers during DNA replication.
Which DNA polymerase is the major replicative enzyme in E. coli?
DNA polymerase III
Temperature-sensitive mutants of Pol III cannot replicate DNA at restrictive temperatures.
What are the nucleotides used in DNA synthesis called?
Nucleoside triphosphates (dNTPs)
Examples include dATP, dTTP, dGTP, and dCTP.
What is the rate of elongation for DNA replication in bacteria?
500 nucleotides per second
In human cells, the rate is approximately 50 nucleotides per second.
What initiates the synthesis of RNA primers during DNA replication?
RNA primase
DNA polymerase III cannot initiate synthesis de novo.
What are Okazaki fragments?
Short segments synthesized on the lagging strand
They are later joined together by DNA ligase.
How many origins of replication do prokaryotes have?
One origin of replication
This leads to a single replication bubble.
What is the typical replication time for prokaryotes?
<1 hour
Eukaryotes, with multiple chromosomes, take approximately 2-3 hours.
What is the role of helicase in DNA replication?
Unwinds the double helix
ATP is required for this process.
What is the purpose of single-strand binding proteins during DNA replication?
Prevent the re-annealing of unwound DNA strands
They stabilize the unwound template strands.
What is the mechanism of proofreading during DNA replication?
3’ → 5’ exonuclease activity
This activity clips back unpaired or misinserted nucleotides.
What must occur before DNA polymerases can add nucleotides?
A primer must be synthesized
The initial nucleotide chain produced is actually a short stretch of RNA.
Fill in the blank: The lagging strand is synthesized as a series of _______.
Okazaki fragments
True or False: DNA polymerases can initiate the synthesis of a polynucleotide.
False
They can only add nucleotides to an existing chain.
What are the four main proteins involved in the initiation of DNA replication?
- Topoisomerase
- Helicase
- Primase
- Single-strand binding proteins
What is the role of DNA ligase during DNA replication?
Joins Okazaki fragments
It seals the gaps between newly synthesized DNA segments.
What is the outcome of the proofreading mechanism in DNA replication?
Reduces error rate to ~1 in 10^9
This results in approximately 0.04 potential mutations per genome replication.
What is the primary function of DNA ligase?
Joins two Okazaki fragments
DNA ligase is essential in DNA replication to connect segments of DNA.
What is the role of DNA polymerase I?
Removes RNA primer from 5’ end of 2nd fragment and replaces with DNA
DNA polymerase I is crucial for DNA replication, particularly in the removal of RNA primers.
How does eukaryotic DNA replication differ from that in E. coli?
Has significant similarities and differences
Key differences include initiation mechanisms and genome size.
What are the key characteristics of bi-directional DNA replication?
Leading and lagging strands, primers, and proofreading
This is a fundamental process in DNA replication ensuring accuracy and efficiency.
List the major differences in eukaryotic DNA replication compared to prokaryotic.
- Different DNA replication initiation
- Larger genomes
- Multiple replication sites
- Linear chromosomes
- Lower rates of DNA synthesis
- More complex enzymology
These differences reflect the complexity of eukaryotic organisms.
What is the significance of the Origin Replication Complex in humans?
Loads onto DNA first for fork initiation
The Origin Replication Complex is crucial for starting DNA replication in eukaryotic cells.
What is the primary function of DNA polymerase α?
Chromosomal replication 5’ to 3’ but lacks exonuclease activity
DNA polymerase α is always associated with a primase for initiation.
What is the role of DNA polymerase δ?
5’ to 3’ polymerase activity and a 3’ → 5’ exonuclease activity
DNA polymerase δ is involved in the elongation phase of DNA replication.
What is the mitochondrial genome structure?
Circular, 16,569 base pairs encoding 37 genes
Mitochondrial DNA is inherited maternally in most species.
Which DNA polymerase is specialized for mitochondrial DNA replication?
Pol γ/PolG
This polymerase is essential for the replication of mitochondrial DNA.
What is the composition of telomerase?
Catalytic subunit (hTERT) and template RNA (hTR)
Telomerase plays a critical role in maintaining telomere length during cell division.
Fill in the blank: Telomeres in humans consist of repeated sequences of _______.
(TTAGGG)n
These repeated sequences help protect chromosome ends.
True or False: Telomerase is active in most somatic cells.
False
Telomerase is repressed in most somatic cells, leading to telomere shortening.
What happens when D loop integrity is compromised in telomeres?
Triggers irreversible exit from the cell cycle producing replicative senescence
This process is crucial for cellular aging and the prevention of uncontrolled cell division.
What is the primary challenge posed by linear chromosomes during replication?
Okazaki fragment placement cannot be replicated by conventional machinery
This challenge leads to the need for specialized mechanisms like telomerase.
List the methods that can be used to assay DNA replication.
- 32P incorporation
- Fluorescence
These methods allow researchers to track and analyze DNA replication processes.
What is a characteristic of the chloroplast genome?
Circular and typically 12-17 Kbp, encodes ~100 genes
Chloroplasts, like mitochondria, are derived from ancient prokaryotic organisms.
