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Replication Flashcards

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1
Q

What is replication ?

A

Copying and transformation of genetic information found in DNA to daughter cells

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2
Q

When does replication occur ?

A

S phase of the cell cycle

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3
Q

The process of replication is :

A

Semiconservative process

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4
Q

What does semiconservative mean ?

A

The Newley formed two daughters DNA contain one original old strand and Newley formed complementary strand.

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5
Q

Why is the process of semiconservative important ?

A

To transfer genetic information in the correct sequence.

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6
Q

DNA replication is also ……………………. Process

A

Bidirectional

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7
Q

What does bidirectional mean?

A

The replication forks move in both directions, away from the origin.

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8
Q

Steps of DNA replication :

A
  1. Separation of the two DNA strands
  2. Synthesis of the two DNA strands
  3. End of replication
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9
Q

Separation of the two DNA strands is considered to be the …….

A

Initiation process of replication either in prokaryotes or eukaryotes

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10
Q

Separation of the two DNA strands steps :

A

1)DNA a protein regcognizes the origin of replication , binds to the DNA and separates the two DNA strands at a very small region .
2) recruitment and loading a complex of two proteins : DNA b ( helicase )& DNA c ( helicase loader )
3) Recruitment of DNA primase
4) separation of the double helix by helicase
5) the two separated strands are kept apart by single strand DNA binding protein
6) Removing supercoils in the helix by DNA topoisomerase
7) NOW, each relaxed single strand acts as a template to the direct synthesis of a new daughter DNA strand.

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11
Q

What is the origin of replication ?

A

Specific DNA sequence in which DNA replication starts

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12
Q

Origin of replication in prokaryotes :

A

-it is single
- Named as OriC

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13
Q

Origin of replication in eukaryotes

A

-they are multiple
- termed as autonomous replication sequences
- rich in AT base pairs

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14
Q

DNA a protein function requires

A

ATP hydrolysis

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15
Q

What recruits the helicase-helicase loader complex is :

A

Combination of Single Stranded DNA and DNAa protein

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16
Q

Helicase inactivation is due to :

A

Binging of helicase (DNAb protein ) with the helicase loader ( DNAc protein)

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17
Q

Why is helicase inactivation is such important ?

A

To prevent helicase from functioning at inappropriate sites (Non-origin regions )

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18
Q

The process of helicase- helicase loader loading process requires :

A

Opening of the DNA helicase hexameric ring to encircle the targeted ssDNA .

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19
Q

The enzyme that recruits DNA primase is :

A

Helicase ( DNAb protein )

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20
Q

DNA primase functions

A

1) Synthesis of an RNA primer on each strand of the origin
2) Generating the primers for the legging DNA strands
3) Release of helicase loader

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21
Q

Helicase activation

A

The process of releasing helicase loader by DNA primase

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22
Q

Separation of the double helix by DNA helicase occurs by ( mechanism ) :

A

Breaking down hydrogen bonds btwn the two DNA strands by ATP hydrolysis

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23
Q

The importance of single strand DNA binding protein in replication :

A

1) prevent the double helix from rejoining
2) protect the single stranded DNA from nucleuses ( cleave it )

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24
Q

What is preprimiring complex ?

