02.11 - DNA Replication Flashcards
What comprises a nucleoside?
Nitrogenous base
Ribose/Deoxyribose
What comprises a nucleotide?
Nitrogenous base
Ribose/deoxyribose
Phosphate group
Which is not a function of nucleotides?
a. Form part of many coenzymes
b. Regulatory functions (e.g. cAMP)
c. Synthetic analogues as drugs
d. Donors of phosphoric groups
All are functions of nucleotides.
Nitrogenous bases that contain two rings are called:
Purines
Nitrogenous bases with a single ring are called:
Pyrimidines
How may hydrogen bonds exist between A and T? C and G?
2, 3
Also known as methyluracil, this nitrogenous base is only found in DNA strands.
Thymine
What links a nitrogenous base and a ribose sugar?
Beta-N-glycosidic bond
The anomeric carbon (C1) of ribose/deoxyribose is attached to which nitrogen atom in nitrogenous bases?
N1 for pyrimidines
N9 for purines
What bond forms between the 3’ OH group and the succeeding 5’ OH group?
3’-5’ phosphodiester bond
What enzyme catalyses the hydrolysis of phosphodiester bonds?
Phosphodiesterases
Which of the following statements is incorrect?
a. Spontaneous hydrolysis of phosphodiester bonds is a very slow process
b. DNA is more stable than RNA
c. The extra -OH group in RNA makes it susceptible to base-catalysed hydrolysis.
d. The 5’ end of a DNA strand harbours a free hydroxyl group.
d. The 5’ end of a DNA strand harbours a free hydroxyl group. (It contains a phosphoryl group. Free -OH group is located in the 3’ end.)
Where in a cell can you find DNA?
a. Cytoplasm
b. Nucleus
c. Mitochondria
d. Chloroplast
All of the above (Remember that DNA in prokaryotes is located in the cytoplasm!)
DNA replication occurs in what phase of the cell cycle?
S phase
In the Meselson-Stahl experiment, which of the following proves that DNA replication is semiconservative?
a. After two generations, the N15 (heavy) concentration is greater than the N14 (light) concentration
b. Transferring of N15 (heavy) DNA strands into a medium containing N14 results in the production of more N15 strands
c. After two generations, half of the DNA was intemediate (N14 and N15-containing), and half was light only (N14 only)
d. None of the above
c. After two generations, half of the DNA was intemediate (N14 and N15-containing), and half was light only (N14 only)
What mode of DNA replication results when the DNA molecule is interspersed with fragments of old and new DNA?
Dispersive
What mode of DNA replication results in the conservation of the original DNA strand?
Conservative
When each resulting DNA contains the original and intact DNA plus a new DNA molecule, replication is said to be:
Semiconservative
What bacteria was used by Meselson and Stahl in their experiment?
E. coli
E. coli were grown by Meselson and Stahl in which medium?
N15 (heavy)
What enzyme catalyses the addition of nucleotides to a growing chain of DNA?
DNA polymerase
The synthesis of the new DNA strand proceeds in what direction?
5’ to 3’
These are short strands of RNA needed to begin the DNA chain.
Primers
In prokaryotes, it is a short sequence composed exclusively of AT base pairs.
Origin of replication
Which of the following is not a characteristic of DNA replication?
a. Semiconservative
b. Unidirectional
c. Based on complementarity
d. None of the above
b. Unidirectional (DNA replication is bidirectional!)
It is a group of proteins that recognises the origin of replication.
DNA A protein
Which enzyme unwinds the double helix ahead of the advancing replication fork?
Helicase
What is the mechanism of action of helicase?
a. Breaking phosphodiester bonds between to consecutive nucleotides
b. Breaking N-glycosidic bonds between a base and a sugar
c. Breaking hydrogen bonds between complementary base pairs
d. None of the above
c. Breaking hydrogen bonds between complementary base pairs
What proteins maintains the separation of parental strands by stabilising them?
Single-stranded DNA-binding proteins (SSBPs)
This family of enzymes remove supercoils that interfere with the further unwinding of the double helix.
DNA topoisomerases
What type of topoisomerase cleaves only one strand of DNA?
Type I (swivelase)
What type of topoisomerase cleaves both strands of DNA?
Type II (gyrase)
Which group of drugs inhibits DNA topoisomerases, thereby promoting supercoiling that impedes DNA replication?
Fluoroquinolones (example is ciprofloxacin)
What enzyme is responsible for the synthesis of primers?
Primase
What enzyme catalyses chain elongation in the 5’-3’ direction and can proofread newly synthesised DNA using its 3’-5’ exonuclease activity?
DNA polymerase III
True or False: DNA polymerases “read” the DNA template in the 3’-5’ direction and synthesises in the 5’-3’ direction.
True
What enzyme removes RNA primers using a 5’-3’ exonuclease activity and fills in the resulting gaps?
DNA polymerase I
This enzyme seals the gaps between the Okazaki fragments by catalysing phosphodiester linkages.
Ligase
What general class of enzymes cleave phosphodiester bonds in a nucleic acid?
Nuclease
______________ cleave internal phosphodiester bonds while ____________ cleave bonds at the 5’ to 3’ end.
Endonucleases, exonucleases
Which of the following statements is incorrect?
a. Removal of mismatched bases utilises the 3’ exonuclease activity.
b. Removal of RNA primer makes use of the 5’ exonuclease activity.
c. DNA polymerase II is also involved in DNA repair.
d. None of the above
d. None of the above
What mammalian enzyme function in gap filling in the synthesis of the lagging strand?
DNA pol alpha
What enzyme is used for mitochondrial DNA synthesis?
DNA pol gamma
What enzyme synthesises both the lagging and the leading strand in mammals?
DNA pol delta
What two enzymes are responsible for DNA proofreading and repair in mammals?
DNA pol beta and epsilon
Which of the following is a characteristic of eukaryotic DNA synthesis?
a. Multiple origins of replication
b. Formation of many replication bubbles
c. End of replication problem
d. All of the above
d. All of the above
Why is there an end of replication problem for linear DNA?
a. There is no 5’ phosphate group for the attachment of DNA polymerase I
b. DNA polymerase does not have a free 3’-OH to attach to
c. Telomerase do not exist in eukaryotes
d. None of the above
b. DNA polymerase does not have a free 3’-OH to attach to
These are highly repetitive DNA sequences at the end of the chromosomes that acts a “caps” that protects DNA from exonuclease activity.
Telomeres
True or False: Telomerse do not exist in prokaryotes.
True (Circular DNA = no end of replication problem = no need for telomeres)
Which of the following is directly correlated with aging?
a. Presence of telomeres
b. Presence of telomerase
c. Shortening of telomeres
d. Inactivation of DNA polymerases
c. Shortening of telomeres
These are enzymes that replace telomeres by the addition of DNA sequences to lengthen the template strand.
Telomerase
It is an RNA-dependent DNA polymerase employed by retroviruses.
Reverse transcriptase
True or False: Reverse transcriptase can also use DNA as a template to create a new strand.
True. It is not exclusively RNA-dependent.
These are bacteria-specific, PABA structural analogs that competitively inhibits the utilisation of PABA for folic acid synthesis (which is required in DNA synthesis).
Sulfonamides
What folic acid derivative is needed in purine synthesis?
Tetrahydrofolic acid/tetrahydrofolate/THF
It is a folic acid analog that inhibits the reduction of dihydrofolate to THF.
Methotrexate
What enzyme catalyses the normal reduction of dihydrofolic acid to THF?
Dihydrofolate reductase
_______________ is a chemotherapeutic drug that is metabolically converted to 5-FdUMP, which blocks the access of dUMP to the binding site for dTMP synthesis.
5-Fluorouracil
Which is not an effect of 5-fluorouracil?
a. Forms a metabolite that inactivates thymidylate synthase
b. Prevents the conversion of deoxyuridine monophosphate (dUMP) to dTMP (deoxythymidine monophosphate)
c. dNTP pool imbalances
d. Increased levels of dTMP
d. Increased levels of dTMP (It results in increased levels of dUMP, since conversion of dUMP to dTMP is inhibited.)
Which of the following can be used as an antibiotic to treat urinary tract infection?
a. Ciprofloxacin
b. Nalidixic acid
c. Etoposide
d. A and B
d. A and B
Ciprofloxacin and nalidixic acid inhibits what type of topoisomerase?
Bacterial Type II topoisomerases
Etoposide and doxorubicin inhibits what type of topoisomerase?
Human Type II topoisomerases
