percentage of G always equaled C and percentage of A always equaled T
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Why is the constant ration of A to T (and G to C) in plant, animal, prokaryotic, and fungal genomes really significant? a) It means the fraction of bases that are purines always balances the fraction that are pyrimidines b) It is what defines the difference between DNA and RNA c) It suggests that A is somehow “paired” with T and G is paired with C d) It suggests that purines pair with purines and pyrimidines pair with pyrimidines
c)
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Watson-Crick model told us about:
replication, coding, repair, and recombination in DNA.
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Watson-Crick model
DNA is a helix w/ width of purine plus a pyrimidine and a sugar phosphate backbone on the outside
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features of Watson-Crick model
- two strands, anti-parallel - H bonding between strands, A-T and G-C always base paired - base pairs stacked = plates parallel
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A-T and G-C make the ___________, with ___________________.
same shape, same length and width
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DNA redundancy
each strand has equivalent information, this is essential to function as genetic material
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Why is information on each DNA strand redundant?
Base pairing rules what is inserted - two identical copies are made, sequence can be copied again and again
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If one strand is 5' TGCCCTAT 3', the complementary strand is: a) 5’ TATCCCGT 3’ b) 5’ ATAGGGCA 3’ c) 5’ ACGGGATA 3’ d) 5’ TGCCCTAT 3’
b)
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DNA and RNA read, written, and synthesized:
5' to 3'.
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DNA could be single stranded and only transiently double-stranded during replication, but:
this has a high mutation rate (viruses).
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How does DNA 'pay' to elongate its 3' end?
By releasing free phosphates: dNTP > dNMP + PPi
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dNTPs can only be added to:
a preexisting 3' OH.
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DNA synthesis always needs a:
primer.
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Lagging strand synthesis requires:
constant addition of RNA-based primers.
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Leading strands run:
long and continuously.
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Lagging strands are:
short patches that are made and then joined later.
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Okazaki fragments
the short sequences of DNA nucleotides made to be joined later (lagging strand)
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DNA polymerase I
removes RNA primers and replaces them with DNA nucelotides
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DNA polymerase III
synthesizes daughter strands
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helicase
separates parent DNA strands
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ligase
contacts Okazaki fragments
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primase
generates RNA primers
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telomerase
lengthens telomeres by adding many copies of a short repetitive sequence to the ends of chromosomes
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topoisomerase
reduces super-coiling of DNA by cutting the backbone, allowing helices to operate
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Synthesis of the leading strand is simple, because:
only adding complementary bases is needed.
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Synthesis of the lagging strand is complicated because:
RNA primers constantly need to be added to follow the add to 3' rule.
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For the leading strand, a ___ is needed at the origin of replication.
primer
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All replication proteins are:
bounded together.
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clamp loader
loads on clamps - helps keep replicative polymerase on its template
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When helicase unwinds DNA, there are two __________ generated.
replication forks
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How many DNA polymerases would be in this picture, and where?
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How many primers would be in this picture and how many primases?
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When does DNA polymerase III drop off the template?
When it meets the 5' end of the primer
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Where does DNA polymerase I start replicating?
3' OH ends
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DNA polymerase I is:
a polymerase and a exonuclease
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DNA polymerase I replaces RNA with:
DNA.
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What is an issue at the end of lagging strand synthesis on linear chromosomes?
Each time, the chromosome will get smaller as it replicates, losing DNA.
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Do somatic cells have telomerase?
No, only embryonic and gremlin cells do
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Telomerase is a ______________.
reverse transcriptase - its a DNA polymerase that reads an RNA template.
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What replication-related problem is solved by telomerase? a) The inability of the cell to initiate DNA synthesis without building on a pre-existing “primer”. b) The inability of the cell to terminate replication of a circular template. c) The requirement for a “promoter” to initiate DNA synthesis
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What is circled in green?
The phosphate group
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What is circled in blue?
The sugar
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What is circled in red?
The nitrogenous base
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What kind of bio molecule is DNA?
Nucleic acid
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What are DNA monomers called?
Nucleotides
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Carbon atoms in a sugar are labeled using:
1', 2', 3', 4', 5'
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Which carbon atom in the sugar is attached to the nitrogenous base?
