Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

flc > dna synthesis > Flashcards

dna synthesis Flashcards

1
Q

what features of the DNA helix are important for replicatin?

A
  • Two antiparallel* polynucleotide chains form a RH helix, in which the bases are on the inside, phosphates and sugars on outside. 10-bp per turn in B-form DNA
  • The polynucleotide chains are linked together by hydrogen bonds between pairs of bases- A,T and G,C. Therefore, via the base pairings rule, if you can open the two strands of the helix, you can use the base pairing rules to make the complementary DNA strands.
  • One strand is complementary in sequence to the other
    Thus, copying each strand generates two daughter duplexes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

why is DNA replication considered as semi conservative

A

. The resulting daughter duplexex contain one parental dna strand and one new dna strand, and therefore the process is called semi conservative.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q
  • How do cells initiate DNA replication and complete it within the S-phase of the cell cycle?
A
  • DNA replication is initiated at specific sites on DNA called replication origins.
  • Replication origins are recognised by an initiation complex
  • DNA at the origin unwinds to form a replication bubble and allow access to the replication machinery
  • DNA synthesis occurs in a specific phase (S) of the cell cycle and involves complete unwinding of the parental DNA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

describe the bacterial cell cycle

A
  • Bacteria have relatively little amounts of DNA and therefore can copy and divide within a short time span .
  • The bacterial cell cycle is largely occupied by the synthesis of the DNA
  • In bacteria, the chromosome is circular, supercoiled. And has a single replication origin . Proteins combine at the origin of replication and result in the unwinding of the two parental strands. This allows the initation of the separated parental strands to begin. This generates a replication bubble.
  • On either side of the replication bubble are replication forks. This is where the parental DNA duplex undergoes unwinding on both sides to make the separate strands. Therefore replication is bidirectional.
  • The replication forks gradually moves through the circular DNA, eventually seprateing and copying the parental dna strands to maek the daughter cells.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

describe the mamalian cell cycle

A
  1. M phase : mitosis
  2. G1- cells are preparing to synthesise the DNA in s phase. synthesis of histones, DNA polymerase, nucleotides
  3. S phase
  4. G2- DNA and cells are prepared for condensation into metaphase chromosomes, and then are segregated.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

In eurkaryotic cells DNA replication initiates at a single replication origin ? true or false

A

false, In eukaryotic cells, DNA replication initiates at multiple replication origins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

which enzyme is responsible for synthesising polynucleotide chains?

A

dna polymerase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

dna polymerase adds nucleotides to which ends of the growing DNA and what does this mean?

A

3’OH. this means it can only act in the 5’-3’ direction and the two strands are synthesised differently.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Which direction can DNA polymerase act on?

A

only 5’-3’

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

give a list of dna polymerases in bacteria

A

I - repair
II - repair
III - replication

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

give a list of dna polymerases in eukaryotes

A 
alpha - replication 
beta -repair
gamma- synthesises circular dna found in mitochondrion 
gamma - replication 
episilon- replication
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are the key properties of DNA polymerase

A

1) Acts in 5′ to 3′ direction.
2) Utilises A-T and C-G base pairing to synthesise new DNA strand.
3) Requires a DNA template, a DNA or RNA primer, the four deoxyribonucleoside triphosphate (dNTP) building blocks and Mg2+ ions.
4) Has a proof-reading editing function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

outline the steps in DNA replication that occur at the replication fork

A
  1. Topoisomerase II unwinds the supercoiled DNA helix to allow for separation.
  2. DNA helicase separates the two strands of DNA, providing two template strands.
  3. DNA binding proteins attach to the exposed single strands to protect them from cleavage by nucleases and stop them from re-binding to one another.
  4. Replication begins on both strands.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

outline the steps in dna replication

A
  1. Primase creates an RNA primer that binds to the template strand. The primer has a 3’oh end for the DNA polymerase to recognise. Primase carries out this role in bacteria.
  2. The 5’ phosphate group of the Deoxyribonucleoside triphosphate binds to the complementary unpaired base in the template strand and provides the 5’ end. st the 3’ end, resulting in elongation in a 5’-3; direction, through hydrogen bonding,. The 3’ OH group of the growing strand then attacks the inner alpha phosphate group, making a 3’ 5’ link creating a phosphodiester bond and thus ejecting pyrophosphate from the complex. The reaction is made irreversible by the hydrolysis of the pyrophosphate via pyrophosphatase to give two phosphates. DNA polymerase catalyses this process.
  3. The 3’ OH of the newly added nucleotide then bonds with the next complementary triphosphate group and the chain continues.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

describe what happens to the leading strand in DNA replication

A
  • Leading strand is in a 3’ to 5’ direction. As DNA is antiparallel, the new strand is produced in a 5’ to 3’ direction. As DNA polymerase can only work in this direction it is the same direction as the replication fork and therefore, the process is continuous. A primer is added and DNA polymerase creates phosphodiester bonds as the complementary 5’ deoxyribonucleoside triphosphate groups attach to the template strand through hydrogen bonds. This occurs in an uninterrupted chain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

describe what happens to the lagging strand in dna replication

A

Lagging strand is in a 5’ to 3’ direction. therefore As DNA polymerase works in a 5’ to 3’ direction, it moves away from the replication fork. A primer is added each time a new section of template strand is exposed, reinitiating replication, with new sections of DNA being created backwards. This forms fragments known as Okazaki fragments with sections of the RNA primer within the new strand. Repair DNA polymerase must then replace the RNA sections with DNA and DNA ligase links the fragments together into one, uninterrupted chain.

