Molecular bio of the gene 4

Question 1

what are the three rules of DNA replication

Answer 1

o DNA replication is semi constructive proven by Meselson and Stahl exp.
o Replication begins at an origin and usually proceeds bidirectionally for efficiency
o The synthesis happens from 5’3’ direction and is semidiscontinuous
This is due to two opposite direction strands; the leading strand is continuous, and the lagging strand is fragmented

Question 2

Which enzyme synthesizes DNA

Answer 2

DNA Polymerase

Question 3

How does dna polymerase know where to bind

Answer 3

the site of polymerization only fits correctly paired base nucleotides the sequence of which is identified by primer sequences

Question 4

What does polymerase soecificity help us identify?

Answer 4

correct and incorrect base pairs in a sequence

Question 5

which direction is DNA synthesized

Answer 5

from the 5’ to 3’ end

Question 6

how do synthesis mistakes get corrected?

Answer 6

Error correction by the 3’ to 5’ exonuclease activity of the DNA polymerase corrects most mistakes the polymerase makes i.e.. ‘proofreading’

Question 7

How often do mistakes in replication occur and how is such a level of accuracy reached?

Answer 7

there’s only one mistake per 10^9 or 10^10 nucleotides added
* So base pair complementarity + DNA polymerase activity site geometry is 1 error per 10^5 nucleotides on top of which proofreading decreases error rate by 10^2 to 10^3 fold
* And together the instinctive rate of replicative DNA polymerases is 1 error per 10^7-10^8 nucleotides

Question 8

What are the mistakes that arent corrected called?

Answer 8

Mutations that alter genetic code

Question 9

What are the features altered by mutations?

Answer 9

o Protein-coding sequences to generate mutant proteins
o Sequences that regulate DNA replication, transcription or translation
o These drive evolution but can be very harmful so they must be kept low

Question 10

what are the characteristics of replication?

Answer 10

o Require very high accuracy (fidelity)
o Require very high processivity
o Need to synthesize two new DNA strands with opposing polarity

Question 11

How are replication segments identified and started?

Answer 11

Replication forms with a primer and the Transcripted DNA is bound tightly to its counter part

Question 12

what other enzymes are used in transcription

Answer 12

Polymerase doesn’t act alone it acts with primers and DNA helicase to aid in keeping the strands separated and to start the transcription

Question 13

what are the two strands of RNA in replication

Answer 13

Lagging and leading strand

Question 14

chracterisitics of lagging strand in replication

Answer 14

o Primase binds and creates short strands of RNA primer
o DNA polymerase iii comes and continues the sequence from the 3’ to 5’ end
o After reaching RNA primers it stops and DNA polymerase I comes in and replaces the primer with nucleotides
o Ligase then joins the DNA into two strands of DNA after every Okazaki fragment

Question 15

What are DNA clamps and how do they help in replication?

Answer 15

o 50-100 without clamp
o 50,000 nucleotides WITH a clamp
o Does this by increasing processivity of the polymerase and all other enzymes by tethering them to the RNA strands
o This is another reason why replication is semidiscontinuous

Question 16

how does replication occus in bacteria compared to eukaryotes

Answer 16

both are bidirectional but eukaryotes have multiple points of origin where replication takes place whereas bacteria have just one that carries on for the whole chain

Question 17

how do points of origin carry out replication?

Answer 17

• DnaA recognizes and binds to these sites and recruits replication enzymes
• Each fork travels at about 1000 nucleotides a second and replicates 2.3 million base pairs each taking roughly 40 mins
• Eukaryotes and prokaryotes both uses this technique, but this process happens at multiple points throughout the strands simultaneously
• And where needed, extra mechanisms are necessary for telomeres