A

DNAa protein, DNAb protein , DNAc protein , SSB proteins

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25
Why is preprimiring complex significant ?
1) Replication initiation 2) Maintaining the separation of the two DNA strands
26
Supercoils formation :
While separating the double helix , this creates coils in front of the separated parts preventing further separation of the helix
27
Topoisomerases Mechanism:
By its nuclease activity ( Strand cutting ) : they make transient cut in the phosphodiester bonds in one strand or in two strands By its ligase activity ( strand resealing )
28
Topoisomerases 1 :
Cuts in one strand
29
Topoisomerases 2
Cut in both strands
30
What is DNA gyrase ?
Topoisomerases 2 , found in plants and bacteria
31
DNA gyrase Function :
Introduce negative supercoils into relaxed circular DNA by ATP hydrolysis.
32
DNA gyrase in facilitating the future replication:
1)Negative supercoils neutralise positive supercoils introduced during opening of the double helix. 2) aids in the transient strand separation during transcription
33
Clinical significance in Anti-biotics and anti-cancers
Antibiotics : quinolone as negram ( Nalidixic acid ) - inhibiting bacterial gyrase preventing bacterial replication and transcription Anticancer drugs : as etoposide -target human topoisomerase 2
34
Steps of Synthesis of the DNA strands :
1) Synthesis of RNA primers. 2) Synthesis of the DNA strands 3) excision of RNA primers and their replacement by DNA 4) connecting the DNA fragments 5) Proofreading of Newley synthesised DNA
35
Synthesis of RNA primers
1) occurs in the direction of ( 5’ - 3’ ) direction 2) By Primase ( RNA polymerase ) 3) using ribonucleotide triphosphate ( GTP, CTP , ATP , UTP )
36
Synthesis of the DNA strand
1) occurs in (5’ - 3’) direction 2) by DNA polymerase 3 3) Using deoxyribonucleotide triphosphate (d GTP , d CTP , d ATP , d TTP ) 4) following the base pairing rule ( DNA sequence that is complementary to the template strand ) 5) the first added deoxyribonucleotide triphosphate will form phosphodiester bond with OH at the 3’ end of RNA primer with the removal of pyrophosphate , the next added deoxyribonucleotide triphosphate will form phosphodiester bond with the previous added one with hydrolysis of Pyrophosphate
37
Providing energy for the reaction of connecting DNA nucleotides :
Hydrolysis of pyrophosphate from the added triphosphate
38
Each DNA molecule consists of :
Leading strand and lagging strands
39
Leading strand is
DNA strand that is synthesised continuously, complementary to the parent strand that has the direction of ( 3’ - 5’ ), with the direction of the advancing replication fork
40
Lagging strand
DNA strand in which many RNA primers are required to form Okazaki fragments that are eventually rejoined to form DNA strand ( synthesised discontinuously) , complementary to the parent strand that has the direction of ( 5’ - 3’ ) , away from the replication fork opening direction
41
What are Okazaki fragments ?
Short stretches of DNA nucleotides
42
Excision of RNA primers and their replacement
1) Occurs by DNA polymerase 1 ( 5’ exonuclease activity ) 2) excise the RNA primer and the gap filled by DNA nucleotides
43
Connecting the DNA fragments:
By DNA ligase
44
What does proofreading means ?
Each nucleotides , that is added, is checked to be correctly matched with its complementary base on the template strand . if NOT , the (3’ - 5’) exonuclease activity correct the mistake .
45
Proofreading occurs by …………………… that has both ………………. & ………………….
DNA polymerase 3 , ( 5’ - 3’ ) polymerase activity & ( 3’ - 5’ ) exonuclease activity
46
What are telomeres ?
1) complexes of Noncoding DNA plus Proteins 2) it is located at the ends of linear chromosomes 3) their DNA consists of thousands of repeats of a six nucleotide sequences ((( 5’ - TTAGGG - 3’ )) at the 3’ end of each DNA strand.
47
Telomeres importance :
1) Maintain the structural integrity of the chromosomes preventing attack by nucleases 2) allow repair system to distinguish a true end from a break in dsDNA
48
DNA overhanging and its significance:
- The 3’ end overhangs the 5’ end by a few hundred nucleotides long - the overhanging end folds back on itself AND binds proteins that protect it from recombination
49
What is end replication problem ?
Following the removal of RNA primer from the 5’ end of the lagging strand , there is no way to fill in the remaining gap with DNA
50
How is the problem of end replication solved ?
By an enzyme called telomerase
51
About telomerase :
- Ribonucleoprotein , found in Germ cells , Stem cells and cancer cells . - it is a reverse transcriptase . - it maintains telomeric length in theses cells by the presence of an RNA molecule in its structure , which is complementary to the TTAGGG repeat.
52
Telomerase Mechanism :
1) It recognises the single 3’ terminus 2) uses its RNA molecule As a template to elongate the parental strand 3) this elongated parental strand is used as a template for synthesis of the telomere of the lagging strand
53
Steps of Replication initiation in Eukaryotes during G1 phase :
1. Association of The ATP- bound origin recognition complex with the replicator 2. Recruitment of ATP-bound Cdc6 and two copies of the Mcm2-7 helicase bound to a second helicase loading protein (Cdt1) 3. Triggering ATP hydrolysis by Cdc6 3”. Loading of head-to-head diner of the Mcm2-7 complex encircling double-stranded origin DNA 3””. The release of Cdc6 and Cdt1 from the origin
54
Steps of replication initiation in eukaryotes during S phase :
1. Activation of helicases ( starts to separate the two DNA strands ) 2. Cdc45 and GINS proteins binding to the Mcm2-7 helicase 3. Formation of Mcm2-7 - GINS ( CMG ) complex
55
What is Origin Recognition Complex ( ORC ) ?
Multi-subunit DNA binding complex that binds to the origin of replication in all eukaryotes in an ATP-dependent manner * the subunits are encoded by ORC1 , ORC2, ORC3, ORC4, ORC5 and ORC6
56
What is pre-replicative complex :
Assembly of many replication factors that are : 1) ORC 2) Cdc6 protein 3) Cdt1 protein 4) Mcm2-7
57
Pre-RCs importance :
It’s required for replication licensing from chromosomes Occurs in G1 phase prior to DNA synthesis during S phase
58
Loading of ( Mcm 2-7 ) complex onto the DNA :
Occurs by ORC, Cdc6 , Cdt1 It is thought that Cdc6p- Cdt1 complex uses ATP hydrolysis to thread DNA through the central hole of the MCM
59
Kinases that are responsible for the conversion of pre-RC into the initiation complex ( activation of Pre-RC ) :
DDK targets the loaded helicase CDK targets two other replication proteins
60
What are replicators ?
Specific DNA sequence on the origin of replication that initiates the initiation of DNA
61
What triggers ATP hydrolysis by Cdc6 is :
The assembly of pre-RC proteins
62
When does the actual unwinding starts ?
After cells pass from the G1 to the S phase
63
About CMG complex :
- the active form of the Mcm2-7DNA helicase -it is the combination of Mcm2-7 ATPase and helicase activities which is stimulated by Cdc45 and GINS

Genetics (3 decks)

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