17
Q

why do okazaki fragments form in the lagging strand

A

due to the lagging strand being in the 5’3’ direction, and the dna polymerase only acting in the 5’ 3’ direction it moves away from the replication fork
A primer is added each time a new section of template strand is exposed, reinitiating replication, with new sections of DNA being created backwards. This forms fragments known as Okazaki fragments with sections of the RNA primer within the new strand.

18
Q

describe how bacteria solves the problem for dna replication ( ie laggign strand)

A
  • Single replication polymerase called pol III, which can replicate both the leading strand and lagging strand.
  • pol III requires a small primer that is hydrogen bonded to the template strand to be able to inititate replication.
  • Ecoli has an enzyme primase, lays down a turn , approx. 11 nucleotides of RNA.
  • This provides the 3’OH end,w hich can be used by pol III to copy the DNA strand.
  • On the lagging strand, since DNA polymerase works in a 5’ to 3’ direction, a primer is added each s time a new section of the template stand is exposed. This results in several okazki fragments, each beginning with RNA, with the rest of it being DNA.
  • When processing the okazaki fragments, the RNA is removed by repair DNA polymerase, and is replaced by DNA.
  • This results in DNA fragments which can be ligated together by DNA ligase.
19
Q

describe how eukrayotes deal with the lagging strand problem

A
  • Eukraryoes have 3 polymerases involved in replication : polymerase delta, which acts on the lagging strand, polymerase Exelon, which copies the leading strand.
  • On the lagging strand, it requires a primer. Polymerase alpha, in complex with primase, lays down the primer.
  • Primase adds RNA and allows it to link onto the DNA.
  • Polymerase alpha then adds DNA onto the RNA, forming an RNA-DNA PRIMER, which is subsequently used by polymerase delta to make more DNA.
  • Polymerase delta, as its synthesising DNA, will encounter the previous okazaki fragment and can displace the RNA, copy in the DNA, and then the nuclease trims the RNA.
  • DNA ligase then links all the fragments.
20
Q

in eukaryotes how many polymerases are involved in dna replication and what are their functions.

A
  • Eukraryoes have 3 polymerases involved in replication : polymerase delta, which acts on the lagging strand, polymerase Exelon, which copies the leading strand.
  • Polymerase alpha, in complex with primase, lays down the primer.
21
Q

what does topisomerase do >

A

removes +ve supercoils ahead of DNA replication forks- solving the ‘DNA winding problem

22
Q

describe the dna winding problem and how it is solved

A

The DNA winding problem occurs when the two strands of the parental DNA become interwined, as such there is one intertwining every ten bps. As the 2 strands are separated for copying, the intertwining goes ahead of the replication fork to form positive super coils. These act as a counter force against the unwinding of the DNA helix. So dna gyrase ( a form of topisonerase) reduces the torsional strain by removing the supercoils.

23
Q

dna synthesis occurs with high fidelity. how does this occur ?

A
  1. DNA polymerase has a low error rate ~ 1 in 108- due to base pairing and proof-reading/editing function of the enzyme
  2. Mismatch repair system- corrects most of the polymerase
    errors. Multienzyme system highly conserved across species
  3. base pairing in dna
24
Q
  • Patients who have inherited mismatch repair genes have a predisposition
A

colon cancer

25
Q

give examples of antibacterial drugs and what kind of inhibitors are they?

A

Ciprofloxacin
Levofloxacin
Novobiocin

they are gyrase inhibitors

26
Q

give examples of antitumour drugs and what kind of inhibitors are they?

A

etoposide
doxorubicin
mitoxantrone

topo II inhibitors

27
Q

examples of antiviral AIDs and what kind of inhibitor are they

A

AZT

reverse transcriptase.

28
Q

list the enzymes involved in dna synthesis

A

→ HELICASE - separates the base pairs producing single strands

→ TOPOISOMERASE - gets rid of coils in DNA that helicase caused

→ PRIMASE - lays down RNA so DNA polymerase knows where to start replicating

→ DNA BINDING PROTEINS - stabilize the single stranded DNA and prevent is reannealing

→ REPLICATIVE DNA POLYMERASE - copies the parental strand

→ REPAIR DNA POLYMERASE - repair the fragments and takes out the RNA so it will be a full DNA strand

→ DNA LIGASE - joins the okazaki fragments togethe

29
Q

what is the protein responsible for protecting the single dna strands from nucleases and from rebinding to one another?

A

dna binding proteins

flc (29 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions