Chapter 14 Flashcards
DNA Structures and Functions
monomers that make up DNA
Nucleotide
the 3’ end of one strand faces the 5’ end of the other strand
anti-parallel
specific nucleotide sequences where DNA begins to unwind
origin of replication
Y-shaped structure formed during initiation of replication
replication fork
strand that is synthesized continuously in the 5’-3’ direction, which is synthesized in the direction of the replication fork
leading strand
during replication, the strand that is replicated in short fragments and away from the replication fork
lagging strand
DNA fragment that is synthesized in short stretches on the lagging strand
okazaki fragments
DNA at the end of linear chromosomes
telomere
Approximately how many base pairs make up a haploid human genome? How many functional genes does it contain?
3 billion base pairs and 20,000-25,000 functional genes are contained in them
What are the building blocks of nucleic acids?
nucleotides
What are the three main components of nucleotides? How do the four nucleotides differ? How does DNA differ from RNA?
nitrogenous base, pentose sugar (5-Carbon), and phosphate group
They differ based on the nitrogenous base (AGCT)
Sugar
Describe the phosphodiester linkages in nucleic acids. What is the significance of the 5’ to 3’ phosphodiester bond?
nucleotides are joined by phosphodiester bonds which are covalent bonds
phospate connects to the hydroxyl of 5’ and one nucleotide of the 3’
How are the nitrogenous bases paired in the double helix? What type of bond holds them together? How many bonds in each pairing?
T double bonds with A and C double bonds with G through Hydrogen bonds
What does it mean to say the two strands of DNA in the double helix are “complementary?” What does it mean to say they are “anti-parallel?”
The nucleotides pair together and the strands are “opposite:
the strands are flipped 5’ matches with 3’
How do the complementary and anti-parallel characteristics of DNA influence how it replicates?
easy to replicate and make a second strand and determines how it is replicated
In DNA replication, the two “old” strands of DNA serve as templates for two new strands. How are the old and new strands paired after replication?
semi conservatively
one old strand pairs with a new one
In Eukaryotes, the chromatin has two different regions. What are they called? How are the similar? How are they different?
Heterochromatin is tightly packaged and the genes are not typically expressed
Euchromatin is less dense and the genes are usually transcribe or read
What is the main enzyme involved in DNA replication?
DNA polymerase adds nucleotides to the growing chain complementary to the template strand
Prokaryotes have how many types of DNA Pol? What are the main function of each
3
III is DNA synthesis
II is DNA repair
I is both
What is the significance of the origin of replication? How does this site(s) differ from prokaryotes to eukaryotes?
where DNA begins to unwind and lets the replication machinery know where to begin
Prokaryotes only have one and eukaryotes have multiple
What is the function of the helicase enzyme? How does it accomplish this task?
opens/unzips the DNA and forms the replication fork
unzips by breaking hydrogen bonds within the nitrogenous base pairs
Where are the replication forks and what takes place in these regions?
Where DNA has opened and single-strand binding proteins coat the single strand to prevent it from reattaching
How does the cell prevent the DNA from winding back up following the helicase?
single-strand binding proteins coat the single strands of DNA
What is topoisomerase enzyme? Why is it important? How does it accomplish its task?
moves along the DNA molecule ahead of the helix to prevent overwinding of the double helix
causes temporary nicks in the DNA structure and then reseals it
In which direction does DNA polymerase add nucleotides to the growing chain? Why can it only operate in this direction?
5’-3’ there is no free OH group to form phosphodiester linkages on the 3’ end
What is the problem DNA polymerase encounters when trying to start the replication process? How is this problem overcome?
the complementary strand has no free OH- group to bind to
RNA Primers
Why is RNA primase so important in DNA replication? How does its job differ on the leading vs. lagging strand?
provides and OH group to the 3’ end to extend the chain
there are multiple on the lagging strand but only one on the leading
What are Okazaki fragments? Why are they made? What are the additional requirements of having to replicate the DNA in this fashion?
small fragments of DNA that are used to synthesis the lagging strand
need DNA ligase to glue together
What is the function of the sliding clamp?
holds the DNA polymerase in place as it adds the nucleotides
How is the RNA (primer regions) removed from the new strands of DNA? How are these gaps repaired?
exonuclease( DNA Pol I)
deoxyribonucleotides added by DNA polI and the ends are joined together by DNA ligase
What is the job of DNA ligase?
joins the new DNA pieces to the synthesized strands
How many origins of replication are in eukaryotes (humans)?
up to 100,000
How do the rates of DNA replication compare in prokaryotes vs. eukaryotes? What cellular features account for some of the difference?
much slower in eukaryotes because there are more compaction levels and more nucleotides that need to be added
What is the significance of having linear forms of DNA rather than circular as in prokaryotes? How have eukaryotic cells overcome this problem? Which cells are vulnerable?
there are sections at the end of strands that there is not a place for the primer to be made and the strand cant fully be replicated
create telomere regions
germ cell and adult stem cells
What is the name of the enzyme that can extend the ends of the chromosomes?
telomerase
