DNA Replication Flashcards
What 3 building blocks make up a nucleotide?
- Nitrogenous base
- Sugar (deoxyribose/ribose)
- Phosphate group
What is removed from the deoxy-Base Triphosphate when it is added to the growing DNA strand?
2 phosphates
Where does DNA replication begin?
Origin of replication
What does DNA helicase require to carry out its role?
ATP
- Hydrolyses ATP
What dosingle strand binding proteins do
- Assist helicase
- Stabilise and straighten single strands of DNA
What sequences of DNA do origins of replication usually have?
AT rich sequences (easier to open)
What DNA polymerases are found in prokaryotes?
DNA polymerase I-IV
- Polymerase III: Major DNA polymerase
- Polymerase I: Removes RNA primers
What are the DNA polymerases in eukaryotes?
alpha, Beta, gamma, delta, epsilon
- Polymerase y: located in mitochondria
What DNa polymerase in eukaryotes is not located in the nucleus and located in the mitochondria?
Polymerase y (gamma)
What makes primers?
DNA primase
What do primers contain?
RNA not DNA
Where does DNA polymerase add to on the DNA strand the new nucleotide?
3’ end
Where does the energy come from to add a nucleotide to the DNA strand?
From the 3 phosphates
- 2 phosphates are removed
In what direction are new nucleotides added?
5’ to 3’ direction
The eading and lagging strands are oriented in what direction?
Leading strand
- 3’ to 5’ direction
- Allows the replicating DNA to be added continously in a 5’ to 3’ direction
Lagging strand
- 5’ to 3’ direction
In prokaryotes what enzyme removes the RNA primer /okazaki fragment and replaces it with DNA?
DNA polymerase I
In eukaryotes what enzyme removes the RNA primer / okazaki fragment and replaces it with DNA?
DNA polymerase delta
What is the RNA primer known as on the lagging strand?
Okazaki fragment
WHat is the function of DNA ligase?
- Joins Okazaki fragments
- Creates phosphodiester bonds
What is the function of topoisomerase?
Prevents DNA tangling
- Breaks DNA then reseals to relieve tension/twists
What is the difference between topoisomerase I and II?
Topoisomerase I
- Breaks single strands of DNA then reseals
Topoisomerase II
- Breaks double strands then reseals
What do quinolone antibiotics target?
Prokaryotic topoisomerases
What strand replication is continuous and what strand replication is dicontinous?
LEading strand
- Continous
Lagging
- Discontinous
Why is DNA replication known as being semi-conservative?
New DNA: one old strand and one new strand
When may DNA polymerase move in a 3’ to 5’ direction?
To correct an error
What enzyme will remove an incorrect nucleotide?
Exonuclease
What are telomeres?
Nucleotides found at the end of chromosomes
What sequences are found on telomeres?
TTAGGG
What cannot attach on telomeres?
RNA primer on lagging strand
What does telomerase do?
- Recognises telomere sequences
- Adds these sequences to new DNA strands
What genetic material do telomerases use?
RNA which it uses as a template to synthesize telomere DNA
What can telomerase also be known as?
RNA-dependent DNA polymerase
What enzyme is telomerase similar to that can be found in certain viruses?
Reverse transcriptase
What side of the DNA does telomerase bind to?
Explain how telomerase allows the formation/duplication/extension of the telomere
3’ flanking end of the telomere
- Complementary to telomerase RNA
- Bases are then added using RNA as a template
- DNA polymerase then adds the NTs to the lagging strand (5’ end) in a 5’ to 3’ (opposite) direction
What kind of cells have many telomerase enzymes?
Cells that require controlled indefinite replication
- Hamatopoetic stem cells
- Epidermis, hair follicles, intestinal mucosa
How can telomerase play a role in cancer?
Allows immortality of cells
- Increased telomerase may lead to cancer
