Chapter 5: Nucleic Acids (DNA Replication) Flashcards
DNA replication: overview
- chromatin disassembly (eukaryotes)
- DNA double helix unwinding
- primer binding
- elongation
- termination
ATP-dependent chromatin remodeling complexes facilitate the sliding or removal of nucleosome from DNA ahead of the replication fork
chromatin disassembly (eukaryotes)
binds and breaks the hydrogen bonds between complementary bases
DNA helicase
breaks hydrogen bond between complementary bases
DNA helicase
point at which the DNA double helix is unwinding, which is constatnly changing (moving)
replication fork
the enzyme primase generates short strands of RNA hat bind to single-stranded DNA to initiate DNA synthesis
primer binding
generates short strands of RNA to prime strands for DNA synthesis
primase
no. of primer in leading strand
one
no. of primer in lagging strand
multiple
polymerase binds to strand at the site of the primer and begins adding new base pairs complementary to the strad by forming new phosphodiester linkages
elongation
binds to strand at site of primer and begin adding new base pairs
polymerase
continuous 5’ to 3’ direction (toward helicase)
leading strand
in short Okazaki fragments (elongation is away from helicase)
lagging strand
fragments in lagging strand
Okazaki fragments
- exonuclease removes all RNA primers
- another exonuclease proofreads newly formed DNA
- DNA ligase joins Okazaki fragments
- telomerase catalyzes synthesis of telomere that act as protective cap
- once completed, the parent strand and its complementary DNA strand coils into familiar double helix shape
termination
- removes all RNA primers from original strands
- proofreads newly formed DNA and remove and replace any errors
exonuclease
joins Okazaki fragments together forming a single unified strand
DNA ligase
catalyzes the synthesis of telomere sequence at the ends of the DNA
telomerase
alleviates positive supercoiling ahead of replication fork
topoisomerase
- keep the parental strands apart
- also protect strands from degradatioin and prevent secondary structure formation
single-strand binding proteins
- nuclear SSB protein found in all eukaryotes
- required for multiple processes in DNA metabolism such as DNA replication, DNA repair, DNA recombination, telomere maintenance and DNA damage signalling.
Replication protein A (RPA)
“reads” each parental strand and catalyzes the polymerization of a complementary daughter strand
DNA polymerase III
precursors for DNA replication
deoxyribonucleotide triphosphate (dNTP)
in 5’ to 3’ synthesis, a __ __ is released as a phosphoester bond is formed between 5’-phosphoryl group of the nucleotide being added to the chain and the 3’-OH of the nucleotide on the daughter strand
pyrophosphate group
DNA pol III can only catalyze DNA chain in what direction
5’ to 3’
serve as starting point for DNA replicatioin
RNA primer
length of RNA primer
10 - 12 nucleotides
where is the new primer synthesized in the lagging strand
at replication fork
exist between Okazaki fragments and are easily recognizable by the DNA mismatch repair machinery prior to ligation
nicks
Final steps of synthesis on lagging strand
- removal of primers
- repair of gaps
- sealing of fragments
catalyzes the removal of RNA primer and its replacement with DNA nucleotides
DNA polymerase I
covalently links the DNA fragments together
DNA ligase
is also able to proofread the newly synthesized strand
DNA polymerase III
dismantles after the convergence of the two replication forks
replisome complex
in eukaryotes, it removes the RNA primer at the beginning of each Okazaki fragment
Ribonuclease H (RNAse H)
after the first round, the new lagging strand is __ than its template
shorter
after the second round, both the leading ang lagging strands have become __ than the original parental DNA
shorter
repetitive sequences that code for no particular gene
telomeres
in humans, a six base pair sequence, _____, is repeated __ to __ times
- TTAGGG
- 100 to 1000 times
Telomeres shorten as a result of cellular replication, leading to a permanent cell cycle arrest, also known as __ __
replicative senescence
are formed by telomere ends in order to be protected from cell’s DNA repair systems
protective loops
protein complex known to protect telomeres in many eukaryotes from DNA repair mechanisms, as well as to regulate telomerase activity
Shelterin
Shelterin is also called
telosome
individual DNA molecule bound to a group of proteins
chromosome
typically, a chromosome is __ by mass DNA, and __ by mass protein
- 15% DNA
- 85% protein
- have similar, but not identical, DNA base sequences
- both code for the same traits but for different forms of trait
homologous chromosomes
where does DNA replication begin
replication origin
replication occurs __ at the rate of about __ new nucleotides every second
- bidirectionally
- 500
the human genome consists of approx. how many nucleotide pairs
3 billion
just one chromosome may nearly be __ times longer than bacterial chromosome
100
two Y-shaped structures called replication forks are formed, together making up what’s called a __ __
replication bubble
class of anticancer drug that interfere with DNA replication because their structures are similar to molecules required for normal DNA replication
antimetabolites
an essential and necessary element for the synthesis of nucleotides and other biomolecules after reduction by dihydrofolate reductase
folic acid
replication of DNA produces two daughter molecules in which each daughter molecule contains
- one parent strand
- one newly synthesized strand
in DNA replication, the DNA double helix unwinds under the influence of
DNA helicase
in DNA replication, the new strand that is synthesized in small segments is called
lagging strand
(murag Okazaki fragment man)
in DNA replication, the unwinding of DNA double helix occurs at
many locations within double helix
chromosme is a protein-DNA complex that contains
single DNA molecule