The 1' carbon
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Which carbon atom in the sugar is attached to the phosphate group?
The 5' carbon
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glycosidic bond
the bond between the 1' carbon and the nitrogenous base in a nucleotide
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Is the glycosidic bond polar or non-polar?
Polar (C-N electronegativity)
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What is the purpose of DNA?
Storing genetic information
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What part of the DNA stores genetic information?
The nitrogenous base
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What four nitrogenous bases are in DNA?
Adenine, guanine, cytosine, and thymine
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What four nitrogenous bases are in RNA?
Adenine, guanine, cytosine, and uracil
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What is the difference between purines and pyrimidines?
Purines have two rings while pyrimidines have one ring
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What is the difference between the 5' and 3' end of a pentose sugar?
The 3' end has a hydroxyl group attached and the 5' end has a phosphate group attached
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How many hydrogen bonds occur between adenine and thymine?
Two
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How many hydrogen bonds occur between guanine and cytosine?
Three
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DNA is ____________.
double-stranded
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DNA runs __________.
anti-parallel
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What is the name of the bond that connects two nucleotides?
Phosphodiester bond
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What atoms are involved in the phosphodiester bond?
Oxygen and phosphorous
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Is the phosphodiester bond polar or non-polar?
Polar (O-P electronegativity)
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Two nucleic acid motors are joined by:
coupling an exergonic reaction with an endergonic reaction.
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exergonic reaction in joining nucleic acid monomers
hydrolysis of the phosphoanhydride bond between phosphate groups
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endergonic reaction in joining nucleic acid monomers
3' -OH group and phosphate attached to 5' (= phosphodiester bond)
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Do nucleic acids have a charge?
DNA and RNA are negatively charged (because of the phosphate groups)
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Where does DNA replication begin?
At the origin of replication (ORI)
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What enzyme binds to the ORI?
Helicase
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Why might eukaryotic organisms have more than one origin of replication?
So that DNA replication can occur in a shorter amount of time (DNA is large)Wh
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What interaction holds DNA strands together?
Hydrogen bonds
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What does the blue triangle represent?
Helicase
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When helicase is unwinding DNA, what potential issue could arise?
The DNA can become over-twisted in front and under-twisted behind
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What enzyme can resolve supercoiling in DNA?
Topoisomerase
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What direction does DNA polymerase III move along the template strand?
3' to 5'
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What direction does DNA polymerase III synthesize the daughter strand?
5' to 3'
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What enzyme informs DNA pol III where to begin daughter strand synthesis?
Primase
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How does the cell obtain the same strands of DNA every time DNA is replicated?
A-T and G-C, base-stacking and base-pairing, ways to find errorsQ
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Which would be the consequence of DNA replication without ligase? A) It would result in lots of ‘nicks’ or breaks in the DNA sugar-phosphate backbone. B) Only the leading strand would be replicated, as the cell would be unable to replicate the lagging strand. C) Replication would stall once all the nucleotides had been used up in the cell. D) Replication would be unable to start. E) The cell would need to repair multiple incorrectly paired bases between the template and newly synthesized strands of the DNA.
A)
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The phosphodiester bond between the 5' -PO4 and 3' -OH is not formed in the Okazaki fragment. Which enzyme is inhibited or malfunctioning? A) DNA polymerase III B) Primase C) Helicase D) DNA Polymerase I E) Ligase
E)
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A piece of double-stranded DNA has 30% A. What will be the % G? A) 30% B) 40% C) 20% D) 70% E) Indeterminate from the given information.
C)
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The nitrogenous base is linked to the ribose or deoxyribose sugar via a __________ at the _ carbon. A) Glycosidic bond, 5’ B) Peptide bond, 2’ C) Hydrogen bond, 4’ D) Phosphoanhydride bond, 3’ E) Phosphodiester bond, 1’ F) None of the above
F)
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How so mutations occur? (1)
Through replication errors
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Replication errors can be:
mistakes or replication of a damaged template.
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How do mutations occur? (2)
Through erroneous repair of DNA damage
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Cancer is caused by:
somatic mutations.
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risk factors for cancer
genotoxin exposure, age
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Replicative DNA polymerase produces a mutation:
1/10^6 times
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DNA polymerase proofreading
enzyme's groove must fit the base pair or it will start over