Lecture 4: DNA Replication Flashcards
What is the central dogma
DNA
(Transcription)
RNA
(Translation)
Protein
What are the the three steps of DNA synthesis
-Initiation
-Elongation
-Termination
When during the cell cycle does DNA replication occur
During the S phase
What is the principle of semi conservative DNA replication
-DNA replication is fast and accurate
-Rarely has errors such as insertions or deletions
-The involvement of an older strand allows for proof reading as DNA synthesis occurs
What are the 3 steps of DNA replication
- DNA unwinds at the origin of replication
- New Bases are dded to the complementary stand. One new strand is made in pieces
- Primers are removed, new DNA nucleotides are put in place of primers and the backbone is sealed by DNA ligase
What type of chromosomes to prokaryotes have
circular chromosomes
*DNA replication starts at one position in circular chromosome and works its way around the entire chromosome
What speeds up DNA replication in prokaryotes
Many origins of replication.
What enzyme unwinds DNA?
DNA Helicase
*It is a multi subunit enzyme that uses the energy of ATP Hydrolysis to break hydrogen bonds between base pairs
*It spins down the track of DNA
_____________ prevents super coiling and promotes heathy strand separation
Topoisomerase
What are the steps of DNA replication
- The initiator protein binds to the double stranded DNA at the origin of replication and slightly unwinds the DNA
- DNA helicase binds to the unwound DNA and continues the unwinding process.
- DNA topoisomerase promotes strand separation by removing supercoils in from of DNA Helices. Since stranded DNA binding proteins (SSB) stabilize the stands of DNA, allowing the seperated strand to serve as templates. A replication fork is now evident
- DNA primer binds to the leading strand template and synthesizes a short RNA primer that is complementary to DNA template
- DNA polymerase III uses the RNA primer to initiate DNA synthesis by adding deoxyribonucleotides to its 3’ end. The leading strand requires only
What does DNA polymerase install in the template strand
it installs a new dNTP in accordance with whatever is opposite the nucleotide it detects in the template strand
If it encounters a C it will install a G
An _____________ is ejected during installation event this drives the unfavorable event forward
inorganic pyrophosphate
Another enzyme _____________ immediately cleaves the PPI into two inorganic phosphates
inorganic pyrophaphatase
DNA polymerase adds nucleotides in the __________________________ and the opposite strand travels in the _________________
5’ to 3’ direction
*DNA polymerase only works in this direction. The lagging stand is synthesize differently
3’ to 5’
What are the steps of DNA synthesis of the lagging strand?
-DNA Polymerase III extends multiple RNA primers along the length of the strand. These little chunks of DNA are called Okazaki fragments.
-DNA polymerase enzymes must constantly start new ones in order to keep up with leading strand
DNA is synthesize at which end of each primer to generate Okazaki fragments that grow
3’ end
In which strand is DNA synthesis discontinuous and requires multiple RNA primers?
Lagging strand
What enzyme links together adjacent Okazaki fragments.
DNA ligase.
What are two major differences in Prokaryotic DNA and Eukaryotic DNA production
-Numerous different polymerases with specialized functions
-Much larger linear chromosomes vs smaller circular chromosomes in bacteria
What is the function of Helices
Unwinds DNA at replication fork
What is the role of single stranded binding proteins
-keeps single stranded DNA from reannealing
-Protects single stranded DNA from degradation by nuclease
What is the function of DNA primase
synthesis RNA primers on leading and lagging strands
What is the function of DNA polymerase
-installs new dNTP into the growing strand in 5’ –> 3’ direction
- 3’ –> 5’ exonuclease activity (to remove mismatched nucleotides)
-degrades RNA primers (DNA polymerase alpha only)
What is the function of DNA ligase
it forces phosodiester linkages between adjacent dNMPs hybridizes on the same template strand
What is the function of topoisomerases
nicks and re-ligate strand to mitigate supercoiling during replication
What disease is a genetic deficiency of WRN gene –> believed to encode a DNA helices enzyme involved in Telomere lengthening?
-premature aging
-proof of concept that telomere shortening is highly correlated with aging process
Werner Syndrome
Antibiotics block what?
Topoisomerase
What do cancer chemotherapies target
etoposide block eukaryotic topoisomerase
Prokaryotic cells do not have ________________
telomerase
Origin of replication
-Prokaryotes: sinle
-Eukaryotes: multiple
